ANS Flashcards
What does the anatomical arrangement of ANS strive to achieve?
localise the autonomic output to certain areas for greater efficiency
convey the correct autonomic neurotransmitters to receptors in target structures
distribute autonomic fibres to all parts of the body through
Give example of how autonomic output is localised to certain areas for greater efficiency?
- cranium: parasympathetic (cranial outflow - studied in Year 2)
- spinal cord lateral horn: T1-L2/3 - sympathetic (areas where sympathetic cell bodies are situated)
- spinal nerves S2-S4: - parasympathetic (sacral outflow) they will go to pelvic organs with parasympathetic input
Give example of how ANS convey the correct autonomic neurotransmitters to receptors in target structures?
postganglionic to convey NA -sympathetic
first ganglionic neurons to convey Ach - parasympathetic
Give example of how ANS does distribute autonomic fibres to all parts of the body ?
- sympathetic trunk ganglia – paravertebral paired chained ganglia
- prevertebral ganglia - in abdomen lying anterior to aorta - parasympathetic ganglia - within target organs
Differences between ANS VS SNS?
Somatic NS- nerve cell bodies lie in anterior horn and come out of ventral ramus and join spinal nerve - go as one neuron to target structure. Neurotransmitter is acetylcholine
axon is myelinated
ANS- neurons reside in the lateral horn (only see lateral horn in cross section of spinal cord between T1 and L2/L3).
Sympathetic fibre will run through anterior horn and join spinal nerve through ventral ramus. It will continue as pre ganglion neuron (myelinated) and will go to autonomic ganglion and then synapse and continue as post ganglionic neuron (unmyelinated) and give off Acetylcholine for parasympathetic and noradrenaline for sympathetic targets.
Slower conduction due to post ganglion neurons being unmyelinated
What does lateral horn contain?
cell bodies of sympathetic neurons
Where is lateral horn present?
Lateral horn is only present in the spinal cord between T1 - L2/3, and sympathetic fibres emerge from vertebral column at these same levels:
= thoracolumbar outflow.
Where do parasympathetic fibres emerge from?
Parasympathetic fibres emerge from spinal nerves S2 - 4 = sacral outflow.
(from pelvis)
(Nerves are named according to where they emerge from the vertebral column),
Describe thoracolumbar outflow?
T1 -L2/3
Short pre ganglionic neuron and will be myelinated (white in color) and will synapse in sympathetic ganglion. Post ganglionic neuron will be grey and unmyelinated and go to target organs (smooth muscles, blood vessels and glands)
Describe sacral outflow?
fibres emerging from S2-S4
long, myelinated, pre ganglionic fibre (white) will synapse in parasympathetic ganglion in pelvis mainly and post ganglion neuron (grey and unmyelinated) will go to target organs in pelvis, uterus, bladder, rectum etc..
Describe sympathetic chains?
lie on either side of vertebral column
31 pairs of spinal nerves and all contain somatic motor and sensory fibres in their ventral and dorsal rami
ALL SPINAL NERVES ALSO CONTAIN SYMPATHETIC FIBRES IN THEIR VENTRAL AND DORSAL RAMI.
how do spinal nerves above and below T1-L2/3 receive their sympathetic fibres?
By making use of the paired sympathetic trunks lying on each side of the vertebral column from C1 – Cc1.
What does sympathetic trunk do for us?
The sympathetic trunk lies just lateral to thevertebral bodiesfor the entire length of thevertebral column.
It interacts with spinal nerves via rami communicantes.
The sympathetic trunk permits preganglionic sympathetic fibersto rejoin the spinal nerve at the same vertebral level.
But the sympathetic trunk also permits preganglionic sympathetic fibres to ascend to spinal levels above T1 and descend to levels below L2/3.
