Autonomic Nervous System

Question 1

In most autonomic effectors, there is both sympathetic and parasympathetic innervation. What is the advantage of this?

Answer 1

gradient of response, not all-or-nothing, can respond quickly

Question 2

Which autonomic fibres are myelinated?

Answer 2

The preganglionic fibre is, the postganglionic fibre is not

Question 3

Compare the relative lengths of the neurones in the ParaNS and SympNS

Answer 3

In SympNS, pre is short and post is long

In ParaNS, pre is long and post is short

Question 4

Where do sympathetic and parasympathetic fibres arise?

Answer 4

Sympathetic = lateral horn at T1-L2 levels
Parasympathetic = arise is the brainstem and sacral cord

Question 5

What is the ratio of pre to post ganglionic fibres?

Answer 5

1:35

Question 6

Where to the pre and post neurones synapse?

Answer 6

Pre synapses in ganglia, post synapses at the target tissue

Question 7

Describe the possible routes that an sympathetic efferent fibre could take

Answer 7

Cell body in the lateral horn, exists through the ventral root, goes through white rami communicans into sympathetic ganglion:

• it can synapse here and then postganglionic fibre leaves through grey rami communicans
• it can ascend or descend the chain and synapse at a different level
• can transverse the chain, axons are myelinated (splanchnic nerves) and synapse in the prevertebral ganglia

Question 8

Which prevertebral ganglia correlates to which splanchnic nerve? At what spinal levels do they originate and what tissue they supply

Answer 8

• coeliac ganglion - greater splanchnic nerve (T6-T9, foregut)
• superior mesenteric ganglion - lesser splanchnic nerve (T9, T10, midgut)
• inferior mesenteric ganglion - least splanchnic nerve (T11, T12, hindgut)

Question 9

The fate at the ganglion determines the target organ. Give all examples

Answer 9

Immediate synapse - Skin via SN’s
Ascend chain - Head and Neck
Descend chain - repoductive system
Transerve chain - gut

Question 10

In the autonomic nervous system there are two efferent neurones joint at the ganglia. What is the exception to this rule?

Answer 10

The preganglionic innervation of the adrenal medulla. Neuroendocrine cells replace postganglionic neurone and secrete adrenaline and noradrenaline directly into the blood.

Question 11

Describe the route of autonomic afferent fibres

Answer 11

Sympathetic - through sympathetic ganglion to DRG

Parasympathetic - to cranial nerve sensory nuclei to DRG to dorsal horn

Question 12

5 pathways in the parasympathetic division

• where the pregan cell body is
• which nerve it follows
• its ganglion
• its target organ

Answer 12

1. Edinger-Westphal, CNIII, ciliary ganglion, pupillary constrictor
2. Superior salivatory, CNVII, pterygopalatine/submandibular ganglion, nose, eyes, SM and SL glands
3. Inferior salivatory, CNIX, otic ganglion, parotid gland
4. Dorsal nucleus of X, CNX, cardiac, pulmonary, enteric ganglion
5. S2-S4, pelvic splanchnic, renal, bladder

Question 13

Explain referred pain

Answer 13

Visceral and somatic fibres pass to same spinal nerve
Organ pain misinterpreted as skin pain
Pain is diffuse, poorly localised and poorly described

Question 14

What are 3 syndromes of the autonomic nervous system?

Answer 14

1. Raynauds syndrome - paradoxical constriction of peripheral blood vessels
2. Horner’s syndrome - unopposed paroxysm supply in face, miosis, ptosis, hot red dry skin
3. Hirschsprung’s disease (megacolon) - colon not stimulated to contract