Cerebrum Section 3: White Matter

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Questions and Answers

Which of the following fibers are classified under the motor fibers in the internal capsule?

Anterior thalamic radiation

Superior thalamic radiation

Inferior thalamic radiation

Corticopontine fibers (correct)

What type of fibers are found in the genu of the internal capsule?

Corticonuclear fibers (correct)

Corticopontine fibers

Corticospinal fibers

Corticorubral fibers

Which artery supplies the posterior part of the posterior limb of the internal capsule?

Internal carotid artery

Middle cerebral artery

Anterior cerebral artery

Anterior choroidal artery (correct)

What is a consequence of lesions in the internal capsule?

Contralateral hemiplegia Signup and view all the answers

Which of the following bundles connects the frontal pole with the occipital pole?

Superior longitudinal bundle Signup and view all the answers

What is the main function of association fibers?

Connect distant gyri in the same hemisphere Signup and view all the answers

The fornix is associated with which two structures?

Hippocampus and mammillary body Signup and view all the answers

Which type of association fibers connect adjacent gyri?

Short associative fibers Signup and view all the answers

What is the primary function of commissural fibers in the white matter of the cerebrum?

Interconnect identical cortical areas of both hemispheres Signup and view all the answers

Which part of the corpus callosum connects the anterior parts of the two frontal lobes?

Genu Signup and view all the answers

Which of the following best describes projection fibers?

They link the cerebral cortex to subcortical centers and the spinal cord Signup and view all the answers

What is the largest commissure in the brain?

Corpus callosum Signup and view all the answers

Which part of the corpus callosum is responsible for connecting the parietal lobes?

Body Signup and view all the answers

What type of fibers interconnect different regions of the cerebral cortex within the same hemisphere?

Association fibers Signup and view all the answers

What feature distinguishes the splenium of the corpus callosum?

It connects the posterior parts of the parietal, temporal, and occipital lobes Signup and view all the answers

Which fibers are involved in connecting the cerebral cortex with the thalamus?

Projection fibers Signup and view all the answers

What is the function of the anterior commissure?

It connects the olfactory regions of the two hemispheres. Signup and view all the answers

Which structure forms the fork-like structure known as the forceps major?

Fibers connecting the occipital lobes Signup and view all the answers

Where is the internal capsule located in relation to the thalamus and lentiform nucleus?

Medially to the thalamus and laterally to the lentiform nucleus. Signup and view all the answers

Which part of the internal capsule is located between the head of the caudate nucleus and the lentiform nucleus?

Anterior limb Signup and view all the answers

Which fibers are primarily responsible for sensory and motor innervation of the opposite half of the body?

Projection fibers Signup and view all the answers

What structure connects the crura of the fornix and the hippocampi of the two sides?

Hippocampal commissure Signup and view all the answers

Which part of the internal capsule is the concavity of the bend facing laterally?

Genu Signup and view all the answers

Which commissure crosses the midline through the inferior lamina of the stalk of the pineal gland?

Posterior commissure Signup and view all the answers

Study Notes

Cerebrum (Part 3) - White Matter

The cerebrum's white matter is a densely packed collection of myelinated nerve fibers.
White matter fibers are categorized into three types: commissural, association, and projection fibers.

Commissural Fibers

These fibers connect corresponding cortical areas of both cerebral hemispheres.
Key commissures include:
- Corpus callosum: The largest commissure, forming a C-shaped structure connecting the medial surfaces of both hemispheres. It is attached to the fornix by the septum pellucidum.
- Anterior commissure: A small, round bundle of fibers crossing the midline in the lamina terminalis. Connects the olfactory regions of both hemispheres.
- Posterior commissure: A small bundle of fibers crossing the midline through the inferior lamina of the pineal gland's stalk.
- Hippocampal commissure: Connects the crura of the fornix and hippocampi of both sides.
- Habenular commissure: Connects white matter fibers via the superior lamina of the pineal gland's stalk.

Projection Fibers

These fibers link the cerebral cortex to subcortical structures like the corpus striatum, thalamus, brainstem, and spinal cord.
Key structures involved in projection include:
- Corona radiata
- Internal capsule: A compact bundle of projection fibers between the thalamus and caudate nucleus medially, and the lentiform nucleus laterally. Consists of ascending and descending nerve fibers.
  - Ascending (sensory) fibers travel from the thalamus to the cerebral cortex.
  - Descending (motor) fibers travel from the cerebral cortex to the cerebral peduncle of the midbrain. Fibers in the internal capsule are crucial for sensory and motor functions of the opposite side of the body.

Association Fibers

These fibers link different regions of the cerebral cortex in the same hemisphere.
Examples include:
- Superior longitudinal fasciculus: Connects the frontal pole to the occipital pole, and can connect frontal to temporal poles.
- Inferior longitudinal fasciculus: Connects the occipital pole to the temporal pole.
- Uncinate fasciculus: Connects the frontal lobe with the temporal lobe, curving around the lateral sulcus.
- Cingulum: Connects structures within the limbic system (cingulate gyrus, parahippocampus to uncus).

Fornix

A large bundle of association fibers connecting the hippocampus to the mammillary body.
It appears as an arched, prominent bundle of white fibers below the corpus callosum and along the lower border of the septum pellucidum.
The fornix in each hemisphere forms a single, close-knit structure beneath the corpus callosum.
Parts of the fornix include the fimbria, crura, body, and anterior columns.
The crus arches below the splenium and behind the thalamus. The two crura merge in the midline to create the fornix body; this then divides into two columns which extend to the mammillary bodies.

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Description

Explore the intricacies of the cerebrum's white matter, including its composition and types of fibers. This quiz covers critical commissural fibers and their connections between the cerebral hemispheres. Test your knowledge on the corpus callosum, anterior commissure, and more.