Exam 4 Review:  Chapter 15:  Inner Ear - Hearing

inner ear - The portion of the ear, a complex system of interconnecting cavities, located within the petrous part of the temporal bone which is involved in both hearing and balance/equilibrium and includes the semicircular canals, vestibule, and cochlea; structurally it consists of the membranous labyrinth which is housed in the bony labyrinth.

bony labyrinth* - The cavity in the petrous part of the temporal bone which houses and protects the membranous labyrinth of the inner ear.

membranous labyrinth* - The fluid-filled membranous sacs of the inner ear which are associated with the senses of hearing and balance/equilibrium; includes the semicircular canals, vestibule, and cochlea; housed in the bony labyrinth in the petrous part of the temporal bone; pressure waves in the endolymph fluid within this structure are detected by mechanoreceptors in the transduction of sensory stimuli related to hearing (in the cochlea) and to equilibrium (in the vestibule and semicircular canals).

endolymph - The fluid, a plasma filtrate, in the membranous labyrinth of the inner ear; pressure waves in this fluid are detected by mechanoreceptors in the transduction of sensory stimuli related to hearing (in the cochlea) and to equilibrium (in the vestibule and semicircular canals).

perilymph - The fluid, a plasma filtrate, which surrounds the membranous labyrinth of the internal ear, and separates it from the walls of the chambers in which the labyrinth lies; the scala tympani and scala vestibuli of the cochlea contain perilymph; pressure waves in this fluid are detected by mechanoreceptors in the transduction of sensory stimuli related to hearing (in the cochlea).

[*Note:   labyrinth = a maze.]

Identify and describe:

 

1. the location and specific sites, including cellular components, for reception and transduction for the sensations of:

 

(d) hearing:  mechanoreceptors (basically all of one type), the stereocilia and kinocilia, of the inner row of cochlear hair cells located within the spiral organ (of Corti) within the cochlea.


List and describe:
 

4. the sequence of components and physiological events in transduction of hearing.

 

There are two components to the transduction of hearing.  First, the sound vibrations in air must be converted to fluid vibrations within the endolymph of the scala media = cochlear duct.  In this first sequence of events, mechanical energy is merely transferred from one structure to the next, before actual transduction can occur.
1.  mechanical vibrations (sound waves) strike the tympanic membrane, causing it to vibrate.
2.  the vibrations of the tympanic membrane cause the malleus (hammer) to vibrate.
3.  the vibrations of the malleus (hammer) cause the incus (anvil) to vibrate.   
4.  the vibrations of the incus (anvil) cause the stapes (stirrup) to vibrate.   
5.  the vibrations of the stapes (stirrup) cause the membrane of the oval window to vibrate.   
6.  the vibrations of the oval window cause fluid vibrations which cycle back and forth through the perilymph of the scala vestibuli and scala tympani.   
7.  the back-and-forth vibrations within the perilymph cause some portion of the vestibular and basilar membranes lining the cochlear duct to vibrate; the specific region along the cochlear duct which responds depends on the frequency of the vibrations.
8.  the vibrations of some portion of the vestibular and basilar membranes lining the cochlear duct cause fluid vibrations in the endolymph of the scala media = cochlear duct.
9.  the vibrations in the endolymph of the scala media = cochlear duct are at right angles (perpendicular) to the back-and-forth vibrations within the perilymph.
10.  the vibrations in the endolymph of the scala media = cochlear duct cause vibrations in the tectorial membrane of the spiral organ (of Corti) in a specific region; the specific region along the spiral organ (of Corti) which responds depends on the frequency of the vibrations.
In the second sequence of events, mechanical energy is transducted into nerve impulses.
1.  vibrations in the tectorial membrane of the spiral organ (of Corti) in a specific region mechanically stimulate the stereocilia (mechanoreceptors) of specific cochlear hair cells of the spiral organ (of Corti).
2.  the movement of the stereocilia (mechanoreceptors) of specific cochlear hair cells opens gated potassium and chloride ion channels on the cochlear cell membrane and alters the cell's membrane resting potential.
5.  the resulting ion flows opens additional gated calcium ion channels.
6.  depolarization and increased intracellular calcium ion levels causes neurotransmitter release to the associated dendrites of the afferent sensory cochlear nerve fibers.
7.  the effect of the neurotransmitter (probably glutamate) generates an action potential = nerve impulse which is transmitted to the CNS.