Cranial Nerves Overview

Cerebral Metabolism

• The brain is the most energy-consuming organ, using 20% of the body's oxygen.
• Brain cells solely use glucose to function and require a continuous supply of oxygen and glucose.
• Hypoglycemic conditions can cause brain cells to dysfunction, leading to loss of consciousness.
• Lack of cerebral blood flow causes cerebral hypoxia, which can cause irreversible brain damage.
• A lack of oxygen for as little as 10 seconds can cause loss of consciousness, and 5-6 minutes can cause brain cell death.

Cranial Nerves

• There are 12 pairs of cranial nerves, numbered from I to XII, which arise from the brain and travel to the head, face, neck, and shoulders.
• Cranial nerves can be either motor, sensory, or mixed (both motor and sensory).
• They are sensitive to changes in circulation and intracranial pressure, and can become dysfunctional in conditions such as stroke, tumor, or brain injury.
• Cranial nerve dysfunction can indicate a disturbance on the opposite side of the brain.
• Cranial nerves can act as antennae, sensing changes in intracranial pressure.

Individual Cranial Nerves

• I. Olfactory: responsible for smell
• II. Optic: responsible for vision
• III. Oculomotor: responsible for extraocular movements and pupil response
• IV. Trochlear: responsible for extraocular movements
• V. Trigeminal: responsible for facial sensation and masseter muscle control of chewing
• VI. Abducens: responsible for extraocular movements
• VII. Facial: responsible for facial expressions and taste over the anterior two-thirds of the tongue
• VIII. Auditory or Vestibulocochlear: responsible for hearing and equilibrium
• IX. Glossopharyngeal: responsible for elevation of pharynx in swallowing, taste over the posterior one-third of the tongue, and salivation
• X. Vagus: responsible for gag reflex and parasympathetic control of the body
• XI. Accessory: responsible for turning the head and shrugging
• XII. Hypoglossal: responsible for tongue movement