The Ear Anatomy

Your ears aren’t only for hearing— they are also important for controlling a sense of position and balance. Each ear is split into three sections: the outside; the middle; and the inner ear. The middle and inner parts of the ear are located within the temporal bones of the skull, in hollow cavities on either side of the head.

The outer ear

The outer part of your ear is made up of a pinna and an ear lobe. The pinna is the shell-like part of your outer ear, made of cartilage and skin. It directs sound waves from the outside into your external auditory canal (ear canal) which, in turn, sends sound waves to the tympanic membrane (also known as the ear drum). The tympanic membrane is a thin, semi-transparent membrane that separates the outer and middle ears.

The middle ear

The middle ear is an air-filled space containing three tiny bones (known as ossicles) called the malleus (hammer), incus and stapes (stirrup). The sound waves that reach the tympanic membrane cause the membrane to vibrate. This vibration is then transmitted to the ossicles, which amplify the sound and transmit the vibration to the oval window (a thin membrane between the middle and the inner ears).

The Eustachian tube is a narrow tube that connects the middle ear to the back of your nose and throat (known as the nasopharynx). Its function is to allow air to flow into the middle ear and to drain mucus from the middle ear to the nasopharynx. When you swallow, your Eustachian tube opens up to allow air to flow into the middle ear, so that the air pressure on either side of the tympanic membrane is the same. In situations where there is a sudden change in air pressure ( e.g. during take-off and landing on a plane), the pressure in the middle ear is not the same as the outside air pressure. This can make your ear drum bulge or retract and less capable of transmitting vibrations, causing temporary hearing problems. You can equalize the pressure by swallowing or ‘popping’ your ears.

The inner ear

The inner ear (also known as the labyrinth) contains 2 main structures — the cochlea involved in hearing and the vestibular system (consisting of 3 semicircular canals, the saccule, and the utriculum) responsible for maintaining balance.

The cochlea is filled with fluid and contains the organ of Corti — a structure that contains thousands of specialized sensory hair cells with projections called cilia. Vibrations transmitted from the middle ear cause tiny waves to form in the inner ear fluid, which causes the cilia to vibrate. Hair cells convert these vibrations into nerve impulses or signals that are sent to the brain via the auditory nerve, where they are interpreted as sound.

The round window (fenestra cochlea) is a membrane that connects the cochlea to the middle ear. It helps to dampen the vibrations of the cochlea.

Semicircular canals also contain fluid and hair cells, but these hair cells are responsible for detecting motion rather than sound. When you move your head, the fluid inside the semicircular canals (which sit at right angles to each other) also moves. This fluid motion is detected by the hair cells, which then send nerve impulses about the position of your head and body to the brain to help you maintain your balance.

The utricle and saccule operate in a similar way to the semicircular canals, allowing you to sense the position of your body relative to gravity and make postural adjustments as needed.

See Also
The Eye Anatomy