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Autonomic nervous system part 1

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Principal Efferent Outputs of the CNS:

Somatic nervous system:

links the central nervous system to various peripheral organs directly via nerve

The main tissue innervated by the somatic nervous system is

system involves nerve fibres but the efferent way into the body is via hormones (e.g. hypothalamo-adenohypophysial axis)

Autonomic nervous system is working all the time in the body without us realising - it is continually trying to maintain

There are two branches of autonomic:

- activated during a threatening (fight or flight) situation in which you need to be really active

- you don't need to be active so you're allowing various other activities to take place

Principal targets and functions of the autonomic nervous system

Sympathetic: Pupil dilation, trachea and bronchiole dilation, glycogenolysis and gluconeogenesis, lipolysis, renin secretion, relaxes detrusor, thick viscous secretion from salivary glands, piloerection, sweating, heart rate,

Parasympathetic: Pupil constriction, ciliary muscle contraction, trachea constriction, contraction of detrusor, copious water secretion form salivary glands etc

The trachea and bronchioles are NOT actually innervated by sympathetic fibres - the SNS influences the smooth muscle in these tissues via the release of

if you denervated the heart, the heart rate would

- the normal influence on the heart rate is very much parasympathetic dominated

Blood Vessels - in skeletal muscle, the SNS is associated with dilatation which is unusual and it isn't associated with innervation but more likely due to circulating catecholamines

In the skin, there is sympathetic innervation that goes to the sweat glands - but in this case, the post-ganglionic sympathetic fibres that innervate the sweat glands

release noradrenaline. They instead release

so they are cholinergic sympathetic fibres.

Parasympathetic Nervous System:

From the lower part of the brain/ spinal cord there are two main outflows

The top outflow consists of

of the cranial nerves: Oculomotor Nerve (CN III), Facial Nerve (CN VII), Glossopharyngeal Nerve (CN IX), Vagus Nerve (CN X)

They contain parasympathetic nerve fibres

Facial Nerve - innervates glands that are high up in the body e.g. tears and

Glossopharyngeal Nerve - influences activity in the tissues that are higher up

Vagus - outflow from the CNS via the Vagus goes to an array of organs (lung, heart, stomach, pancreas, small intestine)

There is also an outflow at the bottom in the

region where you have an outflow mainly via the splanchnic nerve - the nerves go to the

organs and there is another outflow to the lungs and intestine

Some organs receive both cranial AND sacral influence via the parasympathetic nervous system

Sympathetic nervous system:

There is

cranial outflow

The sympathetic nervous system has

thoracolumbar

outflows (T1-L3)

The pre-ganglionic fibres tend to leave the spinal cord and join together in a row of linked ganglia called the

in a sympathetic chain that lies adjacent to the spinal cord

It is possible that when one part of the sympathetic nervous system is activated, the effect can spread across the whole of the sympathetic chain

Some tissues and organs are innervated by both the sympathetic and parasympathetic (lacrimal glands, salivary glands, heart and lung)

The adrenal medulla only receives pre-ganglionic fibres and instead of activating a post-ganglionic fibres (like all other sympathetic pathways), in this case

cells are stimulated to release catecholamines into the general circulation

sympathetic ganglia send fibres off to the skin and blood vessels in the region of innervation

Parasympathetic and sympathetic tend to oppose each other and innervate the same organs and tissues but their outflows are very different

Summary: Parasympathetic =

Sympathetic:



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