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The outer, middle, and inner ear work together to transduce sound waves from pressure changes into electrical impulses. LEARNING OBJECTIVE [ edit ] Describe the anatomy of the ear as relates to hearing KEY POINTS [ edit ] The human ear can has three distinct components: the outer ear, which is responsible for gathering sound energy and funneling it to the eardrum; the middle ear, which acts as a mechanical transformer; and the inner ear, where the auditoryreceptors are located. The outer ear consists of the visible part of the ear (or pinna), the external auditory canal (meatus), and the tympanic membrane (tympanum) or eardrum. The human pinna is formed primarily of cartilage and is attached to the head by muscles and ligaments; the deep central portion of the pinna is called the concha, which leads into the external auditory canal. The middle ear cavity is air-filled while the inner ear is fluid-filled; if sound waves were to impinge directly on the oval window, the membrane would barely move. The inner ear includes the semicircular canals, the vestibule, and the cochlea, which contains receptors for transduction of the mechanical wave into an electrical signal. The inner hair cells are most important for conveying auditory information to the brain. TERMS [ edit ] cochlea the complex, spirally coiled, tapered cavity of the inner ear in which sound vibrations are converted into nerve impulses ossicle a small bone (or bony structure), especially one of the three of the middle ear transduce to convert energy from one form to another Give us feedback on this content: FULL TEXT [edit ] Transduction of Sound In order to hear a sound, the auditory system must accomplish three basic tasks. First it must deliver the acoustic stimulus to the receptors; second, it must transduce the stimulus from pressure changes into electrical signals; and third, it must process these electrical signals (via nerve impulses), sending them to the brain so that they can efficiently Register for FREE to stop seeing ads indicate the qualities of the sound source such as pitch, loudness, and location. How the auditory system accomplishes these tasks is acomplex process. The human ear can be divided into three fairly distinct components according to both anatomical position and function: the outer ear, which is responsible for gathering soundenergy and funneling it to the eardrum; the middle ear, which acts as a mechanical transformer; and the inner ear, where the auditory receptors (hair cells) are located. Structure and Function The human ear is a complicated machine . The outer ear consists of the visible part of the ear (or pinna), the external auditory canal (meatus), and the tympanic membrane (tympanum) or eardrum. The human pinna is formed primarily of cartilage and is attached to the head by muscles and ligaments. The deep central portion of the pinna is called the concha, which leads into the external auditory canal; this, in turn, leads to the tympanic membrane. Diagram of the ear The ear can be broken up into three distinct sections: the outer ear, the middle ear, and the inner ear. Each section has its own complex functions that aid in transmission of sound via nerve impulses to our brains for processing. Vibrating objects, such as vocal cords, create sound waves or pressure waves in the air. When these pressure waves reach the ear, the ear transduces this mechanical stimulus (pressure wave) into a nerve impulse (electrical signal) that the brain perceives as sound. The pressure waves strike the tympanum, causing it to vibrate. The mechanical energy from the moving tympanum transmits the vibrations to the three bones of the middle ear. The stapes transmits the vibrations to a thin diaphragm called the oval window, which is the outermost structure of the inner ear. Why must vibrations of the tympanic membrane be transmitted via the ossicle chain and not simply transferred directly? The reason is that the middle ear cavity is air-filled while the inner ear is fluid-filled. If sound waves were to impinge directly on the oval window, the membrane would barely move. Most of the sound would be reflected back because the fluid in the inner ear is denser than air and resists being moved much more than air does. Consequently, in order to drive the movement of the oval window and vibrate the fluid, greater pressure is needed. The inner ear can be divided into three parts: the semicircular canals, the vestibule, and the cochlea, all of which are located in the temporal bone. The semicircular canals and the vestibule affect the sense of balance and are not concerned with hearing. However the cochlea, and what goes on inside it, provides the key to understanding many aspects of auditory perception. The inner ear The inner ear can be divided into three parts: the semicircular canals, the vestibule, and the cochlea, all of which are located in the temporal bone. The structures of the inner ear are found in the labyrinth, a bony, hollow structure that is the most interior portion of the ear. Here, the energy from the sound wave is transferred from the stapes through the flexible oval window and to the fluid of the cochlea. The vibrations of the oval window create pressure waves in the fluid (perilymph) inside the cochlea. The cochlea is a whorled structure, like the shell of a snail. It contains receptors for transduction of the mechanical wave into an electrical signal . Inside the cochlea, the basilar membrane is a mechanical analyzer that runs the length of the cochlea, curling toward the cochlea's center. Transduction In the human ear, sound waves cause the stapes to press against the oval window. Vibrations travel up the fluidfilled interior of the cochlea. The basilar membrane that lines the cochlea gets continuously thinner toward the apex of the cochlea. The tube of the cochlea is divided into three chambers: the scala vestibuli, the scala media (or cochlear duct), and the scala tympani. The three scalae wrap around inside the cochlea like a spiral staircase (‘scala' is Latin for ‘stairway'). The scala vestibuli forms the upper chamber; at the base of this chamber is the oval window. The lowermost of the three chambers is the scala tympani. It too has a basal aperture, the round window, which is closed by an elastic membrane. The scala media, or cochlear duct, separates the other two chambers along most of their length. Higher Processing The inner hair (auditory) cells are most important for conveying auditory information to the brain. They are indirectly anchored to the basilar membrane. About 90 percent of the afferentneurons carry information from inner hair cells, with each hair cell synapsing with 10 or so neurons. Outer hair cells connect to only 10 percent of the afferent neurons; each afferent neuron innervates many hair cells. The afferent, bipolar neurons that convey auditory information travel from the cochlea to the medulla, through the pons and midbrain in the brainstem, finally reaching the primary auditory cortex in the temporal lobe.