HOW TO PREPARE UGC NET PSYCHOLOGY SUBJECT: PHYSIOLOGICAL PSYCHOLOGY

Unit 2: Biological Basis of Behavior

What is that makes an organism living? The answer is presence of the basic unit of life called cell. All organism composed of cell. Some are composed of single cell called unicellular organism- are capable of independent existence and performing essential function of life and others are like us, multicellular organism.

The structure of cell:

The surface of the cell called membrane or plasma membrane- a structure that separate the inside of the cell from outside environment. It is composed of two layers of fat molecules that are free to flow around one another. Most chemicals can’t cross the membrane but specific protein channels in the membrane permit a controlled flow of water, oxygen, carbon dioxide, sodium, potassium, calcium, chloride and other important chemicals. Except red blood cells (RBC), all animal cells contain a nucleus- a machinery to keep neuron alive; a mitochondria- a structure that perform metabolic activities and provide energy that the cell require for all other activities, Mitochondria required fuel and oxygen to function; a ribosomes- are the sites at which the cell synthesizes new protein molecules, protein provide building material for all the cell and facilitate various chemical reactions. Some ribosomes float freely within the cell whereas other are attached to Endoplasmic reticulum- A network of tin tubes that transport new synthesize protein to other locations.

Kinds of cell:

The nervous system consists two kinds of cell- neuron and glia. Neuron are the information career of the nervous system, they convey message to other neuron, muscles or to gland over great distances. The glia, generally smaller than the neuron, have many functions but do not convey information over great distances.

Neuron:

Neuron founds in many sizes and shapes but they have certain features in common. Larger neuron have these components: dendrites, cell body (soma), axon and synaptic terminals. The tiniest neuron found with lack axon and lack defined dendrites so they convey information either through graded potential or through dendrites that’s mean if the neuron doesn’t have axon than it’s possible to transmit information to other neuron. Dendrites are usually short and have many branches (looks like a tree branches) which receive stimulation from other neuron. Axon, on the other hand, quite long in a cylindrical tube form that extent from cell body or soma. The function of the axon is to conduct nerve impulse to other neuron, muscle or to gland. In many cases axon has a white fatty covering called “myelin sheath”- a sheath of proteins ½ mm in thickness contains specialized glial cells that wrap themselves around the axon. This covering increase the speed with which nerve impulse send down to axon. Myelin sheath is particularly prevalent where rapid transmission of action potential is critical for example- along axon that stimulate skeletal muscles. Neurons have small gaps between them are called “Nodes of Ranvier”. The insulation provided by myelin sheath allows for salutatory conduction in which the nerve impulse jump from one Nodes of Ranvier to another. This greatly increase the speed of transmission of the action potential down to axon. Finally near its end axon divides into small number of branches known as axon terminals.

Multiple Sclerosis:

A type of disease by which myelin sheath of a neuron is damaged and created a barrier for passing impulse to another. Because myelin sheath prevent from short circuiting one another like as electrical wires. This disorder, in which symptoms first become evident between ages 16 - 30 year. The immune system attack and damaged own myelin sheath.

Types of neuron:

Basically neuron are classified into three categories: sensory neuron (Afferent neuron), motor neuron (Efferent neuron) and inter neuron (Intrinsic neuron).

1.      Sensory neuron are highly sensitive at one end for particular type of stimulation Such as light, sound, touch etc. They transmit impulses received by receptors to central nervous system. Receptors are the specialized cells in the sense organs, muscles, skin and joints that detect physical or chemical changes and translate these events to impulses that travel along the sensory neuron.

2.      Motor neuron has its cell body (soma) in spinal cord. It receive excitation from other neuron through its dendrites and conduct impulses. Typically, motor neuron carry out going signals from central nervous system to muscles or gland. 

3.      Inter neuron- if a cell’s dendrites and axon are entirely contained within a single structure called inter neuron of that structure. Interneuron found only in brain, eye and spinal cord.

4.      Mirror neuron: are the group of neuron found in the premotor cortex that respond both to witnessed (observed) movements in others and to the analogous movement of self. Similar neurons have also found in the sensory association cortex in parietal lobe that linked to empathy- those feeling of concern, compassion and sympathy for others and even the development of language in humans. Typically, mirror neuron fire not only when a person enacts a particular but also when a person simply observe another individual carrying out the same behavior. That’s mean this neuron involves in observational learning. The discovery of mirror neuron suggest that the capacity of even young children to imitate others may be an inborn behavior.

Glia:

Glia (or neuroglia), the other major components of the nervous system, do not transmit information over long distances as neurons do, although they perform many other functions. The term glia, derived from a Greek word meaning “glue,” reflects early investigators’ idea that glia were like glue that held the neurons together. Although that concept is obsolete, the term remains. Glia are smaller but more numerous than neurons. The brain has several types of glia with different functions.

The star-shaped astrocytes wrap around the presynaptic terminals of a group of functionally related axons. By taking up ions released by axons and then releasing them back to axons, an astrocyte helps synchronize the activity of the axons, enabling them to send messages in waves. Astrocytes also remove waste material created when neurons die and control the amount of blood flow to each brain area. An additional function is that during periods of heightened activity in some brain areas, astrocytes dilate the blood vessels to bring more nutrients into that area. Uncertainty surrounds another possible function: Neurons communicate by releasing certain transmitters, such as glutamate. After a neuron releases much glutamate, nearby glia cells absorb some of the excess. We know that the glia convert most of this glutamate into a related chemical, glutamine, and then pass it back to the neurons, which convert it back to glutamate, which they get ready for further release. (It’s a recycling system.) The uncertain question is whether glia cells also release glutamate and other chemicals themselves

Microglia, very small cells, also remove waste material as well as viruses, fungi, and other microorganisms. In effect, they function like part of the immune system.

Oligodendrocytes in the brain and spinal cord and Schwann cells in the periphery of the body are specialized types of glia that build the myelin sheaths that surround and insulate certain vertebrate axons.

Radial glia guide the migration of neurons and their axons and dendrites during embryonic development. When embryological development finishes, most radial glia differentiate into neurons, and a smaller number differentiate into astrocytes and oligodendrocytes.

The Nerve Impulses: Resting and Action Potential

Information moves along the neuron in the form of a neural impulse called action potential- An electro-chemical impulse that travels from the cell body down to the end of axon. Each action potential is result of movement by electrically charged molecules, known as ions, in and out the neuron. The neuron are very selective about what ions can flow in and out the cell that is the cell membrane of neuron is semipermeable- which means that some ions can pass through easily but others are not allowed in the membrane are open. The proteins that regulate the flow of ions are such sodium (Na⁺), potassium (K⁺), calcium (Ca⁺⁺) and chloride (Cl^-). Each ion channel is very selective permitting only one type of ion to flow it when it is open.

When neuron is not generating an action potential, is referred to as a resting neuron (polarization). At rest cell membrane is not permitting to Na⁺ ions to flow inside of neuron and these ions are found at high concentration outside of the neuron. In contrast, the membrane is permeable to K⁺ ions, which tend to concentrate inside of the neuron. In this way the resting neuron maintain high concentration of Na⁺ ions outside of the neuron and low inside it (inside of the neuron more negative than outside). The electrical potential of a neuron at rest is term ‘resting membrane potential’ and range from -50 to -100 millivolts (-70 millivolts). 

When the neuron is stimulated by an excitatory input, the voltage difference across the cell membrane is reduced, the process called ‘depolarization’. If the depolarization is large enough, the voltage sensing Na⁺ channels located at the top of axon is open briefly and Na⁺ Ions flood into the cell. The electrical potential of a neuron at depolarization ranging from -50 millivolts to +40 millivolts. The speed of action potential as it travels downs vary from 2 to 200 miles per hour (1 to 120 meter per second).

All or none law: like a gun, neuron either fire that is transmit an electrical impulse along the axon or doesn’t fire. Neuron is either on or off with nothing between the on and off stage. More typically, the size of an action potential is constant and can’t be triggered by a stimulus unless it reached at threshold level. Thus, in response to any synaptic input, a neuron either fire an action potential or it doesn’t, and if fire action potential, the potential is always same size.                                                                                                                                                                    

Synapses:

The axon tips of a neuron make a functional connection with the dendrites or cell bodies of other neuron at synapses. The terminal button does not actually touch the dendrites or cell bodies of receiving cell, there is a slight gap called ‘synaptic cleft’ between the terminal button and the cell body of receiving cell.

A number of small bulb, called boutons are found at the end of axon. Boutons have in them small bodies or vesicles that contain neurotransmitters- a chemical substance that diffuse across the synaptic cleft and stimulates or inhibit the next neuron. These chemicals released from the vesicles into synaptic cleft when a nerve impulse reached the buttons of the transmitting cell. The neurotransmitter combines with the specialized receptor molecules in the receptor region of receiving cell.

Communication between Synapses: Neurotransmitters

Neurotransmitters are the chemical messengers that transmit information from one neuron to another ones. The major neurotransmitters are Acetylcholine, Dopamine, Serotonin, Epinephrine (Adrenalin), Nor-epinephrine (nor-adrenalin), GABA (Gamma-Aminobutyric Acid), Glutamate and Glycine.

Acetylcholine (Ach):

1.      Acetylcholine found throughout the nervous system is usually excitatory (Brain and ANS) but it can also be inhibitory, depending on the type of receptor molecules in the membrane of the receiving neuron.

2.      It is also found at all neuromuscular junctions therefore anything that interferes with the action of Ach can produce paralysis.

3.      Acetylcholine is particularly prevalent in an area of the forebrain called hippocampus, which plays a key role in formation of new memories.

4.      Ach play a prominent role in Alzheimer disease that affect many older people by causing impairment of memory and other cognitive functions.

Dopamine (DA):

1.      DA produced by the neurons located at the brain region “substantia nigra” involved in movement, attention and learning.

2.      Release of dopamine in certain areas of the brain produce intense feeling pf pleasure, and current research is investigating the role of DA in the development of addictions.

3.      Degeneration of DA has been linked to “Parkinson disease” and too much dopamine in some areas of the brain caused “schizophrenia”.

Norepinephrine (Noradrenalin):

1.      Mainly produce by the neurons in the brain stem. Any drug that causing norepinephrine to increase or decrease in the brain is correlated with an increase or decrease in the individual’s mood level.

2.      Cocaine and amphetamines prolong the action of norepinephrine by slowing down its reuptake. Because of this delay, the receiving neuron are activated for a longer period, which causes these drugs stimulating psychological effects. In contrast, lithium, speeds up the reuptake for norepinephrine, causing a person mood level to be depressed.

Serotonin (5HT):

1.      Serotonin found throughout the nervous system and primarily Inhibitory except hippocampus.

2.      This neurotransmitter play a crucial role in mood regulation like as norepinephrine for example, low level of serotonin have been associated with feelings of depression.

3.      Serotonin is also important in the regulation of sleep and appetite, it is also used to treat the eating disorder bulimia.

4.      It is implicate in the regulation of pain, dreaming, suicide, coping with stress and alcoholism.

Glutamate:

1.      The excitatory neurotransmitter glutamate is present in more neurotransmitters of the CNS than any other transmitters.

2.      Of the three or more subtypes of glutamate receptors, one in particular, NDMA subtype thought to affect learning and memory.

3.      Disruptions in glutamate neurotransmission have been implicated in schizophrenia.  

GABA (Gamma-aminobutyric acid):

1.      GABA found throughout central nervous system, is a major inhibitory transmitter in brain.

2.      It is implicate in sleep, aggression, eating disorders and anxiety disorders.

Neuropeptides:

Researchers often refers neuropeptides as neuromodulators, because they have several properties that set them apart from other transmitters. Whereas the neuron synthesizes most other neurotransmitters in the presynaptic terminals, it synthesizes neuropeptides in the cell body and then slowly transport them to other parts of the cell. Whereas other neurotransmitters are released at the axon terminals, neuropeptides are mainly released by dendrites, and also by the cell body and sides of the axon. Whereas a single action potential can release other neurotransmitters, neuropeptides release require repeated stimulation. However, after a few dendrites release a neuropeptides, the released chemical primes other nearby dendrites to release the same neuropeptide also, including dendrites of other cell.

Hormones:

Hormone is a chemical that secreted by cells in one part of body and conveyed by the blood to influence other cells. A neurotransmitter like a telephone signal: it conveys a message from sender to the intended receiver whereas hormones function more like a radio station: they convey a message to any receiver tuned in to the right station. Neuropeptides are intermediate. They are like hormones, except they diffuse only within the brain and the blood doesn’t carry them to other parts of the body. Among the various types of hormones are protein hormones and peptides hormones, composed of chain of amino acids. Protein are longer chain of amino acids, peptides are short chain of amino acids and neuropeptides are considered as chain of amino acids. Hormones are secreted by endocrine glands whose makeup endocrine system.

1.      Pituitary gland: attached to the hypothalamus, consists two different glands, the posterior pituitary and the anterior pituitary, which released different sets of hormones. The posterior pituitary, composed of neural tissue, can be considered an extension of hypothalamus. Neurons in the hypothalamus synthesizes the hormones oxytocin and vasopressin, which migrate down axons to the posterior pituitary. Later, the posterior pituitary release these hormones into the blood.

2.      The anterior pituitary, composed of glandular tissues, synthesizes six different hormones, although hypothalamus control their release. The hypothalamus secretes releasing hormones, which flow through the blood to the anterior pituitary.

3.      Pituitary gland also known as master gland because it controls the functioning of the rest of the endocrine system. The trophic hormone released by anterior pituitary used to control rest endocrine system.

4.      Hormones released by anterior pituitary are: 

Adrenocorticotropic hormone (ACTH) - control the secretion of adrenal cortex (cortisone) whereas adrenal medulla (adrenalin and noradrenalin) control by autonomic nervous system.

Thyroid – stimulating hormone (TSH) - control the secretion of thyroid gland.

Somatotropin (GH) – also known as growth hormone promotes growth throughout the body.

Prolactin – controls secretions of the mammary gland (increase milk production).

Follicle – stimulating hormone (FSH) – control secretions of gonads.

Luteinizing hormone – increase the production of progesterone (females) and testosterone (male); stimulate ovulation.

3.      Pineal gland – Melatonin - Increases sleepiness, influences sleep–wake cycle, also has a role in onset of puberty.

4.      Thyroid gland – Thyroxine and Triiodothyronine - Increases metabolic rate, growth, and maturation.

5.      Parathyroid – Parathyroid hormone - Increases blood calcium and decreases potassium.

6.      Adrenal cortex – Aldosterone - Reduces secretion of salts by the kidneys.

                         – Cortisol and corticosterone - Stimulates liver to elevate sugar, increase metabolism of proteins and fats.

7.      Adrenal medulla – Epinephrine, norepinephrine Similar to effects of sympathetic nervous system.

8.      Pancreas – Insulin – Increases entry of glucose to cells and increases storage as fats.

                – Glucagon – Increases conversion of stored fats to blood glucose.

9.      Ovary – Estrogens – Promote female sexual characteristics.

          – Progesterone – Maintains pregnancy.

10. Testis – Androgens – Promote sperm production, growth of pubic hair, and male                               sexual characteristics.

11. Liver – Somatomedins – Stimulate growth.

12. Kidney – Renin – Converts a blood protein into angiotensin, which regulates blood pressure and contributes to hypovolemic thirst.

13. Thymus – Thymosin (and others) – Support immune responses.

14. Fat cells – Leptin – Decreases appetite, increases activity, necessary for onset of puberty

Cranial Nerve:

The medulla control vital reflexes- including breathing, heart rate, vomiting, salivation, coughing and sneezing- through the cranial nerves- which control sensation from the head, muscle movements in the head, and much of the parasympathetic output to the organs. Some cranial nerves include both sensory and motor components, whereas other have just one or another. Just as the lower part of body connected to spinal cord via sensory and motor neve, the receptors muscles of the head and organs connect to the brain by 12 pairs of cranial nevres.

·        To remember cranial nerves- “on old Olympus topmost top” and “A fat armed German viewed some hopes”

Number	Name	Type	Function
1	Olfactory nerve	Sensory	Smell
2	Optic nerve	Sensory	Vision
3	Oculomotor nerve	Motor	Eye Movement
4	Trochlear nerve	Motor	Eye Movement
5	Trigeminal nerve	Mixed	Jaw Movement and Face Sensations
6	Abducens nerve	Motor	Eye Movement
7	Facial nerve	Mixed	Tongue Sensitivity
8	Statoacoustic nerve	Sensory	Balance and Hearing
9	Glossopharyngeal	Mixed	Movement and Teste of Tongue
10	Vagus nerve	Mixed	Movement of lungs, heart, muscles for voice
11	Spinal-accessory nerve	Motor	Movement of neck
12	Hypoglossal nerve	Motor	Swallow and speech articulation

Organization of Brain:

Major division of vertebrate brain according to neurologist:

Hindbrain (Rhombencephalon):

1.      Myelencephalon- Medulla

2.      Metencephalon- pons, Cerebellum

Midbrain (Mesencephalon): Tectum, Tegmentum, Superior colliculus, Inferior colliculus, Substentia nigra

Forebrain (Prosencephalon):            

1.      Diencephalon- Thalamus, Hypothalamus

2.      Telencephalon- Cerebral Cortex

                      Hippocampus, Basal ganglia

There are number of ways to conceptualize the brain:

1.      Hindbrain- which include all the structures located hind or posterior part of brain, closest to the spinal cord.

2.      Midbrain- located middle of the brain.

3.      Forebrain- include all the structures located in the front or anterior portion of the brain.

According to (MacLean, 1973) human brain as three concentric layers:

1.      The central core (brainstem), which regulates our most primitive behaviors.

2.      The Limbic system which control our emotions.

3.      The cerebrum which regulate our higher intellectual processes.

Brain stem:

In the autonomy of human brain and many other vertebrates, the brain stem is the posterior part of the brain, adjoining and structurally continuous with spinal cord. In humans, it described as including medulla oblongata (Myelencephalon), pons (part of metencephalon) and less frequently part of diencephalon are included. The brain stem provide the main motor and sensory connection to face and neck via cranial nerve. Of the 12 pairs of cranial nerve 10 comes from brain stem (3-12). This is the part of the brain as the nerve connections of the motor and sensory system from the main part of the brain to rest of the body pass through brain stem.

Brain stem also play a crucial role in cardiac and respiratory functions (involuntary), sleep cycles, maintaining consciousness that is necessary for life.

The Medulla:

A narrow structure that control breathing and some reflex actions that help maintain upright posture. Also at this point, the major nerve tract cross over so that the right side of the brain is connected to left side of the body and the left side of the brain connected to right side of the body.

The Pons:

The word ‘pons’ comes from the Latin meaning ‘bridge’. A portion of the brain through which sensory and motor information passes and which contain the structures relating to sleep, arousal and regulation of muscle tone and reflex. Also connect medulla and thalamus. This structure joining two halves of cerebellum which lies adjacent to it.

Cerebellum:

Also called ‘little brain’. Off to the back of the brain a large and complex structure called cerebellum. This structure receive sensory and other inputs from the spinal cord, brainstem and forebrain; it processes this information and then send outputs to many parts of the brain to help make our movements precise, coordinated and smooth. Damage to the cerebellum results jerky, uncoordinated movements.

The cerebellum is important for learning new motor responses (Thompson, 1994). It also involves in intellectual function ranging from the analysis of information (sensory) to problem solving (bower & person, 2003, 2007).