What is the function of the vestibular branch of cranial nerve VIII?

The vestibular branch of cranial nerve VIII, also known as the vestibulocochlear nerve, is primarily responsible for balance and spatial orientation. This branch transmits sensory information from the vestibular apparatus of the inner ear, which includes the semicircular canals and otolithic organs. These structures detect changes in head position and motion, enabling the body to maintain balance and posture. As a result, the vestibular branch plays a crucial role in helping the body respond appropriately to gravitational forces and ensuring equilibrium during movement.

The other functions listed in the options are performed by different cranial nerves. Eye movement is controlled by cranial nerves III (oculomotor), IV (trochlear), and VI (abducens), while hearing is the function of the cochlear branch of cranial nerve VIII. The action of swallowing is facilitated by cranial nerve IX (glossopharyngeal) and cranial nerve X (vagus). Thus, the vestibular branch's specific function in balance and spatial orientation makes it the correct answer in this context.