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| Autonomic Nervous System |
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| It is also called the visceral nervous system as it controls the functioning of the visceral (internal) organs. |
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| The autonomic nervous system (ANS) consists of two sets of motor neurons and a collection of ganglia. The two sets of neurons are |
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| Pre-ganglionic nerve fibres - They are neurons that emerge from the CNS and enter the ganglions. Their nerve cells are in the CNS. |
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| Post-ganglionic nerve fibres - They are the neurons that leave the ganglions and reach the smooth muscle/ gland. Their nerve cells are in the ganglions. |
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| The preganglionic nerve synapses with the dendrites of the post ganglionic nerve in the ganglions. |
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| Structurally, the ANS consists of two divisions - Sympathetic and Parasympathetic divisions. |
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| Sympathetic nervous system - It has the following features- |
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| i) It is made up entirely of spinal nerves of the chest (thoracic) and waist (lumbar) region. Thus, they simultaneously affect many organs and tissues to produce widespread, coordinated effects. |
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| ii) It has ganglia close to the spinal cord. |
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| iii) The ganglia are linked to each other. |
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| iv) The pre-ganglionic nerve fibre is shorter than the post-ganglionic nerve fibre. |
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| v) Each pre-ganglionic nerve fibre transmits impulses to many post-ganglionic nerve fibres. Thus, this system has widespread effects. |
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| vi) It generally has an accelerating effect which prepares the body for action in emergencies. |
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| vii) Its functions include |
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| a) dilation of pupils |
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| b) increase rate and force of heart beat |
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| c) increase in secretion of sweat |
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| d) decreases urine output |
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| e) releases adrenaline at the effector (gland or muscle) - thus, the postganglionic sympathetic fibres are called adrenergic. Except those that terminate on the sweat glands because they use acetyl choline. |
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| f) inhibition of peristalsis |
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| g) dilation of blood vessels to brain and skeletal muscle. |
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| h) These functions help the sympathetic nervous system to play |
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| an important role in emergencies. |
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| Parasympathetic nervous system |
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| It has the following features- |
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| i) It is made up of four pairs of cranial nerves and three pairs of sacral nerves. |
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| ii) The ganglia are far away from the spinal cord and close to or within the effectors. |
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| iii) The ganglia are not linked to each other. |
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| iv) The pre-ganglionic nerve fibre is longer than the post-ganglionic nerve fibre. |
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| v) Each pre-ganglionic nerve fibre transmits impulses only to one post-ganglionic nerve fibre. Thus, this system has limited effect. |
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| vi) It generally has a slowing-down effect which balances the effect of the sympathetic system. |
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| vii) Its functions include |
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| a. constriction of pupils |
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| b. decrease rate and force of heart beat |
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| c. decrease in secretion of sweat |
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| d. increases urine output |
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| e. releases acetylcholine at the effector (gland or muscle) - thus, the postganglionic parasympathetic fibres are called the cholinergenic. |
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| f. stimulation of peristsalsisperistalsis |
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| g. constriction of blood vessels to brain and skeletal muscle. |
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| Together, the parasympathetic and sympathetic nervous systems work to maintain a steady state. |
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| Autonomic Nervous System |
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