Lecture 22 Auditory 1

Question 1

Are each of the following parts of the ear air-filled or fluid-filled: external, middle, inner ear?

Answer 1

external (air) middle (air) inner (fluid filled)

Question 2

What two nerves come together to form CN VIII?

Answer 2

vestibular and cochlear nerves (innervate hair cells

Question 3

Which parts of the branchial arches come together to form the ear (external, middle and inner)

Answer 3

the first branchial cleft and the 1st branchial pouch between arch 1 and arch 2 (separated by the ear drum)

Question 4

The bones of the ear are formed from which brachial arches?

Answer 4

cartilage from BA 1 forms the malleus and incus, cartilage from BA 2 forms the stapes

Question 5

What developmental material forms the membranous labyrinth?

Answer 5

the otic placode (thickening of surface ectoderm) invaginates to form the otic pit which is later innervated by CN VIII

Question 6

What nerves (off which branches) serve the sensory innervation of the outer ear?

Answer 6

auriculotemporal n. (branch of mandibular branch V3), greater auricular n. (branch of the cervical plexus), Arnolds/ Alderman’s nerve (branches of CN VII, CN X) (can contribute to coughing or gagging when ear is stimulated)

Question 7

Sensory to the ear via VII and X use which nucleus in the brain?

Answer 7

trigminal chief and spinal nuclei of V

Question 8

Describe the different sources of ear drum innervation (complicated).

Answer 8

outer surface (V3, VII and X) inner surface (IX)

Question 9

What would you expect to see on the outside surface of the ear drum?

Answer 9

cone of light (in the down and front position), imprint of the incus

Question 10

What is sound?

Answer 10

Sound is a mechanical disturbance propagated through an elastic medium (wave disturbance that transfers progressively in space

Question 11

What are two ways that the period of a wave can be measured?

Answer 11

length of the period in time (Hz = cycles/sec) or space (wavelength=meters) BONUS: pure tone sounds are sinusoidal

Question 12

Decibel system is calculated in a _____ scale and the calculation is made in relation to P2 which is a reference sound based on what?

Answer 12

logarithmic; P2 is a reference for 0 dB, it is generally considered the threshold of perceivable sound

Question 13

Is hearing sensitivity the same over all frequencies? explain.

Answer 13

hearing sensitivity is not the same at all frequencies, it is best in the speech frequency range

Question 14

What is the general range of Hz a human can generally detect?

Answer 14

20 Hz- 20,000 Hz— means sensing sounds 1,000,000x louder than the slightest tone perceivable

Question 15

The external auditory meatus is contained with a cranial bone, which?

Answer 15

temporal bone

Question 16

Describe the orientation of the tympanic membrane.

Answer 16

it faces down and in front of the ear

Question 17

The middle ear is open to the outer would via which opening

Answer 17

the auditory/ eustachian tube opens into the nasopharynx

Question 18

Name the three membranes of the middle ear.

Answer 18

tympanic membrane, oval window and round window

Question 19

Describes the two muscle found in the middle ear.

Answer 19

tensor tympani (CNV) attaches to the malleus and to the anterior wall of the middle ear; and the stapedius (CN VII) attaches to the stapes and the posterior middle ear

Question 20

What caries the sensory innervation to the middle ear?

Answer 20

tympanic branch of the petrosal nerve (CNIX) while salvation parasympathetics continue on BONUS: VII passes through in a canal behind the middle ear and exits through the stylomastoid foramen

Question 21

What is the function(s) of the middle ear bones?

Answer 21

amplify and transfer the of sound from the air to the fluid of the inner ear (the area of the drum is 21 times greater than the area of the oval window

Question 22

Describe the general structure the inner ear.

Answer 22

the bony ducts surround the membranous ducts inside includes the hair cells (the vestibular part, the membranous ducts are against the walls, while in the cochlear part of the membranous divide the bony ducts

Question 23

What three ducts does the membrane divide the chochlea into?

Answer 23

Scala vestibuli, the scala media and the scala tympani

Question 24

Describe the membranous borders of the scala media.

Answer 24

Reissner’s membrane and the basilar membrane (contains the hair cells) both connect to the bony lip of the labyrinth

Question 25

What membrane lays over the top of the hair cells?

Answer 25

the tectorial membrane

Question 26

Describe the path of the fluid filled cochlea.

Answer 26

stapes moves the oval window at the base of the cochlea, fluid moves as wave course toward the apical part of the cochlea in the scala vestibuli and through the helicotrema before coursing back down through the scala tympani to the basal side to the round wind. movement of waves causes a pressure differential

Question 27

Describe how the basalar membrane changes changes from base to apex.

Answer 27

base has a narrow and stiff basilar membrane and the apex has a wide and floppy membrane (low frequency)

Question 28

Describe how the motion of the basalar membrane move and how that relates to opening mechanoreceptors

Answer 28

their movement is not purely up and down, there is some shear movement between the membranes which can cause the bending of hair cells

Question 29

How are hair cells activated?

Answer 29

when cilia bend toward the largest cilia, tip links connecting the cilia pull open K+ channels causing depolarization, Ca2+ entry and transmitter release, activating auditory nerve fibers

Question 30

Contrast the functions of outer and inner hair cells.

Answer 30

IHCs carry auditory info to CNS, OHC seem to function to amplify the signal and their motility play an important role in the sharp sensitivity of basilar membrane (push back on membrane), OHC also get feedback on motility from the brainstem

Question 31

What is an otoacoustic emission?

Answer 31

sounds that are generated as a byproduct of the electro-motile vibrations produced by outer hair cells (can be monitored)

Question 32

Describe the fluid that is contained in the scala media.

Answer 32

endolymph is hi in K+ and low in Ca++

Question 33

T/F Only part of the length of the basilar membrane vibrates maximally

Answer 33

true, only part of the basilar membrane will be activated maximally (tonotopic organization)