Autonomic Nervous System Flashcards
What are the 2 parts of the nervous system?
CNS PNS (projects into peripheries)
What does the CNS consist of?
Brain
Spinal cord
Retina
CNII
What does the PNS consist of?
Spinal + cranial nerves except CNII
ANS (SNS + PNS)
Somatic sensory + motor nerves
What is the SNS responsible for?
Fight or flight response i.e. increases HR, constricts blood vessels, slows GI transit speed, contracts spinchters (urinary/anal), activate sweat glands, dilate pupils etc. - anything that you don’t want to do whilst exercising or panicking for e.g.
What is the PNS responsible for?
Rest and digest (pee, poo + point) i.e. decreases HR, dilates blood vessels, directs blood to GI tract for digestion, relaxes sphincters (urinary/anal), deactivate sweat glands, constrict pupils etc. - anything that you want to do when conserving energy, activating bowel activity, urinating, defecating, having an erection etc.
What does the spinal nerve contain?
Motor, sensory + sometimes autonomic nerves
Where does the motor (efferent) nerves outflow to?
Somatic motor (skeletal muscle) Branchio-motor (pharyngeal arch muscle) Visceral/autonomic motor (organs/vessels)
Where does the sensory (afferent) nerves outflow to?
Somatic sensory (sensations from somatic tissues) Visceral sensory (sensations from organs/vessels) Special visceral sensory (taste for e.g.)
Describe the different parts of the neuron.
Dendrites: receptive projections sensitive to neurotransmitter input
Soma (cell body): metabolic centre
Axon: one-way rapid communication between cell body + axon terminals
Axon terminals: form connections with other neurons/effector tissue via synapses
What do autonomic neuronal pathways in periphery consist of?
Cell body in brainstem/spinal cord (lateral horn of grey matter T1-L2 or S2-4) -> pre-ganglionic -> peripheral ganglion -> post-ganglionic -> target
What are the 2 principle neurotransmitters in the PNS?
Acetylcholine
Noradrenaline
What neurotransmitters and receptors do the somatic efferent, SNS + PNS use?
Somatic efferent: ACh -> nicotinic
SNS: ACh -> nicotinic + NA -> a or b (except sweat glands + chromaffin adrenal medulla where ACh activates muscarinic receptors)
PNS: ACh -> nicotinic + ACh -> muscarinic
How can the same neurotransmitter bring about different effects?
Different receptors or sometimes same receptor can have different effects e.g. 5 types of muscarinic ACh receptors (M1-M5)
Where does the spinal cord terminate in terms of vertebral level?
L1/2
Where does the sympathetic chain sit and what is its role?
Either side of vertebral column extending up to near the skull base down to the tip of the sacrum
Distributes sympathetic neurons to the body; all sympathetic nerves pass through it
Where do sympathetic nerves emerge from the CNS and with what?
Only with spinal nerves T1-L2
Where do nerves travel in the SNS?
From lateral horn cells -> preganglionic -> sympathetic chain ganglion -> postganglionic -> spinal nerves, visceral branches + arterial plexi (horizontally)
Fibres also travel up + down the chain (vertically)
How does the sympathetic chain communicate with spinal nerves?
Via rami communicans:
- Grey rami (seen joining all spinal nerves) - sympathetic neurons passing from chain into spinal nerve i.e. postganglionic
- White rami (only seen leaving T1-L1 spinal nerves) - sympathetic neurons passing into chain i.e. preganglionic
What does the splanchnic nerve do?
Emerge from sympathetic chain + take sympathetic nerves to organs of the body by passing ganglia near specific organs e.g. thoracic + cardiac spanchnic nerves
What is the condition if a patient loses sympathetic supply to the head, what are the symptoms + what can cause it?
Horner’s syndrome
Symptoms: miosis (pupil constriction), vasodilation, ptosis (drooping of upper eye lid) + lack of sweating (anhidrosis)
Causes: Trauma, surgery, disease or internal jugular vein (IJV) cannulation in diabetes (damages sympathetic chain in cervical region of neck)
Where must the sympathetic nerves to the head + face pass?
They must pass up the sympathetic chain and then go back down to T1 level + go up to brain too
What diseases will be treated by a sympathectomy?
Hyperhidrosis (excessive sweating)
Raynaud disease with tissue damage as extremities have poor blood supply + are cold
What SNS ganglia sit around the gut tube blood supply + supply the gut tube? Show the chain of events that occur in the supply of the gut.
Pre-aortic ganglia (supplied by the splanchnic nerves) - lateral horn cells -> preganglionic -> sympathetic chain ganglion -> splanchnic nerves -> pre-aortic ganglion -> post-ganglionic
What is the autonomic supply to the gut tube? Why is this useful?
Foregut is supplied by sympathetic coeliac ganglion (T5-9) + parasympathetic vagus nerves (CNX)
Midgut is supplied by sympathetic superior mesenteric ganglion (T10-T11) + parasympathetic vagus nerves (CNX)
Hindgut is supplied by sympathetic inferior mesenteric ganglion (T12-L1) + parasympathetic pelvic splanchnic nerves (S2-4)
- helps you determine referred pain/where pain would be felt
How does adrenaline reach cells with no sympathetic innervation?
Chromaffin cells of adrenal medulla mainly release adrenaline (95%) into the blood so the systemic release provides an additional mechanism for reaching cells with no sympathetic innervation
What is the parasympathetic outflow from the CNS?
Nuclei sit in brainstem where there is outflow with CN III (3), VII (7), IX (9) + X (10)
-> nuclei at the bottom sit in the sacral part of the spinal cord where there it outflow with S2-4 spinal nerves (pelvis splanchnic nerves) = PS outflow from CNS is with 4 cranial nerves + 3 spinal nerves
How do parasympathetic neurons from cranial nerves synapse + travel to target?
Starts in the brain stem nucleus -> emerge with CN III, VII, IX or X (preganglionic) -> peripheral ganglion -> travel with CN V (5)(postganglionic) -> target
What occurs to the pupils if there is loss of parasympathetic innervation?
No pupil light reflex (direct or consensual) so they are constantly dilated due to unopposed sympathetic action
What is Frey-Baillarger syndrome?
Where there is gustatory sweating of face following parotid surgery/injury (glands responsible for making saliva) so parasympathetic nerves that normally cause salivation regrow to innervate the muscarinic receptors of the sweat glands which are normally sympathetically innervated -> in response to tasting food, parasympathetic nerves will respond by instructing sweat glands to produce sweat + blood vessels to dilate = excessive sweating + flushing when eating certain food
