Mod7-Obj2: Structures of the ear relating to hearing and balance

Question 1

Structure of the ear: Hearing and balance

Three major areas of the ear

Answer 1

1. ) External (outer) ear
   - hearing only
2. ) Middle ear (tympanic activity)
   - hearing only
3. ) Internal (inner) ear
   - hearing and balance
   - Activated independently, respond seperately

Question 2

Structure of the Ear: External ear

Answer 2

1. ) Auricle (pinna)
   - elastic cartilage
2. ) External acoustic meatus
   - Auditory canal extends to the eardrum
   - Earwax secreting glands
3. ) Tympanic membrane (eardrum)
   - Thin translucent membrane
   - Vibrates in response to sound

Question 3

Role of the external ear

Answer 3

Auricle funnels sound waves into the external acoustic meatus
-Earwax traps foreign particles

Question 4

External ear: sound waves

Answer 4

Sound waves entering external acoustic meatus vibrate tympanic membrane which then transfers sound energy to bones of the middle ear

Question 5

Structure of the ear: Middle Ear (tympanic cavity)

Answer 5

-Air-filled cavity in the temporal bone
-Flanked
+Laterally by eardrum
+Medially by bony wall containing:
*Oval window
*Round window
-Auditory ossicles
-Pharyngotympanic tube (eustachian tube)

Question 6

Pharyngotympanic tube

Answer 6

Connects middle ear to nasopharynx

-Equalises air pressure in the middle ear cavity with external air pressure

Question 7

Auditory ossicles

Answer 7

1.) Malleus-hammer
2.) Incus-anvil
3.) Staples-stirrup
The role of the auditory ossicles is to transmit and amplify the vibration motion of the eardrum to the oval window

Question 8

Structure of the ear: Internal Ear
(Located in the temporal lobe)
1.) Bony labyrinth

Answer 8

1.) Bony labyrinth: tunnels in the temporal bone subdivided into…
-Vestibule
-Semicircular canals
-Cochlea
filled with perilymph

Question 9

Structure of the ear: Internal Ear

2.) Membranous labyrinth

Answer 9

Series of interconnecting sacs and ducts with the bony tunnels
-filled with endolymph

Question 10

Cochlea

Answer 10

Spiral, bony chamber

• Extends from the vestibule
• Coils around like a snail shell
• Contains cochlear duct (houses spiral organ of corti, the receptor organ for hearing)

Question 11

Cochlea

Answer 11

Cavity of cochlea divided into 3 chambers

• Middle chamber is the cochlear duct that contains endolymph
• Other 2 chambers contain perilymph (top chamber=oval window, bottom chamber=round window)

Question 12

Spiral organ of corti

Answer 12

Cochlear hair cells-auditory receptors (mechanoreceptors)

• Sound waves traveling through the cochlea induce movement of the basilar membrane. This movement causes the cilia of the hairs to move or bend against the tectorial membrane, initiating a depolarisation
• Impulses generated in hair cells transmit fibres 9sensory neurons) in the vestibulocochlear nerve (CNVIII)

Question 13

Pathway of sound waves through the ear

Answer 13

Tympanic membrane
to
Ossicles (Auditory)
to 
Oval window
to 
Cochlea (perilymph)
to 
Spiral Organ of Corti
to 
Round window

Question 14

Sound 4 stages: stage 1

Answer 14

Sound waves vibrate the tympanic membrane

Question 15

Sound 4 stage: Stage 2

Answer 15

Auditory ossicles vibrate. Pressure is amplified

Question 16

Sound 4 stages: Stage 3

Answer 16

Pressure wave created by stapes pushing on the oval window, move through perilymph

Question 17

Sound 4 stages: Stage 4:

Answer 17

Pressure waves of the perilymph vibrate the basilar membrane and bend receptor hair cells that are embedded in overlaying tectorial membrane. Generation of impulse in cochlear nerve

Question 18

Balance or equilibrium

Answer 18

Is the response felt by the vestibule and semicircular canals to various head movements (receptors are found here)

Question 19

Role of equilibrium

Answer 19

Provides information about the location of our head we need to know how rapid the movement and in which direction or involved in acceleration or deceleration

Question 20

Equilibrium depends on

Answer 20

Inputs from the internal ear as well as vision and information from stretch receptors of muscles and tendons

Question 21

2 types of equilibrium

Answer 21

1. ) Static equilibrium

2. ) Dynamic equilibrium

Question 22

Static equilibrium

Answer 22

Evaluating the position of the head relative to gravity. It is requited when the head is motionless, or moving in straight line-detected by hair cells in the vestibule (saccule and utricle)

Question 23

Dynamic equilibrium

Answer 23

Required when the head is rotating, or moving in an angular direction-detected by hair cells in the semicircular canals

Question 24

Equilibrium receptors

Answer 24

Mechanoreceptors: hair cells

• Hair cells are distorted in response to a stimulus
• Distorted hair cells depolarise and an impulse generated
• Impulses travel via the vestibulocochlear nerve to the reflex centres of the brainstem, cerebellum and vestibular cortex

Question 25

Equilibrium receptors: Linear movement

Answer 25

Linear movement for hair cells in vestibule

Question 26

Equilibrium receptors:

Rotational movement

Answer 26

Rotational movement for hair cells in semicircular canals

Question 27

Vestibule: Contain 2 membranous sacs

Answer 27

Contain equilibrium receptors

1. ) Saccule is continuous with cochlear duct
2. ) Utricle is continuous with semicircular canals

Question 28

Static equilibrium: Vestibule

Answer 28

Utricle & saccule contains hair cells that are embedded in jellylike substance

• Tiny stones are embedded in the surface of the jelly. When head position is changed, gravity pulls on the stones and distorts the jelly and hair cells
• Distortion of the hair cells is the stimulus for their depolarisation and the transmission of impulses to underlying sensory neurons

Question 29

Semicircular canals

Answer 29

3 fluid filled canals that lies in three planes of space

-Equilibrium receptors that respond to rotational movement of the head

Question 30

Dynamic equilibrium: Semicircular canals

Answer 30

Contains hair cells surrounded by endolymph

• Angular movement moves endolymph
• Hair cells are distorted and depolarised