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Human Nervous System 1 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 2 What does the nervous system do? Humans perform various activities simultaneously For example walking, hearing, seeing … I can’t understand any of thistask !! of The nervous system performs the important effective coordination and regulation of these activities How is this jump performed by your body? Imagine, while crossing a road, you 1. The nervous system collects information about what is happening observe busorgans travelling towards through variousasense ( the eyefast watches the bus travelling fast towards you,avoid the ear hears the sound of the approaching you. To an accident shouldn’t you bus, the brain gets this information and decides that an accident is likely …) : Coordination jump out of the way? 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 3 Parts of the nervous system Central Nervous System (CNS) Peripheral Nervous System Function: Regulation of all activities of the body Two parts Brain Spinal cord 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. 4 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 5 Neurons • Each neuron has many dendrites but only one Dendrites axon with multiple branches Synapse : connection point between two neurons • The longest axon in the body is approx. 1 m Cell body long! Nucleus • 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 Axon neurons to form a complex network 6 Neurons look like this Neurons in spinal cord Neurons in the brain 7 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 8 The conduction of an electric impulse in a neuron 2 A pin prick generates an electric impulse in the first neuron This impulse is first carried by the dendrite to the cell body… Dendrites …from the axon to the synapse… …from the synapse ndthe impulse is regenerated in the 2 neuron Cell body Nucleus From the cell body to the axon … Synapse Axon Synapse First neuron In this fashion the impulse reaches the brain Second neuron 9 Types of neurons 1. Sensory 2. Motor 3. These carry electric impulses from sensory organs to the brain and the spinal cord These carry electric impulses from the brain and the spinal cord to the motor limbs like legs and also to skin, glands etc. Associative These coordinate between the motor and sensory neurons in the brain and the spinal cord 10 The human brain The brain helps us In short we are aware distinguish The makes between Thesense brain helps us mother’s of brain our existence because The brain Weenables can recall us the past of the images affectionate touch interpret what we hear …her angry smack ! of our brain that we see to because think of the brain and... through our ears through our eyes 11 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 12 The structure of the brain 1 The brain located within the skull 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 13 The structure of the brain 2 The three main parts of the brain 1. Fore-brain Cerebrum is the main constituent ü Fore brain is the 2. Mid-brain largest and most Controls important movement of eyes, part of the the size of the eye lens and brain.actions We shall learn some involuntary 3. Hind-brain more about this later. Cerebellum Coordinates voluntary activities and helps the body maintain balance Medulla Oblongata Controls some involuntary actions like blood circulation , breathing etc. 14 The structure of the brain External view Cerebrum Cerebellum Medulla 15 The structure of the brain Sectional view Cerebrum Mid-brain Hind brain Cerebellum Medulla Spinal cord 16 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 17 Regions of the cerebrum that control various activities of the body Movement Sense of touch Thought process Vision Sense of taste Speech Sense of smell Hearing View of cerebrum from the left side Cerebellum 18 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 19 Reflex action Sometimes the nervous Pain stimulus system has to respond very quickly to external stimuli …and the hand is pulled back these neurons decide which The neuron pain stimulus reaches motor to activate for the association neuron in the quick response to the stimulus spinal cord Association neurons 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 …carried by sensory coordination between neurons sensory neurons and motor neurons in the spinal cord This coordination is performed by association neurons Motor neuron Spinal cord (cross section) Muscle contracts when it receives the impulse from the motor neuron … 20 The End 21