Internal capsule | |
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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 paired white matter structure, as a two-way tract, carrying ascending and descending fibers, to and from the cerebral cortex. The internal capsule is situated in the inferomedial part of each cerebral hemisphere of the brain. It carries information past the subcortical basal ganglia. As it courses it separates the caudate nucleus and the thalamus from the putamen and the globus pallidus. It also separates the caudate nucleus and the putamen in the dorsal striatum, a brain region involved in motor and reward pathways. [1]
The internal capsule is V-shaped in transection forming an anterior and posterior limb, with the angle between them called the genu.
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. [2] [3]
The internal capsule is V-shaped when cut horizontally in a transverse plane, and consists of three parts: the genu, anterior limb, and posterior limb.
The genu is the bend, or flexure in the V of the internal capsule. It is formed by fibers from the corticobulbar tract. The fibers in this region are named the geniculate fibers that carry upper motor neurons from the motor cortex to cranial nerve nuclei that mainly govern muscle motion of the head and face. The geniculate fibers originate in the motor 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.
The anterior limb of the internal capsule (or crus anterius) is situated in front of the genu, between the head of the caudate nucleus and the lentiform nucleus. [4] It contains:
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. [4]
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. [4]
The posterior third of the posterior limb contains:
The retrolenticular part contains fibers from the optic system, coming from the lateral geniculate nucleus of the thalamus. More posteriorly, this becomes the optic radiation. Some fibers from the medial geniculate nucleus (which carry auditory information) also pass in the retrolenticular internal capsule, but most are in the sublenticular part.
The sublenticular part is beneath the lentiform nucleus, and contains fibers connecting with the temporal lobe. These include the auditory radiations and temporopontine fibers.
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.
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.
The internal capsule provides passage to ascending and descending fibres running to and from the cerebral cortex. [1] Fibers include frontopontine fibers from the frontal lobe to the pontine nuclei; thalamocortical radiations; corticobulbar fibers from the cortex to the medulla oblongata, and corticospinal fibers.
The lenticulostriate arteries supply a large part 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 ]
Due to the orderly somatotropic arrangement of elements of the posterior limb of the internal capsule, small lesions can produce selective functional deficits. [4]
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. [1]
Articles related to anatomy include:
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.
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) tracts that run to and from the cerebrum from the pons. Mainly, the three common areas that give rise to the cerebral peduncles are the cerebral cortex, the spinal cord and the cerebellum. The region includes the tegmentum, crus cerebri and pretectum. By this definition, the cerebral peduncles are also known as the basis pedunculi, while the large ventral bundle of efferent fibers is referred to as the cerebral crus or the pes pedunculi.
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.
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.
The lateral ventricles are the two largest ventricles of the brain and contain cerebrospinal fluid. Each cerebral hemisphere contains a lateral ventricle, known as the left or right lateral ventricle, respectively.
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.
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.
The lentiform nucleus are the putamen (laterally) and the globus pallidus (medially), collectively. Due to their proximity, these two structures were formerly considered one, however, the two are separated by a thin layer of white matter - the external medullary lamina - and are functionally and connectionally distinct.
The dentate nucleus is a cluster of neurons, or nerve cells, in the central nervous system that has a dentate – tooth-like or serrated – edge. It is located within the deep white matter of each cerebellar hemisphere, and it is the largest single structure linking the cerebellum to the rest of the brain. It is the largest and most lateral, or farthest from the midline, of the four pairs of deep cerebellar nuclei, the others being the globose and emboliform nuclei, which together are referred to as the interposed nucleus, and the fastigial nucleus. The dentate nucleus is responsible for the planning, initiation and control of voluntary movements. The dorsal region of the dentate nucleus contains output channels involved in motor function, which is the movement of skeletal muscle, while the ventral region contains output channels involved in nonmotor function, such as conscious thought and visuospatial function.
The anterior choroidal artery is a bilaterally paired artery of the brain. It is typically a branch of the internal carotid artery which supplies the choroid plexus of lateral ventricle and third ventricle as well as numerous structures of the brain.
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 frontopontine fibers or frontopontine tract are corticopontine fibers projecting from the cortex of the frontal lobe to the pons. In the internal capsule, the fibers descend predominately in the anterior limb, passing inferior to the thalamus to reach the mesencephalon (midbrain) where they descend in the medial portion of base of the cerebral peduncles. In the pons, the fibers flare out between the pontine nuclei.
The anterolateral central arteries or lenticulostriate arteries are a group of small arteries mostly arising from the middle cerebral artery that enter the brain through the anterior perforated substance to provide arterial supply to parts of the basal ganglia. They are end arteries.
The pontocerebellar fibers are the second-order neuron fibers of the corticopontocerebellar tracts that cross to the other side of the pons and run within the middle cerebellar peduncles, from the pons to the contralateral cerebellum. They arise from the pontine nuclei as the second part of the corticopontocerebellar tract, and decussate (cross-over) in the pons before passing through the middle cerebellar peduncles to reach and terminate in the contralateral posterior lobe of the cerebellum (neocerebellum). It is part of a pathway involved in the coordination of voluntary movements.
The recurrent artery of Heubner, Heubner's artery or distal medial striate artery is It is a branch of the anterior cerebral artery. It supplies the head of the caudate nucleus and adjacent part of the anterior limb of internal capsule, olfactory regions, and parts of the putamen and septal nuclei.
The anatomy of the cerebellum can be viewed at three levels. At the level of gross anatomy, the cerebellum consists of a tightly folded and crumpled layer of cortex, with white matter underneath, several deep nuclei embedded in the white matter, and a fluid-filled ventricle in the middle. At the intermediate level, the cerebellum and its auxiliary structures can be broken down into several hundred or thousand independently functioning modules or compartments known as microzones. At the microscopic level, each module consists of the same small set of neuronal elements, laid out with a highly stereotyped geometry.
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.