The uncus is an anterior extremity of the
parahippocampal gyrus. It is separated from the apex of the
temporal lobe
The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain.
The temporal lobe is involved in proc ...
by a slight fissure called the incisura temporalis (also called
rhinal sulcus
In the human brain, the entorhinal cortex appears as a longitudinal elevation anterior to the parahippocampal gyrus, with a corresponding internal furrow, the external rhinal sulcus (or rhinal fissure), separating it from the inferiolateral surface ...
).
Although superficially continuous with the hippocampal gyrus, the uncus forms
morphologically a part of the
rhinencephalon.
An important landmark that crosses the inferior surface of the uncus is the
band of Giacomini.
The term comes from the Latin word
uncus, meaning ''hook'', and it was coined by
Félix Vicq-d'Azyr (1748–1794).
[JC Tamraz, YG Comair. Atlas of Regional Anatomy of the Brain Using MRI (2006), p 8.]
Clinical significance
The part of the
olfactory cortex that is on the temporal lobe covers the area of the uncus, which leads into the two significant clinical aspects of the uncus: uncinate fits and
uncal herniations.
*
Seizures, often preceded by hallucinations of disagreeable odors, often originate in the uncus.
* In situations of
tumor
A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
,
hemorrhage
Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, vag ...
, or
edema
Edema, also spelled oedema, and also known as fluid retention, dropsy, hydropsy and swelling, is the build-up of fluid in the body's tissue. Most commonly, the legs or arms are affected. Symptoms may include skin which feels tight, the area ma ...
, increased pressure within the cranial cavity, especially if the mass is in the middle fossa, can push the uncus over the tentorial notch against the
brainstem
The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is ...
and its corresponding
cranial nerves
Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and ...
and can result in a
brain herniation. If the uncus becomes herniated the structure lying just medial to it,
cranial nerve III, can become compressed. This causes problems associated with a non-functional or problematic CN III - the pupil on the
ipsilateral side fails to constrict to light and absence of medial/superior movement of the orbit, resulting in a fixed, dilated pupil and an eye with a characteristic "down and out" position due to dominance of the abducens and trochlear nerves. Further pressure on the midbrain results in progressive lethargy, coma and death due to compression of the mesencephalic
reticular activating system. Brainstem damage is typically
ipsilateral to the herniation, although the contralateral
cerebral peduncle may be pushed against the tentorial notch, resulting in a characteristic indentation known as
Kernohan's notch and ipsilateral
hemiparesis
Hemiparesis, or unilateral paresis, is weakness of one entire side of the body ('' hemi-'' means "half"). Hemiplegia is, in its most severe form, complete paralysis of half of the body. Hemiparesis and hemiplegia can be caused by different medi ...
, since fibers running in the cerebral peduncle
decussate (cross over) in the lower medulla to control muscle groups on the opposite side of the body.
The landmark that helps you find the amygdala on a coronal section of the brain.
Function
A sparse amount of literature exists to propose a comprehensive overview of the functionality of the uncus. A study has indicated that psychotic-like experiences were associated with reduced expansion within the uncus between the ages of 14 and 19 in cannabis-using individuals.
Additional images
File:Uncus animation small.gif, Position of uncus (red)
File:Gehirn, basal - beschriftet lat.svg, Basal view of a human brain
File:Gray732.png, Scheme of rhinencephalon. (Uncus labeled at bottom right.)
References
External links
*
* http://www.neuroanatomy.wisc.edu/coursebook/neuro3(2).pdf
{{Authority control
Hippocampus (brain)
Gyri