![]() The Organ of Corti resides on the basilar membrane inside the scala media. Waves from these regions press against and transmit wave energy to the scala media through the basilar membrane (within the floor of the scala media). Oscillation of the oval window induce waves through the scala tympani and then scala vestibule of the cochlea. Between these fluid-filled areas is the scala media (Figure 1B). ![]() ![]() It is continuous with the scala vestibule (lining the inner portion of the cochlea) at the helicotrema. The scala tympani lies within the outer portion of the cochlea. In cross-section, each aspect of the cochlea has 3 sections: the scala tympani, scala vestibule, and scala media (Figure 2). The cochlea is a fluid-filled (perilymph) structure that spirals 2 ½ turns around a central pillar (modiolus). This conversion occurs within the cochlea of the inner ear. Within the cochlea, mechanical energy converts to electrical energy by auditory receptor cells (hair cells). The 3 middle ear bones amplify this energy and transfer it into the cochlea. Movement of the tympanic membrane initiates vibration of 3 small bones within the middle ear: the malleus, incus, and stapes which transfer the vibration to the inner ear at the oval (vestibular) window (Figure 1A). Contact between the eardrum and environmental pressure waves causes movement of the membrane. Sound waves reach the outer ear and travel down the external acoustic meatus to reach the eardrum (tympanic membrane). Humans typically hear within a frequency range of 20-20,000 Hz. We measure frequency in Hertz (Hz cycles of compression and rarefaction per second). The number of periods of compression and rarefaction within a specified amount of time is the frequency of a specific sound. This causes increases and decreases in pressure (i.e., alternating compression and rarefaction) of air within the environment. Energy waves travel through a medium by moving molecules. Peripheral Auditory System: How sound reaches the brain.
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