Nervous system- sympathetic nervous system Flashcards
How many neurons make up a SNS pathway?
2
Which spinal level does the preganglionic neurons originate from?
T1- L2/3
What are the neurotransmitters released by the preganglionic and postganglionic neurons in a typical SNS pathway?
What are the exceptions to this pathway
Preganglionic: ACh [nAChR]
Postganglionic: noradrenaline {alpha-/beta- adrenergic receptor]
Exceptions:
- Adrenal gland (Chromaffin cells)
- the adrenal gland acts as the sympathetic ganglia itself
- spinal cord (pregang.) > Ach [nAChR] in adrenal gland > adrenal gland releases NE or E** into the bloodstream - Sweat glands
- Post-ganglionic releases ACh [mAChR] instead of NE
Spinal cord (pregang.) > Ach [nAChR] in sympathetic chain > postgang. > ACh [mAChR] (sweat gland )
- Kidneys
- postganglionic sympathetic nerves releases DOPAMINE [D1 receptors]
- controls amount of blood filtering
Where in the spinal cord do the nerves of the pre-ganglionic neurons in SNS arise from?
ipsilateral intermediolateral nucleus of the lateral horn
After the axons go through the ventral (anterior) root to leave the spinal cord, what rami do they become before they are called spinal nerves?
anterior rami
After the SNS nerves exit the dorsal root, do they go via the white rami or grey rami?
White rami communicantes
is the preganglionic sympathetic outflow nerve tract from the spinal cord
Contains both myelinated and unmyelinated preganglionic fibres (GVE and GVA)
Myelination gives ‘white’ communicantes its name
What does the white rami communicantes contain
preganglionic sympathetic outflow from the spinal cord
Describe sympathetic pathway from organ sensory to effector
organ > DRG (cell body) >
1) dorsal horn: synapse to interneuron or
2) lateral horn: synapse to preganglionic
> [efferent] preganglionic neuron } > (sympathetic chain) > postganglionic neuron/visceral effector
*note: the afferent fibers are not classified as either sympathetic or parasympathetic
only the EFFerent fibres a
re considered SNS or PANS/PSNS
What is the effect/function of SNS on blood vessels
maintain total peripheral resistance through the continual, slight constriction of arterioles
Why is it that in PKU, patients have autonomic signs? Explain in terms of the adrenal gland.
In PKU, patients lack phenylalanine hydroxlase which converts Phe to Tyrosine.
Tyrosine is the precursor of DA, NA and Adrenaline in the adrenal chromaffin cell.
Adrenaline helps activate the sympathetic NS.
Therefore, the synthesis and release of adrenaline in the adrenal cells will be compromised in PKU.
Where is the sympathetic innervation of the heart from?
from the upper thoracic sympathetic chain which forms a plexus (nerve mesh) around the aorta/atria- cardiac plexus
*Note: lungs= pulmonary plexus
Where do the nerves from the cervical paravertebral ganglia originate from? What spinal level are they at? What structures do they innervate?
Pregang. from SC > exit T1 > sympathetic chain > ascend chain > cervical ganglia
- Superior cervical ganglia (~C2-3) ->
heart, head, neck
* Largest - Middle cervical ganglia (where C6 is) -> heart, neck
- Inferior cervical ganglia (~C7; merges with first thoracic)-> heart, lower neck, arm, posterior cranial arteries
Describe the pathway of the sympathetic innervation of the eyes
Pupil dilator pathway
Cortex (first order) > ciliospinal center synapse (Budge’s centre)- C8- T2 lateral horn of spinal cord > ascend to superior cervical ganglion (post-ganglionic neurons) > synapse in SCG > third order neurons travel via carotid plexus and enter the orbit via V1
summary:
- cortex
- C8-T2 lateral horn
- Ascend to SCG
- Carotid plexus
- To orbit via CN V1
What do alpha-1 adrenergic receptors do
smooth muscles contraction
*Alpha receptors= constrict peripheral vessels (gut) and redistribute the blood to exercising muscles)
What do alpha-2 adrenergic receptors do?
Inhibition of transmitter release
smooth muscle contraction
*Alpha receptors= constrict peripheral vessels (gut) and redistribute the blood to exercising muscles)
