1 Human Nervous System. 2 What are we going to learn ? Function of nervous system Parts of nervous...
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Transcript of 1 Human Nervous System. 2 What are we going to learn ? Function of nervous system Parts of nervous...
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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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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 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