Cranial nerve Nuclei

A cranial nerve consists of motor fibres (motor nerve) or sensory fibres (sensory nerve) or both (mixed nerve).

During the development of spinal cord due to the appearance of a longitudinal groove (the sulcus limitans), the lateral wall of the neural tube is divided into two parts or laminae:

• (a) Dorsal alar lamina → The cells are sensory in function.

• (b) Ventral basal lamina → The cells are motor in function.

The cells of each of these two laminae, gets arranged into two longitudinal columns:

• The somatic columns

• The visceral columns - visceral components lying close to the sulcus limitans.

Thus, there are four functional components/columns in the lateral wall of the spinal cord from ventral to dorsal side, viz.

During development:

• An extra branchial (special) column appears between somatic and visceral columns in both basal and alar laminae to supply the derivatives of pharyngeal arches.

• An extra special somatic column appears in the most lateral part of the alar lamina to receive sensations of hearing and balance.

Thus, there are seven functional columns in the brainstem