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Central Nervous System

6 out of 9

Pyramidal fibers are:

A Projection fibres

B Association fibres

C Commissural fibres

D Association & commissural fibres

Ans. A Projection fibres

White matter of cerebrum: ­

The white matter of cerebrum is composed mostly of myelinated nerve fibers, and comprises of three groups: ­

I. Association fibers or Arcuate fibers: ­

Association (Arcuate) fibers connect different cortical areas of the same hemisphere to one another. All are ispilateral. They are short and long arcuate fibers.

The long association (Arcute) fibers are: ­

a. Uncinate fasciculus b. Cingulum c. Superior longitudinal fasiculus

d. Inferior longitudinal fasiculus e. Fronto-occipital fasiculus

II. Commissural fibers: -Connects the two hemispheres to each other Q, linking corresponding or homotopic loci and also heterotopic loci they are: ­

a. Corpus callosum b. Anterior commissure c. Commissure of fornix

d. Posterior commissure e. Habenular- commissure

III. Projection fibers: -Connect the cerebral cortex with the grey matter of the brainstem and spinal cord and comprises of both incoming and out goings fibers (=tract). Most of the projection fibers form internal capsule. Many important tracts egcorticospinal (pyramidal tract) and cortico­pontine are made up of projection fibers (Note ~ Tract = bundle of fibers)