septum pellucidum

Brain: Septum pellucidum
Scheme of rhinencephalon. (Septum pellucidum visible at top center.)
Median sagittal section of brain. (Septum pellucidum visible at center.)
Gray's	subject #189 840
NeuroNames	hier-238
MeSH	Septum+Pellucidum
Dorlands/Elsevier	Septum pellucidum

The septum pellucidum (also called the septum lucidum) is a thin, triangular, vertical membrane separating the lateral ventricles of the brain. It separates the anterior horn of the left and right lateral ventricles. It runs as a sheet from the corpus callosum down to the fornix. When the hemispheres are cut apart, the septum remains on one hemisphere, usually the left. The septum pellucidum is implicated in pleasure, mood, rage, sexual gratification and more. Lesions of the septum lead to sham rage. Stimulation of the medial forebrain bundle (primary efferent of the septum) restores normal behavior.

Layers

The septum pellucidum actually consists of two layers or laminae of both white and gray matter, called the laminae septi pellucidi.

These layers are normally fused; however, in approximately one-tenth of humans, there is a slit-like cavity between them, referred to as cavum septum pellucidum, cavum septi pellucidi, or "fifth ventricle" ^[1][2]. The last term has lost favor in recent years, as the space is usually not continuous with the ventricular system and does not contain cerebrospinal fluid ^[3]. Indeed fifth ventricle has been used for other purposes in recent years.^[4].

Location

The septum pellucidum is located in the midline of the brain, between the two cerebral hemispheres. It is attached superiorly (above), anteriorly (in front), and inferiorly (below) to the corpus callosum, the large collection of nerve fibers that connect the two hemispheres.

Inferiorly and posteriorly (in back), it is attached to the anterior part of the fornix.

On either side are the two lateral ventricles, pockets of cerebrospinal fluid within the cerebral hemispheres.

Pathology

Absence of the septum pellucidum or corpus callosum, caused by mutations in the HESX1 gene, is associated with septo-optic dysplasia. This may result in hypothalamic dysfunction and hypopituitarism, as well as problems of vision, coordination, and intelligence, as well as other unusual symptoms.

Additional images

Mesal aspect of a brain sectioned in the median sagittal plane.	Horizontal section of right cerebral hemisphere.	Coronal section through anterior cornua of lateral ventricles.	Coronal section of brain through anterior commissure.
The fornix and corpus callosum from below.	Diagram showing the positions of the three principal subarachnoid cisternæ.

References

External links

• Roche Lexicon - illustrated navigator, at Elsevier 13048.000-3