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| Parts of the Nervous System - 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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| Autonomic Nervous System |
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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 |
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| 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 |
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| 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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| The ANS consists of two divisions: |
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 Sympathetic nervous system |
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Parasympathetic nervous system |
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| It has the following features: |
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It is entirely made up of spinal nerves of the chest (thoracic) and waist (lumbar) region. |
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It has ganglia close to the spinal cord. |
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The ganglia are linked to each other. |
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The pre-ganglionic nerve fibre is shorter than the post-ganglionic nerve fibre. |
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Generally it has an accelerating effect which prepares the body for action in emergencies. |
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Its functions include |
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| - dilation of pupils |
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| - increase rate and force of heart beat |
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| - increase in secretion of sweat |
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| - decreases urine output |
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| - releases adrenaline at the effector (gland or muscle) |
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| - inhibition of peristalsis |
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| - dilation of blood vessels to brain and skeletal muscle |
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| It has the following features: |
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It is made up of four pairs of cranial nerves and three pairs of sacral nerves. |
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The ganglia are far away from the spinal cord and close to the effectors. |
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The ganglia are not linked to each other. |
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The pre-ganglionic nerve fibre is longer than the post-ganglionic nerve fibre. |
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Generally it has a slowing-down effect which balances the effect of the sympathetic system. |
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Its functions include |
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| - constriction of pupils |
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| - decrease rate and force of heart beat |
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| - decrease in secretion of sweat |
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| - increases urine output |
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| - releases acetylcholine at the effector (gland or muscle) |
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| - stimulation of peristalsis |
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| - 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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