Forebrain: Subcortical White Matter

Question 1

Forebrain: Subcortical White Matter

All white matter consists of = ?

Answer 1

All white matter consists of myelinated axons.

• In cerebrum, the white matter is deep to the cortex and thus is called subcortical.

Question 2

Forebrain: Subcortical White Matter

Subcortical white matter fibers are classified into three categories:
1. ?
2. ?
3. ?

Answer 2

Subcortical white matter fibers are classified into three categories:

1. Projection fibers are white matter tracts that connect the hemispheres of the brain with lower brain structures or with the spinal cord. They “project” from the cortex to the lower brain structures or spinal cord. link
2. Commissural fibers are white matter tracts that connect gray matter between the left and right hemispheres of the brain. The main commissure that allows for the passage of information between the two hemispheres is called the corpus callosum.
3. Association fibers are white matter tracts that connect different bits of gray matter within the same hemisphere of the brain. These connections do not cross the midline.

Question 3

Forebrain: Subcortical White Matter

Projection fibers extend from ?

Answer 3

Projection fibers extend from

• subcortical structures to the cerebral cortex and
• from the cerebral cortex to the spinal cord, brainstem, basal ganglia and thalamus

All projection fibers travel through the internal capsule

Parts of internal capsule:

• Anterior limb
• Genu
• Posterior limb

Question 4

Forebrain: Subcortical White Matter

Lesion of internal capsule = ?

Answer 4

Occlusion/hemorrhage of arteries supplying internal capsule is common.

Small lesion could have severe consequences:

• Contralateral decrease in voluntary movement
• Contralateral loss of conscious somatosensation

Question 5

Forebrain: Subcortical White Matter

Commissural fibers= ?

Answer 5

• Connect homologous areas of the cerebral hemispheres.
• Corpus callosum is the largest group of commissural fibers, linking many areas of the right and left hemispheres.
• Clearly visible on medial surface.
• Cingulate gyrus surrounds the corpus callosum.

Question 6

Forebrain: Subcortical White Matter

Callosotomy = ?

Answer 6

• Surgically removed (callosotomy): in case of intractable epilepsy when excessive neuronal activity cannot be controlled by medications or surgical damage of a single cortical site.
• Prevents excessive firing from spreading, from one hemisphere to the other, limiting seizure to one hemisphere.
• Rarely seen for rehabilitation, as performed infrequently; recovery spontaneous.
• People with callosotomies, report conflict between their hands, e.g. left hand begin at task and right hand interfere with left hand activity.
• Competitive hand movements resolve with time; compensation occurs.

Question 7

Forebrain: Subcortical White Matter

Association fibers connect = ?

• What other kinds of association fibers are there?

Answer 7

Connect cortical regions within one hemisphere.

Short association fibers connect adjacent gyri.

Long association fibers connect lobes within one hemisphere:

• Cingulum connects frontal, parietal, and temporal lobe cortices
• Uncinate fasciculus connects frontal and temporal lobe cortices
• Superior longitudinal fasciculus connect cortices of all lobes
• Inferior longitudinal fasciculus connects temporal and occipital lobes

Question 8

Forebrain: Subcortical White Matter

Basal ganglia = ?

Answer 8

Collection of gray matter nuclei located deep within the white matter of the cerebral hemispheres.

Question 9

Forebrain: Subcortical White Matter

Major components of basal ganglia = ?

Answer 9

Major components of basal ganglia:

• caudate nucleus
• putamen
• globus pallidus
• subthalamic nucleus, and
• substantia nigra

Question 10

Forebrain: Subcortical White Matter

Basal ganglia are vital for = ?

Answer 10

Basal ganglia are vital for normal motor function:

• help initiate movement
• regulate muscle tone

Also involved with cognitive functions:

• Goal-directed behavior
• Social behavior
• Emotion

Question 11

Forebrain: Subcortical White Matter

What are 1-6?

Answer 11

1. Posterior limb of the internal capsule =
2. Primary auditory cortex =
3. Secondary somatosensory area =
4. Primary visual cortex =
5. Caudate nucleus =
6. Secondary visual cortex =