Fornix (neuroanatomy)

Fornix
	File:Gray747.png Diagram of the fornix. Right=anterior
Details
Latin	Fornix
Identifiers
MeSH	A08.186.211.577.265
NeuroNames	hier-250
NeuroLex ID	Fornix
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TH	{{#property:P1694}}
TE	{{#property:P1693}}
FMA	{{#property:P1402}}
	Anatomical terms of neuroanatomy [[[d:Lua error in Module:Wikidata at line 863: attempt to index field 'wikibase' (a nil value).\|edit on Wikidata]]]

The fornix (Latin: arch) is a C-shaped bundle of nerve fibers in the brain that carries signals from the hippocampus to the mammillary bodies and then to the anterior nuclei of thalamus. The fornix is part of the limbic system. While its exact function and importance in the physiology of the brain is still not entirely clear, it has been demonstrated in humans that surgical transection – the cutting of the fornix along its body – can cause memory loss. There is some debate over what type of memory is affected by this damage, but it has been found to most closely correlate with recall memory rather than recognition memory. This means that damage to the fornix can cause difficulty in recalling long-term information such as details of past events, but it has little effect on the ability to recognize objects or familiar situations.

Structure

The fibres begin in the hippocampus on each side of the brain as fimbria; the separate left and right sides are each called the crus of the fornix (plural crura). The bundles of fibres come together in the midline of the brain, forming the body of the fornix. The lower edge of the septum pellucidum (the membrane that separates the lateral ventricles) is attached to the upper face of the fornix body.

Scheme of rhinencephalon

The body of the fornix travels anteriorly and divides again near the anterior commissure. The left and right parts separate, but there is also an anterior/posterior divergence.

The posterior fibres (called the postcommissural fornix) of each side continue through the hypothalamus to the mammillary bodies; then to the anterior nuclei of thalamus, which project to the cingulate cortex.
The anterior fibers (precommissural fornix) end at the septal nuclei and nucleus accumbens of each half of the brain.

Commissure

The lateral portions of the body of the fornix are joined by a thin triangular lamina, named the psalterium (lyra). This lamina contains some transverse fibers that connect the two hippocampi across the middle line and constitute the commissure of fornix also called the (hippocampal commissure).

The terminal lamina creates the commisure plate. This structure gives existence to the corpus callosum, the septum pellucidum, and the fornix. The fornix splits into two columns at the front, (anterior pillars) and then splits into two posterior crura. These two crura are joined together through the hippocampal commissure. The beginning of the splitting is called the psalterium or Lyra Davidis. The latter name is used because the structure resembles a lyra (or triangular harp): The two crura are the "chassis" of the lyra, and the commisure connections are the fibers.

Columns

The columns (anterior pillars; fornicolumns) of the fornix arch downward in front of the interventricular foramina and behind the anterior commissure, and each descends through the grey matter in the lateral wall of the third ventricle to the base of the brain, where it ends in the mamillary bodies.

Crus

The crura (posterior pillars) of the fornix are prolonged backward from the body.

They are flattened bands, and, at their commencement, are intimately connected with the under surface of the corpus callosum.

Diverging from one another, each curves around the posterior end of the thalamus, and passes downward and forward into the temporal horn of lateral ventricle.

Here, it lies along the concavity of the hippocampus, on the surface of which some of its fibers are spread out to form the alveus, while the remainder are continued as a narrow white band, the fimbria of hippocampus, which is prolonged into the uncus of the parahippocampal gyrus.

Additional images

Fornix.gif

Fornix (animation. click to move)
Velum interpositum.
Medial aspect of a brain sectioned in the median sagittal plane.
Coronal section of brain through intermediate mass of third ventricle.
Coronal section of lateral and third ventricles.
Central part and anterior and posterior cornua of lateral ventricles exposed from above.
Gray750.png

Tela chorioidea of the third ventricle, and the choroid plexus of the left lateral ventricle, exposed from above.
Diagram showing the positions of the three principal subarachnoid cisternæ.
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Fornix
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Fornix