Human Nervous System

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? I can’t understand any of this !! • 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 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? • 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 • Decide the appropriate action to be taken ( The brain decides that jumping out of the way is the best action) : Effective • Send that response to the correct part of the body ( the legs) through the network of neurons : Regulation

4. Parts of the nervous system • Central Nervous System (CNS) • Function: Regulation of all activities of the body • Two parts • Brain • Spinal cord • 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.

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

6. Neurons • Each neuron hasmany 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 Synapse : connection point between two neurons Dendrites Cell body Nucleus Axon

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 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 synapse the impulse is regenerated in the 2nd neuron …from the axon to the synapse… Cell body From the cell body to the axon … Nucleus Synapse In this fashion the impulse reaches the brain Axon Synapse Second neuron First neuron

10. Types of neurons • Sensory • These carry electric impulses from sensory organs to the brain and the spinal cord • Motor • 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

11. The human brain In short we are aware of our existence because of our brain The brain helps us distinguishbetween mother’s affectionate touchand... The brain enables usto 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 hearthrough our ears …her angry smack !

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 brain located within the skull 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

14. The structure of the brain 2 The three main parts of the brain • Fore-brain • Cerebrum is the main constituent ü Fore brain is the largest and most important part of the brain. We shall learn more about this later. • Mid-brain • Controls movement of eyes, the size of the eye lens and some involuntary actions • Hind-brain • Cerebellum • Coordinates voluntary activities and helps the body maintain balance • Medulla Oblongata • Controls some involuntary actions like blood circulation , breathing etc.

15. The structure of the brainExternal view • Cerebrum • Cerebellum • Medulla

16. The structure of the brainSectional view • Cerebrum • Mid-brain • Hind brain • Cerebellum • Medulla • Spinal cord

17. Top view of the cerebrum 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

18. 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 Cerebellum 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 spineû Cartilage disc between bones of spinal cord

20. Association neurons Pain stimulus Motor neuron Spinal cord (cross section) …carried by sensory neurons Reflex action these neurons decide which motor neuron to activate for quick response to the stimulus The pain stimulus reaches the association neuron in the spinal cord …and the hand is pulled back • 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 …

21. The End