Posterior commissure

Posterior commissure (PC) is a small rounded fiber bundle crossing the midline of the brain. It is located at the junction of the thalamus and midbrain and is part of the epithalamus. It plays a role in bilateral pupillary light reflex and is involved in the coordination of eye movements.

Anatomy

The posterior commissure is located near the pineal gland, above the cerebral aqueduct and below the habenular commissure. It is composed of commissural fibers that cross the midline of the brain. The fibers originate from several areas of the brain, including the superior colliculus, pretectal area, and medial geniculate body.

Function

The posterior commissure is involved in several functions. It plays a role in the bilateral pupillary light reflex, which is the constriction of both pupils in response to light shone in one eye. This reflex is mediated by the Edinger-Westphal nucleus, which sends fibers to the posterior commissure.

The posterior commissure also plays a role in the coordination of eye movements. It is involved in the vertical gaze system, which allows for upward and downward movements of the eyes. The fibers of the posterior commissure connect the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) on one side of the brain to the oculomotor and trochlear nuclei on the other side, allowing for coordinated vertical eye movements.

Clinical significance

Damage to the posterior commissure can result in several neurological disorders. These include Parinaud's syndrome, which is characterized by an inability to move the eyes upward, and Argyll Robertson pupil, which is a disorder of the pupillary light reflex.

See also

• Anterior commissure
• Commissure of fornix
• Corpus callosum

Posterior commissure

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