H&N11 - Autonomic Innervation of the Head & Neck

Question 1

2 features of autonomic outflow from the CNS

Answer 1

1. ) Parasympathetic - craniosacral outflow
   - cranial (4 cranial nerves) and sacral (S2-S4)
2. ) Sympathetic - thoracolumbar outflow (T1-L2)
   - cell bodies in lateral horn of grey matter of spinal cord

Question 2

4 functions of sympathetic innervation to the head and neck structures

Answer 2

1. ) Eye (dilator pupillae) - dilates the pupil
2. ) Eye Lid (superior tarsal muscles) - assists eyelid retraction
3. ) Blood Vessels (smooth muscle) - vasconstriction
4. ) Sweat Glands - sweating

Question 3

4 features of how the sympathetic chain reaches the head and neck structures

Spinal Cord
Superior Cervical Ganglion
Blood Vessels
Lung Apex

Answer 3

1.) Spinal Cord - sympathetics innervating the head and neck structures come out from mainly T1-T2 segment

2. ) Superior Cervical Ganglion - top of sympathetic chain
   - contains the cell bodies of the postganglionic fibres supplying the head and neck
   - preganglionic fibres ascend the chain to reach the top
   - middle cervical ganglion supplies the neck and chest
3. ) Blood Vessels - the sympathetic nerves ‘hitch hikes’ on blood vessels to reach its destination in the head and neck
   - join the CCA and follow the ECA and ICA branches
   - e.g. nerves going to the eye follow ophthalmic artery, nerves to the sweat glands follow the ECA
4. ) Lung Apex - pathology involving the apex of the lung and CCA and its branches can cause autonomic dysfunction in the eye and face
   - main condition is Horner’s syndrome

Question 4

3 features of Horner’s Syndrome

Answer 4

1. ) Partial Ptosis - partial drooping of the upper eyelid
   - loss of sympathetic innervation to the smooth muscle (superior tarsal muscle) that adjoins levator palpebrae superioris (LPS)
   - not severe because you still have parasympa innervation to the skeletal component of LPS
2. ) Miosis - excessive constriction of the pupil
   - loss of sympathetic innveration to iris dilator muscle
   - unopposed action of pupillae sphincter (parasympa)
3. ) Anhidrosis - dry face, inability to sweat
   - loss of sympathetic innervation to sweat glands

Question 5

4 features of the parasympathetic innervation to the head and neck

Brainstem x4
Hitch-Hike x4
Parasympathetic Ganglia x4
CN V

Answer 5

1. ) Brainstem - all arise from parasympathetic nuclei in the brainstem
   - edinger westphal, superior salivary, inferior salivary, dorsal motor

2.) Hich-Hike - follow the path of one of 4 cranial nerves - oculomotor (3) facial (7) glossopharyngeal (9) vagus (10)

3. ) Parasympathetic Ganglia - contains the cell body of the postganglionic fibres
   - ciliary, pterygopalatine, submandibular, otic

4.) Cranial Nerve V - hitch hike on distal branches of the trigeminal nerve to reach its target tissue (except CN X)

Question 6

Route of the 4 parasympathetic nerves

Edinger Westphal
Superior Salivary
Inferior Salivary
Dorsal Motor

Answer 6

1. ) Edinger Westphal
   - oculomotor nerve –> ciliary ganglion –> Va –> Eye
   - ciliary muscle alters the shape of the lens
   - sphincter pupillae muscle constricts the pupil
2. ) Superior Salivary - 2 paths
   - CN VII –> greater petrosal –> pterygopalatine ganglion –> Va/b –> lacrimal, nasal, palatine glands
   - CN VII –> chorda tympani –> submandibular ganglion
   - -> Vc (lingual) –> salivary glands (except parotid)
3. ) Inferior Salivary
   - CN IX –> tympanic nerve –> lesser petrosal nerve –> otic ganglion –> Vc (auriculotemporal) –> parotid gland
   - otic ganglion is found in the infratemporal fossa
4. ) Dorsal Motor
   - CN X –> meet ganglion at or in target tissue (no hitch-hike)
   - mucosal glands in the pharynx/larynx,
   - smooth muscle of oesophagus and trachea,
   - smooth muscle and mucosal glands within rest of repsiratory and GI tract
   - heart

Question 7

Explain why light shone in one (e.g. left) eye produces a light reflex (pupil constriction) in both eyes

Answer 7

1. ) Light in left pupil detected by sensory afferents from the left retina (CN II)
2. ) Some branches leaves CN II to enter the midbrain and synpase in pre-tectal nucleus
3. ) Connection with Edinger Westphal nuclei means pregang parasympa fibres leave brainstem with both the right and left oculomotor nerve (efferents)
4. ) Eventually, information reaches the sphincter pupillae muscle of the iris causing constriction of both eyes

5.) Direct Light Reflex - eye in which light is shone reacts
Consensual Light Reflex - opposite eye reacts