Basal Nuclei, Cerebral White Matter & Limbic System

Basal nuclei

Clusters of neuron cell bodies buried within the cerebral hemispheres; involved in regulating movement and also associated with behavior, cognition, and perception.

Major structures of the basal nuclei

Caudate nucleus, putamen, and globus pallidus.

Caudate nucleus

C-shaped ring of gray matter located lateral to the lateral ventricle; its tail curls around and points anteriorly.

Putamen

Basal nucleus located posterior and inferior to the caudate nucleus and connected to it by small bridges of gray matter.

Corpus striatum

Caudate nucleus and putamen together.

Globus pallidus

Basal nucleus located medial to the putamen; contains more myelinated fibers and therefore appears pale.

Internal capsule

White matter that separates the basal nuclei of the cerebral hemispheres from gray matter of the diencephalon.

Main functions of the basal nuclei

Inhibit involuntary movement and help initiate voluntary movement.

Globus pallidus and movement

Prevents upper motor neurons from causing spontaneous, inappropriate muscle contractions.

Caudate nucleus and putamen in movement

Inhibit the globus pallidus to help initiate movement.

Basal nuclei dysfunction

Disorders of the basal nuclei can cause problems with movement, behavior, cognition, and perception.

Cerebral white matter

White matter within the cerebral hemispheres composed of axons organized into commissural, projection, and association fibers.

Three types of cerebral white matter fibers

Commissural fibers, projection fibers, and association fibers.

Commissural fibers

White matter fibers that connect the right and left cerebral hemispheres.

Corpus callosum

Largest group of commissural fibers; located at the base of the longitudinal fissure and connects the two cerebral hemispheres.

Projection fibers

White matter fibers that connect the cerebral cortex of one hemisphere with other areas of that hemisphere, other parts of the brain, and the spinal cord.

Corona radiata

Radiating pattern formed by projection fibers as they spread through the cerebral white matter.

Internal capsules

V-shaped bands formed where projection fibers condense.

Association fibers

White matter fibers restricted to a single cerebral hemisphere that connect gray matter of different cortical gyri with one another.

Commissural vs. projection vs. association fibers

Commissural fibers connect the two hemispheres; projection fibers connect the cortex with other brain regions and the spinal cord; association fibers connect cortical areas within the same hemisphere.

Possible pathway through cerebral white matter

Action potential begins in gray matter → travels to another gray matter area by projection fibers → travels to neighboring gray matter by association fibers → travels to the opposite cerebral hemisphere by commissural fibers.

Functional brain systems

Groups of gray matter nuclei that share a common function along with the white matter pathways connecting them.

Limbic system

Functional brain system consisting of the limbic lobe, hippocampus, amygdala, and pathways connecting these structures.

Major functions of the limbic system

Participates in memory, learning, emotion, and behavior and mediates visceral responses to situations.

Why is the limbic system called the "visceral brain"?

It helps mediate responses of the viscera to different situations.

Limbic lobe

Ring of cerebral cortex on the medial side of the brain that includes the cingulate gyrus and parahippocampal gyrus.

Cingulate gyrus

Part of the limbic lobe involved in the limbic system.

Parahippocampal gyrus

Part of the limbic lobe associated with the hippocampal region.

Hippocampus

Limbic system structure involved in learning and memory.

Fornix

C-shaped ring of white matter consisting of a bundle of axons leaving the hippocampus.

Amygdala

Almond-shaped gray matter nucleus anterior to the hippocampus; involved in the behavioral expression of emotion, particularly fear.

Basal nuclei vs. limbic system

Basal nuclei primarily regulate movement, while the limbic system is primarily involved in memory, learning, emotion, behavior, and visceral responses.