The facial nerve innervates the stapedius muscle, which is responsible for limiting movement of the stapes, thereby reducing the intensity of the sound entering the inner ear. The hypoglossal nerve innervates tongue muscles; the accessory nerve supplies the trapezius and sternocleidomastoid muscles; the vagus does not provide any innervation for sound in the ear; and the glossopharyngeal nerve only supplies general sensation to the middle ear cavity and tympanic membrane, plus muscle innervation to the stylopharyngeus muscle.