L11: autonomic innervation of head and neck structures

Question 1

Differentiate between a nucleus and a ganglion

Answer 1

Nucleus = collection of nerve cell bodies within the CNS eg. brainstem 
Ganglion = collection of nerve cell bodies outside the CNS; either relating to autonomic nerve or sensory nerves

Question 2

List sympathetic actions of the head and neck

Answer 2

Smooth muscle of blood vessels
Smooth muscle in eyelid (tarsal muscle) and iris (dilator pupillae)
Sweat glands

Question 3

List parasympathetic actions of the head and neck

Answer 3

Smooth muscle of iris (sphincter pupillae) and muscle in ciliary body (controls thickness of lens)
Lacrimal glands (tears)
Salivary and mucosal glands 
Smooth muscle of the respiratory and gastrointestinal tract

Question 4

Describe sympathetic innervation to head and neck structures

Answer 4

1) 1st order neurone originates at the hypothalamus, descends via brainstem into spinal cord and synapses onto cell body of 2nd order neurone
2) 2nd order neurone (pre-ganglionic) exits at the T1&2 level -> enters and ascends in sympathetic chain & at superior ganglion synapses on to the 3rd order neurone (post-ganglionic)
3) 3rd order neurone runs with common carotid & then along its terminal branches to reach target tissues
a. Branches to the eye and orbit run with the internal carotid artery (dilator pupillae & levator palpebrae superioris)
b. Branches to sweat glands run with branches of external carotid artery

Question 5

List two conditions which could interrupt sympathetic innervation to head and neck

Answer 5

Pathology and/or injury involving:

• common carotid/internal carotid (eg. carotid artery dissection)
• apical lung (eg. lung cancer)

Question 6

List the three classic signs of Horner’s syndrome

Answer 6

1) Partial ptosis (drooping of eyelid)
2) Miosis (constriction of pupil)
3) Anhidrosis (decreased sweating on the affected side of the face)

Question 7

Why does interruption of sympathetic innervation lead to partial ptosis?

Answer 7

Levator palpebrae superioris contracts to elevate the upper eye lid
Two muscle types within it with variable contributions to retraction:
-skeletal muscle: major contribution – oculomotor nerve innervation
-smooth muscle: minor contribution – sympathetic innervation

Question 8

List the 4 cranial nerves which have parasympathetic fibres

Answer 8

Oculomotor
Facial
Glossopharyngeal
Vagus

Question 9

Describe the parasympathetic innervation to the head and neck

Answer 9

Arise from brainstem from parasympathetic nuclei
Run with one of the 4 CNs
Parasympathetic ganglia (4)
Join on to distal branches of the trigeminal nerve (exception to this is the vagus nerve)

Question 10

Describe the parasympathetic fibres of the oculomotor nerve

Answer 10

Parasympathetic nuclei in brainstem – Edinger Westphal
Cranial nerve exits brainstem with – oculomotor (CN III)
Parasympathetic ganglion – ciliary ganglion
Target tissues – sphincter pupillae, ciliary body

Question 11

Describe the parasympathetic fibres of the facial nerve

Answer 11

Parasympathetic nuclei in brainstem – superior salivary nuclei
Cranial nerve exits brainstem with – facial nerve (CN VII)
Parasympathetic ganglion – pterygopalatine & submandibular
Target tissues – lacrimal glands, most of the salivary glands except the parotid & nasal mucosal glands

Question 12

Describe the pupillary light reflex

Answer 12

Light in left pupil -> sensory afferent from left retina (CN II) -> some branches leave CN II to enter midbrain and synapse in pre-tectal nucleus
Connection with the EDW nuclei (left and right)
Pre-ganglionic parasympathetic fibres from EDW leave brainstem with CN III (left and right) -> pre-ganglionic parasympathetics synapse in ciliary ganglion; become post-ganglionic
Reach sphincter pupillae muscle of the iris; direct light reflex = eye in which light shone, consensual light reflex = opposite eye

Question 13

Describe the parasympathetic fibres of the glossopharyngeal nerve

Answer 13

Parasympathetic nuclei in brainstem – inferior salivary nuclei
Cranial nerve exits brainstem with – glossopharyngeal (CN IX)
Parasympathetic ganglion – otic ganglion
Target tissues – parotid gland

Question 14

Describe the parasympathetic component of the vagus nerve

Answer 14

Parasympathetics exit the medulla with other axons forming CN X
Pre-ganglionic parasympathetic fibres run within CN X and its branches
Meet ganglion at or in target tissue
Target tissues: mucosal glands in pharynx/larynx and smooth muscle of oesophagus & trachea, smooth muscle and mucosal glands within rest of respiratory & GI tract + heart