Chp 53 The Sense of Hearing

Question 1

Define the characteristica of the Ear

Answer 1

• Hearing, balance
• contains 3 parts:
  1. outer, middle, inner
• the eardrum seperates the outer ear from the air-filled tympanic cavity of the middle year
• middle ear contains 3 small bones:
  1. The Ossicles-involved in the transmission of sound, and is connected to the throat at the nasopharynx via the pharyngeal opening of the Eustachian tube.
• The inner ear contains the:
  1. otolith organs, utricle, saccule, semicircular, canals belonging to the vesitbular system
  2. Cochlea belongs to the auditory system

Question 2

what are the outer ear elements?

Answer 2

1. Pinna:
   - slightly emphasize sound frequencies in range of 1500-7000 Hz and aids in the localization of sound source
2. External Auditory Canal:
   - extends inward through the temporal bone, lined by wax secreting glands and sealed with the tympanic membrane (eardrum)

Question 3

Name the Middle ear elements :

Answer 3

1. air filled cavity: 2ml volume
2. located in the mastoid region of the temporal bone
3. connected with Pharynx by the Eustachian tube
4. 3 small bones (ossicles): the malleus (hammer), incus (anvil), stapes (stirrup)
5. Suspensory ligament
6. two small muscles:
   - Tensor Tympani muscle
   - Stapedius muscle

with the head of the malleus to the third bone

Question 4

Eustachian tube is responsible for?

Answer 4

allowing equalization of the pressure on either side of eardrum

Question 5

Describe the Inner ear elements and its function:

Answer 5

1. it is responsible for actual process of sound transduction
2. the auditory structures are located in the Cochlea (snail shell) the part of the cavity in the temporal bone called the “Bony labyrinth” filled with fluid: Perylimph (high sodium-low in potassium) and Endolymph (high in Potassium and low in Sodium)

Question 6

Define Cochlea

Answer 6

-embedded in a bony cavity in the temporal bone called the Bony Labyrinth, vibrations of the entire skull can cause fluid vibrations in the coachlea itself

Question 7

functional anatomy of Cochlea

It consists of 3 tubes coiled side by side

Name the 3 Tubes:

Answer 7

(1) the scala vestibuli,
(2) the scala media,
(3) the scala tympani.
- The scala vestibuli and scala media are separated from each other by Reissner’s membrane (also called the vestibular membrane),
- the scala tympani and scala media are separated from each other by the basilar membrane.
- On the surface of the basilar membrane lies the organ of Corti, which contains a series of electromechanically sensitive cells, the hair cells.
- They are the receptive end organs that generate nerve impulses in response to sound vibrations.

Question 8

What is the function of Organ of Corti:

Answer 8

1. Organ of Corti lies on the surface of the basilar fibers and basilar membrane.

-is the Key to Auditory Trasduction!!

2. The actual sensory receptors in the organ of Corti are 2 specialized types of nerve cells called hair cell
3. a single row of internal (or “inner”) hair cells, numbering about 3500 and measuring about 12 micrometers in diameter, and three or four rows of external (or “outer”) hair cells, numbering about 12 000 and having diameters of only about 8 micrometers

Question 9

Describe the Auditory Pathway :

Answer 9

1. Nrv. Fbrs from the spinal ganglion of corti entere the dorsal and ventral conchlear nuclei located in the uppere par of medulla
2. at this point all of the fibers synapse and second-order neurons pass mainly to the opposidte side of the brain stem to terminate in the superior olivery nucleus
3. from the superior olivary nucleus, the auditory pathway pass upward through the lateral lemniscus
4. some of the fibers terminate in the nucleus of the later lemniscus, some bypass nucleus and travel on to the inferior colliculus where all or almost all the auditor fibers synapse
5. from there teh patway ass to the medial geniculate nucleus where all the fivers synapse
6. Finally, the pathway proceeds by way of the auditory radiation to the auditory cortex, located mainly in the superior gyrus of the temporal lobe

Question 10

What part of the Inner Ear transforms sound waves into electrical impulses ?

Answer 10

The part of the inner ear that transforms sound waves into electrical impulses is the cochlea.

Question 11

Describe Cochlea and its function

Answer 11

The cochlea is a snail-shaped structure that coils around a bony axis called the modiolus.

Question 12

cochlea has an outer bony shell that contains a fluid called _______.

Answer 12

The cochlea has an outer bony shell, that contains a fluid called perilymph.

Question 13

Inside the bony shell, there is a membranous duct called the cochlear duct - which contains a fluid called?

Answer 13

endolymph.

Question 14

the Cochlea is actually made up of three fluid-filled tubes - arranged one above the other:

Name them:

Answer 14

1. Above - scala vestibuli
2. Middle- cochlear duct - (or scala media)
3. Below- scala tympani

Question 15

Explain how scala vestibuli and scala tympani are able to communicate with each other?

Answer 15

The cochlear duct ends right below the tip of the cochlea, leaving an opening called the helicotrema right above - so the scala vestibuli and the scala tympani communicate with each other through the helicotrema.

Question 16

What type of Memebrane is both flexible and allows the motion of sound waves to travel from the perilymph and transmit into the endolymph.

Answer 16

vestibular membrane

Question 17

The motion of sound waves travels from where to where ?

Answer 17

travels from the perilymph and transmit into the endolymph.

Question 18

The spiral ligament is covered by a specialized epithelium called the _____ ____ that secrete the endolymph into the cochlear duct.

Answer 18

stria vascularis

Question 19

What type of cells pump potassium ions into the endolymph…. making it a fluid with high potassium concentration.

Answer 19

marginal cells

Question 20

What lies above Basilar Memebrane and is the key to Audiotry Transductin?

Answer 20

Organ of Corti

Question 21

_______ is the # of waves per unit time…

Answer 21

Frequency

Question 22

________ refers to the distance between two consecutive wave crests.

Answer 22

wavelength

Question 23

Sounds with _______ _______ (so more waves per unit time) have a shorter wavelength, and we perceive them as high pitch - like your voice on Helium.

Answer 23

higher frequencies

Question 24

Sounds with ______ ________(so less waves per unit time) have longer wavelengths, and we perceive them as low pitch - like a whale’s call.

Answer 24

lower frequencies

Question 25

define amplitude:

Answer 25

height of the wave, and we interpret it as loudness.

Question 26

The vibration of the basilar membrane stimulates what?

Answer 26

organ of Corti

Question 27

the organ of Corti is stimulated by?

Answer 27

stimulated by the vibration of the basilar membrane.

Question 28

The _______ ______ is a layer of tissue, that’s as long as the cochlear duct itself.

On cross-section, it’s made up of ________ cells called _____ ______ , that have 30 to 300 finger-shaped projections called the stereocilia - which are like hair - on the top or apical end.

Answer 28

organ of Corti

mechanosensory cells

hair cells

Question 29

T or F

he hair cells are arranged in rows, one row of inner hair cells - closer to the modiolus, and three to five rows of outer hair cells - closer to the spiral ligament.

Answer 29

True

Question 30

Inner hair cells are innervated mainly by ____ ____ fibers

-they are incharge of what?

Answer 30

sensory nerve fibers

Auditory transduction.

Question 31

Outer hair cells are innervated mainly by ____ ______ fibers that carry signals ___ ___ brain, and they contract and stretch in response to these signals - which changes the stiffness of the ____ _____in order to intensify or minimize the auditory signal

Answer 31

motor nerve fibers

from the brain

basilar membrane

Question 32

Explain what happens when the hair cells move towards the tectorial membrane?

The potassium concentration is higher in the _______than inside the cells, so when the potassium channel opens, potassium ions enter the hair cell in the apical end, and the cell membrane _______

Answer 32

the shorter stereocilia bend towards the longer ones opening the potassium channels.

endolymph

depolarizes.

Question 33

What type of memebrane can be found at the basal end , which is also close to ______ nerve?

Answer 33

presynaptic membrane

cranial nerve

Question 34

Describe what happens when Depolarization takes place and Calcium Ions are released:

Answer 34

Depolarization goes all the way through the cell from the apical membrane to the presynaptic membrane, where it causes voltage-gated calcium channels to open.

Calcium ions then enter the cell and that triggers vesicles in the cytoplasm that are filled with glutamate (neurotransmitter) to be released into the synaptic space.

Question 35

What happens “After the Glutamate is release into the synaptic space”?

Answer 35

Dendrites of neurons that form the auditory nerve, interpret glutamate as a “go go go” signal, and depolarize, sending an electricalimpulse to the brain.

Question 36

Describe Inner Hair cells and what are they responsible for ?

Answer 36

• Responsible for Sensory Auditory Transduction
• They are arranged in Rows
• One row of hair cells closer to the Medialis
• innervated by sensory nerve fibers

Question 37

What makes up the Organ of Corti Structures?

Answer 37

Organ of Corti is made up of Mechanosensory Hair Cells: have 30-300 Stereocilia

Basal end of the cell = Presynaptic memebrane (close to the Cranial Nerve)

Question 38

Describe the Outer Hair cells and what innervates them?

Answer 38

• there are 3 to 5 rows of Outer hair cells: closer to the Spiral Ligament
• Innervated by the Motor Nerve Fibers that carry signals from the Brain

-They Contract and Stretch in response to Signals changing the stiffness of the basilar membrane inorder to intensify or minimize the auditory signal

Question 39

What happens once the Neurons of the Auditory Nerver Depolorize ?

Answer 39

Once the neurons of the auditory nerve depolarize, their axons head towards the brainstem.

1. First, they enter the medulla on the same side of the body and synapse with neurons in the cochlear nuclei.
2. From the cochlear nuclei, the electric impulse follows three different paths:

Question 40

From the cochlear nuclei, the electric impulse follows three different paths:

Name the 3 paths of electric impulse

Answer 40

1. the electric impulse crosses over and goes up to the inferior colliculus of the midbrain on the opposite side of the body.
2. the impulse also crosses over and goes up to the superior olivary nuclei of the pons on the opposite side of the body.
3. third path goes straight to the superior olivary nuclei on the same side of the body.

Then, from each superior olivary nuclei the impulse goes up to the inferior colliculus of the midbrain on the same side.

Finally, from each inferior colliculus, the electric impulse goes to the medial geniculate nucleus of the thalamus, that sends the impulse to the auditory cortex in the temporal lobe—which include Brodmann’s areas 41 and 42.

Question 41

Ear contains the ____ of ______, which is responsible for transforming sound waves into _______.

Answer 41

organ of Corti,

electricalimpulses.

Question 42

The organ of Corti sits on what type of Memebrane, which - is “tuned” to different frequencies in different regions - called a _____ _____.

Answer 42

The basilar membrane

tonotopic map.

Question 43

What specifically causes stereocilium of specific hair cells to bend, depolarize the cell and convert sound waves into Elecrical impulses?

Answer 43

specific frequencies

Question 44

Name the Auditory Pathway of the Electrical impulses:

(x5)

Answer 44

Electrical impulses follow the auditory pathway:

1. passing through the cochlear nuclei
2. superior olivary nuclei
3. inferior colliculi
4. thalamus
5. finally reaching the auditory cortex where sound is finally interpreted

Question 45

How many Tonotopic maps have been found in the Primary Auditory Cortex and auditory association areas?

Answer 45

6

Question 46

T or F

In each of these 6 Tonotopic Maps:

Hight and Low frequency sounds excite neurons at the Same end of the Map.

Answer 46

False

High and Low frequency sounds excite neurons at the opposite ends of the Map.

Question 47

Where are the High and Low Frequency sounds located on the Tonotopic Map?

Answer 47

Low Frequency sounds are located Anteriorly

High Frequency sounds are located Posteriorly