General classification of basal nuclei
The subcortical nuclei of the telencephalon form a complex gray matter network. A significant portion of them is grouped by anatomists into a single structure termed the corpus striatum (corpus striatum).
The corpus striatum traditionally includes three main anatomical formations:
- Caudate nucleus (nucleus caudatus);
- Lentiform nucleus (nucleus lentiformis);
- Claustrum (claustrum).
In addition to the corpus striatum, the basal nuclei include the amygdaloid body (corpus amygdaloideum), which is located separately within the structures of the temporal lobe.
Structure of the caudate nucleus
The caudate nucleus (nucleus caudatus) has an elongated shape and is topographically closely associated with the lateral ventricle system. Its structure comprises three consecutive parts, each adjacent to a specific part of the ventricle:
- Head (caput) — the largest anterior portion. It directly contributes to the formation of the lateral wall of the anterior horn of the lateral ventricle.
- Body (corpus) — the middle part of the nucleus. Topographically, the body of the nucleus runs parallel along the central part (body) of the lateral ventricle.
- Tail (cauda) — the tapering posterior portion. The tail descends, extending into the temporal lobe, where it participates in forming the wall of the inferior horn of the lateral ventricle.
Lentiform nucleus and claustrum
Lentiform nucleus (nucleus lentiformis) is located somewhat lateral to the caudate nucleus. Its longitudinal axis is oriented sagittally (anterior-posterior). The mass of the nucleus is divided by thin layers of white matter into several segments.
These layers are called the medial and lateral medullary laminae (laminae medullares). They divide the nucleus into:
- Putamen (putamen) — the most lateral part of the complex.
- Globus pallidus (globus pallidus) — located more medially. The globus pallidus itself is further subdivided into medial (globus pallidus medialis) and lateral (globus pallidus lateralis) segments.
Lateral to the lentiform nucleus lies the claustrum (claustrum). This is a very thin sheet of gray matter. The claustrum is separated from the putamen (the lateral part of the lentiform nucleus) by a layer of white matter — the external capsule (capsula externa).
Anatomy of the amygdaloid body
Amygdaloid body (corpus amygdaloideum) is localized in the deep regions of the temporal lobe. Its precise landmark is the space directly anterior to the inferior horn of the lateral ventricle. In some anatomical schools, this structure is viewed not as an isolated nucleus, but as a local thickening of the temporal lobe cortex.
The structure of the amygdaloid body distinguishes several functional-anatomical zones:
- Basolateral part (pars basolateralis);
- Corticomedial part (pars corticomedialis), also referred to as the olfactory part (olfactoria);
- In close association with these structures, the anterior amygdaloid area (area amygdaloidea anterior) is described.
Briefly: answers to topical questions
Which nuclei form the striopallidal system and how are they phylogenetically classified?
The striopallidal system is formed by the caudate nucleus, putamen, and globus pallidus. Phylogenetically, these structures are classified into ancient and new:
- Globus pallidus (globus pallidus) — belongs to the paleostriatum (paleostriatum), representing a phylogenetically older formation.
- Caudate nucleus (nucleus caudatus) and putamen (putamen) — form the neostriatum, which developed later and expanded with the evolution of the cerebral cortex.
Which white matter structure separates the caudate and lentiform nuclei?
The caudate and lentiform nuclei are separated by the internal capsule (capsula interna). This white matter structure serves as the main highway and site for the compact passage of all projection fibers. On axial sections of the brain, it has a characteristic V-shape and additionally separates the lentiform nucleus from the thalamus.
Which specific white matter lamina separates the putamen from the globus pallidus?
The putamen and globus pallidus are separated by the medial medullary lamina (lamina medullaris medialis). It is a thin strip of white matter running between these structures. Meanwhile, the putamen itself lies laterally, covering the globus pallidus and extending beyond it rostrally and caudally.
What functions do the basal nuclei perform within the extrapyramidal system?
Within the extrapyramidal system, the basal nuclei act as control centers for involuntary movements and muscle tone regulation. Their main functions include:
- initiating and stopping movements;
- controlling amplitude, speed, and complex motor patterns;
- suppressing excess, involuntary movements;
- providing cognitive control over motor activity.
Which anatomical structures are located lateral to the claustrum?
Lateral to the claustrum (claustrum) are the extreme capsule (extreme capsule) and the insular cortex (insula cortex). The claustrum separates the medially located external capsule (external capsule) from the laterally located extreme capsule, which lies between the claustrum and the insular cortex.
The parts of the caudate nucleus are easy to remember using the horns of the lateral ventricle: Head — Anterior horn, Body — Central part (body), Tail — Inferior horn.
Class and exam questions
Where exactly are the basal nuclei located?
They lie deep within the white matter at the base of the cerebral hemispheres.
What structures form the lentiform nucleus?
It consists of a laterally located putamen and a medially located globus pallidus.
What separates the claustrum from the lentiform nucleus?
A layer of white matter — the external capsule (capsula externa) — runs between the claustrum and the lentiform nucleus (specifically its part, the putamen).
What else to study on this topic
- Topography of the external capsule (capsula externa)
- Internal capsule (capsula interna) and its connections
- Structure of the medullary laminae (laminae medullares)
- Detailed anatomy of the lateral ventricle walls
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