Neuroanatomy: Internal Capsule Overview

Internal Capsule (Projection Fibers)

• The internal capsule is a wide sheet of white matter composed of projection fibers.
• It's called "internal" because it's located between the lentiform nucleus and the thalamus.
• The internal capsule has a V-shaped appearance in horizontal sections.
• Medially, it is adjacent to the head of the caudate nucleus and the thalamus.
• Laterally, it is adjacent to the lentiform nucleus.

Projection Fibers

• Projection fibers transmit signals from the thalamus to the cerebral cortex (thalamic radiation).
• They also transmit signals from the cerebral cortex to lower centers (e.g., pyramidal tract).

Definition

• The internal capsule is a broad lamina of white matter composed of projection fibers.
• It's named as such because it forms a capsule surrounding the lentiform nucleus.

Relations

• Medially: head of the caudate nucleus and thalamus.
• Laterally: lentiform nucleus.

Parts

• Anterior limb
• Genu
• Posterior limb
• Retrolentiform part
• Sublentiform part

Descending Tracts (Anterior Limb)

• Fronto-pontine fibers
• Corticonuclear tract
• Corticospinal tract (upper limb and trunk)
• Corticospinal tract (lower limb)
• Corticorubral tract

Descending Tracts (Genu)

• Corticobulbar fibers (nuclear fibers)

Descending Tracts (Posterior Limb)

• Corticospinal fibers
• Fronto-pontine fibers
• Corticonuclear tract
• Corticospinal tract (upper limb and trunk)
• Corticospinal tract (lower limb)
• Corticorubral tract
• Parietppontine, temporopontine, & occipitopontine fibers

Descending Tracts (Retro-lentiform)

• Parietpo-pontine & occipitopontine fibers

Descending Tracts (Sublentiform)

• Temporopontine fibers

Ascending Tracts (Anterior Limb)

• Anterior thalamic radiation
• Frontopontine fibers

Ascending Tracts (Posterior Limb)

• Posterior thalamic radiation (optic radiation)
• Frontopontine fibers
• Corticonuclear tract
• Corticospinal tract (upper limb and trunk)
• Corticospinal tract (lower limb)
• Superior thalamic radiation

Ascending Tracts (Retro-lentiform)

• Parietopontine, temporopontine & occipitopontine fibers
• Acoustic radiation

Ascending Tracts (Sublentiform)

• Inferior thalamic radiation (auditory radiation)

Blood Supply

• Anterior part of anterior limb: Anterior Cerebral Artery
• Posterior part of anterior limb, genu, and anterior part of posterior limb: Middle Cerebral Artery
• Posterior part of posterior limb, retrolentiform and sublentiform part: Anterior Choroidal Artery

Basal Nuclei

• The basal nuclei are collections of nerve cells located deep within the cerebral hemispheres.
• They are important for motor control.

Basal Nuclei Components

- Caudate nucleus: located medial to the lentiform nucleus
- Lentiform nucleus: lateral to the caudate nucleus; consists of the globus pallidus and putamen.
- Amygdaloid nucleus: positioned at the anterior end of the tail of the caudate nucleus; involved in processing olfactory sensory information
- Claustrum: a thin sheet of gray matter between the lentiform nucleus and the insula.

Amygdaloid Nucleus

• Small rounded mass in the uncus of the temporal lobe.
• Considered the smell center.

Claustrum

• Thin sheet of gray matter lying between the lentiform nucleus and the insula.
• Related laterally to the external capsule that separates it from the insula.
• Its function is currently unknown.

Horizontal Section of the 2 Cerebral Hemispheres

• Shows the internal capsule's relationship to various brain structures, like the caudate nucleus, putamen, globus pallidus, and the ventricles.

Thalmus

• A significant relay station in the brain.
• The thalamus process sensory, motor, and other brain signals to the cerebral cortex.

MCQ's

• These are multiple-choice questions regarding the internal capsule and anterior commissure.

This quiz explores the internal capsule, a significant structure in the brain composed of projection fibers. You'll learn about its location, anatomy, and the role of projection fibers in connecting the thalamus and cerebral cortex. Test your knowledge and understanding of this crucial neuroanatomical feature.