The cochlea, which is the hearing portion, and the semicircular canals is the balance portion. At the middle ear, the scala vestibuli and the scala tympani connect to the oval and round windows, respectively.Next to the middle ear in the bone of the skull is a small compartment which contains the hearing and balance apparatus known as the inner ear. The scalas are tubular channels that follow the coiled curvature of the cochlea. The interior of the cochlea is divided into three regions, or scalas: the scala vestibuli, the scala tympani, and the cochlear duct (scala media). The cochlea is a coiled canal that contains receptor cells that respond to vibrations transferred from the middle ear. This information is used for establishing equilibrium. Three semicircular canals contain receptor cells for determining angular movements of the head. This labyrinth is made of three semicircular canals and a snail‐shaped cochlea (see Figure 1).įigure 1. The three major regions of the ear are the outer ear, the middle ear, and the inner ear. This double‐layer labyrinth structure is found throughout the following inner ear structures. Perilymph fills the space between the two labyrinths, and endolymph fills the inner labyrinth. The canals consist of an outer bony (osseous) labyrinth that encloses an inner membranous labyrinth. The inner (internal) ear, also called the labyrinth, is a system of double‐walled canals.Contraction of these two muscles restricts the movement of the eardrum and auditory ossicles, reducing damage that may occur when they are exposed to excessive vibration from loud noises. Two muscles in the middle ear, the tensor tympani and the stapedius, connect to the malleus and stapes, respectively.

The auditory tube allows pressure differences between the middle and outer ear to equalize, thus reducing tension on the eardrum. A third opening leads to the auditory (Eustachian) tube, which connects the middle ear to the upper throat. A second membrane‐covered opening to the inner ear, the round window (secondary tympanic membrane), lies just below the oval window. Synovial joints connect the incus, the center bone of the auditory ossicles, to the malleus and stapes on each side. The malleus at one end connects to the eardrum, while the stapes at the other end attaches with ligaments to the oval window, a small, membrane‐covered opening into the inner ear. These bones, called the malleus, incus, and stapes, act as a lever system that amplifies and transfers vibrations of the eardrum to the inner ear. It contains three small bones, the auditory ossicles.

The middle ear (tympanic cavity) is an air‐filled cavity within the temporal bone.

The eardrum (tympanic membrane), at the internal end of the external auditory canal, vibrates in response to incident sound waves. The canal is lined with ceruminous glands that secrete cerumen (earwax), a sticky substance that traps dirt and other foreign objects.

The outer (external) ear consists of the auricle (pinna), a flap of elastic cartilage that protrudes from the head, and the external auditory canal (meatus), a tube that enters the temporal bone.

The organ of hearing, the ear, consists of three major regions, shown in Figure 1.

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Auditory ossicles function