Basal Ganglia Anatomy

Corpus striatum

  • Caudate
  • Putamen
  • Globus pallidus

Caudate nucleus

  • Head
  • Body
  • Tail

Globus pallidus

  • External (lateral)
  • Internal (medial) segments.

Striatum

Collective term for the:

  • Caudate
  • Putamen

Derived from the striations that connect them.

Lentiform nucleus

Collective term for the:

  • Globus pallidus
  • Putamen

Given their lens-shaped appearance. This is an important term to know because it makes sense of the syndrome of hepato-lenticular degeneration.

Pallidum

  • Descriptor for the globus pallidus because bundles of myelinated fibers traverse the globus pallidus, giving it a pale appearance.
  • The pallidum is sometimes referred to as the paleostriatum because the globus pallidus is derived from the phylogenetically older portion of the brain — the diencephalon.
  • The neostriatum refers to the caudate and putamen, which are derived from the phylogenetically newer part of the brain — the telencephalon.

Fiber pathways

  • The corpus striatum also encompasses several fiber pathways that pass between the globus pallidus and the subthalamic nucleus and thalamus: the ansa lenticularis, lenticular fasciculus, subthalamic fasciculus, and thalamic fasciculus.These fibers comprise a considerable portion of the white matter region inferolateral to the thalamus, which is called the fields of Forel (aka prerubral fields or Forel’s Field H).

Basal nuclei vs Basal ganglia

  • Basal ganglia is more correctly referred to as the basal nuclei because a ganglion is a neuronal aggregation within the peripheral nervous system and the basal nuclei lie within the central nervous system, but the term basal ganglia is the common parlance, so we use it here.

ANATOMY

AXIAL VIEW

Key landmarks: the frontal horn and body of the lateral ventricles, thalamus, and the claustrum, and insula

Anatomical Structures

  • Caudate head in the wall of the frontal horn
  • Caudate tail at the posterolateral tip of the thalamus (the body is not visible in this section)
  • Lens-shaped lentiform nucleus, which subdivides into the putamen, laterally, and the globus pallidus, medially

Early in development, the globus pallidus migrates into the medial wall of the putamen…

  • Thus, we can envision the lentiform nucleus as a globus pallidus core surrounded by a putaminal shell.
  • The internal capsule lies in between the lentiform nucleus and the head of the caudate and thalamus.
  • The external capsule lies in between the putamen and the claustrum.
  • The extreme capsule lies in between the claustrum and the insula.

CORONAL VIEW: ANTERIOR

Key landmarks: optic chiasm, frontal horn of lateral ventricle, corpus callosum, and the basal forebrain

Anatomical Structures

  • The combined putamen and head of the caudate.
  • The nucleus accumbens, which is the bridge that persists between the head of the caudate and putamen after the anterior limb of the internal capsule separates the head of the caudate from the putamen.
    • It is important in rewarding behavior.

CORONAL VIEW: POSTERIOR

Key landmarks:

  • Optic tract
  • Frontal horn of lateral ventricle
  • 3rd ventricle
  • Corpus callosum

Anatomical Structures

  • Caudate Head in the wall of the frontal horn
  • Putamen
  • Globus pallidus
  • The lateral medullary lamina separates the putamen and globus pallidus.
  • The medial medullary lamina subdivides the globus pallidus into an internal (or medial) segment and an external (or lateral) segment.
  • The internal capsule lies in between the lentiform nucleus and the caudate.
  • Beneath the globus pallidus, lies the basal forebrain and the horizontally-oriented anterior commissure in between them.
    • Note that the globus pallidus actually extends beneath the anterior commissure as the ventral pallidum

SAGITTAL VIEW

Key landmarks:

  • corpus callosum
  • & the subjacent lateral ventricular system:
    • frontal horn
    • atrium
    • temporal horn

Anatomical Structures

  • Caudate: head and body (the tail is not visible in this section)
  • Putamen (anteriorly)
  • Thalamus (posteriorly)
The internal capsule funnels inferiorly into the cerebral peduncle.

BASAL GANGLIA ISCHEMIC & HEMORRHAGIC STROKES

  • Basal Ganglia Ischemic Stroke
  • Basal Ganglia Hemorrhage

BASAL GANGLIA ANATOMY & CIRCUITRY: ADVANCED INFORMATION

Basal ganglia topography

  • The prefrontal cortex acts through innervation of the head and body of the caudate nucleus.
  • The parietal lobes act through innervation of both the putamen and caudate.
  • The primary auditory cortex projects to the caudoventral putamen and tail of the caudate.
  • The visual cortices project primarily to the nearest portion of the caudate nucleus.

Fields of Forel

Additional fiber pathways pass through Field H and H1 in their ascent into the thalamus they include:

  • The cerebellothalamic fibers from the corticopontocerebellar pathway, the medial lemniscus, the nigrothalamic fibers, and the spinothalamic fibers of the anterolateral system pathway.

The thalamic fasciculus

  • The term is sometimes broadened to include the cerebellothalamic fibers and it is also sometimes used synonymously with the term Field H1, just as the term lenticular fasciculus is sometimes used synonymously with term Field H2.
  • The thalamic fasciculus projects to multiple thalamic nuclei, including the ventroanterior nucleus, which most notably communicates with the globus pallidus; the ventrolateral nucleus, which most notably communicates with the cerebellum; the dorsomedial nucleus, which most notably communicates with the prefrontal cortex and basal ganglia; and the centromedian and parafascicular nuclei (the main intralaminar nuclei), which most notably
    communicate with the striatum and frontal lobes.

BASAL GANGLIA: ADVANCED NOMENCLATURE

Advanced Nomenclature

  • The striatum further subdivides into dorsal and ventral divisions.
  • The dorsal striatum comprises the bulk of the caudate and putamen, whereas the ventral striatum is limited to only the ventromedial caudate and putamen, but the ventral striatum also encompasses the nucleus accumbens and select basal forebrain structures.
  • The dorsal striatum is involved in a wide array of processes, including the sensorimotor circuits, whereas the ventral striatum associates principally with the limbic system and is primarily involved in emotional and behavioral processes.
  • Just as the striatum divides dorsally and ventrally, so the pallidum further subdivides into a dorsal pallidum and ventral pallidum. Similar to the striatum, the dorsal pallidum refers to the bulk of the globus pallidus, whereas the ventral pallidum refers to the anteromedial portion of the globus pallidus that lies below the anterior commissure. However, although we consider the ventral striatum and ventral pallidum to be divisions of the striatum and pallidum, here, certain texts distinguish these ventral structures as entirely separate nuclei (ie, they distinguish the ventral pallidum from the pallidum, itself).
  • The corpus striatum also encompasses several fiber pathways that pass between the globus pallidus and the subthalamic nucleus and thalamus: the ansa lenticularis, lenticular fasciculus, subthalamic fasciculus, and thalamic fasciculus. These fibers comprise a considerable portion of the white matter region inferolateral to the thalamus, which is called the fields of Forel (aka prerubral fields or Forel’s Field H).
  • As a final note, the subthalamic nucleus and substantia nigra are functionally but not developmentally associated with the basal ganglia; therefore, although they are variably included as part of the basal ganglia, we do not include them in our definition of the basal ganglia, here, in accordance with the Terminologia Anatomica.

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