Inner Ear
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Inner Ear
A. Bony labyrinth
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- Consists of the acoustic apparatus , the cochlea housing the cochlear duct for auditory sense, and the vestibular apparatus , the vestibule housing the utricle and saccule, and the semicircular canals housing the semicircular ducts for the sense of equilibrium.
- Is the place where vibrations are transduced to specific nerve impulses that are transmitted through the acoustic nerve to the central nervous system (CNS).
- Is composed of the bony labyrinth and the membranous labyrinth.
A. Bony labyrinth
- Consists of three parts: the vestibule, the three semicircular canals, and the cochlea, all of which contain the perilymph , in which the membranous labyrinth is suspended.
- The vestibule is a cavity of the bony labyrinth communicating with the cochlea anteriorly and the semicircular canals posteriorly.
- The bony cochlea consists of two adjacent ducts: (a) the upper scala vestibuli , which begins in the vestibule and receives the vibrations transmitted to the perilymph at the oval window; and (b) the lower scala tympani , which communicates with the scala vestibuli through the helicotrema at the apex of the cochlea and ends at the round window, where the sound pressure waves are dissipated.
- Is suspended in perilymph within the bony labyrinth, is filled with endolymph , and contains the sensory organs.
- Has comparable parts and arrangement as the bony labyrinth.
- Its utricle and saccule are dilated membranous sacs in the vestibule and contain sense organs called maculae , which detect linear acceleration of the head. The macula of the utricle has a horizontal orientation, and the macula of the saccule has a vertical orientation.
- Its semicircular ducts consist of anterior (superior), lateral, and posterior ducts, and their dilated ends are called ampullae , which detect rotational or angular acceleration.
- Its cochlear duct (scala media) is wedged between the scala vestibuli and scala tympani and contains endolymph and the spiral organ of Corti , with receptor cells (hair cells) for auditory stimuli (the sense of hearing).
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