Autonomic Nerves in Head

The superior cervical ganglion is fusiform in shape. It is produced by the coalescence of the upper three or four cervical ganglia. The preganglionic fibers emerge through the uppermost thoracic spinal nerves and ascend to it as the cervical sympathetic trunk; a relatively small number of these fibers are from adjacent cervical nerve roots. A small proportion of the preganglionic fibers pass through it without interruption and relay at higher levels in the internal carotid ganglia.

The superior cervical ganglion receives and supplies communicating, visceral, vascular, muscular, osseous, and articular rami. It communicates with the last four cranial nerves or their branches, with the vertebral arterial plexus and, occasionally, with the phrenic nerve. It supplies gray rami to the upper three or four cervical spinal nerves, and the contained postganglionic fibers are distributed with the branches of the cervical nerves. Visceral fibers pass to the larynx, pharynx, and heart, and other fibers are carried in vascular plexuses to the salivary, lacrimal, pituitary, pineal, thyroid, and other glands. Vascular fibers are supplied to the internal and external carotid arteries and form plexuses around them; nerve continuations from these plexuses form subsidiary plexuses around all their branches. From the internal carotid plexus, minute caroticotympanic offshoots join the tympanic branch of the glossopharyngeal nerve and thus reach the tympanic plexus. A deep petrosal branch unites with the greater petrosal nerve to form the nerve of the pterygoid canal, which constitutes the sympathetic root of the pterygopalatine ganglion. The sympathetic fibers are postganglionic and run through the ganglion without relaying, to be distributed to vessels and glands in the nose, palate, nasopharynx, and orbit. The sympathetic root of the ciliary ganglion arises from the cranial end of the ipsilateral internal carotid nerves or plexus; its fibers are postganglionic, having relayed in the superior cervical or internal carotid ganglia; they pass through the ganglion and run onward in the ciliary nerves to supply the ocular vessels and the dilator pupillae. In addition to postganglionic efferent fibers, many visceral efferent and afferent fibers are also present in the vascular plexuses. They convey sympathetic efferent output to the pituitary, lacrimal, salivary, thyroid, and other smaller glands in the territories supplied by the carotid arteries, and they also transmit sensory information from the same structures. In a similar fashion, sympathetic fibers are carried to adjacent osseous, articular, and muscular structures.

The middle cervical ganglion is much smaller than the superior ganglion and usually represents fused fifth and sixth cervical ganglia. It contributes gray rami communicantes to the fifth and sixth cervical nerves and sends fibers to the vertebral periarterial plexus. Inconstant strands form interconnections with the vagus, phrenic, and recurrent laryngeal nerves, and visceral branches are supplied to the thyroid and parathyroid glands. The ganglion may give off the middle cervical sympathetic cardiac nerve and contributes several twigs to the esophagus and trachea. Vascular branches help in the innervation of the common carotid, inferior thyroid and vertebral arteries and the jugular veins. Fibers pass to adjacent muscular, osseous, and articular structures, usually alongside the arteries supplying them.

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