White Matter of Cerebrum : Projection, Commissural and Association fibers

WHITE MATTER OF CEREBRUM

The white matter of the cerebral hemisphere basically contains two components

• myelinated nerve fibers of many sizes*
•  neuroglia (mostly oligodendrocytes)

*This note only describes different types of myelinated nerve fibers.

The white matter of the cerebral hemisphere are of three types:

1. commissural fibers
2. association fibers
3. projection fibers

FUNCTIONAL AREAS OF CEREBRAL CORTEX

Cerebral cortex presents functionally specialized areas. For the descriptive purpose, these areas can be located on different lobes of cerebral hemisphere as given below:

Frontal lobe

1.      Motor area or Primary motor area 

Broadmann’s area 4

-         Precentral gyrus and anterior part of paracentral lobule

-         Produce isolated movements on the opposite side of the body

-         Somatotopic representation

o   Inverted and disproportionate to the size of the body part

o   lips, tongue, face, and hands are represented in order on the lower lateral surface

o   arm, trunk, and hip in order on the upper lateral surface

o  foot, lower leg and anal and genital region on paracentral lobule on medial surface

MICROSCOPIC STRUCTURE OF CEREBRAL CORTEX

The cerebral cortex contains three main types of neurons arranged in a layered structure:

1. Pyramidal cells (shaped like a tepee, with an apical dendrite reaching from the upper end toward the cortical surface, and basilar dendrites extending horizontally from the cell body);

2. Stellate neurons (star shaped, with dendrites extending in all directions); and

3. Fusiform neurons (found in deeper layers, with a large dendrite that ascends toward the surface of the cortex).

In addition, following two types of cells are also present: