Anatomy of Hearing Including Ear Structures and Brain Structures

Anatomy of Hearing including Ear Structures and Brain Structures

The ear, an organ for hearing and balance, is anatomically divided into three sections: the outer ear, the middle ear, and the inner ear (Henderson). Each section contains many distinct parts that assist in the task of detecting and interpreting sound which is otherwise known as hearing (Henderson).

The outer ear is composed of the auricle (pinna) and the external auditory canal (ear canal) (Sisco). The outer ear functions to catch sound waves and funnels them through the ear canal to the middle ear (Inner body). A sound wave, also known as a pressure wave, is a “repeating pattern of high pressure and low pressure regions moving through a medium” (Henderson). The human ear is capable of hearing sound waves 20-20,000 Hz (PATTS). The cartilage skin flap that is most externally visible is known as the pinna (Innerbody). The pinna, besides helping to catch sound waves, provides protection for the ear canal and ear drum (Henderson). When many people think of the ear they think of it as only the pinna. The pinna leads to the external auditory canal (Innerbody). The ear canal narrowing at the middle and widening just before the ear drum, acts as a tunnel for sound waves (CCENT). The external auditory canal is approximately 1 inch long and contains cerumen (ear wax) (Innerbody). Glands within the ear secrete the cerumen, which acts as a protectant against bugs and bacteria (CCENT). Although too much cerumen in the ear canal can block transmission of sound, doctors discourage the manual cleaning of the ear canal (CCENT).

The middle ear is an air-filled cavity consisting of the ear drum, three tiny ossicles known as the malleus, incus and stapes, and the eustachian tube (Sisco). The middle ear serves to transmit pressure waves into mechanical vibrations (PATTS). The middle ear is separated from the outer ear by the tympanic membrane (ear drum.)(Hope).The ear drum is about 1/3” in diameter, gray in color, and is attached to the external auditory canal(Sisco). “The eardrum is a very durable and tightly stretched membrane which vibrates as the incoming pressure waves reach it…..compression forces the eardrum inward and a rarefaction forces the eardrum outward, thus vibrating the eardrum at the same frequency of the sound wave.” (Henderson). “The eustachian tube, which opens into the middle ear, is responsible for equalizing pressure between the air outside the ear to that within the middle ear” (CCENT). The movement of the eardrum in turn creates the ossicles, whose functioning is to “create mechanical linkages between the tympanic membrane and the inner ear“, to act as a “lever system” and convert the sound to mechanical waves (Sisco). The malleus, incus and stapes move at the same frequency of the sound wave (Henderson). The malleus is hammer-shaped, has a round head and connects to the tympanic membrane (Sisco). The place of connection is called the umbo (Sisco). The incus is a small bone between the malleus and the stapes (innerbody). The round head of the malleus rests on the incus, which in turn rests on the stapes until vibrations occur (Sisco). The stapes, which as a result of vibrations, and the functioning of the lever system, moves in and out of the oval. “Vibrations are transmitted to the hammer, through the anvil, to the stirrup, thus transmitting airborne acoustic energy to the fluid of the inner ear”(Hope).

The inner ear consists of the round window, oval window, cochlea (with the Organ of Corti), and the auditory nerve which all function to analyze sound waves. The round window connects the middle ear with the lower half of the cochlea and the oval window connects the middle ear with the upper half (Sisco). Both the oval and round windows are membranes (Sisco). The round window’s function is to “aid fluid motion within the cochlea”