Which cranial nerve is primarily involved in hearing?

Cranial nerve 8, also known as the vestibulocochlear nerve, is primarily responsible for hearing and balance. This nerve has two distinct components: the cochlear branch, which is involved in the sense of hearing, and the vestibular branch, which is responsible for balance and spatial orientation.

The cochlear part carries auditory information from the cochlea of the inner ear to the brain. It translates sound waves into electrical signals that the brain interprets as sound, making it essential for hearing. Damage or dysfunction of this nerve can lead to hearing loss or balance disorders, emphasizing its critical role in these functions.

In contrast, the other cranial nerves mentioned have different primary functions. Cranial nerve 5 (trigeminal nerve) is involved in sensory information from the face and motor functions such as chewing. Cranial nerve 7 (facial nerve) is primarily responsible for facial expressions and some aspects of taste. Cranial nerve 10 (vagus nerve) is involved in parasympathetic control of the heart and digestive tract, and does not play a direct role in hearing.

Therefore, cranial nerve 8 is the correct answer as it is specifically dedicated to the functions of hearing and balance.