Cerebral White Matter

Cerebral White Matter

Question 1. Define white matter and discuss its various types.
Answer.

The white matter of the cerebrum is made up of myelinated nerve fibres, which connect various parts of the cerebral cortex on the same side, with the opposite side and also with the other parts of the CNS.

Types of white fibres. There are three types of white fibres in the cerebrum: association fibres, commissural fibres and projection fibres.

Association fibres (intrahemispheric): These fibres connect different areas of the cerebral cortex of the same hemisphere. They are further classified into two types:

1. Short association fibres, which connect the adjacent gyri and
2. Long association fibres, which connect the distant gyri.

Commissural fibres: These fibres connect the cortical areas of one cerebral hemisphere with the corresponding cortical areas of the opposite hemisphere. The bundles of such fibres are called commissures. The important commissures in the brain are

1. Corpus callosum,
2. Anterior commissure and
3. Posterior commissure.

Projection fibres: These fibres connect the cortical areas with the subcortical centres such as the corpus striatum, thalamus, hypothalamus, brainstem and spinal cord. They include both motor and sensory fibres of long tracts. The most important bundles of projection fibres are

1. Internal capsule and
2. Fornix.