The uncus is an anterior extremity of the

parahippocampal gyrus The parahippocampal gyrus (or hippocampal gyrus') is a grey matter cortical region of the brain that surrounds the hippocampus and is part of the limbic system. The region plays an important role in memory encoding and retrieval. It has been in ...

. It is separated from the apex of the

temporal lobe The temporal lobe is one of the four Lobes of the brain, 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 ...

by a slight fissure called the incisura temporalis (also called rhinal sulcus). Although superficially continuous with the hippocampal gyrus, the uncus forms morphologically a part of the

rhinencephalon In animal anatomy, the rhinencephalon (from the Greek, ῥίς, ''rhis'' = "nose", and ἐγκέφαλος, ''enkephalos'' = "brain"), also called the smell-brain or olfactory brain, is a part of the brain involved with smell (i.e. olfaction). ...

. An important landmark that crosses the inferior surface of the uncus is the

band of Giacomini The dentate gyrus (DG) is part of the hippocampal formation in the temporal lobe of the brain, which also includes the hippocampus and the subiculum. The dentate gyrus is part of the hippocampal trisynaptic circuit and is thought to contribute ...

. The term comes from the Latin word

uncus The uncus is an anterior extremity of the parahippocampal gyrus. It is separated from the apex of the temporal lobe by a slight fissure called the incisura temporalis (also called rhinal sulcus). Although superficially continuous with the hippo ...

, meaning ''hook'', and it was coined by

Félix Vicq-d'Azyr Félix Vicq d'Azyr (; 23 April 1748 – 20 June 1794) was a French physician and anatomist, the originator of comparative anatomy and discoverer of the theory of homology in biology. Biography Vicq d'Azyr was born in Valognes, Normandy, the son ...

(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 An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or neural oscillation, synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much o ...

, 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 (biology), tissue. Most commonly, the legs or arms are affected. Symptoms may include skin which feels t ...

, 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 cont ...

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 f ...

and can result in a

brain herniation Brain herniation is a potentially deadly side effect of very high pressure within the skull that occurs when a part of the brain is squeezed across structures within the skull. The brain can shift across such structures as the falx cerebri, the te ...

. If the uncus becomes herniated the structure lying just medial to it,

cranial nerve III The oculomotor nerve, also known as the third cranial nerve, cranial nerve III, or simply CN III, is a cranial nerve that enters the orbit through the superior orbital fissure and innervates extraocular muscles that enable most movements o ...

, can become compressed. This causes problems associated with a non-functional or problematic CN III - the pupil on the

ipsilateral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

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 The reticular formation is a set of interconnected nuclei that are located throughout the brainstem. It is not anatomically well defined, because it includes neurons located in different parts of the brain. The neurons of the reticular formatio ...

. Brainstem damage is typically

to the herniation, although the contralateral

cerebral peduncle The cerebral peduncles are the two stalks that attach the cerebrum to the brainstem. They are structures at the front of the midbrain which arise from the ventral pons and contain the large ascending (sensory) and descending (motor) nerve tra ...

may be pushed against the tentorial notch, resulting in a characteristic indentation known as

Kernohan's notch Kernohan's notch is a cerebral peduncle indentation associated with some forms of transtentorial herniation (uncal herniation). It is a secondary condition caused by a primary injury on the ''opposite'' hemisphere of the brain.#refWolf, Wolf et al, ...

and ipsilateral

hemiparesis Hemiparesis, or unilateral paresis, is weakness of one entire side of the body (''wikt:hemi-#Prefix, hemi-'' means "half"). Hemiplegia is, in its most severe form, complete paralysis of half of the body. Hemiparesis and hemiplegia can be caused ...

, since fibers running in the cerebral peduncle

decussate Decussation is used in biological contexts to describe a crossing (due to the shape of the Roman numeral for ten, an uppercase 'X' (), ). In Latin anatomical terms, the form is used, e.g. . Similarly, the anatomical term chiasma is named aft ...

(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

. (Uncus labeled at bottom right.)

References

External links

* * http://www.neuroanatomy.wisc.edu/coursebook/neuro3(2).pdf {{Authority control Hippocampus (brain) Gyri