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LECTURE : 4

Biological Basis of Behaviour•The Nervous System•Neurons•Divisions of the Nervous system•Brain

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NEURONS: PRIMARY UNITS

OF THE NERVOUS SYSTEM Neurons range in length from less than a millimetre tomore than a meter in length. Yet all neurons are madeup of essentially the same parts.

The human nervous system is composed of 100 billionneurons.

Cell Body:Is the central part of the nerve cell. Itcontains the cells control centre, or nucleus, and othercomponents necessary for the cells preservation andnourishment.

Dendrites: Are small branches that extend out fromthe cell body and receive messages from other neurons.

 Axons: The axons are small branches at the other endof the neuron that perform a function opposite that ofthe dendrites. Axon carry messages away from the cellbody and transmit these messages to the next neuron.

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CONTD.

Myelin Sheath:a layer of fatty tissuesegmentally encasing the fibers of manyneurons ; enables vastly greatertransmission speed of neural impulses asthe impulse hops from one node to the next.

 Action Potential:a neural impulse; a briefelectrical charge that travels down an axon.The action potential is generated by themovement of positively charged atoms in andout of channels in the axon’s membrane.

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STRUCTURE OF A NEURON

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CONTD.

Information travels in the nervous system throughthree types of neurons. Thesensory neurons send information from the body’s tissues andsensory organs inward to the brain and the spinal

cord , which process the information.

The processing involves a second class of neuronsthe central nervous system’s owninterneurons,which enable its internal communication.

The central nervous system then sendsinstructions out to the body’s tissues via themotor neurons.

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THE NERVOUS SYSTEM

The body’s speedy, electrochemicalcommunication system, consisting of all thenerve cells/neurons of the peripheral and thecentral nervous systems.

Neurons are the elementary components of thenervous system.

Neurons communicating with other neurons formour body’s primary information system, thenervous system.

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THE NERVOUS SYSTEM

The brain and spinal cord form the centralnervous system (CNS). The Peripheralnervous system (PNS) links the centralnervous system with the body’s sense

receptors, muscles, and glands. The sensoryand the motor axons carrying this PNSinformation are bundled into the electricalcables that we know as nerves.

The optic nerve, for example , bundles nearly amillion axon fibres into a single cable carryingthe information that each eye sends to thebrain.

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THE PERIPHERAL NERVOUS

SYSTEM

The Peripheral Nervous System can bedivided into two components:

1. The Somatic Nervous System: Controlsthe movements of our skeletal muscles .

2. The Autonomic Nervous System:Controls glands and the muscles of ourinternal organs . It usually operates on itsown to influence the internal functioning,

including our heartbeat, digestion, andglandular activity.

The autonomic nervous system is a dualsystem consisting of thesympathetic andparasympathetic nervous system.

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CONTD.

TheSympathetic Nervous Systemarousesus for defensive action. If something alarms orenrages you, the sympathetic nervous systemwill accelerate your heart beat, slow yourdigestion, raise your blood sugar level, coolyou with perspiration , dilate your arteriesthus making you alert and ready for action.

When the stress subsides , the parasympathetic nervous systemproducesopposite effects. It conserves energy as it calms

you by decreasing your heart rate , loweringyour blood sugar and so forth.

In everyday situation these both work togetherto keep us in a steady internal state .

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THE CENTRAL NERVOUS SYSTEM

(SPINAL CORD AND BRAIN)

Spinal Cord The CNS’s spinal cord is an information highwayconnecting the peripheral nervous system to the brainascending neural tracts send up sensory information, and

descending tracts send back motor-control information.

The neural pathways which enable the pain reflex , areautomatic response to the stimuli, illustrate the spinalcord’s work.

When your finger touches a flame , neural activity excitedby the heat travels via sensory neurons to interneurons inyour spinal cord. These interneurons respond by activatingmotor neurons to the muscles in your arm. That is why itfeels your hand jerks away not by your choice , but on itsown.

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BRAIN

The other part of your central nervous system , your brain,receives information , interprets it and decides responses.In doing so the brain rather acts like a computingmachine . It receives slightly differing images of of anobject from the two eyes , computes their difference , andinstantly infers how far away the object must be to projectsuch a difference .

In our brains, one neural network is interconnected withother networks that do different things . There are noarrows to tell us where one network ends and the nextbegins,; what distinguishes them in their specific functions.Each is a subnetwork, contributing its little bit ofinformation to the whole information processing systemthat we call the brain.

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Brain•Introduction to the structure

and functions of the brain

•Genetics influence on Behavior

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STRUCTURE AND FUNCTIONS OF

THE BRAIN

 All mental functions require the integrated

functioning of many parts of the brain : no

function of the brain is carried out solely in one

part. Still, the brain does have many specialised

parts, each bearing primary responsibilities forcertain activities.

The most convenient classification divides the

brain into three major parts: the hind brain, themidbrain and the forebrain.

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Each part of the brain interacts with the entire

nervous system, and the parts work together in

intellectual, physical and emotional functions.

The brain is an organ that is elastic to some

degree, it changes over the course of

development.

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 FUNCTIONS

Hindbrain Medulla Sensory and motor

nerves crossover

Pons Regulation of sleep-

wake cycle

Cerebellum Reflexes (e.g.,

balance), coordinates

movements

Midbrain Hearing , vision relay

point, Pain registered

Forebrain Thalamus Major message relay

center, regulates

higher brain centers

and peripheral

nervous systemHypothalamus Emotion and

motivation, stressreactions

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FOREBRAIN: CEREBRAL

HEMISPHERES

The two cerebral hemispheres take up most of the room

inside the skull. They balloon out over the brain stem,

fold down over it and hide most of it from view. They are

more highly developed in humans than in animals.

The account for 80 percent of the weight of the human

brain, and they contain about 70 percent of the neurons

in the central nervous system.

The outer layer of the cerebral hemispheres is called the

cerebral cortex. If the cerebral cortex were to spread

out , it could cover 2 to 3 feet . To fit inside the skull , the

cerebral cortex has developed intricate folds.

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Cerebral

Hemispheres

Occipital lobe Receives and processes

visual information

Temporal lobe Complex vision,

hearing and smell,

balance and

equilibrium, emotions

and motivations and

some language

comprehensionsParietal lobe Processing sensory

information,

visual/spatial abilitiesFrontal lobe Goal- directed

behavior,

concentration,

emotional control and

temperament,

voluntary movement,coordinates messages

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GENETIC INFLUENCE ON

BEHAVIOR

Genes play their role by influencing the creation orsynthesis of protein in cells, which influences thenature and of the type of cells that are our neurons.

The nature of our neurons is just not effected by ourgenes but is also influenced by our experience in theenvironment – experience can and does alter neurons.

The nature of our neurons then works with theenvironment to shape our behavior and mental

processes.

Differences in our neurons play a role by influencinghow we interact with the environment and how theenvironment influences us.

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Studies of Twins:

Monozygotic Twins: Twins formed from a single

ovum; they are identical in appearance because

they have the same genetic structure.

Dizygotic Twins: Twins formed from the

fertilization of two ova by two sperms.