Autonomic Nervous System

Question 1

What are the 2 parts of the nervous system?

Answer 1

CNS 
PNS (projects into peripheries)

Question 2

What does the CNS consist of?

Answer 2

Brain
Spinal cord
Retina
CNII

Question 3

What does the PNS consist of?

Answer 3

Spinal + cranial nerves except CNII
ANS (SNS + PNS)
Somatic sensory + motor nerves

Question 4

What is the SNS responsible for?

Answer 4

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.

Question 5

What is the PNS responsible for?

Answer 5

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.

Question 6

What does the spinal nerve contain?

Answer 6

Motor, sensory + sometimes autonomic nerves

Question 7

Where does the motor (efferent) nerves outflow to?

Answer 7

Somatic motor (skeletal muscle)
Branchio-motor (pharyngeal arch muscle)
Visceral/autonomic motor (organs/vessels)

Question 8

Where does the sensory (afferent) nerves outflow to?

Answer 8

Somatic sensory (sensations from somatic tissues)
Visceral sensory (sensations from organs/vessels)
Special visceral sensory (taste for e.g.)

Question 9

Describe the different parts of the neuron.

Answer 9

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

Question 10

What do autonomic neuronal pathways in periphery consist of?

Answer 10

Cell body in brainstem/spinal cord (lateral horn of grey matter T1-L2 or S2-4) -> pre-ganglionic -> peripheral ganglion -> post-ganglionic -> target

Question 11

What are the 2 principle neurotransmitters in the PNS?

Answer 11

Acetylcholine

Noradrenaline

Question 12

What neurotransmitters and receptors do the somatic efferent, SNS + PNS use?

Answer 12

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

Question 13

How can the same neurotransmitter bring about different effects?

Answer 13

Different receptors or sometimes same receptor can have different effects e.g. 5 types of muscarinic ACh receptors (M1-M5)

Question 14

Where does the spinal cord terminate in terms of vertebral level?

Answer 14

L1/2

Question 15

Where does the sympathetic chain sit and what is its role?

Answer 15

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

Question 16

Where do sympathetic nerves emerge from the CNS and with what?

Answer 16

Only with spinal nerves T1-L2

Question 17

Where do nerves travel in the SNS?

Answer 17

From lateral horn cells -> preganglionic -> sympathetic chain ganglion -> postganglionic -> spinal nerves, visceral branches + arterial plexi (horizontally)
Fibres also travel up + down the chain (vertically)

Question 18

How does the sympathetic chain communicate with spinal nerves?

Answer 18

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

Question 19

What does the splanchnic nerve do?

Answer 19

Emerge from sympathetic chain + take sympathetic nerves to organs of the body by passing ganglia near specific organs e.g. thoracic + cardiac spanchnic nerves

Question 20

What is the condition if a patient loses sympathetic supply to the head, what are the symptoms + what can cause it?

Answer 20

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)

Question 21

Where must the sympathetic nerves to the head + face pass?

Answer 21

They must pass up the sympathetic chain and then go back down to T1 level + go up to brain too

Question 22

What diseases will be treated by a sympathectomy?

Answer 22

Hyperhidrosis (excessive sweating)

Raynaud disease with tissue damage as extremities have poor blood supply + are cold

Question 23

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.

Answer 23

Pre-aortic ganglia (supplied by the splanchnic nerves) - lateral horn cells -> preganglionic -> sympathetic chain ganglion -> splanchnic nerves -> pre-aortic ganglion -> post-ganglionic

Question 24

What is the autonomic supply to the gut tube? Why is this useful?

Answer 24

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

Question 25

How does adrenaline reach cells with no sympathetic innervation?

Answer 25

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

Question 26

What is the parasympathetic outflow from the CNS?

Answer 26

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

Question 27

How do parasympathetic neurons from cranial nerves synapse + travel to target?

Answer 27

Starts in the brain stem nucleus -> emerge with CN III, VII, IX or X (preganglionic) -> peripheral ganglion -> travel with CN V (5)(postganglionic) -> target

Question 28

What occurs to the pupils if there is loss of parasympathetic innervation?

Answer 28

No pupil light reflex (direct or consensual) so they are constantly dilated due to unopposed sympathetic action

Question 29

What is Frey-Baillarger syndrome?

Answer 29

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