Posterior limb of internal capsule
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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 globus pallidus (GP), also known as paleostriatum or dorsal pallidum, is a subcortical structure of the brain. It consists of two adjacent segments, one external, known in rodents simply as the globus pallidus, and one internal, known in rod ...
. The internal capsule contains both
ascending ''Ascending'' is a science fiction novel by the Canadian writer James Alan Gardner, published in 2001 by HarperCollins Publishers under its various imprints.HarperCollins, Avon, HarperCollins Canada, SFBC/Avon; paperback edition 2001, Eos Books. ...
and descending axons, going to and coming from the cerebral cortex. It also separates the caudate nucleus and the putamen in the dorsal
striatum The striatum, or corpus striatum (also called the striate nucleus), is a nucleus (a cluster of neurons) in the subcortical basal ganglia of the forebrain. The striatum is a critical component of the motor and reward systems; receives glutamate ...
, a brain region involved in motor and reward pathways. The corticospinal tract constitutes a large part of the internal capsule, carrying motor information from the
primary motor cortex The primary motor cortex (Brodmann area 4) is a brain region that in humans is located in the dorsal portion of the frontal lobe. It is the primary region of the motor system and works in association with other motor areas including premotor co ...
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 The cerebral crus (crus cerebri) is the Anatomical terms of location, anterior portion of the cerebral peduncle which contains the motor tracts, travelling from the cerebral cortex to the pons and spine. The plural of which is cerebral crura. In ...
(a part of the cerebral peduncle) and below the pons it is referred to as the corticospinal tract.


Structure

The internal capsule consists of three parts and is V-shaped when cut horizontally, in a transverse plane. * the bend in the V is called the ''
genu Genu, a Latin word for "knee," may refer to: * Genu of internal capsule * Genu of the corpus callosum * Genu recurvatum * Genu valgum * Genu varum Genu varum (also called bow-leggedness, bandiness, bandy-leg, and tibia vara) is a varus deform ...
'' * the anterior limb or ''crus anterius'' is the part in front of the genu, between the head of the caudate nucleus and the
lenticular nucleus The lentiform nucleus, or lenticular nucleus, comprises the putamen and the globus pallidus within the basal ganglia. With the caudate nucleus, it forms the dorsal striatum. It is a large, lens-shaped mass of gray matter just lateral to the inter ...
* the posterior limb or ''crus posterius'' is the part behind the genu, between the thalamus and lenticular nucleus * the ''retrolenticular portion'' is caudal to the lenticular nucleus and carries the
optic radiation In neuroanatomy, the optic radiation (also known as the geniculocalcarine tract, the geniculostriate pathway, and posterior thalamic radiation) are axons from the neurons in the lateral geniculate nucleus to the primary visual cortex. The optic ...
(from medial part of lateral geniculate nucleus) also known as the ''geniculocalcarine tract.'' The fiber from lateral part of lateral geniculate nucleus is carried through the ''retrolenticular portion.'' * the ''sublenticular portion'' is beneath the lenticular nucleus and are tracts involved in the auditory pathway from the medial geniculate nucleus to the
primary auditory cortex The auditory cortex is the part of the temporal lobe that processes auditory information in humans and many other vertebrates. It is a part of the auditory system, performing basic and higher functions in hearing, such as possible relations to ...
(Brodmann areas 41 and 42)


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 nerve 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 ...
s 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) contains: # fibers running from the thalamus to the frontal lobe # fibers connecting the
lentiform The lentiform nucleus, or lenticular nucleus, comprises the putamen and the globus pallidus within the basal ganglia. With the caudate nucleus, it forms the dorsal striatum. It is a large, lens-shaped mass of gray matter just lateral to the inter ...
and
caudate nuclei The caudate nucleus is one of the structures that make up the corpus striatum, which is a component of the basal ganglia in the human brain. While the caudate nucleus has long been associated with motor processes due to its role in Parkinson's di ...
# fibers connecting the cortex with the
corpus striatum The striatum, or corpus striatum (also called the striate nucleus), is a nucleus (a cluster of neurons) in the subcortical basal ganglia of the forebrain. The striatum is a critical component of the motor and reward systems; receives glutamat ...
# fibers passing from the frontal lobe through the medial fifth of the base of the cerebral peduncle to the
nuclei pontis Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucle ...
# thalami pontine fibers


Posterior limb

The ''posterior limb'' of internal capsule (or occipital part) is the portion of the internal capsule posterior to the genu. The anterior two-thirds of the occipital part of the internal capsule contains fibers of the corticospinal tract, which arise in the motor area of the cerebral cortex and, passing downward through the middle three-fifths of the base of the cerebral peduncle, are continued into the pyramids of the
medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involun ...
. The posterior third of the occipital part contains: # sensory fibers, largely derived from the thalamus, though some may be continued upward from the medial lemniscus # the fibers of
optic radiation In neuroanatomy, the optic radiation (also known as the geniculocalcarine tract, the geniculostriate pathway, and posterior thalamic radiation) are axons from the neurons in the lateral geniculate nucleus to the primary visual cortex. The optic ...
, from the lower visual centers to the cortex of the occipital lobe; # acoustic fibers, from the lateral lemniscus to the temporal lobe # 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 The lenticulostriate arteries, anterolateral central arteries, or antero-lateral ganglionic branches are a group of small arteries arising from the initial part M1 of the middle cerebral artery that supply the basal ganglia. Structure The lenticul ...
, 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 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 ant ...
, which is a branch of the
anterior cerebral artery 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 t ...
. The inferior half of the ''posterior limb'' is supplied by the
anterior choroidal artery The anterior choroidal artery originates from the internal carotid artery. However, it may (rarely) arise from the middle cerebral artery. Structure The anterior choroidal artery originates from the distal carotid artery 5 mm after the origin of t ...
, which is a branch of the
internal carotid artery The internal carotid artery (Latin: arteria carotis interna) is an artery in the neck which supplies the anterior circulation of the brain. In human anatomy, the internal and external carotids arise from the common carotid arteries, where these b ...
. In summary, the blood supply of the internal capsule is * Anterior limb: lenticulostriate branches of middle cerebral artery (superior half) and
recurrent artery of Heubner 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 ant ...
of the
anterior cerebral artery 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 t ...
(inferior half) * Genu: lenticulostriate branches of middle cerebral artery * Posterior limb: lenticulostriate branches of middle cerebral artery (superior half) and
anterior choroidal artery The anterior choroidal artery originates from the internal carotid artery. However, it may (rarely) arise from the middle cerebral artery. Structure The anterior choroidal artery originates from the distal carotid artery 5 mm after the origin of t ...
branch of the
internal carotid artery The internal carotid artery (Latin: arteria carotis interna) is an artery in the neck which supplies the anterior circulation of the brain. In human anatomy, the internal and external carotids arise from the common carotid arteries, where these b ...
(inferior half) 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. Working anterior to posterior: * The anterior limb of the internal capsule contains: ::1) Frontopontine fibers project from
frontal cortex The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a groove betwe ...
to the pons; ::2) Thalamocortical radiations are the fibers that connect the medial and
anterior 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 ...
nuclei of the thalamus to the frontal lobes (these are severed during a
prefrontal lobotomy A lobotomy, or leucotomy, is a form of neurosurgical treatment for psychiatric disorder or neurological disorder (e.g. epilepsy) that involves severing connections in the brain's prefrontal cortex. The surgery causes most of the connections to ...
). * The genu contains
corticobulbar fiber In neuroanatomy, the corticobulbar (or corticonuclear) tract 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 (also called ...
s, which run between the cortex and 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 ...
. * The posterior limb of the internal capsule contains
corticospinal fiber 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 (''cort ...
s, sensory fibers (including the medial lemniscus and the
anterolateral system 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 cor ...
) from the body and a few corticobulbar fibers. Other fibers within the internal capsule: * 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 In neuroanatomy, the optic radiation (also known as the geniculocalcarine tract, the geniculostriate pathway, and posterior thalamic radiation) are axons from the neurons in the lateral geniculate nucleus to the primary visual cortex. The optic ...
. 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 contains fibers connecting with the temporal lobe. These include the
auditory radiation The acoustic radiations or auditory radiations are structures found in the brain, in the ventral cochlear pathway, a part of the auditory system. Acoustic radiation arising in the medial geniculate nucleus and end in primary auditory cortex (trans ...
s and temporopontine fibers.


Clinical significance

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. Lesions of the genu of the internal capsule affect fibers of the corticobulbar tract. 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.


References


External links

* * * {{Authority control Rostral basal ganglia and associated structures