1 Human Nervous System. 2 What are we going to learn ? Function of nervous system Parts of nervous system Types of neurons Conduction of impulse through.

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Human Nervous System

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What are we going to learn ?

Function of nervous system Parts of nervous system Types of neurons Conduction of impulse through neurons Brain Spinal cord Reflex action

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What does the nervous system do?

Imagine, while crossing a road, you observe a bus travelling fast towards

you. To avoid an accident shouldn’t you jump out of the way?

How is this jump performed by your body?

1. The nervous system collects information about what is happening through various sense organs ( the eye watches the bus travelling fast towards you, the ear hears the sound of the approaching bus, the brain gets this information and decides that an accident is likely …) : Coordination

2. Decide the appropriate action to be taken ( The brain decides that jumping out of the way is the best action) : Effective

3. Send that response to the correct part of the body ( the legs) through the network of neurons : Regulation

Humans perform various activities simultaneously For example walking, hearing, seeing …

The nervous system performs the important task of effective coordination and regulation of these activities

I can’t understand any of this !!

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Parts of the nervous system

Peripheral Nervous System Function: Exchange messages between

the CNS and other parts of the body Neurons are connected to each other to

form a network This network connects the brain and

spinal cord with all parts of the body

Autonomous nervous system Consists of neuron network in the heart, lungs,

stomach etc.

Two parts Brain Spinal cord

Central Nervous System (CNS) Function: Regulation of all activities of the body

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Nerves

Two types1. Neurons

Cells which are capable of generating and conducting electrochemical impulses

2. Neuroglia These support the neurons and supply nutrients to them

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Neurons

Dendrites

Cell body

Nucleus

Axon

Synapse : connection point between two neurons

• Each neuron has many dendrites but only one axon with multiple branches

• The longest axon in the body is approx. 1 m long!

• The point where two neurons meet is called a synapse

• One neuron may have 1000 to 10000 synapses !

• In this manner each neuron connects to multiple neurons to form a complex network

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Neurons look like this

Neurons in spinal cord Neurons in the brain

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The conduction of an electric impulse in a neuron 1Neurons carry any sensation received by the sensory organs (for example: the prick of a pin on a fingertip) to the brain by

means of an electric impulse

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The conduction of an electric impulse in a neuron 2

Axon

Synapse

Dendrites

Synapse

Nucleus

A pin prick generates an electric impulse in the first neuron

This impulse is first carried by the dendrite to the cell body…

From the cell body to the axon …

…from the axon to the synapse… …from the synapse the impulse is regenerated in the 2nd neuron

First neuron Second neuron

In this fashion the impulse reaches the brain

Cell body

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Types of neurons

1. Sensory These carry electric impulses from sensory organs to

the brain and the spinal cord

2. Motor These carry electric impulses from the brain and the

spinal cord to the motor limbs like legs and also to skin, glands etc.

3. Associative These coordinate between the motor and sensory

neurons in the brain and the spinal cord

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The human brain

The brain enables usto thinkWe can recall the past because of the brain

The brain makes sense of the images

that we see through our eyes

The brain helps us interpret what we hear

through our ears

The brain helps us distinguish

between mother’s affectionate touch

and... …her angry smack !

In short we are aware of our existence because

of our brain

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The work of the brain

Sensory neurons carry sensations to the brain

Interpreting these sensations and deciding the action required is done in various parts of the brain

The impulse of the required action is carried to the appropriate limb by motor neurons

The brain helps us think, generates our emotions, defines our personality, …

The brain stores innumerable events of the past We call this our memory

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The structure of the brain 1

The brain weighs about 1.4 Kg it is protected by the skull made of bones Within the skull there are three strong protective layers called as meninges The space within these layers is filled with fluid which cushions the brain from external shocks The brain contains about 10000 crore neurons

The brain located within the skull

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The structure of the brain 2

The three main parts of the brain1. Fore-brain

Cerebrum is the main constituent ü

2. Mid-brain Controls movement of eyes,

the size of the eye lens and some involuntary actions

3. Hind-brain Cerebellum

Coordinates voluntary activities and helps the body maintain balance

Medulla Oblongata Controls some involuntary actions like blood

circulation , breathing etc.

Fore brain is the largest and most

important part of the brain. We shall learn more about this later.

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The structure of the brainExternal view

Cerebrum

Cerebellum

Medulla

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The structure of the brainSectional view

Cerebrum

Mid-brain

Hind brain Cerebellum

Medulla

Spinal cord

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Cerebrum The largest part of the brain; Numerous folds on its

surface These folds enable accommodation of maximum neurons

in minimum space Function related to thinking, emotions, personality,

decision making Interpret the information received from the sensory

organs Relate this information to related items stored in memory

and decide how to respond Convey the response to the appropriate part of the body

Cerebrum is divided into two equal halves The right half controls the left part of the body

and the left half controls the right part of the body

Top view of the cerebrum

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Regions of the cerebrum that control various activities of the body

Thought process

MovementSense of touch

Vision

Cerebellum

Hearing

Speech

Sense of taste

Sense of smell

View of cerebrum from the left side

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Spinal cord The spinal cord is a long

narrow tube made of neurons

Begins at the medulla: 45 cms long

Protected by the bones of the spine

Function Conducting the impulses

received from sensory organs to the brain

Routing the motor impulses received from the brain to the appropriate organs

Coordinating reflex actions

Spinal cord

Bones of the spineû

Cartilage disc between bones of spinal cord

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Association neuronsPain stimulus

…carried by sensory neurons

Spinal cord (cross section)

Motor neuron

Reflex action Sometimes the nervous

system has to respond very quickly to external stimuli

For example, when your finger touches the flame of a candle

In such cases response is given by the spinal cord without involving the brain

This is called reflex action which requires coordination between sensory neurons and motor neurons in the spinal cord

This coordination is performed by association neurons

Muscle contracts when it receives the impulse from the motor neuron …

…and the hand is pulled back

The pain stimulus reaches the association neuron in the

spinal cord

these neurons decide which motor neuron to activate for quick response to the stimulus

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The End