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Biological Basis of Behvaiour

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  • Easy to understand in English Langauge
  • 5 Hours 45 Min Videos
  • Online Notes

INTRODUCTION

Everything we think, feel or do have an important basis in biological processes and events – and primarily in the activities of the NERVOUS SYSTEM

  • The Nervous System is a complex network of nerves and cells that carry messages to and from the different parts of the body.
  • NEURONS are the building blocks of the Nervous System. They are the specialized cells for communication and processing of information.
  • The human brain contains more than 100 billion neurons.
  • Neurons are one-way channels of communication.

 

NEUROPSYCHOLOGY deals with how the brain and the rest of the nervous system influence a person’s cognition and behaviors.

 

THE STRUCTURE & FUNCTION OF NEURON

        

  • Dendrites receive signals from other neurons and carry information toward the cell body.
  • Cell body (or soma) contains a nucleus and other cellular components.
  • Axon carries information away from the cell body.
  • Axon terminals transmit signals to other neurons.
  • Myelin sheath is composed of fatty material, provides insulation and increases the speed of signal conduction.
  • Rodes of Ranvier are periodic gaps in the myelin sheath which recharge the signal as it travels along the axon.
  • Glial cells- derived from glia, or “glue” in Greek. They are non-neuronal cells which provide nutrients, hold neurons in place, produce myelin sheath, help to form blood-brain barrier and remove pathogens and dead neurons.

 

            

  • Ependymal cells play an important role in the production and regulation of cerebrospinal fluid (CSF).
  • Oligodendrocytes functions to provide support and insulation to axons (myelin formation) in the central nervous system of some vertebrates, equivalent to the function performed by Schwann cells in the peripheral nervous system.
  • Sattelite cells provide nutrient support and protection. They may also help to regulate the neuronal environment and be involved in neurotransmission.
  • Astrocytes are the most numerous cell type within the central nervous system (CNS) and perform a variety of tasks, from axon guidance and synaptic support, to the control of the blood brain barrier and blood flow. 
  • Microglia mediate immune responses in the central nervous system by acting as macrophages, clearing cellular debris and dead neurons from nervous tissue through the process of phagocytosis (cell eating).

Synaptic junction between the two neurons

 

  • Synapse – The junction between the axon of one neuron and the dendrite of another, through which the two neurons communicate. 
  • Neurotransmitter – Chemicals released by neurons that carry information across synapses.
  • Synaptic Vesicles – Structures in the axon terminals that contain various neurotransmitters. 

       

Release of neurotransmitters at the synaptic cleft

 

  • When a neuron sends a message to another neuron, it sends an electrical signal down the length of its axon. At the end of the axon, the electrical signal changes to a chemical signal. 
  • The axon then releases the chemical signal with chemical messengers called neurotransmitters into the synapse the space between the end of an axon and the tip of a dendrite from another neuron. 
  • The neurotransmitters move the signal through the synapse to the neighbouring dendrite, which converts the chemical signal back into an electrical signal. The electrical signal then travels through the neuron and goes through the same conversion processes as it moves to neighbouring neurons.

CONDUCTION OF NERVE IMPULSE

  • Nerve impulse is overall physiological changes that occur in a neuron due to mechanical, chemical or electrical disturbance created by a stimulus. It propagation through axon, synapse and neuromuscular junction is called Nerve Impulse conduction.

Transmission of nerve impulse along nerve fibre can be summarized in the following phases:

                                                  

 

         

 

              

 

                    Graph showing different phases of nerve impulse conduction

 

  

CONDUCTION OF NERVE IMPULSE

Polarization (Resting potential):

  • A neuron at resting is electrically charged but not conducting.
  • The Axoplasm or plasma membrane of a resting neuron is negatively charged as compared to the interstitial fluid.
  • The potential difference measured at this stage is called resting potential which is about -70mV. The interstitial fluid has high concentration of Na+ ion which is about 16 times higher outside the neuron than inside neuron. Similarly, the axoplasm has high concentration of K+ ion which is about 25 times higher inside than in outer interstitial fluids.
  • Due to difference in concentration of ions, Na+ ion tends to diffuse into the axoplasm and K+ ion tends to diffuse outside the axoplasm.
  • The membrane of neuron at resting is more permeable to K+ ion than Na+ ion. So, K+ leaves the neuron faster than Na+ enter the neuron.
  • The difference in permeability results in accumulation of high concentration of cation (+ve charged ion) outside the neuron compared to the concentration of cation inside.
  • This state of resting neuron is called Polarized state and it is electro-negatively charged.

Depolarization (Action Potential):

  • Any stimulus beyond the threshold can initiate an impulse.
  • When such stimulus is applied in the resting neuron, it opens the sodium channel. Now the permeability of Na+ ion suddenly increases at the point of stimulus causing depolarization.
  • The diffusion of Na+ ion increases by 10 times from outside to inside. As a result the axoplasm become positively charges, which is exact opposite to polarized state, so called as depolarized state or reverse polarized state.
  • The depolarization of the membrane stimulates the adjacent voltage channel, so the action potential passes as a wave along the length of neuron.

Repolarization:

  • When the concentration of Na+ ion inside axoplasm increases, the permeability to Na+ decreases and the sodium channel starts to close.
  • The Na-K pump activates, so that Na+ are pumped out and K+ inside until the original resting potential is restored. The process is known as repolarization and it starts from the same point from where depolarization starts.
  • The entire process of polarization, depolarization and repolarization occur within fraction of seconds. Now, again the neuron is read for another impulse.

 

Saltatory conduction: 

    • Transmission of nerve impulses is very rapid. However, nerve impulse conduction along unmyelinated neuron is slow than that of myelinated neuron. It is because, the myelin sheath act as insulator, so that the impulse have to jump from one node of Raniver to another. 
  • This speed up the conduction process, and this type of conduction is known as Saltatory conduction.

                                   

 

SYNAPTIC TRANSMISSION OF NERVE IMPULSE

 

TYPES OF NEURON

 

             

 

On the basis of structure, neurons are broadly divided into four basic types: 

  1. unipolar- have only one structure that extends away from the soma. These neurons are not found in vertebrates, but are found in insects where they stimulate muscles or glands. 
  2. Bipolar- has one axon and one dendrite extending from the soma. An example of a bipolar neuron is a retinal bipolar cell, which receives signals from photoreceptor cells that are sensitive to light and transmits these signals to ganglion cells that carry the signal to the brain.
  3. Multipolar neurons are the most common type of neuron. Each multipolar neuron contains one axon and multiple dendrites. Multipolar neurons can be found in the central nervous system (brain and spinal cord). The Purkinje cell, a multipolar neuron in the cerebellum, has many branching dendrites, but only one axon.
  4. Pseudounipolar cells share characteristics with both unipolar and bipolar cells. A pseudounipolar cell has a single structure that extends from the soma (like a unipolar cell), which later branches into two distinct structures (like a bipolar cell).

 

On the basis of function, neurons are broadly divided into three basic types: 

 

  1. Sensory neurons- They are activated by sensory input, and send projections to other elements of the nervous system, ultimately conveying sensory information to the brain or spinal cord. Most sensory neurons are pseudounipolar, meaning they have an axon that branch into two extensions—one connected to dendrites that receive sensory information and another that transmit this information to the spinal cord.
  2. Motor neurons- located in the central nervous system, and they project their axons outside of the CNS to directly or indirectly control muscles. The interface between a motor neuron and muscle fiber is a specialized synapse called the neuromuscular junction. The structure of motor neurons is multipolar. This is the most common type of neuron.
  3. Interneurons- They act as an intermediary in passing signals between two other neurons. Located in the CNS, they operate locally, meaning their axons connect only with nearby sensory or motor neurons.

 

ROLE OF NEUROTRANSMITTERS

ACETYLCHOLINE- Excitatory neurotransmitter as it stimulates muscles action, found mostly in the neuromuscular junctions. Also found in hippocampus thus, involved in learning & memory

  • Too little – DEMENTIA & ALZHIMER’s disease 
  • Too much – DEPRESSION

DOPAMINE - found in the brain region called   substantia nigra. It has role in movement, attention & learning.

  • Too little- DEPRESSION &  PARKINSON’S DISEASE
  • Too much – SCHIZOPHRENIA

NOREPINEPHRINE - found in autonomic nervous system (ANS). It has role in control & alertness and even involve in wakefulness

  • Too little – DEPRESSION
  • Too much – SCIZOPHRENIA

GABA- GAMINOBUTRRIC ACID- is an Inhibitory neurotransmitter. It is found in brain & spinal cord. Its receptor sites get affected by tranquilizers. It has a role in eating & sleeping disorder

  • Too little- ANXIETY DISORDER

SEROTONIN- found in Lower part of the brain. It functions as Excitatory/ Inhibitory--- depending on brain area that it is found. It is associated with sleep, mood and appetite.

  • Lowers in case of depression.

ENDORPHINS - role in pain relief. It is referred as a Feel-good hormone. Eg; when we cut a finger, it is functional. Opium- heroine/ morphine bind the receptors of endorphins so that pain is not felt. Hence, such substances are addictive in nature. 

GLYCINE- Inhibitory neurotransmitter. It is found in brain stem, spinal cord and retina.

SUBSTANCE P- Role in pain detection.

 

MAJOR DIVISIONS OF THE NERVOUS SYSTEM

The nervous system has two main parts:

  • The central nervous system is made up of the brain and spinal cord.
  • The peripheral nervous system is made up of nerves that branch off from the spinal cord and extend to all parts of the body.

The nervous system transmits signals between the brain and the rest of the body, including internal organs. In this way, the nervous system’s activity controls the ability to move, breathe, see, think, and more. 

The peripheral nervous system can be further divided based on the functions each area performs:

  • The sensory or afferent division of the PNS includes nerves that have a sensory function and carry impulses to the CNS for integration.  These are typically receptors that detect stimuli both from within the body (interoceptors) and outside the body (exteroceptors).  An example of an internal stimulus could include the rise and fall of blood pressure or various ions within the body.  Exteroceptors detect external stimuli such as those involved in touch, vision, hearing, taste, and smell.  
  • The motor or efferent division include nerve fibres that carry impulses away from the CNS to initiate an effector.  

 

There are two main subdivisions of the motor division:  

  • the somatic nervous system (SNS) which is responsible for voluntary motor responses and 
  • the autonomic nervous system (ANS) which is responsible for involuntary motor responses.

 

The two divisions of the autonomic nervous system are: 

  • The sympathetic division and 
  • The parasympathetic division
  • The sympathetic system is associated with the fight-or-flight response.
  • The parasympathetic activity is referred to by the epithet of rest and digest. Homeostasis is the balance between the two system.

                       

PERIPHERAL NERVOUS SYSTEM

  • Made up of all nerves and neurons that are not contained in brain and spinal cord.
  • Carry nerve impulses from the sensory receptors  inward to the CNS
  • Carry nerve impulses outward from CNS for the movement of muscles.
  • Allow CNS to control muscle and glands of the body.

 

            

 

THE AUTONOMIC NERVOUS SYSTEM

      

 

  

 

THE AUTONOMIC NERVOUS SYSTEM

 

THE SOMATIC NERVOUS SYSTEM

  • Somatic Nervous System - Carry messages from the senses to the CNS and from the CNS to the skeletal muscles.
  • Sensory Pathway - Comprised of nerves that carry from sensory receptors to CNS called sensory or afferent neurons.
  • Motor Pathway - Comprised of nerves that carry messages to the voluntary muscles called motor or efferent neurons.

                                          

 

REFLEX ACTION

A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus. When a person accidentally touches a hot object, they automatically jerk their hand away without thinking. A reflex does not require any thought input. The path taken by the nerve impulses in a reflex is called a reflex arc.

 

THE CENTRAL NERVOUS SYSTEM

  • CNS is composed of the brain and spinal cord.
  • Both brain and spinal cord are composed of neurons and glial cells control the life sustaining functions of the body as well as the thought, emotions and behavior.
  • It guides movement, and registers sensations throughout the body.

ANATOMICAL SUBDIVISIONS OF THE HUMAN BRAIN

VENTRICLE: One of the hollow spaces within the brain, filled with cerebrospinal fluid (CSF).

 

BRAIN DEVELOPMENT

 

HYDROCEPHALUS: Occurs due to blocked flow of CSF. It leads to enlargement of the ventricles and subsequent brain damage.

                                

 

ANATOMICAL SUBDIVISIONS OF THE HUMAN BRAIN

 

CEREBRUM

  • Divided into 2 cerebral hemispheres, 1 on each side by a deep cleft or fissure (deep ridge).
  • The two hemispheres are connected by nerve fibres called corpus callosum.
  • Covered by a sheet of neurons (gray matter) on each hemisphere called as cerebral cortex.
  • A fissure is also called sulci, deeper sulci mark division of each hemisphere.
  • Under cortical covering of cerebrum is nerve fibers (white matter due to white myelin)

                                                        

FUNCTIONS OF THE HUMAN BRAIN

 

FUNCTIONS OF THE FOREBRAIN

 

FUNCTIONS OF THE MIDBRAIN

 

  • Lies above the medulla and pons, near the end of brain stem.
  • Contains an extension of reticular activating system. 
  • Contain primitive vision centres- superior colliculi.
  • Contain primitive hearing centres- inferior colliculi.
  • Plays a role in the regulation of visual reflexes.

 

FUNCTIONS OF THE HINDBRAIN

 

Reticular Activating System

  • The Reticular Activating System (RAS) is a bundle of nerves at our brainstem that filters out unnecessary information so the important stuff gets through.
  • The RAS is the reason you learn a new word and then start hearing it everywhere. 
  • It’s why you can tune out a crowd full of talking people, yet immediately snap to attention when someone says your name or something that at least sounds like it.
  • It extends from hindbrain to the midbrain. 
  • It regulates arousal, alertness and attention.


STRUCTURE OF CEREBRAL CORTEX

  • The outer surface of the brain is called cerebral cortex.
  • The cortex from above is divided into 2 halves or 2   cerebral hemispheres: right and left.

 

The surface of the cortex is divided into four lobes: 

  • Frontal lobe
  • Parietal lobe
  • Occipital lobe
  • Temporal lobe

 

STRUCTURE OF CEREBRAL CORTEX

 

FRONTAL LOBE

  • The area that produces movement of body parts is found in primary motor cortex.
  • Damage to this area does not produce paralysis but loss of fine muscle movement. 
  • Prefrontal cortex is responsible for memory, intelligence, concentration, temper and personality.
  • It helps us to make plans, set goals and priorities and language.
  • Frontal lobe also helps in controlling emotions by its connection with limbic system. 

OCCIPITAL LOBE

  • These lobes contain regions that contribute to our visual field or how our eyes see the world.
  • This region is primary visual cortex.
  • Visual association cortex is the part which helps in identifying and making sense of the visual information from eyes.

TEMPORAL LOBE

  • Primary auditory cortex helps us hear sounds and gives sounds their meaning. Eg., bark of the dog.
  • When injuries occur in left hemisphere people may lose ability to understand spoken words.
  • It also has olfactory region (sensation).

PARIETAL LOBE

  • These are at the top and back of the brain.
  • This consists of Somatosensory Cortex.
  • It is an area of neurons running down the front of the parietal lobe.
  • It receives signals from vision, hearing, motor, sensory and motor.
  • Also gustatory and information from skin is carried.

STRUCTURE OF CEREBRAL CORTEX

 

DAMAGE TO CEREBRAL CORTEX

(MOTOR CORTEX) FRONTAL LOBE DAMAGE 

Loose of control over fine movements. Eg. fingers

(SOMATOSENSORY CORTEX) PARIETAL LOBE DAMAGE

Left Hemisphere: loose writing ability & difficulty in locating body parts.

Right Hemisphere: unaware of left side of body

(VISUAL CORTEX) OCCIPITAL LOBE DAMAGE 

Left Hemisphere: Loose of VISION in right visual field.

Right Hemisphere: Loose of VISION in left visual field.

 

(AUDITORY CORTEX) TEMPORAL LOBE DAMAGE

Left Hemisphere: Loose ability to understand spoken words.

Right Hemisphere: can’t recognize melodies, tones, rhythms.

 

ASSOCIATION AREAS OF CORTEX

WERNICKE’S AREA

  • An area in left temporal lobe that through its connection with other brain areas, plays a role in speech comprehension.
  • Damage to this region leads to Wernicke’s APHASIA.

BROCA’S AREA

  • A region in the prefrontal cortex that plays a role in the production of speech. This area allows a person to speak smoothly and fluently.
  • Damage to this region leads to Broca’s APHASIA.

SPATIAL NEGLECT

  • Damage to association areas of the right hemisphere can produce an odd condition called spatial neglect.
  • A person fails to recognize the left side of the visual field.
  • Spatial neglect can affect the left hemisphere.
  • This condition occurs less frequently and in much milder form than right hemisphere in case of left hemisphere.

 

Brain and Behaviour: Functions

LEFT BRAIN RIGHT BRAIN
  • Recognizing and remembering names
  • Emotional inhibitions
  • Words for meaning
  • Producing logical thoughts/ideas
  • Processing information sequentially
  • Serious, systematic problem-solving
  • Logical appeals
  • Critical, analytical reading/listening
  • Problem-solving through logic
  • Verbal instructions/information
  • Remembering through language
  • Reading for details and facts
  • Realistic stories
  • Emotional responses (strong)
  • Interpreting body language
  • Producing humorous thoughts/ideas
  • Processing information subjectively and in patterns
  • Playful problem-solving
  • Emotional appeals
  • Creative, synthesizing, associating, applications in reading/listening
  • Problem-solving through intuition
  • Demonstrational instruction/information
  • Remembering through images

                         

 Brain and Behaviour: Functions

 

 

SPLIT BRAIN RESEARCH

 

Some Intriguing Effects of Severing the Corpus Callosum 

A man whose corpus callosum has been cut stares at a central point on a screen. The word tenant is flashed across the screen so that the letters ten appear to the left of the central point and the letters ant appear to the right. Because of the way our visual system is constructed, stimuli presented to the left visual field of each eye stimulate only the right hemisphere of the brain; items on the right side of the visual field of each eye stimulate only the left hemisphere. Therefore, when asked "What do you see?" the man answers: "Ant." But when asked to point to the word he saw with his left hand he points to the "ten" in the word "tenant." Findings such as these provide evidence for lateralization of function in the two cerebral hemispheres.

THE HUMAN EYE: STRUCTURE AND FUNCTION

 

Eye converts the light energy into a neural code understandable to our nervous system.

 

  • Cornea is the transparent layer through which light rays enter the eye.
  • Pupil is an opening in the eye, just behind the cornea, through which light rays enter the eye. It widens in dim light and constricts in bright light.
  • Iris is the colored part of the eye; adjusts the amount of light that enters by constricting or dilating the pupil.
  • Lens is a curved structure behind the pupil that bends light rays, focusing them on the retina.
  • Anterior chamber is filled with aqueous humor.  It remove waste products of lens, maintain intra-occular pressure and shape of the eye.
  • Vitreous humor is transparent jelly-like tissue fill eye ball behind the lens. Its pressure helps to keep retina in place.
  • Cilliary muscles adjust the shape of lens to focus on nearby objects, a process called accommodation.
  • To see distant object, the lens becomes thinner & flatter.
  • To see nearby object, the lens becomes thicker & rounder.
  • Retina is a light sensitive layer at the back of the eye where light signals are converted into electric signals or nerve impulse.
  • There are two types of retinal cells:                                                                                                                                
  1. Rods: sensory receptors for vision, functions best in dim light.
  2. Cones: sensory receptors for sensation of colour,  functions best in bright light.
  • Fovea is in the centre of the retina where cones are highly concentrated. 
  • The retina contains about 5 million cones and about 120 million rods.
  • Optic nerve carry visual information to brain via electrical signal.
  • Blind spot is the point in the back of the retina through which the optic nerve exits the eye. This exit point has no rods and cones and is therefore insensitive to light.
  • Sclera is an opaque, tough, protective outer layer which provides form & protection.
  • Choroid is the central layer between retina and sclera which provide nourishment to the outer layers of the retina via blood vessels.

EXTRAOCULAR MUSCLES

  • Four Rectus muscles- responsible for straight movements: 

                up, down, outside, inside

  • Two Oblique muscles- responsible for angled movements: 

                superior (up) & inferior (down)

Image formation at the retina

THE HUMAN EYE: LIGHT PATHWAY

                                                                      

Light rays first pass through cornea and then enter the eye through the pupil. After entering through the pupil, light rays pass through the lens. Light rays leaving the lens are projected onto the retina is actually upside down and reversed; but the brain reverses this image, letting us see objects and people correctly.

 

PATHWAY OF NERVE SIGNAL IN RETINA

Once stimulated, the rods and cones transmit neural information to other neurons called bipolar cells. These cells, in turn, stimulate other neurons called ganglion cells. Axons from the ganglion cells converge to form the optic nerve and carry visual information to the brain.

 

LIGHT: THE PHYSICAL STIMULUS FOR VISION

We can perceive only a small part of the total electromagnetic spectrum that is the visible spectrum.

 

Certain physical properties of light contribute to our psychological experiences of vision: 

  • Wavelength is the distance between successive peaks and valleys of light energy. 
  • Hue is the color that we experience due to the dominant wavelength of a light.
  • Brightness is the physical intensity of light. 
  • Saturation is the degree of concentration of the hue of light. It is experienced as the purity of a color or the extent to which light contains only one wavelength.

 

BASIC FUNCTIONS OF THE VISUAL SYSTEM

    • ACUITY is the visual ability to see fine details.
  • Types of visual acuity are:
  1. Static Visual Acuity (SVA) – ability to discriminate different objects when they are at rest.
  2. Dynamic Visual Acuity (DVA) – ability to resolve detail when object and/or viewer is in motion.
  • DARK ADAPTATION is the process through which our visual system increases its sensitivity to light when we move from bright light to dim environment.
  • The dark-adapted eye is about 100,000 times more sensitive to light than the light-adapted eye.

 

MAJOR DEFECTS OF VISION

 NEAR-SIGHTEDNESS (MYOPIA)

  • can see nearby objects clearly
  • can’t see farther objects clearly
  • image formed in front of retina
  • stiffly curved cornea
  • eyeball too long
  • correction by concave lens

                   

FAR-SIGHTEDNESS (HYPERMETROPIA)

  • can see farther objects clearly.
  • can’t see nearby objects clearly
  • image formed at the back of retina
  • too flat cornea
  • eyeball too short 
  • correction by convex lens

 

Presbyopia

  • This defect of vision usually happens in old age. 
  • ciliary muscles become weak and can no longer adjust the eye-lens. 
  • muscles become inflexible in this condition 
  • cannot see nearby objects clearly.
  • can be corrected  by wearing spectacles having convex lens.

 

THEORIES OF VISION

TRICHROMATIC OR COLOR PERCEPTION THEORY

A theory of color perception suggests that we have three types of cones, each primarily receptive to different wavelengths of light.

  • BLUE (400 – 500 nm)
  • Green (475 – 600 nm)
  • Red (490 – 650 nm)

 

We perceive color from the joint action of the three receptors.

Light of a particular wavelength produce differential stimulation of each receptor.

Overall color is determined by the overall stimulation pattern.

                                                               

                                             Trichromatic or color perception theory

 

OPPONENT – PROCESS THEORY

Theory describes the processing of sensory information related to color at levels above the retina.

The theory suggests that we possess six different types of neurons:

  • RED – GREEN opponent channel
  • YELLOW – BLUE opponent channel
  • BLACK – WHITE opponent channel

Activation of one color of the pair resulted in the inhibition of the other. For example, one perceives either red or green, but never reddish green or greenish red.

                                          

This theory explains the phenomenon of negative afterimages.

Negative Afterimages are sensations of complementary color that we experience after staring at a stimulus of a given color. 

 

VISION AND THE BRAIN

  • Brain processes visual information hierarchically.
  • Feature detectors are the neurons present within the visual cortex that respond primarily to stimuli possessing certain features.
  • There are three types of feature detectors:
  1. Hypercomplex cells are the neurons in the visual cortex that respond to complex complex aspects of visual stimuli, such as width, length, and shape. 
  2. Complex cells are the neurons in the visual cortex that respond to stimuli moving in a particular direction and having a particular orientation.
  3. Simple cells are the neurons that respond to bars and lines presented in certain orientations (horizontal, vertical, and so on).

Blindsight – A rare condition resulting from damage to the primary visual cortex in which blind individuals respond to certain aspects of visual stimuli like color or movement, as if they could see.

Prosopagnosia – A rare condition in which brain damage impairs a person’s ability to recognize faces. 

 

THE HUMAN EAR: STRUCTURE AND FUNCTION

 

  • Ears are important for hearing and for controlling a   sense of position and balance. 
  • Each ear is divided into three sections:

                              -The outer ear

                              -The middle ear

                              -The inner ear

  • The middle and inner parts of the ear are located in hollow spaces on either side of the head within the temporal bones of the skull.

 

  • The external part of the ear consists of the pinna and ear lobe. 
  • The pinna directs sound waves from the outside into the external auditory canal (ear canal), which in turn channels sound waves to the tympanic membrane (known as the eardrum), causing it to vibrate. 
  • The tympanic membrane is a thin, semi-transparent, flexible membrane that separates the outer and middle ear.
  • The middle ear is an air-filled space that contains three tiny bones known as ossicles which transmit sound. The bones are known individually (according to their shapes) as the:

                   -Malleus (hammer).

                   -Incus (anvil).

                   -Stapes (stirrup).

                          

The structure of middle Ear

 

The Eustachian tube is a narrow tube that connects the middle ear to the back of the nose and throat. During swallowing, the Eustachian tube opens up to allow air into the middle ear, so that air pressure on either side of the tympanic membrane is the same. 

The inner ear contains two main structures:

  • The cochlea has shape of a snail and is involved in hearing. The round window (fenestra cochlea) is a membrane that connects the cochlea to the middle ear. It helps dampen the vibrations in the cochlea.
  • The vestibular system (consisting of the semicircular canals, saccule and utricle), which is responsible for maintaining balance and a sense of position.

The cochlea is filled with fluid and contains the organ of corti – a structure that contains thousands of specialized sensory hair cells with projections called cilia. It has approximately 30,000 hearing nerve endings in the hair cells. Vibrations of oval window cause movements of the fluid in the cochlea which further bends the tiny hair cells. The hair cells then convert these vibrations into nerve impulses, or signals, which are sent via the auditory nerve to the base of the brain (brainstem) and the brain where they are interpreted as sound.

 

SOUND: THE PHYSICAL STIMULUS FOR HEARING

            Sound waves consist of alternating compressions of the air.

Frequency in a sound wave refers to the rate of the vibration of the sound traveling through the air. This parameter decides whether a sound is perceived as high pitched or low pitched. In sound, the frequency is also known as Pitch

Amplitude refers to the magnitude of compression and expansion experienced by the medium the sound wave is traveling through.  This amplitude is perceived by our ears as loudness

                           

  1. a) Low Amplitude                               b) High Amplitude

Timbre is the quality of sound resulting from the complexity of a sound wave. It helps to distinguish the sound of a trumpet from a saxophone.

  • Human hearing range: 20 Hz to 20,000 Hz.
  • Most sensitive range: 1,000 Hz to 5,000 Hz.
  • Long term exposure to sound intensity above 85 dB can produce permanent hearing loss.
  • Car air bag can cause permanent hearing damage (170 dB) when deploy.

THEORY OF PITCH PERCEPTION

Place Theory or Travelling Wave Theory

  • It suggests that sounds of different frequencies stimulate different areas of the basilar membrane, the portion of the cochlea containing sensory receptors for sound.
  • High- frequency sounds cause maximum displacement at the narrow end of the basilar membrane near the oval window.
  • Lower frequency causes maximum displacement toward the wider, farther end of the basilar membrane.
  • This theory does not explain our ability to discriminate among very low-frequency sounds.

 

Frequency Theory or Temporal Code Theory

  • It suggests that sounds of different frequencies induce different rates of neural activity in the hair cells of the inner ear.
  • High-pitched sounds produce high rates of activity in the auditory nerve, whereas low-pitched sounds produce lower rates.
  • It is accurate upto 1,000 Hz- the maximum rate of firing for individual neurons.
  • The theory may include a Volley Principle- the assumption that sound receptors for other neurons begin to fire in volleys. For example, a sound with a frequency 5,000 Hz tone might generate a pattern of activity in which each of five groups of neurons fires 1000 times in rapid succession.
  • This theory explain our ability to discriminate among very low-frequency sounds.

 

SOUND LOCALIZATION

  • It is the ability of our auditory system to determine the direction of a sound source. Our head creates a sound shadow, a barrier that reduces the intensity of sound on the “shadowed” side.
  • The sound behind us and to our left will be slightly louder in our left ear.
  • The shadow effect is strongest for high-frequency sounds, which have difficulty bending around the head.
  • When sound comes directly in front or in back of us, it is difficult to determine the location as it reaches to both ears at the same time. By turning head, slight difference is created in the time it takes to reach each ear.

 

TOUCH & OTHER SKIN SENSES

Pain Perception: Gate Control Theory

  • It suggests that the spinal cord contains a mechanism that can block transmission of pain to the brain.
  • Pain messages carried by large fibres cause this “gate” to close.
  • Pain messages carried by the smaller fibres, the one related to throbbing pain- do not.
  • Acupunture stimulate activity in large nerve fibres.

 

SMELL & TASTE: THE CHEMICAL SENSE

Receptors for our sense of smell are located in the olfactory epithelium, at the top of the nasal cavity. Molecules of odorous substances are dissolved moisture present in the nasal passages. This brings them into contact with receptor cells, whose neural activity gives rise to sensations of smell.

Human olfactory receptors can detect only substances with molecular weights between 15 and 300. This is why we can smell alcohol mixed in a drink but cannot smell table sugar.

Stereochemical theory suggests that substances differ in smell because they have different molecular shapes.

        

All tastes can be perceived equally well everywhere on the tongue. People used to think that there were specific zones for sweet, sour, salty and bitter- but this has been proven to be wrong.

                           

KINESTHESIA & VESTIBULAR SENSE

  • Kinesthesia is the sense that gives us information about the location of our body parts with respect to one another and allows us to perform movement.
  • Kinesthetic information comes from receptors in joints, ligaments, and muscle fibres.
  • When we move our body, these receptors register the rate of change of movement, speed as well as the rate of change of the angle of the bones in our limbs, the transform this mechanical information into neural signals for the brain.
  • We also receive important kinesthetic information from our other senses, especially vision and touch. 
  • Vestibular sense gives us information about the body position, movement and acceleration for maintaining our sense of balance.

 

  • The sensory organs for the vestibular sense are located in the inner ear.
  • Two-fluid filled vestibular sacs provide information about the position of the head and body with respect to gravity by tracking changes in linear movement.
  • When our body accelerates (or decelerates) along a straight line, hair cells bend in proportion to the rate of change in our motion.
  • This differential bending of hair cells causes attached nerve fibres to discharge neural signals that are sent to the brain.
  • Three-fluid filled semicircular canals provide information about rotational acceleration around three principal axes.

Vestibular system detects changes in motion rather than constant motion.

MUSCULAR  AND GLANDULAR SYSTEM

The muscles are responsible for many types of movements and behaviours which are internal as well as external. 

The types of muscles in our body are:

  1. Skeletal muscles
  2. Cardiac muscle
  3. Smooth muscles

                               

                

 

    

 

The major functions of the muscular system are:

  1. Overall movements of the body such as walking, running, and manipulation of objects with hands, maintenance of body posture, respiration, and production of body heat.
  2. Muscles also help in communication functions such as speaking, writing, typing, gestures, and facial expressions.
  3. They also help in constriction of organs and vessels which help propel and mix food and water in digestive tract, propel secretions from organs and regulate blood flow through vessels.

 

Muscle Tone: This refers to the constant tension produced over long periods of time. It is necessary for keeping the back and legs straight, the head held in an upright position and the abdomen from bulging. 

Muscle contraction is very important to enable the individual to perform long term activities like running, marathon, listening to long lecture, shooting and such other activities.

Energy for muscle contraction is supplied to the muscles in the form of adenosine tri-phosphate (ATP). Muscle fatigue results when ATP is used during muscle contraction faster than it can be produced in the muscle fibbers. 

 

From the psychological point of view, the most common type of fatigue is ‘psychological fatigue’. This involves the central nervous system rather than the muscles themselves. The muscles are still capable of contracting, but the individual ‘perceives’ that additional muscle contraction is impossible. 

For example, a burst of activity in a tired athlete in response to spectator encouragement is an example of how psychological fatigue can be overcome. It is important for the nurse to know these functions of muscles and help the patients to maintain rest, relaxation, and exercise to keep the health fit.

Duct Glands: The duct glands release their secretions through small ducts or tubes into the body cavities or on to the surface of the body. For example, salivary gland, sweat glands, lacrimal glands which produce tears, glands which secrete digestive juices, etc. These glands are activated during emotional situations.  For example- 

  • sweating increases during fear or anger, 
  • tears increase during grief, 
  • saliva decreases during fear and make our mouth become dry, 
  • Digestion slows down during emotions, but constant emotion leads to increased secretion of hydrochloric acid leading to peptic or duodenal ulcers.

Endocrine Glands (Ductless Glands): Endocrine glands are more important from the point of view of behaviour. Endocrine glands release their secretions called ‘hormones’ directly into blood stream. The normal secretions of these hormones promote healthy and normal personality. But over or under secretion of these hormones affect the development of body, general metabolism, mental development and emotional behaviour. 

                                                  

                                                         Endocrine Secretion of Hormones

         

THE GLANDULAR SYSTEM

  • Pituitary gland: This is also called the master gland, because it controls the functions of many glands. There are two lobes in this gland: 
    1. Anterior lobe  
  • Posterior lobe

The anterior lobe secretes hormones called trophic hormones which influence the secretions of other glands. For example, thyrotrophic hormone, gonadotrophic hormone, etc. The anterior lobe controls the growth of body, prolactin secretion in women, insulin secretion, metabolic activities, sexual activities, etc. The hyperactivity of this gland leads to gigantism and under activity leads to dwarfism.

The anterior lobe produces two kinds of hormones:

  1. Hormones that control other hormone-producing glands
  2. Hormones that have a direct effect on the body

The group of hormones that control glands includes:

  • Thyroid-stimulating hormone (TSH): regulates hormone production in the thyroid gland.
  • Adrenocorticotropic hormone (ACTH): stimulates the adrenal glands to produce hormones such as adrenalin (epinephrine) or steroids.
  • Follicle-stimulating hormone (FSH): regulates hormone production in the ovaries and testicles.
  • Luteinizing hormone (LH): also has an effect on hormone production in the ovaries and testicles.

The group of hormones that have a direct effect includes:

  • Growth hormone (GH), also called somatotropic hormone (STH): has an effect in many parts of the body – particularly the liver, bones, fat tissue and muscle tissue.
  • Prolactin: influences the mammary glands and ovaries.

The posterior pituitary does not produce any hormones of its own, rather, it stores and secretes two hormones made in the hypothalamus— 

  1. Oxytocin- affects the womb and mammary glands, and causes contractions in childbirth, for instance.
  2. Anti-diuretic hormone- regulates water uptake in the kidneys and makes the blood vessels narrower.

  • Thyroid gland: It secretes thyroxin hormone. The normal secretion of thyroxin hormone regulates oxygen consumption and helps energy output.  Hyperthyroidism causes increased nervous tension or excitement, insomnia and over activity. Hypothyroidism causes sluggishness, forgetfulness, stupidity, dullness, etc. Hypothyroidism in childhood leads to a disease called cretinism and during adulthood it leads to myxoedema.

  • Parathyroid gland: These glands are four in number. They secrete a hormone called Parathyroxin. Hyposecretion leads to excitability, muscular tremors, spasms and cramps, complete decline in secretion leads to disease called tetany. Mentally, the individual becomes highly sensitive to criticisms and unable to control emotions. Hyperactivity results in lassitude, lack of interest, physical weakness and softness of bones due to lack of calcium, and lethargy due nervous weakness.

                                                    

  • Adrenal glands: These glands have two parts: 
  • Medulla and 
  • Cortex. 

The outer part is called cortex. It produces a hormone called cortin. Under secretion of cortin leads to lethargy, fatigue, lack of interest in sexual activities, irritability, depression, poor memory, sleep disturbances, indecisiveness, etc.  Over secretion of cortin results in over excitability, activeness, appearance of premature sexual characteristics, etc. Excess secretion in women leads to appearance of masculine characteristics.

              

Adrenal medulla secretes a hormone called Adrenaline and Noradrenalin (epinephrine and nor-epinephrine).  This hormone plays a very important role during emotional experiences. Adrenaline mobilizes the person for emergencies. It causes rapid heartbeat, high blood pressure, respiration, release of more energy, increasing muscular strength and decreases the function of digestive and excretory organs.

                                                      Function of Adrenal Gland

Sex glands: These glands secrete sex hormones.  At least a few male and female traits are related to the balance existing between male and female hormones.  Sex hormones are necessary for the development of interest in sex and personality traits. The sex hormones in males are called Androgens and in females they are called Estrogens and Progesterone. Under or over secretion affects the personality development. So also, early and late maturation affects personality and behaviour in various ways.

                   

 

The pancreas has two main functions: an exocrine function that helps in digestion and an endocrine function that regulates blood sugar. 

As a part of the digestive system, it secretes pancreatic juice into the duodenum through the pancreatic duct. This juice contains bicarbonate, which neutralizes acid entering the duodenum from the stomach; and digestive enzymes, which break down carbohydrates, proteins, and fats in food entering the duodenum from the stomach. 

As an endocrine gland, it functions mostly to regulate blood sugar levels, secreting the hormones insulinglucagonsomatostatin, and pancreatic polypeptide. Pancreas produces insulin. When the insulin quantity in blood goes very high, the sugar level comes down particularly in brain, resulting in giddiness, sweating, unconscious, lack of energy in limbs, etc.

             

 

BIOLOGICAL BASIS OF EMOTION

The following systems all interact to assist the body in experiencing and processing emotions:

  • The limbic system, 
  • Autonomic nervous system, and 
  • Reticular activating system

The limbic system is the area of the brain most heavily implicated in emotion and memory. Its structures include the hypothalamus, thalamus, amygdala, and hippocampus. 

                                    

                                                                       The limbic system

Role of Limbic System

  • The hypothalamus plays a role in the activation of the sympathetic nervous system, which is a part of any emotional reaction. 
  • The thalamus serves as a sensory relay center; its neurons project signals to both the amygdala and the higher cortical regions for further processing. 
  • The amygdala plays a role in processing emotional information and sending that information on to cortical structures. 
  • The hippocampus integrates emotional experience with cognition.

 

  • The processes of the limbic system control our physical and emotional responses to environmental stimuli. This system categorizes the experience of an emotion as a pleasant or unpleasant mental state. 

 

  • Based on this categorization, neurochemicals such as dopamine, noradrenaline, and serotonin increase or decrease, causing the brain’s activity level to fluctuate and resulting in changes in body movement, gestures, and poses.

Role of Amygdala

  • The amygdala, located in the left and right temporal lobes of the brain, has received a great deal of attention from researchers investigating the biological basis of emotions, particularly of fear and anxiety.
  • The amygdala plays a decisive role in the emotional evaluation and recognition of situations as well as in the analysis of potential threats.
  • It handles external stimuli and induces vegetative reactions.
  • Two parts of the amygdala include the basolateral complex and the central nucleus. 

                                                   

  • The basolateral complex has dense connections with a variety of sensory areas of the brain. It plays a critical role in classical conditioning and in attaching emotional value to learning processes and memories. 
  • The central nucleus plays a role in attention. It has connections with the hypothalamus and various areas of the brainstem and regulates the activity of the autonomic nervous and endocrine systems 
  • Research suggests that the amygdala is involved in mood and anxiety disorders. 
  • Changes in amygdala structure and function have been found in adolescents who either are at risk for or have been diagnosed with a mood or anxiety disorder.
  • It has also been suggested that functional differences in the amygdala could be used to differentiate individuals suffering from bipolar disorder from those suffering from major depressive disorder.

KlüverBucy syndrome is a syndrome resulting from bilateral lesions of the medial temporal lobe (including amygdaloid nucleus). It is a rare behavioral impairment characterized by inappropriate sexual behaviors and mouthing of objects. Other signs and symptoms, include a diminished ability to visually recognize objects, loss of normal fear and anger responses, memory loss, distractibility, seizures, and dementia.

 

Role of Hippocampus

  • Hippocampal structure and function are linked to a variety of mood and anxiety disorders. 
  • Individuals suffering from posttraumatic stress disorder (PTSD) show marked reductions in volume in several parts of the hippocampus, which may be the result of decreased levels of neurogenesis and dendritic branching.
  • Studies have found improvements in behavior as well as increase in hippocampus volume following either pharmacological or cognitive behavioral therapy in individuals suffering from PTSD.

Role of Autonomic Nervous System

  • The autonomic nervous system (ANS) is part of the peripheral nervous system in humans.
  • It is regulated by the hypothalamus and controls our internal organs and glands, including such processes as pulse, blood pressure, breathing, and arousal in response to emotional circumstances. 
  • The ANS is generally thought to be outside of voluntary control.
  • The ANS can be further subdivided into the sympathetic and parasympathetic nervous systems. 

 

  • The parasympathetic and sympathetic divisions of the ANS have complementary functions, and they operate in tandem to maintain the body’s equilibrium. 
  • Equilibrium of the body, in which biological conditions (such as body temperature) are maintained at optimal levels, is known as homeostasis. 

The Reticular Activating System

  • The reticular activating system (RAS) is a network of neurons that runs through the core of the hindbrain and into the midbrain and forebrain.
  • The RAS is involved with arousal and attention, sleep and wakefulness, and the control of reflexes. 
  • The RAS is believed to first arouse the cortex and then maintain its wakefulness so that sensory information and emotion can be interpreted more effectively.
  • It helps us fulfil goals by directing our concentration toward them and plays a role in individuals’ responses to situations and events.

                                                     

 

Role of the Cerebral Hemispheres in Emotion

Role of the Cerebral Hemispheres in Emotion—and in Psychological Disorders Growing evidence indicates that activation of the left cerebral hemisphere is associated with positive affect, while activation of the right hemisphere is associated with negative affect. Further, activation of anterior portions of both hemispheres is associated with the valence (pleasantness/unpleasantness) of emotions, while activation of the posterior portions of the hemispheres is associated with arousal—the intensity of emotions. Together, these findings suggest that depressed persons should show reduced activity in the right posterior regions, while anxious persons should show increased activity in these regions. These results have been confirmed in recent studies. 

 

BIOLOGICAL BASIS OF MOTIVATION

Role of Hypothalamus

  • It’s a small area below the thalamus.
  • It contains fibre and tracts related to motivated behavior of biological sort.
  • It controls secretion of hormones from pituitary gland.
  • Regulates body temperature, thirst, hunger, sleeping, waking, sexual activity and emotions.

 

               

There are mainly four biological motives:

  • HUNGER
  • THIRST
  • SLEEP
  • SEX

Drive Reduction Theory

A theory of motivation developed by Clark L. Hull, the Drive-Reduction Theory focuses on how motivation originates from biological needs or drives.

A “drive” is a state of arousal or tension triggered by a person’s physiological or biological needs. These needs include hunger, thirst, need for warmth, etc. In this theory, Hull stated that drives give rise to an individual’s motivation. Furthermore, Hull explained that an individual is in a state of need when his survival is threatened. When a person’s drive emerges, he will be in an unpleasant state of tension and the person will behave in such a way that this tension is reduced. To reduce the tension, he will begin seeking out ways to satisfy his biological needs. For instance, you will look for water to drink if you are thirsty. You will seek for food if you are hungry.

According to the theory, any behaviour that reduces the drives will be repeated by humans and animals. This is because the reduction of the drive serves as a positive reinforcement (i.e. a reward) for the behaviour that caused such drive reduction.

Drive Reduction Theory

 

 

 

Reduction of Hunger Drive

 

Hypothalamic Centres related to Hunger Motive

Hunger Motive

  • The digestive system influences hunger in several ways. 
  • After a meal, the stomach and intestines send nerve impulses to the brain to help people recognize that they are full.
  • The body converts food to Glucose, a simple sugar that acts as an energy source for cells. The level of glucose in the blood affects hunger. 
  • Low blood glucose increases hunger; high blood glucose decreases hunger.

 

Biological Basis of Hunger Motivation

Eating Disorders

Hyperphagia describes the extreme, unsatisfied, drive to consume food. 

Aphagia is the inability or refusal to swallow. Bilateral lesions in the adjacent ventrolateral hypothalamus (VLH) were later found to cause aphagia (absence of eating), which led to death by starvation.

Night Eating Syndrome (NES) is a night binging disorder: lack of appetite upon wakening in the morning, extremely elevated appetite in the evening (hyperphagia) and sleeping disturbances.

Prader-Willi syndrome (PWS): A rare condition characterized by a chronic feeling of hunger that, coupled with a metabolism that utilizes drastically fewer calories than normal, can lead to excessive eating and life-threatening obesity.

Anorexia Nervosa The male or female suffering from anorexia nervosa will typically have an obsessive fear of gaining weight, refusal to maintain a healthy body weight and an unrealistic perception of body image. Many people with anorexia nervosa will fiercely limit the quantity of food they consume and view themselves as overweight, even when they are clearly underweight. Anorexia can have damaging health effects, such as brain damage, multi-organ failure, bone loss, heart difficulties, and infertility. The risk of death is highest in individuals with this disease.

Bulimia Nervosa- This eating disorder is characterized by repeated binge eating followed by behaviors that compensate for the overeating, such as forced vomiting, excessive exercise, or extreme use of laxatives or diuretics. Men and women who suffer from Bulimia may fear weight gain and feel severely unhappy with their body size and shape. The binge-eating and purging cycle is typically done in secret, creating feelings of shame, guilt, and lack of control.  

Binge Eating Disorder- Individuals who suffer from Binge Eating Disorder will frequently lose control over his or her eating. Episodes of binge-eating are not followed by compensatory behaviors, such as purging, fasting, or excessive exercise.  Many people suffering from BED may be obese and at an increased risk of developing other conditions, such as cardiovascular disease. Men and women who struggle with this disorder may also experience intense feelings of guilt, distress, and embarrassment related to their binge-eating, which could influence the further progression of the eating disorder.

 

 

Control Mechanism for Regulation of Water Intake

 

SEXUAL MOTIVE

This is a biological motive, arises in the organism as a result of secretion of sex hormones.

  • Gonads- primary sex glands
  • Male sex hormone- Testosterone
  • Female sex hormone- Estrogen

Sex need is not essential for the survival of the individual, but it is essential for the survival of the species. 

Amphetamines are the chemicals release by brains of sexually attracted persons.

Phenylethylamines are the amphetamine like substances – first stage in falling in love.

Low level of these hormones leads to peak sexual drive.

 

                  

 

Phases of Sexual Response Cycle

 

 

 

GENETICS AND BEHAVIOR

Heredity: Biologically determined characteristics passed from parents to their offspring.

Chromosomes: Threadlike structures containing genetic material, found in nearly every cell of the body.

Genes: Segments of DNA that serve as biological blueprints, shaping development and all basic bodily process.

All human beings have 23 pairs of chromosomes:

22 of these are autosomes, while the remaining pair (either XX, female, or XY, male) represents a person’s sex chromosomes. 

These 23 pairs of chromosomes work together to create the person we ultimately become.

Each of our chromosomes has a characteristic structure. Historically, scientists have used a staining technique that colours the chromosomes into a banding pattern. These banding patterns make each of our individual chromosomes easier to identify, like a map. A set of chromosomes, as seen under a microscope, is known as a karyotype. Any deviation from the normal karyotype is known as a chromosome abnormality. While some chromosome abnormalities are harmless, some are associated with clinical disorders.

 

                                      

Normal Human Karyotype

 

                   

Sex Determination in Humans

The sex of a human baby is determined by the composition of its sex chromosomes (a single distinct pair among humans' 23 pairs of chromosomes). Females possess two copies of the same chromosome (referred to as the 'X' chromosome); males have one copy of the X chromosome and one copy of the smaller, hook-shaped Y chromosome.

When fertilization occurs, the new gamete (the initial cell from which a fetus grows) always inherits one of the mother's X chromosomes, and either an X or a Y from the father, depending on which chromosome the fertilizing sperm cell happened to inherit. One could say, then, that the father-or, at least, his sperm-determines the sex of the child. 

Chromosomal Anomalies

Chromosomal anomalies may sometimes be associated with physical and/or mental impairments. Most human cells contain 46 chromosomes (23 pairs), half of which are inherited from each parent. Only the reproductive cells (the sperm cells in males and the ova in females) have 23 individual chromosomes, not pairs. When the sperm and ovum combine at fertilization, the fertilized egg that results contains 23 chromosome pairs. A fertilized egg that will develop into a female contains chromosome pairs 1–22 and the XX pair. A fertilized egg that will develop into a male contains chromosome pairs 1–22 and the XY pair.

Chromosomal anomalies affect sex chromosomes and autosomes equally.  

Chromosomal anomalies cause various disorders. Anomalies that affect autosomes (the 22 paired chromosomes that are alike in males and females) are more common than those that affect sex chromosomes (X and Y).

Chromosomal abnormalities fit into several categories but broadly may be considered as numerical or structural.

Numerical abnormalities (aneuploidy) include

  • Trisomy (an extra chromosome)
  • Monosomy (a missing chromosome)

Structural abnormalities include

  • Translocations (anomalies in which a whole chromosome or segments of chromosomes inappropriately join with other chromosomes).
  • Deletions and duplications of various parts of chromosomes

Human disorders due to chromosome alterations in autosomes 

There only 3 trisomy that result in a baby that can survive for a time after birth; the others are too devastating and the baby usually dies in utero.

  1. Down syndrome (trisomy 21): The result of an extra copy of chromosome 21. People with Down syndrome are 47, 21+. Down syndrome affects 1:700 children and alters the child's phenotype either moderately or severely:
  • characteristic facial features, short stature; heart defects
  • susceptibility to respiratory disease, shorter lifespan
  • prone to developing early Alzheimer's and leukemia
  • often sexually underdeveloped and sterile, usually some degree of mental retardation.
  • Down Syndrome is correlated with age of mother but can also be the result of nondisjunction of the father's chromosome 21.
  1. Patau syndrome (trisomy 13): serious eye, brain, circulatory defects as well as cleft palate. 1:5000 live births. Children rarely live more than a few months.
  2. Edward's syndrome (trisomy 18): almost every organ system affected 1:10,000 live births. Children with full Trisomy 18 generally do not live more than a few months.

Nondisjunction of the sex chromosomes (X or Y chromosome): 

  • Klinefelter syndrome: 47, XXY males. Male sex organs; unusually small testes, sterile. Breast enlargement and other feminine body characteristics. Normal intelligence.
  • 47, XYY males: Individuals are somewhat taller than average and often have below normal intelligence. At one time (~1970s), it was thought that these men were likely to be criminally aggressive, but this hypothesis has been disproven over time.
  • Trisomy X: 47, XXX females. 1:1000 live births - healthy and fertile - usually cannot be distinguished from normal female except by karyotype.
  • Monosomy X (Turner's syndrome): 1:5000 live births; the only viable monosomy in humans - women with Turner's have only 45 chromosomes! XO individuals are genetically female, however, they do not mature sexually during puberty and are sterile. Short stature and normal intelligence. (98% of these fetuses die before birth)

Alterations in chromosome structure:

Sometimes, chromosomes break, leading to 4 types of changes in chromosome structure:

  1. Deletion: a portion of one chromosome is lost during cell division. That chromosome is now missing certain genes. When this chromosome is passed on to offspring the result is usually lethal due to missing genes.

Example - Cri du chat (cry of the cat): A specific deletion of a small portion of chromosome 5; these children have severe mental retardation, a small head with unusual facial features, and a cry that sounds like a distressed cat.

  1. Duplication: if the fragment joins the homologous chromosome, then that region is repeated

Example - Fragile X: the most common form of mental retardation. The X chromosome of some people is unusually fragile at one tip - seen "hanging by a thread" under a microscope. Most people have 29 "repeats" at this end of their X-chromosome, those with Fragile X have over 700 repeats due to duplications. Affects 1:1500 males, 1:2500 females.

  1. Translocation: a fragment of a chromosome is moved("trans-located") from one chromosome to another - joins a non-homologous chromosome. The balance of genes is still normal (nothing has been gained or lost) but can alter phenotype as it places genes in a new environment. Translocation can also cause difficulties in egg or sperm development and normal development of a zygote. Acute Myelogenous Leukemia is caused by this translocation.

Some of the most common chromosomal abnormalities include:

  • Down's syndrome or trisomy 21
  • Edward's syndrome or trisomy 18
  • Patau syndrome or trisomy 13
  • Cri du chat syndrome or 5p minus syndrome (partial deletion of short arm of chromosome 5)
  • Wolf-Hirschhorn syndrome or deletion 4p syndrome
  • Jacobsen syndrome or 11q deletion disorder
  • Klinefelter's syndrome or presence of additional X chromosome in males
  • Turner syndrome or presence of only a single X chromosome in females
  • XYY syndrome and XXX syndrome

 

Major Numerical Abnormalities

  • Huntington's disease (HD) is a fatal genetic disorder that causes the progressive breakdown of nerve cells in the brain. It deteriorates a person's physical and mental abilities usually during their prime working years and has no cure.
  • Phenylketonuria (PKU) is an inborn error of metabolism that results in decreased metabolism of the amino acid phenylalanine. Untreated, PKU can lead to intellectual disability, seizures, behavioral problems, and mental disorders. It may also result in a musty smell and lighter skin.

 

NATURE vs. NURTURE DEBATE

Nature: Our genetics determine our behavior. Our personality traits and abilities are in our nature. We genetically inherit physical traits from our parents, but we also inherit personality traits, intelligence, and preferences. Studies show that we inherit genes that are related to certain personality traits.

Nurture: Our environment, upbringing, and life experiences determine our behavior. We are nurtured to behave in certain ways. The household and city we grew up in, how we were raised by our parents, teachers, and friends -these are environmental factors that determine who we are. Often Identical twins grow up to have very different personalities and preferences.

Today it is generally accepted that nature and nurture work in tandem to create the people we ultimately become.

Adoption and twin studies show that both nature and nurture are factors in human development.

The environment in which a person is raised can trigger expressions of behavior for which that person is genetically predisposed; genetically identical people raised in different environments may exhibit different behavior.

Effect of Nature & Nurture

 

BEHAVIOR GENETICS is the study of the effects of heredity on behavior. 

Behavioral genetics tries to answer this question: To what extent are our abilities, personality traits, sexual orientations, sociability, and psychological disorders determined by genes inherited from our parents?

                             

 

ADOPTION AND TWIN STUDIES

In adoption studies, identical twins raised by different families can give insight into the nature-versus-nurture debate. Since the child is being raised by parents who are genetically different from his or her biological parents, the influence of the environment shows in how similar the child is to his or her adoptive parents or siblings. Adoption studies make a strong case for the influence of environment, whereas twin studies make a strong case for genetic influence.

                          

Twin Studies are used to help us answer the question of "nature vs. nurture:' because identical twins share the same genetic makeup, we can assume that differences between them are due to environmental factors.

Genes & Success 

Studies show that for children living in poverty, it did not matter whether they had good genes or not. The negative impact of the environment almost always played a greater role in their future success than their genes.

For children in middle class and wealthy homes, having good genes became very important to determining their future success. Genes played a much greater role in the future success of each child.

METHODS OF PHYSIOLOGICAL PSYCHOLOGY

Invasive Techniques

A medical procedure that invades (enters) the body, usually by cutting or puncturing the skin or by inserting instruments into the body.

Non - Invasive Techniques

A non-invasive procedure is a conservative treatment that does not require incision into the body or the removal of tissue.

Types of Invasive Techniques

  • LESION METHODS
  • CHEMICAL METHODS
  • MICROELECTRODE STUDIES
  • ANATOMICAL METHODS
  • DEGENERATIVE TECHNIQUES
  • (covered under above methods)

LESION METHODS

  • Part of the brain is removed, damaged or destroyed.
  • Behavior of subject is assessed to determine functions of the lesioned structure.

Types of lesions:-

  1. Aspiration lesions: Cortical tissue (grey matter) is drawn out by suction through a fine-tipped handheld glass pipette.
  2. Radio-Frequency lesions: small sub-cortical lesions are made by passing a radio-frequency current through the target tissue, heat from current destroys the tissue.
  3. Knife Cuts: sectioning (cutting) is used to eliminate conduction in a nerve or tract.
  4. Cryogenic Blockage: coolant is pumped through an implanted cryoprobe; neurons near the tip are cooled until they stop firing (temp is maintained above freezing level to prevent structural damage); when tissue is warmed up, normal neural activity returns.

CHEMICAL METHODS

Chemical Stimulation: Using a small injection tube, called a cannula, any pharmacological agent can be placed in a restricted brain region.

Microiontophoresis: Iontophoresis means literally "carried by ions." Microiontophoresis is the most precise form of chemical stimulation of the brain possible today.  In this method, a cluster of micropipettes is employed. BY passing a small electrical current through a pipette containing an ionized solution, molecules of the substance can be released from the pipette onto the target cell. 

Microdialysis: It is a related procedure by which chemicals are extracted from the fluid surrounding nerve cells for purposes of analysis. Dialysis is a process by which molecules are separated from a solution by using a special membrane that allows molecules of a particular size to cross the membrane freely.

Chemical procedures are also useful in producing specific brain lesions. In this approach, a neurotoxin, or nerve poison, is injected through a stereotaxically positioned cannula. 

Neurotoxins 

  • 6 Hydroxydopamine (6HDA) - Destroys dopamine neurons but leaves other neurons   alone. 

Advantage: Allows you to only kill one type of neuron. 

  • Kanic Acid - Destroys somas (cell bodies) of neurons, but leaves axon tracts from other neurons alone. 

Advantage: Can kill neurons in one area, but does not disturb neuron tracts from other areas

 

MICROELECTRODE STUDIES

Microelectrodes are very small electrodes with very small tips that can be used to record the electrical activity of single nerve cells.

Stereotactic surgery is a minimally invasive form of surgical intervention which makes use of a three-dimensional coordinate system to locate small targets inside the body and to perform on them some action such as ablation, biopsy, lesion, injection, stimulation, implantation, radiosurgery, etc. It can be used to place tiny electrodes within animal brain causing damage in particular part or changes in that part recorded.

stereotaxic apparatus is a mechanism that fastens to the head in a fixed position relative to standard features of the skull. From these skull landmarks, the approximate location of hidden brain structures can be determined. 

stereotaxic atlas, a map of the typical brain and skull for the species, is used to calculate the coordinates of the tissue to be lesioned

                                      

A stereotaxic apparatus

ANATOMICAL METHODS

For most kinds of microscopic investigations, the tissue to be imaged must be this enough for light to pass through it, and portions of it must be of different colors or transparency so that important features are distinguishable. A variety of histological (having to do with the study of the minute structure of tissues) procedures have been devised to meet these objectives.

 It has four procedural steps:

  1. Fixation- The tissue to be examined must first be prepared by fixation, a procedure to preserve the features of interest. Fixation is often accomplished by using an agent - such as formalin - to harden the tissue. Freezing is another useful approach to stabilizing neural tissue.
  2. Preservation of tissue- One typical procedure is to first embed the tissue in a substance such as paraffin to facilitate holding the specimen.
  3. Sectioning of tissue- It then can be cut by using a microtome, a specialized automatic slicing machine that produces thin, regular sections if the fixed and embedded tissue. The resulting thin sections may then be mounted on glass slides in preparation for viewing.
  4. Staining of tissue- Staining is a procedure to selectively darken or color particular features of the sectioned tissue. By choosing an appropriate stain, different features of the tissue are highlighted.
  • The Golgi silver stain has the property of completely staining a few individual cells in the specimen. Because only a few cells are stained, they stand out with exquisite clarity. The Golgi method is probably the best histological procedure for visualizing single nerve cells.
  • Nissl staining is useful for visualizing the distribution of cell bodies in the specimen.
  • Myelin stains selectively color this protective coating, a procedure that is useful for mapping connecting pathways in brain tissue.

 

Uses of histological techniques 

  • Confirming lesion sites or electrode locations 
  • In combination with neural tracing techniques
  • In combination with autoradiography or immuno-histochemistry techniques

Nissl Stains – e.g., cresyl violet – stains mainly cell bodies 

Golgi Silver Stain – stains whole neurons 

Myelin Stains (Fibre stains) – e.g., Weigert stain – stains mainly myelin

 

Immunocytochemistry 

  • Makes use of antibodies for specific proteins, such as receptors or enzymes. 
  • The antibody is labelled with a fluorescent die or a radioactive element (commercially available). 
  • Brain tissue is sliced and exposed to a solution containing the labelled antibody. 
  • Brain slices are viewed under microscope to identify the regions where protein of interest is distributed. 

                                            

Immunocytochemistry

Autoradiography 

  • auto (self–generating) + radiography (using radioisotopes to give you a print on film) 
  • Uses radioactive isotopes with unstable nuclei that throw off energy that can be recorded. 
  • Used to locate receptor sites.

 

       

 

Types of Non-Invasive Techniques

  • COMPUTERIZED TOMOGRAPHY (CT) SCAN
  • MAGNETIC RESONANCE IMAGING (MRI)
  • POSITRON EMISSION TOMOGRAPHY(PET)
  • THE ELECTROENCEPHALOGRAM (EEG)
  • MAGNETOENCEPHALOGRAPHY (MEG)
  • FUNCTIONAL MAGNETOENCEPHALOGRAPHY (FMEG)
  • EVENT-RELATED POTENTIAL (ERP)
  • ELECTRICAL STIMULATION OF THE BRAIN (ESB) 
  • SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE (SQUID)
  • MAGNETIC RESONANCE (MR) SPECTROSCOPY
  • NEAR INFRARED SPECTROSCOPY (NIRS)

Computerized Tomography (CT) Scan

Computerized tomography (CT) was the first of the new brain-imaging technologies. It is a computer assisted X-ray procedure. Instead of producing the usual shadow imaging of a conventional X-ray, in CT an image of a horizontal slice of tissue is reconstructed. In CT, narrow X-ray beams are passed through the head in a particular cross-sectional slice from a wide variety of angles. The amount of radiation absorbed along each line is measured. From the measurements associated with each beam, a computer program can determine the density of tissue at each point in the slice. An X-ray scanner is rotated 1 degree at a time over 180 degree. It reveals structural abnormalities, such as cortical atrophy or lesions caused by a stroke or trauma. 

                                        

 

Magnetic Resonance Imaging (MRI)

Magnetic resonance imaging (MRI) also provides a mathematically reconstructed image of slices of living tissue. MRI exploits a phenomenon known as nuclear magnetic resonance, in which radio-frequency energy in a strong magnetic field is used to generate signals from a particular atom - usually hydrogen - contained within the tissue. A strong magnetic field causes hydrogen atoms to align in the same orientation. When a radio frequency wave is passed through the head, atomic nuclei emit electromagnetic energy.  The MRI scanner is tuned to detect radiation emitted from the hydrogen molecules. Finally, computer reconstructs the image.

Certain properties of the phenomenon of magnetic resonance confer great advantages to MRI as an imaging technique. 

  • First, unlike in CT, no ionizing radiation is employed. 
  • Second, MR images have extremely fine spatial resolution, providing neuroanatomical images of exquisite detail. 
  • Third, because of technicalities in the MRI procedure, it is possible to obtain slices at any angle, not just in the horizontal plane, as is the case with CT. Three-dimensional images of the brain may also be generated. 
  • Finally, advanced MRI methods have recently permitted the imaging of brain function as well as structure, measuring both brain blood flow and oxidative metabolism. 

 

Positron Emission Tomography (PET)

It provides images indicating the functional or physiological properties of the living human brain. PET involves the injection of a positron emitting radionuclide (e.g., 2-deoxyglucose). One common tracer is labelled fluorodeoxyglucose (FDG), a subcourse that is taken up by cells when they need glucose for nutrition. Over the course of a few minutes, metabolically active portions of the brain will accumulate more FDG than well less active regions. By determining where FDG is accumulating in the brain, patterns of differential brain activation can be mapped. Positrons interact with electrons which produce photons (gamma rays) traveling in opposite directions. PET scanner detects the photons. Computer determines how many gamma rays from a particular region and a map is made showing areas of high to low activity.

 

The Electroencephalogram (EEG)

The electroencephalogram (EEG) is the neurologist’s term for the electrical activity that may be recorded from electrodes placed on the surface of the scalp. It measures electrical activity of brain via electrodes placed at specific location on the skull. The EEG is generated primarily by the activity of large numbers of nerve cells within the brain. The encephalogram has proven to be most useful in studying the sleep-waking cycle and in diagnosing epilepsy.

                                 

 

Magneto encephalography (MEG)

MEG measures changes in magnetic fields on the scalp surface that are produced by changes in patterns of neural activity. One important difference between MEG and EEG is that the skull is electrically resistant but magnetically transparent.

Advantage of MEG over EEG – It has greater accuracy and more reliable localization due to minimal distortion of the signal.

Clinical Uses – Evaluation of epilepsy: to localize the source of epileptiform brain activity, usually performed with simultaneous EEG

 

Functional Magneto encephalography (fMEG)

The fMRI is a series of MRIs that measures both the structure and the functional activity of the brain through computer adaptation of multiple images. Specifically, the fMRI measures signal changes in the brain that are due to changing neural activity. In an fMRI, a patient can perform mental tasks and the area of action can be detected through blood flow from one part of the brain to another by taking pictures less than a second apart and showing where the brain “lights up.” 

 

Event-Related Potential (ERP)

It is a component of the EEG that is triggered in association with sensory, motor, or mental event. ERPs are used extensively to study the time course of higher-level processes in the human brain, such as perception and attention. ERPs are typically small fluctuations produced by the processing of a sensory stimulus or motor events.

 

Electrical stimulation of the brain (ESB) 

It is an effective means of demonstrating functional neural connections between two brain regions. If an electrical stimulation of one area evokes an electrical response in another, there must be some functional pathway linking the two regions of the brain. By using specialized techniques, stimulation may be confined to a single nerve cell. Usually, the effects of ESB are apparent immediately following stimulation. Electrical stimulation of the lateral hypothalamus - an area deep within the brain related to feeding - may have no immediate effect but will increase the amount of food that a cat will eat the following day by as much as 600 per cent.

Human Brain Stimulation:

  • The problem for a neurosurgeon attempting to remove diseased tissue in regions of the brain that support higher mental functions - such as language - is that those functions are not always carried out by exactly the same brain areas, particularly in individuals with a long history of brain disease.
  • ESB provides the "gold standard" by which the functional properties of a region of brain may be determined before the tissue is surgically removed.
  • For this reason, ESB is often carried out with the surface of the brain exposed during neurosurgery. The patient is conscious, since it is necessary to determine whether stimulation of a particular cortical region affects speech perception of production. Such an operation is possible because the brain itself does not have pain receptors; only a topical anaesthetic is required to deaden the nerves of the scalp and skull.
  • As different regions of the brain are stimulated, speech perception and production are tested.
  • Electrical stimulation of the human brain is also carried out - although much less frequently - by using electrodes that have been surgically implanted within the brain of patients undergoing prolonged (e.g. several weeks) of monitoring often for the localization of epileptic disorders. Studies of such patients have also contributed to the understanding of certain higher mental functions.

 

Superconducting Quantum Interference Device (SQUID)

SQUID is a very sensitive device for measuring weak magnetic fields. It captures images of brain. It detects tiny changes in magnetic fields in the brain. It can map various brain functions. SQUID uses Josephson effect phenomena to measure extremely small variations in magnetic flux. Typically, a SQUID is a ring of superconductor interrupted by one or more Josephson junctions.

                       

Magnetic Resonance (MR) spectroscopy

It is a non-invasive diagnostic test for measuring biochemical changes in the brain, especially the presence of tumours. 

Spectroscopy is a series of tests that are added to the MRI scan of your brain or spine to measure the chemical metabolism of a suspected tumor. MR spectroscopy analyzes molecules such as hydrogen ions or protons.

Proton spectroscopy is more commonly used. There are several different metabolites, or products of metabolism, that can be measured to differentiate between tumor types:

  • Amino acids
  • Lipid
  • Lactate
  • Alanine
  • N-acetyl aspartate
  • Choline
  • Creatine
  • Myoinositol

 

The frequency of these metabolites is measured in units called parts per million (ppm) and plotted on a graph as peaks of varying height. By measuring each metabolite’s ppm and comparing it to normal brain tissue, the neuro-radiologist can determine the type of tissue present.

While magnetic resonance imaging (MRI) identifies the anatomical location of a tumor, MR spectroscopy compares the chemical composition of normal brain tissue with abnormal tumour tissue.

 

Near Infrared spectroscopy (NIRS)

It is a spectroscopic method that uses the near-infrared region of the electromagnetic spectrum (from 780 nm to 2500 nm). It measures blood oxygenation, de-oxygenation & total haemoglobin in brain. Functional near infrared spectroscopy (fNIRS) is a non-invasive optical imaging technique that uses low levels of light to measure blood flow changes in the brain associated with brain activity, such as performance of a task.  The NIRS systems provide non-invasive measurements of oxygen saturation, haemoglobin and cytochrome C levels.

 

NEUROPLASTICITY

Neuroplasticity refers to the brain's ability to change and adapt as a result of experience. 

Neuro refers to neurons, the nerve cells that are the building blocks of the brain and nervous system, and plasticity refers to the brain's malleability.

Neuroplasticity is the brain’s ability to alter the structure of its neural network. It can form new neurons, make new neural connections, and rearrange or eliminate pre-existing connections. In other words, neuroplasticity is a person’s ability to change.

 

History and Research on Brain Plasticity

  • Up until the 1960s, researchers believed that changes in the brain could only take place during infancy and childhood. 
  • By early adulthood, it was believed that the brain's physical structure was mostly permanent. 
  • Modern research has demonstrated that the brain continues to create new neural pathways and alter existing ones in order to adapt to new experiences, learn new information, and create new memories.
  • In the 1920s, researcher Karl Lashley provided evidence of changes in the neural pathways of rhesus monkeys. 
  • By the 1960s, researchers began to explore cases in which older adults who had suffered massive strokes were able to regain functioning, demonstrating that the brain was much more malleable than previously believed.

 

How Brain Plasticity Works

The brain possesses the remarkable capacity to reorganize pathways, create new connections, and, in some cases, even create new neurons. The first few years of a child's life are a time of rapid brain growth. At birth, every neuron in the cerebral cortex has an estimated 2,500 synapses; by the age of three, this number has grown to a whopping 15,000 synapses per neuron.

During childhood, the person’s environment will stimulate their brain, reinforcing certain connections. For example, when a child is taught how to draw, the neurons responsible for fine motor control will develop synapses. As a child practices drawing, the neural connections for that skill will become denser and more entrenched.

The average adult, however, has about half that number of synapses because as we gain new experiences, some connections are strengthened while others are eliminated. During adolescence, the brain eliminates neural connections that are no longer being used.   This process is known as synaptic pruning. 

Neurons that are used frequently develop stronger connections and those that are rarely or never used eventually die. By developing new connections and pruning away weak ones, the brain is able to adapt to the changing environment.

                               

Characteristics of Neuroplasticity

  • It can vary by age. Generally, young brains tend to be more sensitive and responsive to experiences than much older brains.
  • It involves a variety of processes. Plasticity is on-going throughout life and involves brain cells other than neurons, including glial and vascular cells.
  • It can happen for two different reasons. Plasticity can occur as a result of learning, experience, and memory formation, or as a result of damage to the brain. 
  • Environment plays an essential role in the process. The interaction between the environment and genetics also plays a role in shaping the brain's plasticity.
  • Brain plasticity is not always good. Brain changes are often seen as improvements, but this is not always the case. In some instances, the brain might be influenced by psychoactive substances or pathological conditions that can lead to detrimental effects on the brain and behavior.

 

TYPES OF BRAIN PLASTICITY

  1. Functional Neuroplasticity – It is the brain's ability to move functions from a damaged area of the brain to other undamaged areas.
  2. Structural Neuroplasticity – It is the brain's ability to actually change its physical structure as a result of learning.

 

Neuroplasticity and Psychology

  • Neuroplasticity is a key element of mental health counselling. When people in therapy learn new coping skills, they are literally building the neural connections that promote resilience. 
  • As people learn new habits, their new synapses will replace the connections that prompted unhealthy behaviors and cognitive distortions.
  • Some medications can also improve neuroplasticity. Most people with depression will also have reduced neuroplasticity. Antidepressants can often enhance neuroplasticity and even reverse the damage done during a depressive episode.
  • In some cases, improving neuroplasticity can itself be part of mental health treatment. 
  • Brains in the early stages of dementia often use neuroplasticity to compensate for cognitive decline. 
  • Aerobic exercise and cognitively challenging activities can increase a brain’s overall neuroplasticity. 

 

Neuroplasticity, Healing, and Adaptation

When a part of the brain is damaged or impaired, neuroplasticity can help it work around the issue. Here are some strategies a brain can use:

  • Reassign Brain Functions to a Similar Area

If part of a person’s brain is damaged in early life, the brain can “shift” this function to a similar part of the brain. For example, say a child damaged their right parietal lobe, which helps them know their body’s position in space. The brain may reassign this skill to the matching left parietal lobe. This will allow the child to physically navigate their environment despite the brain damage.

  • Develop another Way to Do the Task

Sometimes a brain function can’t be relocated. However, neurons can be rearranged to compensate for that lost brain function. 

For example, if a person struggles to tell faces apart, they may have trouble recognizing friends and family. To fix the issue, their brain may learn how to distinguish between individual voices, allowing the person to recognize loved ones as soon as they talk.

  • “Translate” Sensory Input

Sensory cortices are the parts of the brain responsible for senses such as sight or touch. These cortices process data in a similar “language.” When one cortex doesn’t get information from its matching sense, the brain may feed it data from other senses instead.

For example, a person who is blind from birth will not get any sensory input from their eyes. Rather than let the visual cortex go to waste, the brain can use the sense of touch to “translate” information. So rather than using light to create a representation of their environment, a blind person can use touch to read Braille or navigate a room. 

BIOLOGICAL BASIS OF SLEEP

SLEEP is a process in which important physiological changes accompanies by major shifts in consciousness.

Sleep is an important part of your daily routine. Quality sleep – and getting enough of it at the right times -- is as essential to survival as food and water.  

Without sleep you can’t form or maintain the pathways in your brain that let you learn and create new memories, and it’s harder to concentrate and respond quickly.

Sleep plays a housekeeping role that removes toxins in your brain that build up while you are awake. 

 

SLEEP MECHANISMS

Two internal biological mechanisms–

  • Circadian Rhythm 
  • Homeostasis

They both work together to regulate when you are awake and sleep.  

Circadian rhythms are the cyclic changes in bodily process occurring within a single day. It occurs in 24 hour cycles.  It is generated by a “biological clock” whose activity is modulated by various external stimuli. These external cues ensure that the internal clock is in sync with the external environment. They control your timing of sleep and cause you to be sleepy at night and your tendency to wake in the morning without an alarm.

Sleep-wake homeostasis keeps track of your need for sleep.  The homeostatic sleep drive reminds the body to sleep after a certain time and regulates sleep intensity.  This sleep drive gets stronger every hour you are awake and causes you to sleep longer and more deeply after a period of sleep deprivation.

 

Factors that influence your sleep-wake needs include medical conditions, medications, stress, sleep environment, and what you eat and drink.  

Specialized cells in the retinas of your eyes process light and tell the brain whether it is day or night and can advance or delay our sleep-wake cycle.

 

ANATOMY OF SLEEP

Several structures within the brain are involved with sleep.

Hypothalamus- Within the hypothalamus is the suprachiasmatic nucleus (SCN) – clusters of thousands of cells that receive information about light exposure directly from the eyes and control your behavioral rhythm. 

Brain stem- Sleep-promoting cells within the hypothalamus and the brain stem produce a brain chemical called GABA, which acts to reduce the activity of arousal centres in the hypothalamus and the brain stem. 

Thalamus- During most stages of sleep, the thalamus becomes quiet, letting you tune out the external world.  But during REM sleep, the thalamus is active, sending the cortex images, sounds, and other sensations that fill our dreams. 

Pineal Gland- receives signals from the SCN and increases production of the hormone melatonin, which helps put you to sleep once the lights go down. 

Basal Forebrain - Release of adenosine from cells in the basal forebrain and probably other regions supports your sleep drive.  Caffeine counteracts sleepiness by blocking the actions of adenosine.

Amygdala- an almond-shaped structure involved in processing emotions becomes increasingly active during REM sleep. 

                             

SLEEP STAGES

There are two basic types of sleep:  

  1. RAPID EYE MOVEMENT (REM) SLEEP 
  2. NON-REM (NREM) SLEEP 

Non-Rem (NREM) Sleep

  • It is characterized by a reduction in physiological activity. As sleep deepens, a person’s 
  • brain waves slow down and gain amplitude, 
  • both breathing and the heart rate slow down, 
  • Individual’s blood pressure drops.

NREM sleep consists of three stages:

  1. NI: Stage 1
  2. N2: Stage 2
  3. N3: Stage 3 & 4

 

SLEEP STAGES

  • Wake Stage- It is characterised by:
  • Relaxed wakefulness
  • Alpha waves (8-13 cps)
  • Beta waves ((14-30 cps)
  • Tense  muscles
  • Eyes moving erratically
  • EMG- High voltage
  • EEG- low voltage
  • Fast and random waves
  • STAGE 1: Light sleep (5%)
  • Irregular breathing
  • Muscles relax 
  • Reflex muscles twitch- hypnic jerk
  • Theta waves (4-7 Hz)
  • Transition stage
  • About to sleep awareness
  • EEG- Low amplitude high frequency
  • EMG- lower than wake stage
  • Slow heart rate

 

  1. STAGE 2: True sleep (45-55%)
  • Eye movements stop
  • Brain waves slow down
  • Occasional burst of rapid     waves- sleep spindles (12-16Hz)
  • K – Complex formation – suppress cortical arousal
  • EMG- Low 
  • Theta waves & Delta waves
  • STAGE 3 & 4: Deep sleep or slow wave sleep
  • It occurs in longer periods during the first half of the night.  
  • heartbeat and breathing slow to their lowest levels 
  • muscles are relaxed 
  • difficult to awaken you
  • Brain waves become even slower. 
  • Delta waves appear (large and slow) 0.5-2Hz
  • No eye movements
  • EEG- High amplitude, low frequency
  • EMG- very low level
  • Growth hormones released

  • REM SLEEP
  • Occur in regular interval every 60-90min.
  • Saw-teeth like wave- Notched waves- Theta waves
  • Waves are fast and close
  • Look similar to wake stage
  • Irregular breathing, muscle atonia
  • Paralysis protect from self-damage
  • Dream stage
  • REM decreases with age
  • Few K-complexes form
  • Electroencephalogram (EEG)- rapid low voltage, mixed frequency
  • Electromyography (EMG)- drops to zero
  • Electrooculography (EOG)- Burst of eye movement, increase with sleep
  • Excessive beta waves

Role of REM in learning-

  • Consolidate memories
  • Eliminate unnecessary information
  • If trained animal deprived of REM Sleep show poor performance
  • After intense training- more REM sleep 

 

EEG OF SLEEP STAGES

Hypnogram- A hypnogram is a diagram of the stages of sleep as they occur during a period of sleep. This hypnogram illustrates how an individual moves through the various stages of sleep.

                                         

A Hypnogram

                

 

 

 

SLEEP DISORDERS

Sleep disorders are a group of conditions that affect the ability to sleep well on a regular basis. 

Symptoms of sleep disorders include:

  • difficulty falling or staying asleep
  • daytime fatigue
  • strong urge to take naps during the day
  • irritability or anxiety
  • lack of concentration
  • depression

Types of Sleep Disorders

Insomnia refers to the inability to fall asleep or to remain asleep. It can be caused by jet lag, stress and anxiety, hormones, or digestive problems.

Sleep Apnea is characterized by pauses in breathing during sleep. This is a serious medical condition that causes the body to take in less oxygen. It can also cause you to wake up during the night.

Parasomnias are a class of sleep disorders that cause abnormal movements and behaviors during sleep. They include:

  • sleepwalking
  • sleep talking
  • groaning
  • nightmares
  • bedwetting
  • teeth grinding or jaw clenching

Restless Leg Syndrome (RLS) is an overwhelming need to move the legs. This urge is sometimes accompanied by a tingling sensation in the legs.

Narcolepsy is characterized by “sleep attacks” that occur during the day. This means that you will suddenly feel extremely tired and fall asleep without warning. The disorder can also cause sleep paralysis, which may make you physically unable to move right after waking up.   

Night Terror is a partial waking from sleep with behaviors such as screaming, kicking, panic, sleep walking, thrashing, or mumbling.  

Sleepwalking, formally known as Somnambulism is a behavior disorder that originates during deep sleep and results in walking or performing other complex behaviors while asleep. 

Circadian Rhythm Disorders are disruptions in a person's circadian rhythm—a name given to the "internal body clock" that regulates the (approximately) 24-hour cycle of biological processes in animals and plants.

Sleep Drunkenness (SD) consists of difficulty in coming to complete wakefulness accompanied by confusion, disorientation, poor motor coordination, slowness, and repeated returns to sleep. 

Cataplexy is a sudden and uncontrollable muscle weakness or paralysis that comes on during the day and is often triggered by a strong emotion, such as excitement or laughter.   It is most commonly associated with narcolepsy.

REM Sleep Behavior Disorder (RBD) is characterized by the acting out of dreams that are vivid, intense, and violent.

 

 

 

Course Content

Sensory systems: General and specific sensations, receptors and processes
Neurons: Structure, functions, types, neural impulse, synaptic transmission. Neurotransmitters
The Central and Peripheral Nervous Systems – Structure and functions. Neuroplasticity
Methods of Physiological Psychology: Invasive methods – Anatomical methods, degeneration techniques, lesion techniques, chemical methods, micro electrode studies. Non-invasive methods – EEG, Scanning methods
Muscular and Glandular system: Types and functions Biological basis of Motivation: Hunger, Thirst, Sleep and Sex. Biological basis of emotion: The Limbic system, Hormonal regulation of behavior

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Farheen Mehboob
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Structure and function of the nervous system

This understanding will eventually improve our understanding of how our emotions affect health and disease.

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