Lecture 8

Question 1

What is the conduction pathway sequence in auditory canal?

Answer 1

Tympanic membrane to auditory ossicles (malleus, incus, stapes) to oval window

Question 2

Malleus (Hammer)

Answer 2

Attaches to the tympanic membrane; so named because it articulates with the “anvil”

Question 3

Incus (Anvil)

Answer 3

Intermediate bone between the stapes and the malleus; incus refers to the “anvil”, on which the hammer strikes

Question 4

Stapes

Answer 4

Third bone in the series; so named because it is shaped like a stirrup due to the opening for the stapedial artery; inserts onto the oval window

Question 5

Oval Window

Answer 5

Stapes attaches to the membrane covering the oval window; oval window opens into the scala vestibuli

Question 6

Round Window

Answer 6

This membrane covered region is at the end of the scala tympani

Question 7

Tensor Tympani

Answer 7

Inserts on the malleus and pulls handle of malleus inward; retract reflexively in response to loud sounds in order to dampen the vibrations of the auditory ossicles

Question 8

Stapedius

Answer 8

Inserts on the stapes and pulls stapes outward; retract reflexively in response to loud sounds in order to dampen the vibrations of the auditory ossicles

Question 9

Impedance Matching

Answer 9

Tympanic membrane surface area is about 17 times that of the surface area of the stapes; this increases the force from the ossicular lever system to the cochlear fluid by 22x; fluid has greater inertia than air and requires this increase in force in order to cause vibration in the fluid

Question 10

What makes up the cochlea?

Answer 10

Scala vestibuli, scala media, scala tympani, and reissner’s membrane (vestibular membrane)

Question 11

Reissner’s Membrane (Vestibular Membrane)

Answer 11

Separates scala media from scala vestibuli

Question 12

Basilar Membrane

Answer 12

Separates scala media from scala tympani; contans fibers that project from the modiolus of the cochlea to the outer wall; distal ends are not fixed but are embedded in the basilar membrane; fibers can vibrate

Question 13

Basilar Fibers

Answer 13

Length increases from the oval window to the apex of the cochlea (helicotrema); diameter of the fibers decrease from oval window to the apex of the cochlea; as a result, stiff, short fibers near the oval window beat at a high frequency and long, limber fibers near the apex of the cochlea vibrate at a low frequency

Question 14

Organ of Corti

Answer 14

Generates nerve impulses in response to vibration of basilar membrane; hair cells stimulate nerve fibers that lead to the spiral ganglion of Corti; stereocilia from the hair cells touch or are embedded in the overlying tectorial membrane; bending of the hairs in one direction depolarizes them and bending them in the opposite direction hyperpolarizes them

Question 15

What is the scala media filled with?

Answer 15

Endolymph (high concentration of potassium and low concentration of sodium)

Question 16

What is the scala vestibuli and scala tympani filled with?

Answer 16

Perilymph (low concentration of potassium and high concentration of sodium)

Question 17

Place Principle

Answer 17

Nervous system detects sound frequencies by determining positions along the basilar membrane that are most stimulated

Question 18

Components of the Nervous System Pathway

Answer 18

Spiral organ of corti, dorsal and ventral cochlear nuclei, superior olivary nucleus, lateral lemniscus’ nucleus, medial geniculate nucleus (thalamus), and auditory cortex