The ear is a unique organ that is not only necessary for hearing, but also for maintaining balance. Concerning ear anatomy, the ear can be divided into three regions. These include the outer ear, middle ear, and inner ear. The ear converts sound waves from our surroundings into nerve signals that are carried by neurons to the brain. Certain components of the inner ear also help to maintain balance by sensing changes in head motions, such as tilting side to side. Signals about these changes are sent to the brain to be processed to prevent feelings of imbalance as a result of common movements.
The human ear consists of the outer ear, middle ear, and inner ear. The structure of the ear is important to the process of hearing. The shapes of ear structures help to funnel sound waves from the outside environment into the inner ear.
Pinna - also called the auricle, this portion of the ear is attached externally to the head. It aids in the perception of sound direction and amplifies and directs sound to the ear canal.
Auditory canal - also called the ear canal, this hollow, tube-shaped cylindrical structure connects the outer ear to the middle ear. The canal is composed of cartilage and fibrous connective tissue. It secretes a waxy substance, ear wax, to help clean the canal and to protect against bacteria, bugs, and other organisms that may enter the ear.
Eardrum - also called the tympanic membrane, this membrane separates the outer and middle ear. Sound waves cause this membrane to vibrate and these vibrations are transmitted to three tiny bones (the ossicle) in the middle ear. The three bones are the malleus, incus, and stapes.
Malleus - bone that is connected to the eardrum and to the incus. Shaped like a hammer, the malleus transmits vibration signals received from the eardrum to the incus.
Incus - bone that is connected to and located between the malleus and the stapes. It is shaped like an anvil and transmits sound vibrations from the malleus to the stapes.
Stapes - the smallest bone in the body, the stapes is connected to the incus and the oval window. The oval window is an opening that connects the middle ear with the vestibule of the bony labyrinth in the inner ear.
Auditory tube - also called the eustachian tube, this cavity connects the upper portion of the pharynx, called the nasopharynx, to the structures of the middle ear. The auditory tube helps to drain mucus from the middle ear and to equalize pressure.
Bony Labyrinth - hollow passages within the inner ear consisting of bone lined with a layer of connective tissue called periosteum. Contained within the bony labyrinth is a membranous labyrinth or system of ducts and canals that is separated from the bony walls by a fluid called perilymph. Another fluid called endolymph is contained within the membranous labyrinth and separated from the perilymph fluid. The bony labyrinth is divided into three regions: the vestibule, semicircular canals, and cochlea.
Vestibule - central region of the bony labyrinth that is separated from the stapes of the middle ear by an opening called the oval window. It is located between the semicircular canals and the cochlea.
Semicircular canals - connecting ducts within the ear consisting of the superior canal, posterior canal, and horizontal canal. These structures help maintain balance by detecting head movements.
Cochlea - shaped like a spiral, this structure contains fluid-filled compartments which sense pressure changes. The organ of Corti within the cochlea contains nerve fibers that extend to form the auditory nerve. Sensory cells within the organ of Corti help to convert sound vibrations to electrical signals that are transmitted to the central nervous system.
How We Hear
Hearing involves the conversion of sound energy to electrical impulses. Sound waves from the air travel to our ears and are carried down the auditory canal to the ear drum. Vibrations from the eardrum are transmitted to the ossicles of the middle ear. The ossicle bones (malleus, incus, and stapes) amplify the sound vibrations as they are passed along to the vestibule of the bony labyrinth in the inner ear. The sound vibrations are sent to the organ of Corti in the cochlea, which contains nerve fibers that extend to form the auditory nerve. As the vibrations reach the cochlea, they cause the fluid inside the cochlea to move. Sensory cells in the cochlea called hair cells move along with the fluid resulting in the production of electro-chemical signals or nerve impulses. The auditory nerve receives the nerve impulses and sends them to the brainstem. From there the impulses are sent to the midbrain and then to the auditory cortex in the temporal lobes. The temporal lobes organize sensory input and process the auditory information so that the impulses are perceived as sound.
By Regina Bailey
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