Uncus

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Uncus
Gray727 uncus of parahippocampal gyrus.png
Medial surface of left cerebral hemisphere. Uncus is shown in orange.
Human brain inferior-medial view description 3.JPG
Human brain inferior-medial view (Uncus is #5)
Identifiers
NeuroNames 40
TA98 A14.1.09.235
TA2 5516
FMA 74884
Anatomical terms of neuroanatomy

The uncus is an anterior extremity of the parahippocampal gyrus. It is separated from the apex of the temporal lobe by a sulcus called the rhinal sulcus. [1] Although superficially continuous with the hippocampal gyrus, the uncus forms morphologically a part of the rhinencephalon.

Contents

An important landmark that crosses the inferior surface of the uncus is the band of Giacomini or tail of the dentate gyrus. [2]

The term comes from the Latin word uncus, meaning hook, and it was coined by Félix Vicq-d'Azyr (1748–1794). [3]

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: herniations and seizures

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, 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 indicates the amygdala.

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. [5]

Additional images

Related Research Articles

Articles related to anatomy include:

<span class="mw-page-title-main">Brainstem</span> Posterior part of the brain, adjoining and structurally continuous

The brainstem 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 continuous with the thalamus of the diencephalon through the tentorial notch, and sometimes the diencephalon is included in the brainstem.

<span class="mw-page-title-main">Brodmann area</span> 52 distinct regions of the brains cerebral cortex

A Brodmann area is a region of the cerebral cortex, in the human or other primate brain, defined by its cytoarchitecture, or histological structure and organization of cells. The concept was first introduced by the German anatomist Korbinian Brodmann in the early 20th century. Brodmann mapped the human brain based on the varied cellular structure across the cortex and identified 52 distinct regions, which he numbered 1 to 52. These regions, or Brodmann areas, correspond with diverse functions including sensation, motor control, and cognition.

<span class="mw-page-title-main">Rhinencephalon</span>

In animal anatomy, the rhinencephalon, also called the smell-brain or olfactory brain, is a part of the brain involved with smell. It forms the paleocortex and is rudimentary in the human brain.

<span class="mw-page-title-main">Limbic lobe</span> Region of a cerebral cortex

The limbic lobe is an arc-shaped cortical region of the limbic system, on the medial surface of each cerebral hemisphere of the mammalian brain, consisting of parts of the frontal, parietal and temporal lobes. The term is ambiguous, with some authors including the paraterminal gyrus, the subcallosal area, the cingulate gyrus, the parahippocampal gyrus, the dentate gyrus, the hippocampus and the subiculum; while the Terminologia Anatomica includes the cingulate sulcus, the cingulate gyrus, the isthmus of cingulate gyrus, the fasciolar gyrus, the parahippocampal gyrus, the parahippocampal sulcus, the dentate gyrus, the fimbrodentate sulcus, the fimbria of hippocampus, the collateral sulcus, and the rhinal sulcus, and omits the hippocampus.

<span class="mw-page-title-main">Corticobulbar tract</span> Motor pathway in the brain connecting the motor cortex to the medullary pyramids

The corticobulbartract is a two-neuron white matter motor pathway connecting the motor cortex in the cerebral cortex to the medullary pyramids, which are part of the brainstem's medulla oblongata region, and are primarily involved in carrying the motor function of the non-oculomotor cranial nerves, like muscles of the face, head and neck. The corticobulbar tract is one of the pyramidal tracts, the other being the corticospinal tract.

<span class="mw-page-title-main">Precentral gyrus</span> Motor gyrus of the posterior frontal lobe of the brain

The precentral gyrus is a prominent gyrus on the surface of the posterior frontal lobe of the brain. It is the site of the primary motor cortex that in humans is cytoarchitecturally defined as Brodmann area 4.

<span class="mw-page-title-main">Cerebellar tentorium</span> Vertebrate brain structure separating the cerebellum from the occipital lobes

The cerebellar tentorium or tentorium cerebelli is one of four dural folds that separate the cranial cavity into four (incomplete) compartments. The cerebellar tentorium separates the cerebellum from the cerebrum forming a supratentorial and an infratentorial region; the cerebrum is supratentorial and the cerebellum infratentorial.

<span class="mw-page-title-main">Lobes of the brain</span> Parts of the cerebrum

The lobes of the brain are the four major identifiable regions of the human cerebral cortex, and they comprise the surface of each hemisphere of the cerebrum. The two hemispheres are roughly symmetrical in structure, and are connected by the corpus callosum. Some sources include the insula and limbic lobe but the limbic lobe incorporates parts of the other lobes. The lobes are large areas that are anatomically distinguishable, and are also functionally distinct. Each lobe of the brain has numerous ridges, or gyri, and furrows, sulci that constitute further subzones of the cortex. The expression "lobes of the brain" usually refers only to those of the cerebrum, not to the distinct areas of the cerebellum.

<span class="mw-page-title-main">Brain herniation</span> Potentially deadly side effect of very high pressure within the skull

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 tentorium cerebelli, and even through the foramen magnum. Herniation can be caused by a number of factors that cause a mass effect and increase intracranial pressure (ICP): these include traumatic brain injury, intracranial hemorrhage, or brain tumor.

<span class="mw-page-title-main">Posterior cerebral artery</span> Artery which supplies blood to the occipital lobe of the brain

The posterior cerebral artery (PCA) is one of a pair of cerebral arteries that supply oxygenated blood to the occipital lobe, part of the back of the human brain. The two arteries originate from the distal end of the basilar artery, where it bifurcates into the left and right posterior cerebral arteries. These anastomose with the middle cerebral arteries and internal carotid arteries via the posterior communicating arteries.

<span class="mw-page-title-main">Duret haemorrhages</span> Medical condition

Duret haemorrhages are small linear areas of bleeding in the midbrain and upper pons of the brainstem. They are caused by a traumatic downward displacement of the brainstem.

<span class="mw-page-title-main">Rhinal sulcus</span> Groove in the brains temporal lobe

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. The rhinal sulcus separates the parahippocampal uncus from the rest of the temporal lobe in the neocortex. The rhinal sulcus and the hippocampal sulcus were both present in early mammals.

<span class="mw-page-title-main">Olfactory tract</span> Part of the olfactory system

The olfactory tract is a bilateral bundle of afferent nerve fibers from the mitral and tufted cells of the olfactory bulb that connects to several target regions in the brain, including the piriform cortex, amygdala, and entorhinal cortex. It is a narrow white band, triangular on coronal section, the apex being directed upward.

The sensory cortex can refer sometimes to the primary somatosensory cortex, or it can be used as a term for the primary and secondary cortices of the different senses : the visual cortex on the occipital lobes, the auditory cortex on the temporal lobes, the primary olfactory cortex on the uncus of the piriform region of the temporal lobes, the gustatory cortex on the insular lobe, and the primary somatosensory cortex on the anterior parietal lobes. Just posterior to the primary somatosensory cortex lies the somatosensory association cortex or area, which integrates sensory information from the primary somatosensory cortex to construct an understanding of the object being felt. Inferior to the frontal lobes are found the olfactory bulbs, which receive sensory input from the olfactory nerves and route those signals throughout the brain. Not all olfactory information is routed to the olfactory cortex: some neural fibers are routed to the supraorbital region of the frontal lobe, while others are routed directly to limbic structures. The direct limbic connection makes the olfactory sense unique.

<span class="mw-page-title-main">Collateral fissure</span> Brain structure

The collateral fissure is a large sulcus on the tentorial surface of the cerebral hemisphere and extends from near the occipital pole to within a short distance of the temporal pole. It is also known as the medial occipitotemporal sulcus.

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. Kernohan's notch is an ipsilateral condition, in that a left-sided primary lesion evokes motor impairment in the left side of the body and a right-sided primary injury evokes motor impairment in the right side of the body. The seriousness of Kernohan's notch varies depending on the primary problem causing it, which may range from benign brain tumors to advanced subdural hematoma.

<span class="mw-page-title-main">Tentorial notch</span> Brain structure in humans and some mammals

The tentorial notch refers to the anterior opening between the free edge of the cerebellar tentorium and the clivus for the passage of the brainstem.

<span class="mw-page-title-main">Anatomical terms of neuroanatomy</span> Terminology used to describe the central and peripheral nervous systems

This article describes anatomical terminology that is used to describe the central and peripheral nervous systems - including the brain, brainstem, spinal cord, and nerves.

References

PD-icon.svgThis article incorporates text in the public domain from page 826 of the 20th edition of Gray's Anatomy (1918)

  1. Smith, Callum. "Rhinal sulcus | Radiology Reference Article | Radiopaedia.org". Radiopaedia. Retrieved 2022-08-15.
  2. Pfleger, René. "Uncus | Radiology Reference Article | Radiopaedia.org". Radiopaedia. Retrieved 17 October 2019.
  3. Atlas of Regional Anatomy of the Brain Using MRI. Berlin/Heidelberg: Springer-Verlag. 2006. p. 8. doi:10.1007/3-540-30672-2. ISBN   978-3-540-27876-4.
  4. "uncinate fits". Concise Medical Dictionary. Oxford University Press. 2010. doi:10.1093/acref/9780199557141.001.0001/acref-9780199557141-e-10495 . Retrieved 14 August 2024.
  5. Yu, Tao (2020). "Cannabis-associated psychotic-like experiences are mediated by developmental changes in the parahippocampal gyrus" (PDF). Journal of the American Academy of Child and Adolescent Psychiatry. 59 (5): 642–649. doi:10.1016/j.jaac.2019.05.034. PMID   31326579. S2CID   198135290 . Retrieved 15 August 2020.