The autonomic nervous system of the head and neck consists of sympathetic and parasympathetic divisions, both of which maintain internal homeostasis and control involuntary functions such as gland secretion, blood vessel diameter, and pupillary responses. Both divisions utilise a two-neuron relay involving a preganglionic nerve fibre synapsing in a ganglion followed by a postganglionic nerve.
Sympathetics
Origin: Preganglionic sympathetic fibers arise in the intermediolateral columns of the spinal cord between T1 and T3.
Pathway: Fibers ascend in the sympathetic chain to synapse in the superior cervical ganglion (C2-C3 level), the main sympathetic ganglion for the head and neck.
Postganglionic fibers: These follow peri-arterial plexuses (especially around the internal and external carotid arteries) to reach target tissues such as sweat glands, smooth muscle of blood vessels, dilator pupillae (pupil dilation), and tarsal muscle of the eyelid.
Key functions:
pupillary dilation (mydriasis)
eyelid elevation (superior tarsal muscle)
vasoconstriction
sweat production of the face
Parasympathetics
Origin: Preganglionic parasympathetic fibers originate from brainstem nuclei of cranial nerves 3 (oculomotor), 7 (facial), 9 (glossopharyngeal), and 10 (vagus).
Ganglia: Four parasympathetic ganglia in the head include; ciliary, pterygopalatine, submandibular, and otic.
Pathways: Preganglionic fibers travel with their respective cranial nerves, synapse in one of the ganglia, and then short postganglionic fibers supply target glands or muscles, often via branches of the trigeminal nerve.
Key functions:
Pupil constriction (sphincter pupillae, oculomotor nerve)
Lens accommodation (ciliary muscle, oculomotor nerve)
Tear (lacrimal) and nasal gland secretion (facial nerve)
Submandibular and sublingual gland secretion (facial nerve)
Parotid gland secretion (glossopharyngeal nerve)
Visceral control in neck and thorax via vagus nerve (vagus nerve)