Week 10 - hearing and equilibrium

Question 1

whats the beyond the eardrum (middle ear)

Answer 1

an air filled space connected to the pharynx by the eustachian tube

Question 1

external ear

Answer 1

pinna and the ear canal, sealed at its end by the tympanic membrane or eardrum.

Question 2

inner ear

Answer 2

cochlea for hearing and the
vestibular apparatus for equilibrium.

Question 3

Sound as a wave

Answer 3

At the peaks of the waves, the molecules are crowded together
and the pressure is high; at the troughs the molecules are far apart
and the pressure is low.

Question 4

What do we percieve frequency as

Answer 4

pitch
low frequency as low pitched and high frequency as high pitched

Question 5

frequency

Answer 5

number of waves per second
Hertz

Question 6

human sound range

Answer 6

Humans hear sounds in the range 16–20,000 Hz — ~10 octaves.

Question 7

where is acuity the highest for humans when percieveing sound

Answer 7

Acuity is highest 1000–3000 Hz.

Question 8

amplitude

Answer 8

pressure difference between peak and trough

Question 9

what does loudness depend on

Answer 9

the larger the amplitude, the louder the sound
Loudness depends on frequency as well, e.g. a sound of 30,000
Hz is beyond the range of human hearing, so it won’t be loud no
matter how large its amplitude.

Question 10

what separates outer ear from inner ear

Answer 10

eardrum

Question 11

what does the sound waves vibrate

Answer 11

eardrum

Question 12

how do bones convey vibrations to inner ear

Answer 12

The eardrum vibrates the malleus bone, which moves
the incus , which moves the stapes , which pushes like a piston against the oval window, a membrane between middle and inner ear.

Question 13

ossicles

Answer 13

maleus, incus and stapes
smallest bone sin the body, act as a lever system carrying vibrations from eardrum to much smaller oval window

Question 14

what oval window lead into

Answer 14

cochlea, which contains the receptor cells

Question 15

ducts in cochlea

Answer 15

vestibular, tympanic and cochlear ducts

Question 16

what do the vestibular and tympanic ducts contain and where do they communicate

Answer 16

perilymph (like plasma)
they communicate at helicotrema

Question 17

what the does the cochlear duct contain

Answer 17

endolymph (like intracellular fluid)

Question 18

how does wave wave energy enter and exit

Answer 18

Wave energy enters the cochlea at the oval window and exits,
eventually, back into the middle ear through another membrane
called the round window.
En route, the waves shake the cochlear duct, which contains the
auditory receptor cells (hair cells),

Question 19

what does the cochlear duct contain

Answer 19

organ of corti

Question 20

position of organ of corti

Answer 20

The organ of Corti sits on the basilar membrane and under the tectorial membrane

Question 21

what does organ of corti contain

Answer 21

auditory receptor cells — mech-
anoreceptors called hair cells. They are epithelial cells, not neurons,
and number ~20,000 per cochlea.

Question 22

sterocilia

Answer 22

Each hair cell has 50–100 stiff “hairs” called stereocilia, which extend into the tectorial membrane. They bend when waves in the perilymph deform the basilar and tectorial membranes.

Question 23

what happens when cilia bend towards longest cilium

Answer 23

hair cell excites its neuron
The hair cell depolarizes and releases transmitter, activating a primary sensory neuron.
Axons of these neurons form the auditory nerve (also called the cochlear nerve), a branch of cranial nerve VIII

Question 24

what happens when cilia bends away

Answer 24

The hair cell hyperpolarizes, so it releases less transmitter and
doesn’t excite its neuron as much.

Question 25

The basilar membrane responds to different frequencies
at different points

Answer 25

The membrane is narrow and stiff near the round and oval windows, wider and more flexible at its other end.
High-frequency waves maximally displace the membrane at the oval-window end; low-frequency waves maximally displace the other end. So the brain can deduce the frequency by noting which hair cells
are most active

Question 26

what reveals pitch to the brain

Answer 26

pattern of mebrane motion

Question 27

where is primary auditory cortex

Answer 27

temporal lobe

Question 28

The brain localizes sounds based on loudness
and timing

Answer 28

If a sound is louder in the right ear than in the left then it is coming from the right side of the head. Loudness is conveyed by firing
frequency, i.e. louder sounds make auditory sensory neurons fire at a faster rate.
If the sound reaches the right ear before the left then it is coming from the right side of the head.

Question 29

conductive hearing loss

Answer 29

sound can’t be transmitted through the
external or middle ear.

Question 30

sensorineuronal hearing loss

Answer 30

there is damage to the hair cells or
elsewhere in the inner ear. Mammals can’t replace dead hair cells,
90% of hearing loss in the elderly (presbycusis) is
sensorineural.

Question 31

presbycusis

Answer 31

hearing loss in elderly - sensorineuronal

Question 32

central hearing loss

Answer 32

there is damage to the cortex or the path-
ways from cochlea to cortex. Typically the patient’s trouble is in
recognizing and interpreting sounds, rather than in detecting them.

Question 33

Rinne test

Answer 33

you hold a tuning fork against the mastoid bone
and then beside the ear, and ask when the sound is louder. Normally
it is louder through the ear canal. If it is louder through the bone, there
is conductive loss.

Question 34

Weber test

Answer 34

you hold the tuning fork to the patient’s forehead,
in the midline, and ask in which ear the sound is louder. With
sensorineural loss, it is louder in the good ear. With conductive loss, it
is louder in the bad ear, because it doesn’t have to compete with
sounds heard through that ear canal.

Question 35

what senses head position and motion

Answer 35

vestibular apparatus (utricule and saccule)

Question 36

what do utricule and saccule do

Answer 36

contain hair cells that are activated when
the head tilts relative to gravity

Question 37

what do semicircular canals do

Answer 37

fluid-filled hoops that detect head
rotation, e.g. when your head turns rightward, the fluid in the tubes
sloshes leftward, activating hair cells.

Question 38

Equilibrium pathways project mainly to
the cerebellum

Answer 38

Vestibular hair cells activate primary sensory neurons of the vestibular nerve, which is a branch of cranial nerve VIII.
These neurons may either pass directly to cerebellum or synapse in the medulla, whence they proceed to the cerebellum or up through thalamus to cortex.
Your brain uses vestibular information to infer your own position and motion, and keep you upright.