5. Review of sympathetic nervous system Flashcards
Describe the basic anatomy of the sympathetic nervous system
Consists of a sympathetic chain which has ganglia anterior to the vertebrae
This is connected to the sympathetic trunk to allow for a two neurone system
Pre-ganglionic neurones attach to the sympathetic trunk and the ganglia occur in the sympathetic chain
The post-ganglionic neurones then leave towards the blood vessels and skin
Describe the basic anatomy of the spinal cord
Spinal nerves are part of the peripheral nervous system
31 pairs of spinal nerves that enter and leave spinal cord at each vertebral level
A large number of these are concentrated in the cauda equina at the base of the spinal cord - the conus medullaris
Contains autonomic nervous system for involuntary functions of the body
Give the divisions of the spinal cord
Cervical nerves: C1-C8
Thoracic nerves: T1-T12
Lumbar nerves: L1-L5
Sacral nerves: S1-S5
Describe the grey and white matter of the spinal cord
White matter: Nerves covered in myelin (made of fat and protein)
Grey matter: Neurones with no myelin covering
Give the function of the grey matter in the spinal cord
Forms the butterfly shaped area in centre of spinal cord Dorsal horn (posterior) receives information from receptors in skeletal muscles/organs/glands and passes this up ascending spinal tracts to the brain Ventral horn (anterior) conveys motor information down descending spinal tracts from brain to skeletal muscles
Give the function of the white matter in the spinal cord
White matter contains spinal tracts - large bundles of nerves carrying information up and down the spinal cord
These can be sensory or motor
State where the pre and post ganglionic neurones are situated
The pre-ganglionic motor neurones are in the lateral horn of the grey matter
The post ganglionic neurones have their cell bodies in the ganglia and project out to the skin and blood vessels
Describe the basic anatomy of the sympathetic chain
Form ‘beads on a string’ alongside the sympathetic trunk
Define ‘sympathetic trunk’
Paired bundle of nerve fibres that run from the base of the skull to the coccyx
Consists of ventral, lateral horns and roots
Relate the sympathetic chain to the innervation of blood vessels
The thoraco-lumbar sympathetic ganglia supply vasoconstrictor nerves to arterioles/blood vessels that supply oxygen to the skeletal muscles in the chest, upper limbs and back
These are known as the ‘chain of beads’
The distribution of blood and O2 is controlled by turning these on and off - there are no vasodilator nerves
Describe the sympathetic supply to the head
At the top of the sympathetic chain, there are three nerves that project into the cervical region
These cervical sympathetic ganglia are not connected to the cervical ventral roots but to the thoracic ventral roots below
The largest of these is usually the ‘superior cervical ganglion’ and these supply sympathetic nerves to the head - innervation of iris of eye, skin of face, salivary glands
These nerves from plexuses around the carotid arteries and enter the skull together
Briefly describe the transmitters used by the sympathetic nervous system
There are two main neurotransmitters released - acetylcholine and noradrenaline
These differ depending on pre or pos ganglionic neurones (two neurones between spinal cord and muscle)
Describe the neurotransmitters of the preganglionic neurones of the sympathetic nervous system
Preganglionic neurones release aceytlcholine to activate the postganglionic neruones
These neurones have small, myelinated (B type) axons
Describe the neurotransmitter of the postganglionic neurones of the nervous system
These release noradrenaline to the arterial smooth muscle
This initiates contraction by acting on alpha-1-adrenoreceptors
These neurones have unmyleinated (C type) axons
Describe the ganglionic receptors of the autonomic nervous system
All of these receptors are of the cholinergic nicotinic type
Define nicotinic receptor
Cation permeable ion channels activated by acetylcholine neurotransmitter - ligand gated ion channels mediate fast synaptic transmission of neurotransmitter
Define muscarinic receptor
Acetylcholine receptors that from G-protein-receptor complexes in the cell - mediate slow metabolic response via second messenger cascade
Describe the cardiac plexus
Provides sympathetic innervation to the heart
Branches from the upper thoracic sympathetic chain
Located around the aorta and atria - from upper quarter of cardiac trunk
Describe the pulmonary plexus
Provides sympathetic innervation of the lungs
Located around the large bronchioles
Describe sympathetic nerves with glanglia below the diaphragm
These have long preganglionic axons because ganglia are a long way from the spinal cord
These have migrated towards the front of the abdomen and have specialised names e.g. coeliac plexus to stomach and small intestine
Describe the coeliac plexus
From below the diaphragm
Supplies vasoconstrictor tone to the stomach and initial parts of the small intestine
Describe the superior mesenteric plexus
Innervates the small intestine, ascending colon and transverse colon
Describe the inferior mesenteric plexus
Innervates descending colon and rectum
Describe the role of the adrenal gland in the sympathetic nervous system
Some preganglionic fibres travel down to here and this acts as a postganglionic neurone
Secretes adrenaline into capillaries of gland and blood is then carried to rest of the body
Converts noradrenaline to adrenaline (noradrenaline made from dopamine made from DOPA made from tyrosine)
Have extra genes to prevent growth of axon
Give the one exception of postganglionic fibres being noradrenergic
Sweat glands
Sweating triggered by sympathetic outflow via acetylcholine as neurotransmitter
Describe the function of the sympathetic nervous system
Regulates distribution of blood around the body
Keeps all of the arterioles of the vascular beds slightly constricted
Prepares the body for physical action - ‘fight or flight’ response
Describe the resting activity of the sympathetic nervous system
Active at a low level whilst you are awake
Maintained at the ‘resting level of sympathetic nervous system’
Drugs that block these receptors have serious effects as they block the resting tone e.g. can cause postural hypertension - this can prove to be very damaging
Describe the innervation to the heart and brain
Because drugs can block receptors of the sympathetic nervous system and have distressing impacts, there is no sympathetic innervation to the extremely fundamental areas of the body
i.e. none to the coronary arteries (heart) or cerebral arteries (brain) and instead, these have their own supply
Describe how the sympathetic nervous system can prepare the body for action
Can prepare for the ‘fight or flight’ response
Release of noradrenaline constricts blood vessels and raises the blood pressure - increased supply of oxygenated blood to areas that require it
Release of adrenaline into the blood which causes release of glucose from liver and muscle cells - glygogenolysis - and this increases cardiac output, dilates the airways and increases O2 intake
Describe the actions of the sympathetic nervous system during exercise
Constantly adjusts the cardiac output and oxygen supply to the tissues to exactly match the demand
SO at the start of exercise, there is an increase in sympathetic outflow to increase the heart rate and cardiac output
This is adjusted to exactly match the increased blood flow through exercising muscle and so prevents a drop in blood pressure
“Describe how the sympathetic nervous system acts after injury or haemorrhage”
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