Internal capsule

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Internal capsule
Telencephalon-Horiconatal.jpg
Horizontal section of right cerebral hemisphere. (Capsula interna labeled at upper left.)
Gray764.png
The motor tract.
Details
Identifiers
Latin capsula interna
MeSH D020772
NeuroNames 198
NeuroLex ID birnlex_1659
TA98 A14.1.09.524
TA2 5576
FMA 61950
Anatomical terms of neuroanatomy

The internal capsule is a white matter structure situated in the inferomedial part of each cerebral hemisphere of the brain. It carries information past the basal ganglia, separating the caudate nucleus and the thalamus from the putamen and the globus pallidus. The internal capsule contains both ascending and descending axons, going to and coming from the cerebral cortex. It also separates the caudate nucleus and the putamen in the dorsal striatum, a brain region involved in motor and reward pathways.

Contents

The corticospinal tract constitutes a large part of the internal capsule, carrying motor information from the primary motor cortex to the lower motor neurons in the spinal cord. Above the basal ganglia the corticospinal tract is a part of the corona radiata. Below the basal ganglia the tract is called cerebral crus (a part of the cerebral peduncle) and below the pons it is referred to as the corticospinal tract. [1] [2]

Structure

The internal capsule consists of three parts and is V-shaped when cut horizontally, in a transverse plane.

Genu

The genu is the flexure of the internal capsule. It is formed by fibers from the corticonuclear tracts. The fibers in this region are named the geniculate fibers; they originate in the motor part of the cerebral cortex and after passing downward through the base of the cerebral peduncle with the cerebrospinal fibers, undergo decussation and end in the motor nuclei of the cranial nerves of the opposite side. It contains the corticobulbar tract, which carries upper motor neurons from the motor cortex to cranial nerve nuclei that mainly govern motion of striated muscle in the head and face.

Anterior limb

The anterior limb of internal capsule (or frontal part) is situated between the lentiform nucleus and the caudate nucleus. [3] It contains:

  1. thalamocortical fibers (passing from the lateral thalamic nuclei to the frontal lobe) [3]
  2. corticothalamic fibres (passing from frontal lobe to the lateral thalamic nuclei) [3]
  3. fibers connecting the caudate nucleus to the putamen (these fibres are transversely oriented) [3]
  4. fibers connecting the cortex with the corpus striatum
  5. frontopontine fibers [3] (passing from the frontal lobe through the medial fifth of the base of the cerebral peduncle to the nuclei pontis)
  6. thalamic pontine fibers

Posterior limb

The posterior limb of internal capsule (or occipital part) is the portion of the internal capsule posterior to the genu.[ citation needed ] It is situated between the thalamus and the lentiform nucleus. [3]

The anterior half of the posterior limb contains fibers of the corticospinal tract and corticobulbar tract (in an anteroposterior somatotropic arrangement), as well as corticorubral fibres (passing from the frontal lobe to the red nucleus) that accompany the corticospinal tract. [3]

The posterior third of the posterior limb contains:

  1. third-order sensory neurons passing from the posterolateral nucleus of thalamus to the postcentral gyrus (in an anteroposterior somatotropic arrangement) [3]
  2. the fibers of optic radiation, from the lower visual centers to the cortex of the occipital lobe;
  3. acoustic fibers, from the lateral lemniscus to the temporal lobe
  4. fibers that pass from the occipital and temporal lobes to the pontine nuclei

Blood supply

The superior parts of both the anterior and posterior limbs and the genu of the internal capsule are supplied by the lenticulostriate arteries, which are branches of the M1 segment of the middle cerebral artery.

The inferior half of the anterior limb is supplied via the recurrent artery of Heubner, which is a branch of the anterior cerebral artery.

The inferior half of the posterior limb is supplied by the anterior choroidal artery, which is a branch of the internal carotid artery.

In summary, the blood supply of the internal capsule is

As in many parts of the body, some degree of variation in the blood supply exists. For example, thalamoperforator arteries, which are branches of the basilar artery, occasionally supply the inferior half of the posterior limb.

Function

The internal capsule provides passage to ascending and descending fibres running to and from the cerebral cortex. [4]

Working anterior to posterior:

1) Frontopontine fibers project from frontal cortex to the pons;
2) Thalamocortical radiations are the fibers that connect the medial and anterior nuclei of the thalamus to the frontal lobes (these are severed during a prefrontal lobotomy).

Other fibers within the internal capsule:

Pathophysiology

Dynamics of blood supply

The lenticulostriate arteries supply a substantial amount of the internal capsule. These small vessels are particularly vulnerable to narrowing in the setting of chronic hypertension and can result in small, punctate infarctions or intraparenchymal haemorrhage due to vessel rupture.[ citation needed ]

Focal lesions

Due to the orderly somatotropic arrangement of elements of the posterior limb of the internal capsule, small lesions can produce selective functional deficits. [3]

Lesions of the genu of the internal capsule affect fibers of the corticobulbar tract.[ citation needed ]

The primary motor cortex sends its axons through the posterior limb of the internal capsule. Lesions, therefore, result in a contralateral hemiparesis or hemiplegia. While symptoms of weakness due to an isolated lesion of the posterior limb can initially be severe, recovery of motor function is sometimes possible due to spinal projections of premotor cortical regions that are contained more rostrally in the internal capsule. [4]

See also

Related Research Articles

<span class="mw-page-title-main">Thalamus</span> Structure within the brain

The thalamus is a large mass of gray matter located in the dorsal part of the diencephalon. Nerve fibers project out of the thalamus to the cerebral cortex in all directions, allowing hub-like exchanges of information. It has several functions, such as the relaying of sensory signals, including motor signals to the cerebral cortex and the regulation of consciousness, sleep, and alertness.

Articles related to anatomy include:

Pronator quadratus is a square-shaped muscle on the distal forearm that acts to pronate the hand.

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

The brainstem is the stalk-like part of the brain that interconnects the cerebrum and diencephalon 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.

<span class="mw-page-title-main">Midbrain</span> Forward-most portion of the brainstem

The midbrain or mesencephalon is the rostral-most portion of the brainstem connecting the diencephalon and cerebrum with the pons. It consists of the cerebral peduncles, tegmentum, and tectum.

<span class="mw-page-title-main">Pyramidal tracts</span> Include both the corticobulbar tract and the corticospinal tract

The pyramidal tracts include both the corticobulbar tract and the corticospinal tract. These are aggregations of efferent nerve fibers from the upper motor neurons that travel from the cerebral cortex and terminate either in the brainstem (corticobulbar) or spinal cord (corticospinal) and are involved in the control of motor functions of the body.

<span class="mw-page-title-main">Spinothalamic tract</span> Sensory pathway from the skin to the thalamus

The spinothalamic tract is a part of the anterolateral system or the ventrolateral system, a sensory pathway to the thalamus. From the ventral posterolateral nucleus in the thalamus, sensory information is relayed upward to the somatosensory cortex of the postcentral gyrus.

<span class="mw-page-title-main">Dorsal column–medial lemniscus pathway</span> Sensory spinal pathway

The dorsal column–medial lemniscus pathway (DCML) is a sensory pathway of the central nervous system that conveys sensations of fine touch, vibration, two-point discrimination, and proprioception (position) from the skin and joints. It transmits information from the body to the primary somatosensory cortex in the postcentral gyrus of the parietal lobe of the brain. The pathway receives information from sensory receptors throughout the body, and carries this in nerve tracts in the white matter of the dorsal column of the spinal cord to the medulla, where it is continued in the medial lemniscus, on to the thalamus and relayed from there through the internal capsule and transmitted to the somatosensory cortex. The name dorsal-column medial lemniscus comes from the two structures that carry the sensory information: the dorsal columns of the spinal cord, and the medial lemniscus in the brainstem.

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

In neuroanatomy, 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. 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">Anterior cerebral artery</span> Artery supplying the brain

The anterior cerebral artery (ACA) is one of a pair of cerebral arteries that supplies oxygenated blood to most midline portions of the frontal lobes and superior medial parietal lobes of the brain. The two anterior cerebral arteries arise from the internal carotid artery and are part of the circle of Willis. The left and right anterior cerebral arteries are connected by the anterior communicating artery.

<span class="mw-page-title-main">Anterior choroidal artery</span>

The anterior choroidal artery originates from the internal carotid artery. However, it may (rarely) arise from the middle cerebral artery.

<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">Facial motor nucleus</span>

The facial motor nucleus is a collection of neurons in the brainstem that belong to the facial nerve. These lower motor neurons innervate the muscles of facial expression and the stapedius.

The projection fibers consist of efferent and afferent fibers uniting the cortex with the lower parts of the brain and with the spinal cord. In human neuroanatomy, bundles of axons called tracts, within the brain, can be categorized by their function into association fibers, projection fibers, and commissural fibers.

The isothalamus is a division used by some researchers in describing the thalamus.

<span class="mw-page-title-main">Spinal cord</span> Long, tubular central nervous system structure in the vertebral column

The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spinal cord, which contains cerebrospinal fluid. The brain and spinal cord together make up the central nervous system (CNS). In humans, the spinal cord begins at the occipital bone, passing through the foramen magnum and then enters the spinal canal at the beginning of the cervical vertebrae. The spinal cord extends down to between the first and second lumbar vertebrae, where it ends. The enclosing bony vertebral column protects the relatively shorter spinal cord. It is around 45 cm (18 in) long in adult men and around 43 cm (17 in) long in adult women. The diameter of the spinal cord ranges from 13 mm in the cervical and lumbar regions to 6.4 mm in the thoracic area.

The recurrent artery of Heubner, Heubner's artery or distal medial striate artery is an artery in the head. It is named after the German paediatrician Otto Heubner. It is a branch of the anterior cerebral artery. Its vascular territory is the anteromedial section of the caudate nucleus and the anterioinferior section of the internal capsule, as well as parts of the putamen and septal nuclei.

<span class="mw-page-title-main">Corticospinal tract</span> Pyramidal white matter motor pathway

The corticospinal tract is a white matter motor pathway starting at the cerebral cortex that terminates on lower motor neurons and interneurons in the spinal cord, controlling movements of the limbs and trunk. There are more than one million neurons in the corticospinal tract, and they become myelinated usually in the first two years of life.

References

  1. Schmahmann, Jeremy D.; Schmahmann, Jeremy; Pandya, Deepak (2009-02-11). Fiber Pathways of the Brain. Oxford University Press, USA. ISBN   978-0-19-538826-8.
  2. Standring, Susan (2015-09-25). Gray's Anatomy E-Book: The Anatomical Basis of Clinical Practice. Elsevier Health Sciences. ISBN   978-0-7020-6851-5.
  3. 1 2 3 4 5 6 7 8 9 Waxman, Stephen G. (2009). Clinical Neuroanatomy (26th ed.). New York: McGraw-Hill Medical. p. 145. ISBN   978-0-07-160399-7.
  4. 1 2 Emos, Marc Christopher; Suheb, Mahammed Khan; Agarwal, Sanjeev (2022-06-13). "Neuroanatomy, Internal Capsule". StatPearls. PMID   31194338.