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 neurons Brain Spinal cord Reflex action

3 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 !!

4 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

5 Nerves Two types 1. Neurons Cells which are capable of generating and conducting electrochemical impulses 2. Neuroglia These support the neurons and supply nutrients to them

6 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 synapses ! In this manner each neuron connects to multiple neurons to form a complex network

7 Neurons look like this Neurons in spinal cord Neurons in the brain

8 The conduction of an electric impulse in a neuron 1 Neurons 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

9 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 2 nd neuron First neuron Second neuron In this fashion the impulse reaches the brain Cell body

10 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

11 The human brain The brain enables us to think We 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

12 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

13 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 crore neurons The brain located within the skull

14 The structure of the brain 2 The three main parts of the brain 1.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.

15 The structure of the brain External view Cerebrum Cerebellum Medulla

16 The structure of the brain Sectional view Cerebrum Mid-brain Hind brain Cerebellum Medulla Spinal cord

17 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

18 Regions of the cerebrum that control various activities of the body Thought process Movement Sense of touch Vision Cerebellum Hearing Speech Sense of taste Sense of smell View of cerebrum from the left side

19 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 spine û Cartilage disc between bones of spinal cord

20 Association neurons Pain 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

21 The End