In individual is asked to smile broadly. It is observed that the left corner of the mouth cannot be elevated in a normal fashion. The individual is then asked to wrinkle the brow. The brow is observed to wrinkle in a normal fashion. Which cranial is involved in this facial control issue, and is the lesion in that nerve or within the central nervous system?

Cranial nerve 7 and YES the lesion is within the Central Nervous System.

Explanation:

The Central Nervous System ( CNS) consists of the brain and the spinal cord. There are 12 pairs of cranial nerves originating from the nuclei in the inferior surface of the brain, some sensory, some motor and some mixed.

Cranial nerve 7 is also known as the Facial nerves. These nerves are composed of both motor and sensory nerve fibre, arising from nuclei in the lower part of the pons. The motor fibres supply the muscles of facial expression. When lesion occurs at the base of the pon which is part of the CNS, it can affect the facial expressions such as observed, that the left corner of the mouth cannot be elevated in a normal fashion.

Therefore, Cranial nerve 7 ( Facial nerve) is involved in this facial control issue and YES the lesion is within the Central Nervous System.