Posterior commissure
Encyclopedia
The posterior commissure (also known as the epithalamic commissure) is a rounded band of white fibers crossing the middle line on the dorsal aspect of the upper end of the cerebral aqueduct
. It is important in the bilateral pupillary light reflex.
Its fibers acquire their medullary sheaths early, but their connections have not been definitely determined. Most of them have their origin in a nucleus, the nucleus of the posterior commissure (nucleus of Darkschewitsch), which lies in the central gray substance of the upper end of the cerebral aqueduct, in front of the nucleus of the oculomotor nerve.
Some are probably derived from the posterior part of the thalamus
and from the superior colliculus
, whereas others are believed to be continued downward into the medial longitudinal fasciculus
.
The posterior commissure interconnects the protectal nuclei, mediating the consensual pupillary light reflex.
Cerebral aqueduct
The mesencephalic duct, also known as the aqueductus mesencephali, aqueduct of Sylvius or the cerebral aqueduct, contains cerebrospinal fluid , is within the mesencephalon and connects the third ventricle in the diencephalon to the fourth ventricle in the mesencephalon, which is between the pons...
. It is important in the bilateral pupillary light reflex.
Its fibers acquire their medullary sheaths early, but their connections have not been definitely determined. Most of them have their origin in a nucleus, the nucleus of the posterior commissure (nucleus of Darkschewitsch), which lies in the central gray substance of the upper end of the cerebral aqueduct, in front of the nucleus of the oculomotor nerve.
Some are probably derived from the posterior part of the thalamus
Thalamus
The thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...
and from the superior colliculus
Superior colliculus
The optic tectum or simply tectum is a paired structure that forms a major component of the vertebrate midbrain. In mammals this structure is more commonly called the superior colliculus , but, even in mammals, the adjective tectal is commonly used. The tectum is a layered structure, with a...
, whereas others are believed to be continued downward into the medial longitudinal fasciculus
Medial longitudinal fasciculus
The medial longitudinal fasciculus is a pair of crossed fiber tracts , one on each side of the brainstem. These bundles of axons are situated near the midline of the brainstem and are composed of both ascending and descending fibers that arise from a number of sources and terminate in different...
.
The posterior commissure interconnects the protectal nuclei, mediating the consensual pupillary light reflex.
External links
- Overview at www.mrc-cbu.cam.ac.uk
- http://isc.temple.edu/neuroanatomy/lab/atlas/papc/