The anterior extremity of the Parahippocampal gyrus

Parahippocampal gyrus

The parahippocampal gyrus is a grey matter cortical region of the brain that surrounds the hippocampus. This region plays an important role in memory encoding and retrieval....

 is recurved in the form of a hook, the uncus, which is separated from the apex of the temporal lobe

Temporal lobe

The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....

 by a slight fissure, the incisura temporalis.

Although superficially continuous with the hippocampal gyrus, the uncus forms morphologically

Morphology (biology)

In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

 a part of the rhinencephalon

Rhinencephalon

In animal anatomy, the rhinencephalon is a part of the brain involved with olfaction.-Components:The term rhinencephalon has been used to describe different structures at different points in time....

.

The term uncus was coined by Felix Vicq d’Azyr

Félix Vicq-d'Azyr

Félix Vicq d'Azyr 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 of a physician...

 (1748–1794).

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
  Tumor
  A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...
  
  , hemorrhage, or edema
  Edema
  Edema or oedema ; both words from the Greek , oídēma "swelling"), formerly known as dropsy or hydropsy, is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling...
  
  , 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 and its corresponding cranial nerves
  Cranial nerves
  Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves...
  
  . 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
  Reticular activating system
  The reticular activating system is an area of the brain responsible for regulating arousal and sleep-wake transitions.- History and Etymology :...
  
  . Brainstem damage is typically ipsilateral to the herniation, although the contralateral cerebral peduncle
  Cerebral peduncle
  Mainly, the three common areas that give rise to the cerebral peduncles are the cortex, the spinal cord and the cerebellum. The cerebral peduncle, by most classifications, is everything in the mesencephalon except the tectum. The region includes the midbrain tegmentum, crus cerebri and pretectum...
  
   may be pushed against the tentorial notch, resulting in a characteristic indentation known as Kernohan's notch
  Kernohan's notch
  Kernohan's notch is a cerebral peduncle indentation associated with some forms of transtentorial herniation . It is a secondary condition caused by a primary injury on the opposite hemisphere of the brain...
  
   and ipsilateral hemiparesis
  Hemiparesis
  Hemiparesis is weakness on one side of the body. It is less severe than hemiplegia - the total paralysis of the arm, leg, and trunk on one side of the body. Thus, the patient can move the impaired side of his body, but with reduced muscular strength....
  
  , 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 during a coronal section of the brain.