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)
What do B-adrenergic receptors do?
Heart muscle contraction
smooth muscle relaxation
*B-blockers act here!
1 heart 2 lungs
B1- increase cardiac output
B2- relax bronchial smooth muscle (increase ventilation and oxygen uptake)
B2&3- increase glucose release from the liver and increase glucose uptake into the active muscle
increase lipolysis (B3)
What receptor mediates brochodilation?
B2- adrenergic
How does dopamine affect BP?
1) inhibit CNS sympathetic activity (D1-like and D2-like receptors)
2. Vasodilation
3. inhibit ion and water transport in kidney
4. inhibit ion transport in GI tract
Describe response of SNS after injury/haemorrhage (>50% blood loss)
decrease BP >
1. increase veno-constriction
- increase vasoconstriction (away from gut and skin)
- increase renal conservation of fluid (renin and ADH release)
- Increase endogenous vasoconstrictor substances (catecholamines, vasopressin)
* mediated by: alpha receptors
Which class of adrenergic receptors do adrenaline mainly act on?
Beta receptors
What is the formula to calculate BP
BP = Cardiac output x peripheral resistance
What blood vessels or smooth muscle would not have alpha-adrenergic receptors
arterioles in the brain
cardiac smooth muscle
What do B1 receptors do?
increase heart rate and force of contraction (.’. CO)
*helps restore BP
Describe the pathway of which cortisol is released in the adrenal cortex. (HPA axis)
Explain its significance in normal physiology
- hypothalamus (paraventricular nucleus) > synthesize and release VASOPRESSIN/ADH and CORTICOTROPIN RELEASING HORMONE (CRH)
- ADH and CRH acts on anterior pituitary
- Anterior pituitary release ACTH (adrenocorticotropic hormone)
- acts on Adrenal gland
- Adrenal gland produce cortisol, Adrenaline and NA
6a. Cortisol acts on hypothalamus and ant. pituitary (negative feedback)- reduce ADH and CRH release
6b. increase availability of glucose for ‘flight or fight’
6c. suppresses the highly demanding metabolic processes of the immune system (meaning more glucose for muscles)
