BPK 105 Study Guide - Midterm Guide: Vestibular Duct, Cochlear Duct, Basilar Membrane
27 Apr 2018
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Module 5 - Review Questions - Part 5
9. Describe how a wave in the perilymph fluid of the cochlea leads to an electrical signal
in the cochlear nerve. Include relevant anatomical details. How do we distinguish that a
sound is either loud or soft? High pitched or low pitched? [6 marks]
The cochlea: shaped like a snail shell (figure 9.18a
) and contains a bony core shaped like a
screw.
The cochlea is divided into three channels: the scala vestibuli, the scala tympani, and the
cochlear duct (figure 9.18b
).
The cochlear duct is formed by the space between the vestibular membrane and the basilar
membrane and is filled with endolymph.
-Vibrations of the base of the stapes produce waves in the perilymph of the
cochlea.
- The waves pass through the vestibular membrane and cause vibrations of the
endolymph.
- Waves in the endolymph cause displacement of the basilar membrane.
- As the basilar membrane is displaced, the hair cells, seated on the basilar membrane,
move with the movements of the membrane.
- Because one end of the microvilli moves with the hair cells and their other ends are
embedded in the nonmoving tectorial membrane, the microvilli bend.
- The bending of the microvilli stimulates the hair cells, which induces action potentials in
the cochlear nerves (figure 9.19, steps 5–6).
- sounds with higher pitches cause maximum distortion of the basilar membrane nearer
the oval window, whereas sounds with lower pitches cause maximum distortion nearer
the apex of the cochlea.
- In each case, different hair cells are stimulated, and because of the differences in which
hair cells are maximally stimulated, a person is able to detect variations in pitch.
- Sound volume is a function of sound wave amplitude, which causes the basilar
membrane to distort more intensely and the hair cells to be stimulated more strongly.
Loud (high-amplitude) sounds cause the basilar membrane to vibrate more vigorously than soft
(low-amplitude) sounds.
10. Define static equilibrium and describe the structure and function of the components
of the inner ear that determine it. [4 marks]
Static equilibrium evaluates the position of the head relative to gravity.
Document Summary
Module 5 - review questions - part 5: describe how a wave in the perilymph fluid of the cochlea leads to an electrical signal in the cochlear nerve. The cochlea: shaped like a snail shell (figure 9. 18 a ) and contains a bony core shaped like a screw. The cochlea is divided into three channels: the scala vestibuli, the scala tympani, and the cochlear duct (figure 9. 18 b ). The cochlear duct is formed by the space between the vestibular membrane and the basilar membrane and is filled with endolymph. Vibrations of the base of the stapes produce waves in the perilymph of the cochlea . The waves pass through the vestibular membrane and cause vibrations of the endolymph . Waves in the endolymph cause displacement of the basilar membrane. As the basilar membrane is displaced, the hair cells, seated on the basilar membrane, move with the movements of the membrane.
