6.1.1 Autonomic Innervation of Head and Neck Structures

Question 1

What does the autonomic nervous system do?

Answer 1

Controls non-voluntary actions

Maintains internal environment

Question 2

How does the sympathetic nervous system affect different tissues?

Answer 2

Fight or flight

• Smooth muscle in eyelid (superior tarsal muscle) eye lid retraction
• Smooth muscle in iris (dilator pupillae) dilates pupil
• Sweat glands
• Smooth muscle of blood vessels constricts
• Smooth muscle of respiratory tract and GI, bronchodilate and decrease gut motility
• Cardiac muscle, increase rate and force of contraction

Question 3

How does the parasympathetic nervous system affect different tissues?

Answer 3

Rest and digest

• Smooth muscle of iris (sphinter pupillae) constricts pupil
• Smooth muscle in ciliary body, makes lens fatter
• Lacrimal glands ++
• Salivary glands ++
• Mucosal glands ++
• Smooth muscle of respiratory and GI tract ++ (contracts)
• Cardiac muscle, decreases rate and force of contraction

Question 4

How are neurones organised in the ANS?

Answer 4

Pre-ganglionic neurone
Cell body within CNS, axon exits CNS to synapse with another autonomic neruone

Postganglionic neurone
Cell body lies within ganglion outside of CNS, axon exits ganglion to synapse with tissues

Question 5

Sympathetic v Parasympathetic neurone

Answer 5

Sympathetic= short preganglionic, NorAd at target

Parasympathetic= long preganglionic , Ach at target

Preganglionic is myelinated and post is not, therefore parasympathetic faster acting

(Both use Ach at junction between cell body and preganglionic fibre)

Question 6

Explain the outflow of parasympathetic and sympathetic nerves of the ANS

Answer 6

Craniosacral - parasympathetic
Brainstem x4 CNs and Sacral (S2-4) pelvic splanchnics

Thoracolumbar- sympathetic
T1-L2 spinal segments only