Lec 19: Balance and Hearing

Question 1

External and Internal Ears

Answer 1

External & Middle Ear – for hearing only
Internal Ear for balance and hearing

Question 2

External Ear

Answer 2

Portion of the ear that includes the auricle and external acoustic meatus
Terminates at the eardrum

Question 3

Auricle

Answer 3

Part of the external ear that protrudes from the side of the head

Question 4

External Acoustic Meatus

Answer 4

Passageway that leads from the outside of the head to the tympanic membrane of each ear

Question 5

Tympanic Membrane

Answer 5

Also known as the eardrum
Cellular membrane that separates the external from the middle ear (boundary)
Vibrates in response to sound waves

Question 6

Middel Ear

Answer 6

Air-filled space within the temporal bone
Contains auditory ossicles
Between the external and internal ear

Question 7

Auditory Osicles

Answer 7

The three smallest bones in the human body
Contained within the middle ear space
Serves to transmit sounds from the air to the cochlea

Question 8

Pharyngotympanic tube

Answer 8

The tube that runs from the middle ear to the pharynx
Also known as the Eustachian tube.
Protects and drains the middle ear

Question 9

Inner Ear

Bony Labyryinth

Answer 9

Part of the inner ear
Contains the membranous labyrinth that forms the cochlea, vestibule, and semicircular canals
filled with perilymph

Question 10

Inner Ear

Membranous Labyrinth

Answer 10

Membranous structure within the inner ear consisting of the cochlea, vestibule, and semicircular canals
filled with potassium-rich endolymph

Question 11

Vestibule

Answer 11

central cavity of bony labyrinth; contains 2 sacs (utricule and saccule) suspended
in perilymph

monitor head position: they both contain equilibrium receptors called maculae
that respond to the pull of gravity

Question 12

Saccule

Answer 12

leads into the cochlea

Question 13

Utricule

Answer 13

leads into the semicircular canals

Question 14

Semicircular Canals

Answer 14

3 canals that each define two-thirds of a circle and lie in one of the three planes of
space

Question 15

Ampula

Answer 15

is the swollen end of each canal, it houses equilibrium receptors in a region
called the crista ampullaris
Respond to angular head movements

Question 16

Cochlea (defenition)

Answer 16

The auditory portion of the inner ear
Spiral-shaped cavity in the bony labyrinth
The region of the inner ear that is responsible for hearing

Question 17

Cochlea ( 3 chambers)

Answer 17

scala vestibuli – perilymph;
continuous with vestibule & begins at
oval window
* scala media – endolymph; cochlear
duct itself
* scala tympani – perilymph; links to
round window

Question 18

Helicotrema

Answer 18

Opening at the apex of the cochlea through which the scala vestibuli and the scala tympani of the cochlea connect

Question 19

Spiral Ear

Answer 19

Structure located on the inner surface of the basilar membrane of the cochlea containing hair cells that transmit sound vibrations to the nerve fibers within the cochlea
Also called organ of Corti

Question 20

Transmission of Sound to the Inner Ear

Answer 20

 Outer ear – pinna to acoustic meatus to tympanic membrane
 Middle ear – malleus, incus, and stapes to the oval window
 Inner ear – scalas vestibuli and tympani to the cochlear duct
 stimulation of spiral organ and generation of impulses in the cochlear nerve

Question 21

Sound

Answer 21

a pressure disturbance (alternating areas of high and low pressure) originating
from a vibrating object and propagated by the molecules of the medium
* composed of areas of compression and rarefaction that create sound waves
* energy transferred from molecule to molecule in the direction of the sound wave
but will decline with time and distance

Question 22

Frequency =?
Amplitude =?

Answer 22

Frequency of sound waves perceived as pitch; loudness perceived as amplitude

Question 23

Frequency

Answer 23

frequency range of human hearing is 20-20,000 hertz (Hz; waves per second)
* most sensitive to 1500-4000 Hz; can distinguish differences of 2-3 Hz in that range
and perceive them as differences in pitch

Question 24

Amplitude

Answer 24

intensity of sound measured in decibels (dB) – a logarithmic scale, meaning an
increase of 10 dB = 10X increase in sound energy
* loudness is our perception of sound intensity and, interestingly, an increase of 10 dB
is perceived as only about a doubling of loudness
* normal conversation is ~50 dB; noisy restaurant ~70 dB; amplified concert ~120 dB
(prolonged exposure to 90dB considered danger zone for hearing loss)

Question 25

Transmission of Sound to the Internal Ear

Answer 25

sound waves must travel through air, membranes, bones and fluids to
stimulate receptor cells in the spiral organ
* louder sounds cause increased deflection of the tympanic membrane
* only sounds in our hearing range are able to be transmitted through the
cochlear duct, vibrating the basilar membrane and activating the hair cells

Question 26

Basilar Membrane

Answer 26

The part of the membranous labyrinth that borders the scala tympani

Question 27

Sound Transduction

Answer 27

inner hair cells are key; their longest
stereocilia (= hairs; actually microvilli) are
embedded in tectorial membrane; hairs
are connected by fine tip link

Question 28

Movement of the basilar membrane causes:

Answer 28

• bending of hairs → puts tension on tip links
• opens mechanically gated cation channels
  (K+ and Ca++ enter) → receptor potential
• hair cells release NT glutamate to excite
  cochlear nerve
• movement in other direction loosens tip
  links, closes channels → repolarization

Question 29

Outer Hair Cells

Answer 29

Outer row of hair cells that are involved in regulating the tension of the basilar membrane

Question 30

Auditory Pathway

Answer 30

Question 31

Balance

Answer 31

balance organs monitor head movements so we can maintain our orientation ad
balance in space; balance also depends on visual and proprioceptive information

Question 32

Balance Receptors

Answer 32

located in the semicircular canals and the vestibule (utricle and saccule) = vestibular apparatus

Question 33

receptors in vestibule

Answer 33

monitor static equilibrium (linear acceleration & position of head with respect to gravity

Question 34

receptors in semicircular canals

Answer 34

monitor head rotation = dynamic equilibrium

Question 35

Maculae

Answer 35

one macula in each of the utricle and saccule
 each consists of supporting cells and
hair cells
 each hair cell has stereocilia (these are
actually microvilli) and one kinocilium
(true cilium) embedded in the otolithic
membrane

Question 36

Otolithic membrane

Answer 36

Jellylike mass studded
with tiny calcium carbonate crystals called
otoliths

Question 37

Utricular hairs

Answer 37

respond to horizontal
movement or tilting the head (macule is
horizontal, making hairs vertical when head is
upright)

Question 38

Saccular hairs

Answer 38

respond to vertical movement
(macula is nearly vertical meaning that the
hairs extend horizontally into the otolith
membrane

Question 39

What happens at the Level of the Hair Cells?

Answer 39

When you start to move (think of starting to run), the otolithic membrane slides over
the hair cells, bending the hairs; this modifies the amount of NT they release and
either increasing or decreasing it acts as a signal
* When hairs bend toward the kinocilium
* depolarizes vestibular nerve fibers & increases the number of action potentials
* Movement away from the kinocilium:
* hyperpolarizes vestibular nerve fibers & reduces the number of action potentials
* From this information, the brain is informed of the changing position of the head

Question 40

Crista Ampullaris (Crista)

Answer 40

*one in each semicircular canal allowing them to be located in all 3 planes of space
* stimulated primarily by rotational type movements; specifically, changes in velocity
of rotational movements
* support cells plus hair cells whose hairs are extend into a gel-like mass, the cupula
* as with the maculae, movement bends the hairs of the hair cells → signal
* dendrites of vestibular nerve fibers encircle base of each hair cell

Question 41

Comparing Movement of Cupula during a Counter
Clockwise Rotation

Answer 41

Question 42

Equilibrium Pathway to the
Brain

Answer 42

Needs to react quick