Ear

The ear is the organ responsible for hearing and balance in humans and many other animals. It is traditionally described as having three parts: the outer ear, the middle ear, and the inner ear. Each part contributes to how sound is collected, transmitted, and interpreted, and how movement and orientation are perceived.

The outer ear includes the visible pinna, which helps capture sound, and the external auditory canal, which channels waves toward the tympanic membrane, or eardrum. The tympanic membrane vibrates in response to sound, converting air pressure waves into mechanical motion.

The middle ear contains a small air-filled cavity with three auditory ossicles—the malleus (hammer), incus (anvil), and stapes (stirrup). These bones form a lever system that amplifies and transmits vibrations from the eardrum to the inner ear via the oval window. The middle ear also houses the eustachian tube, which helps equalize pressure between the middle ear and the atmosphere.

The inner ear houses the cochlea, responsible for hearing, and the vestibular apparatus, which governs balance. The cochlea converts mechanical vibrations into neural signals through hair cells embedded on the basilar membrane. These signals are carried by the auditory portion of the vestibulocochlear nerve (cranial nerve VIII) to the brain. The vestibular system, including the semicircular canals and otolith organs, detects head movement and orientation, contributing to balance and spatial awareness.

Common disorders include otitis media, otosclerosis, presbycusis, and labyrinthitis, which can affect hearing or balance. The ear’s integrated structure enables the perception of sound and the maintenance of posture and equilibrium.