UNIT 6 - The ear = hearing & equilibrium

Question 1

structure of the outer ear

Answer 1

• auricle (pinna)
• External acoustic meatus
• Tympanic membrane

Question 2

Auricle / Pinna

Answer 2

The visible fleshy structure on the side of head

Question 3

External Acoustic Meatus

Answer 3

▪ Passageway that leads to the tympanic membrane
▪ The skin lining the passageway contains ceruminous glands which secrete cerumen, or earwax

• Earwax helps trap foreign debris and repel insects

Question 4

Tympanic membrane

Answer 4

▪ Thin connective tissue membrane covered by epithelium that separates the outer & middle ear.

▪ Vibrates when sound waves strike it.

Question 5

Structure of the middle ear

Answer 5

• Located whitin the tympanic cavity of the temporal bone
• Houses the ossicles

Question 6

Ear Ossicles - three tiny bones in the middle ear cavity

Answer 6

Which ossicle is in contact with the tympanic membrane?
malleus
Which ossicle inserts into the oval window?
stapes

Question 7

Ear Ossicles - Function - middle ear

Answer 7

together these transmit sound vibrations from the tympanic to the inner ear

Question 8

Muscles of middle ear - Tensor & stapedius - middle ear

Answer 8

Function:

To reduce vibrations of the ossicles when they become excessive to minimize damage to hearing receptors

Question 9

Oval window - middle ear

Answer 9

Membranous area that connects the stapes to a portion of the inner ear called the scala vestibuli

Question 10

Round window - middle ear

Answer 10

▪ A flexible, membranous area between the middle ear cavity and the scala tympani of the cochlea.

▪ We will refer back to this in a few minutes to discuss its function.

Question 11

Pharyngotympanic (Auditory) Tube - middle ear

Answer 11

• Passageway between the middle ear and the nasopharynx.
• Usually is flattened and closed but opens briefly with swallowing or yawning to equalize pressure between the atmosphere and the middle ear cavity.

Question 12

Structure of the Inner ear

Answer 12

General structure:

▪ The inner ear is comprised of a bony labyrinth and a membranous labyrinth.

Question 13

Bony Labyrinth - inner ear

Answer 13

▪ Series of connected chambers within the temporal bone which houses the inner ear structures and gives them their distinct shapes.

▪ Perilymph – fluid located in bony labyrinth and surrounding the membranous labyrinth

Question 14

Membranous Labyrinth - inner ear

Answer 14

▪ Series of membranous tubes that generally follow the contours of the bony labyrinth and form the inner portions of the vestibule, semicircular canals, and cochlea.

▪ Endolymph – fluid located in membranous labyrinth.

Question 15

Functional parts of inner ear

Answer 15

The functional parts of the inner ear include:
◦ vestibule
◦ semicircular canals
- Vestibular apparatus ( involved with equilibrium)
◦ cochlea

Question 16

Structural features of the cochlea - inner ear

Answer 16

▪ Scala vestibuli – open space forming the upper 1/3 of each coil in the cochlea.
- Contains perilymph

Question 17

Structural features of the cochlea - inner ear

Answer 17

▪ Vestibular membrane – separates the scala vestibuli from the cochlear duct.

Question 18

Structural features of the cochlea - inner ear

Answer 18

▪ Cochlear duct – central, membranous portion of the cochlea; it houses the spiral organ (organ of Corti).
- Contains endolymph

Question 19

Structural features of the cochlea

Answer 19

Spiral organ (organ of Corti) – located within the cochlear duct; sits on the basilar membrane.

• It is the sensory receptor for sound

Question 20

Structural festures of the cochlea - inner ear

Answer 20

▪ Hair cells – cells within the spiral organ that convert sound waves into nerve impulses.
- Have “hairs” that are embedded in the tectorial membrane.
- “Hairs” are actually microvilli.

Question 21

Structural features of the cochlea - inner ear

Answer 21

▪ Tectorial membrane – gel-like projection sitting on top of the hair cells.
- Hairs” are embedded in this membrane.

Question 22

Structural features of the cochlea - inner ear

Answer 22

▪ Basilar membrane – supports the spiral organ and separates the cochlear duct from the scala tympani

Question 23

Structural features of the cochlea - inner ear

Answer 23

▪ Scala tympani – open space forming the lower 1/3 of each coil of the cochlea.
- It ends at the round window.
- contains perilymph

Question 24

Structural features of the cochlea - inner ear

Answer 24

Helicotrema – the tip of the cochlea where the scala vestibuli is continuous with the scala tympani.

Question 25

Role of the round window - Inner ear

Answer 25

membranous area that acts as a pressure valve to dissipate waves in the fluid at the end of the scala tympani.

Question 26

Physiology of hearing

Answer 26

Steps in Hearing

1. Sound vibrations enter the external acoustic meatus.
2. Tympanic membrane vibrates.
3. Ossicles (malleus, incus, stapes) vibrate.

Question 27

Steps in hearings pt2

Answer 27

4. Stapes vibrates the oval window.
5. This produces pressure waves in the perilymph of the scala vestibuli.
6. Perilymph bounces off the vestibular membrane, causing it to vibrate.
7. This causes pressure waves in the endolymph within the cochlear duct.

Question 28

Steps in hearing pt3

Answer 28

8. Endolymph bounces off the basilar membrane and causes it to vibrate.
9. The embedded “hairs” of the hair cells bend in response to movement of the basilar membrane.
10. Bending of hair cells triggers a nerve impulse.

Question 29

Steps in hearing pt 4

Answer 29

11. The impulse is sent through the cochlear nerve to the vestibulocochlear nerve (cranial nerve VIII)
12. The impulse travels through several structures including the medulla oblongata, inferior colliculi, and thalamus before being routed to and interpreted in the temporal lobe.

Question 30

Characteristics of sound - pitch

Answer 30

▪ Sounds waves of different pitches (frequencies) “hit” the vestibular membrane (and thus the basilar membrane) at different regions.

▪ Perception of pitch is determined by the location of the hair cells that send the nerve impulse.

Question 31

Characteristics of sound loudness - pt1

Answer 31

▪ A louder noise causes stronger vibrations, thus causing more hair cells to bend.

▪ The more hair cells that are stimulated, the louder the sound that is perceived.

Question 32

Characteristics of sound - loudness pt2

Answer 32

▪ A louder noise causes stronger vibrations, thus causing more hair cells to bend.

▪ The more hair cells that are stimulated, the louder the sound that is perceived.

Question 33

Characteristics of sound - location

Answer 33

Where a sound is coming from is determined by the brain based on:

   ◦ the loudness in each ear
   ◦ the time when the sound reaches each ear

Question 34

Deafness - two types

Answer 34

sensorineural deafness & conduction deafness

Question 35

Sensorineural deafness

Answer 35

due to damage to hair cells, nerves, or even cells of cerebral cortex
 often difficult to correct

Question 36

Conduction deafness

Answer 36

due to something that hinders sound waves from reaching fluids of inner ear (ex. earwax buildup, middle ear infections, or rupture of tympanic membrane)
 usually can be corrected by various measures

Question 37

Static equilibium

Answer 37

▪ The receptors to sense static equilibrium are the maculae.
- Housed in the vestibule.

Question 38

static equilibium pt 2

Answer 38

Being the receptors for static equilibrium means the maculae monitor:
▪ the position of the head
with respect to gravity
▪ linear (straight-line)
acceleration

Question 39

Static equilibium pt3

Answer 39

▪ Each macula is composed of a patch of epithelium that contains hair cells.
▪ These hair cells have “hairs” that are embedded in a gel-like otolithic membrane

Question 40

Static equilibium pt4

Answer 40

▪ Movement of the head causes the otolithic membrane to shift which bends the hair cells.
p. 287

• Bending of the hair cells triggers
  a nerve impulse

Question 41

Dynamic equilibrium pt 1

Answer 41

▪ The receptor to sense dynamic equilibrium is the crista ampullaris.
- Housed in the semicircular canals

Question 42

Dynamic equilibrium pt 2

Answer 42

▪ Being the receptors for dynamic equilibrium means these cristae ampullares* monitor rotational movement.

Question 43

Dynamic equilibrium pt3

Answer 43

▪ Crista ampullaris contains supporting cells and hair cells.

• The hair cells, again, have “hairs” that are
  embedded in a dome- shaped, gel-like
  mass called the cupula.

Question 44

Dynamic equilibrium pt4

Answer 44

▪ Rotational movements cause movement of endolymph in the semicircular canals.
▪ The movement of endolymph shifts the cupula which bends the hair cells.

▪ Bending of the hair cells triggers a nerve impluse

Question 45

Neural pathway

Answer 45

●Nerve impulses for both static and dynamic equilibrium travel to the vestibular branch of the vestibulocochlear nerve (VIII).

●Equilibrium is perceived in the insula and parietal lobe.

Question 46

End

Answer 46

end :)