Lecture #113: Anatomy: Autonomics of the Head and Neck

How does the autonomic (visceral) motor system organize its neurons?

Two-neuron chain – preganglionic neuron in CNS synapses on postganglionic neuron in an autonomic ganglion that innervates target tissues

Where are pre- and post-ganglionic cell bodies located in the sympathetic system?

Preganglionic cell bodies in T1–L2 lateral horn; postganglionic cell bodies in paravertebral (sympathetic chain) and prevertebral ganglia

Where are pre- and post-ganglionic cell bodies located in the parasympathetic system?

Preganglionic cell bodies in brainstem (CN III, VII, IX, X) and S2–S4 spinal cord; postganglionic cell bodies in target organ walls or minute ganglia (e.g., ciliary, pterygopalatine, submandibular, otic)

Which structures in the head receive autonomic innervation?

Lacrimal, salivary, mucous, sweat, and sebaceous glands; smooth muscle of blood vessels, superior tarsal muscle, pupillary muscles (dilator and constrictor), and ciliary muscle

What are the major sympathetic effects in the head?

Vasoconstriction of facial arterioles, pupil dilation, superior tarsal muscle contraction (eyelid elevation), and sweat secretion

What are the major parasympathetic effects in the head?

Stimulate lacrimal and salivary gland secretion, pupil constriction, and lens accommodation for near vision

Where do sympathetic preganglionic axons for the head originate?

Lateral horn of spinal cord segments T1–T2

Where do these sympathetic fibers synapse?

In the superior cervical ganglion, the most superior paravertebral ganglion of the sympathetic chain

Through which pathways do postganglionic sympathetic fibers travel to reach target structures?

They form plexuses around the internal and external carotid arteries (internal and external carotid plexuses)

What does the internal carotid plexus supply?

Ocular arterioles (vasoconstriction), dilator pupillae and superior tarsal muscles, facial sweat glands via V1, and nasal/palatal vasculature via V2

What does the external carotid plexus supply?

Parotid, submandibular, and sublingual glands (sympathetic vasoconstriction); also facial sweat glands and arteriole

What is Horner’s syndrome?

Results from interruption of the sympathetic pathway to the head, causing miosis (pupil constriction), ptosis (eyelid droop), anhidrosis (loss of sweating), and facial flushing loss

List the three levels of lesions causing Horner’s syndrome.

1) First-order central (stroke, spinal tumor); 2) Second-order preganglionic (Pancoast tumor, neck trauma); 3) Third-order postganglionic (carotid artery lesion, skull-base injury)

Name the four parasympathetic ganglia in the head.

Ciliary (V1 link, CN III input), Pterygopalatine (V2 link, CN VII input), Submandibular (V3 link, CN VII input), Otic (V3 link, CN IX input)

Describe the ciliary ganglion pathway.

Preganglionic fibers from CN III oculomotor nerve synapse in ciliary ganglion; postganglionic fibers via short ciliary nerves to ciliary muscle (accommodation) and constrictor pupillae (pupil constriction)

Describe the pterygopalatine ganglion pathway.

Preganglionic fibers from CN VII (facial) via greater petrosal nerve form nerve of pterygoid canal; postganglionic fibers supply lacrimal and mucosal glands of nasal cavity and palate via V2

Describe the submandibular ganglion pathway.

Preganglionic fibers from CN VII (facial) via chorda tympani join lingual nerve (V3); postganglionic fibers innervate submandibular and sublingual glands to stimulate saliva secretion

Describe the otic ganglion pathway.

Preganglionic fibers from CN IX (glossopharyngeal) via tympanic plexus and lesser petrosal nerve synapse in otic ganglion; postganglionic fibers travel with auriculotemporal nerve (V3) to parotid gland

Describe parasympathetic supply of the vagus nerve in the neck.

Preganglionic fibers from dorsal motor nucleus of vagus; postganglionic neurons in pharyngeal and laryngeal walls innervate glands and vessels of pharynx, larynx, thyroid, and parathyroids

What happens in oculomotor nerve damage affecting parasympathetics?

Results in loss of accommodation and pupil constriction with dilated pupil on affected side and possible ptosis from somatic fiber damage

What is Frey’s syndrome?

Gustatory sweating due to aberrant regeneration of postganglionic parasympathetic fibers (meant for salivary glands) into sweat glands after parotid gland surgery