Autonomic Distribution to the Head and the Neck

SYMPATHETIC FIBERS

The sympathetic preganglionic fibers for the eye arise from the intermediolateral column of the thoracic cord and travel in the ipsilateral first, second, and, occasionally, in the third thoracic spinal nerves. They pass through white rami communicantes to the sympathetic trunks; the fibers ascend to the superior cervical ganglion where they relay, although a few synapse higher in the internal carotid ganglia. The postganglionic fibers run either in the internal carotid plexus and enter the orbit through its superior fissure, or else they run alongside the ophthalmic artery in its periarterial plexus. Some of the ocular sympathetic fibers may make a detour through the caroticotympanic nerves and tympanic plexus before rejoining the cavernous part of the internal carotid plexus by means of a branch that emerges from the anterior surface of the petrous part of the temporal bone near the greater petrosal nerve; thereafter, they accompany the other ocular fibers.

Some of the branches passing through the superior orbital fissure form the sympathetic root of the ciliary ganglion; their contained fibers pass through it without relaying to become incorporated in the 8 to 10 short ciliary nerves. Other branches join the ophthalmic nerve or its nasociliary branch and reach the eye in the two to three long ciliary nerves that supply the radial musculature in the iris (dilator pupillae). Both long and short ciliary nerves also contain afferent fibers from the cornea, iris, and choroid. Fibers conveyed in the short ciliary nerves pass through a communicating ramus from the ciliary ganglion to the nasociliary nerve; this ramus is called the sensory root of the ciliary ganglion. The parent cells of these sensory fibers are located in the trigeminal (semilunar) ganglion, and their central processes end in the sensory trigeminal nuclei in the brainstem. The sensory trigeminal nuclei have multiple inter-connections with other somatic and autonomic centers and thus influence many reflex reactions. Other sympathetic fibers from the internal carotid plexus reach the eye through the ophthalmic periarterial plexus and its subsidiary plexuses around the central retinal, ciliary, scleral and conjunctival arteries (see Plate 7-5).

PARASYMPATHETIC FIBERS

The parasympathetic preganglionic fibers for the eye are the axons of cells in the autonomic, (Edinger-Westphal) oculomotor nucleus. They run in the third cranial nerve and exit in the motor root of the ciliary ganglion, where they relay. The axons of these ganglionic cells are postganglionic parasympathetic fibers, which reach the eye in the short ciliary nerves and are distributed to the constrictor fibers of the iris (sphincter pupillae), to the ciliary muscle, and to the blood vessels in the eyeball.

VISUAL CENTERS

The visual reflex centers are located in the tectal and pretectal areas of the mesencephalon. They are connected to the lateral geniculate bodies (lower visual centers) and to the superior colliculi in which the tectospinal tracts originate; these connections provide the anatomic basis for the reflex movements of the head and eyes in response to visual stimuli. The light and accommodation reflexes are affected through pretectal connections. Fibers from the lateral geniculate bodies are connected through synapses in pretectal nuclei to the accessory oculomotor nucleus (Edinger-Westphal nuclei), which controls the sphincter pupillae and the ciliary muscle.

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