Corpus: Ciliary ganglion
from Latin: cilium - cilium - eyelash
1. Definition
2. Anatomy
2.1. Topography
The ciliary ganglion has a diameter of only 1-2 mm. It is located within the orbit about 2 cm behind the bulbus oculi (eyeball), positioned between the rectus lateralis muscle and the optic nerve.
2.2. Histology
The ciliary ganglion contains approximately 2,500 neurons. About twice as many parasympathetic fibers enter the ganglion as exit it, indicating that the ganglion is not merely a relay station but also a site of complex neuronal processing and interconnection.
2.3. Fibres
Sensory, sympathetic, and parasympathetic fibers pass through the ciliary ganglion, but only the parasympathetic fibers synapse within the ganglion. For the sensory and sympathetic fibers, the ganglion acts only as a transit station. All fibers emerging from the ganglion travel into the interior of the eye via the short ciliary nerves (nervi ciliares breves).
2.3.1. Parasympathetic fibres
The parasympathetic fibers of the ciliary ganglion originate from the accessory oculomotor nucleus (Edinger-Westphal nucleus). They travel with the oculomotor nerve (cranial nerve III) through the superior orbital fissure to the orbit, where they enter the ganglion as the motor root (radix oculomotoria). Here they synapse with postganglionic fibers, which then innervate the smooth muscles of the inner eye, including the ciliary muscle and the sphincter pupillae muscle.
2.3.2. Sympathetic fibres
The postganglionic sympathetic fibers of the ciliary ganglion originate from nerve cells in the superior cervical ganglion. They reach the ganglion via the internal carotid plexus and pass through without synapsing to innervate the dilator pupillae muscle, the orbital muscle, and the tarsal muscles.
2.3.3. Sensory fibres
Several somatosensory fibers from the nasociliary nerve (branch of cranial nerve V1) run through the ciliary ganglion as the long sensory root (radix longa ganglii ciliaris). They provide sensory innervation to the cornea and the conjunctiva.
3. Pathology
If the ciliary ganglion is damaged, the corneal reflex is lost, and the pupil can no longer respond to light stimuli.