The ear is an organ of hearing and balance. It is subdivided into the outer (external), middle and inner (internal) ear. The outer ear funnels sound waves onto the tympanic membrane, which vibrates in response. This vibration is mechanically conducted via the ossicles of the middle ear to the cochlea of the inner ear where it is transformed into the electrical signals that can be sent via the cochlear nerve to the brain. Meanwhile, balance controlled by the semicircular canals and otolith organs of the inner ear which communicates with the vestibular nerve. Together, the vestibular and cochlear nerve forms the vestibulocochlear nerve (CN VIII).

CLINICAL CORNER

Hearing loss can either be conductive (from disturbances in conduction such as in damage to the middle ear and tympanic membrane), or sensorineural (from damage to the sensory organs or neuronal pathways). In conduction deafness, air vibrations are not mechanically transmitted the inner ear but bone conducted vibrations can still stimulate hearing. This can be tested by Rinne’s and Weber’s tests (or sophisticatedly by audiometry and examining recorded auditory evoked potentials).
Rinne’s test compares loudness when a tuning fork is held outside the external meatus (air conduction) and when its base is pressed on the mastoid process (bone conduction). Normally and in sensorineural deafness, conduction via air is louder than via bone (vice-versa in conduction deafness).
Weber’s test involves bone conduction equidistant from both ears (e.g. at occipital protruberance). Conduction deafness in one ear means the opposite (healthy) ear hears louder sounds (and vice versa for sensorineural deafness).