The Ear

Question 1

Divisions of the Ear

Answer 1

1. External
2. Middle
3. Internal

Question 2

External Ear (2)

Answer 2

1. Auricle- cartilage that protects external auditory canal, captures waves and sound and “funnels” into ear
2. External Acoustic Meatus- directs sound waves into the ear, lateral 2/3 is cartilage, medial 1/3 is temporal bone, goes from auricle to tympanic membrane
   *contains ceruminous glands that secrete waxy material, and debris trapping hairs

Question 3

Tympanic Membrane

Answer 3

Separates the external and middle ear, vibrates in response to incoming sound waves

Question 4

Middle Ear (5)

Answer 4

1. Tympanic membrane
2. Auditory ossicles- 3 bones- malleus, incus and stapes- which connect tympanic membrane with internal ear (oval window)
3. Eustachian tube (pharyngotympanic tube)- makes pressure equal b/t middle ear and outside (otitis media= middle ear infection that causes redness, swelling and pain)
4. Tensor tympani and stapedius muscles
5. Oval and round windows

*middle ear collects and amplifies sound waves, and transmits sound to internal ear

Question 5

Muscles of Middle Ear

Answer 5

1. Tensor tympani- pulls on malleus (bone of tympanic membrane) to increase stiffness and limit movement
2. Stapedius- pulls on stapes to restrict movement at oval window

*prevents excessive vibration of bony ossicles

Question 6

Oval and Round Windows

Answer 6

Oval Window:
-Stapes pushes against oval window to transmit sound waves to internal ear

Round Window:
-Helps sound waves travel through internal ear

Question 7

Internal Ear

Answer 7

-Innermost compartment encased in temporal bone
-Involved in hearing and balance

1.Bony labyrinth
2. Membranous labyrinth (within bony)

*Perilymph= fluid between bony and membranous, endolymph= fluid within membranous (tube)

Question 8

Bony Labyrinth Components (3)

Answer 8

1. Cochlea
2. Vestibule
3. 3 Semicircular Canals

Question 9

Cochlea

Answer 9

-Sensory organ for hearing
-Sound travels through fluid in pressure waves and sends sound information to brain
-Sound enters through oval window to Scala Vestibuli, passes cochlear duct to Scala Tympani after signal transmitted
-Apex of cochlea= helicotrema *where scala vestibuli and tympani meet
-Contains organ of corti

*cochlear duct (scala media) within membranous labyrinth

Question 10

Vestibule

Answer 10

Utricle and saccule within membranous labyrinth

-Detects head position, gravity and linear acceleration
-Maintains stability and posture

*balance and equilibrium

Question 11

Semicircular Canals

Answer 11

3 semicircular canals, semicircular ducts within membranous labyrinth

-Detects rotational motion in 3 different planes
-Maintains balance

Anterior= nodding yes
Posterior= side to side “roll”
Lateral= shaking head no

Question 12

Sensory Hair Cells

Answer 12

-Cells with hair-like projections (called stereocilia)
-Detects motion
-Involved in hearing and balance

*external stimuli bends hairs one way or another which sends signal through nerve to determine motion
*volume determined by how many hair cells are stimulated

Question 13

Sound Transmission Review (3)

Answer 13

1. Sound waves transmitted through external ear to tympanic membrane
2. Vibrations pass through ossicles of middle ear, which amplify sound
3. Stapes pushes against oval window and sound waves are transmitted to cochlea

Question 14

Organ of Corti

Answer 14

Also called spiral organ, contains basilar membrane (bottom) and tectorial membrane (top) with hair cells in between

-Waves in perilymph move basilar membrane up and down
-Stereocilia of hair cells are pushed against and pulled away from tectorial membrane
-Greater displacement= more neurotransmitter release

Question 15

OVERALL Process of Hearing (6)

Answer 15

1. Sound waves travel through external acoustic meatus to tympanic membrane causing vibration
2. This vibrates the ossicles which amplifies the sound
3. Stapes pushes against oval window which causes waves in perilymph, and sound travels through scala vestibuli
4. Waves of perilymph push against basilar membrane as they travel
5. Hair cells push against tectorial membrane and bend, which causes neural signal to be transmitted
6. Impulses travel to CNS via cochlear branch of CN VIII

*higher pitch sounds= shorter hairs can pick up, goes through scala tympani to exit through round window
*lower pitch sounds= picked up by longer hair cells, travels further (towards helicotrema) before going to scala tympani

Question 16

Dynamic vs. Static Equilibrium

Answer 16

Dynamic: maintaining balance when head and body are moved suddenly
-Semicircular ducts of semicircular canals

Static: maintaining posture and stability when body is motionless
-Saccule and utricle of vestibule

*via hair cells

Question 17

Semicircular Canals for Balance

Answer 17

-Membranous labyrinth filled with endolymph, each duct is continuous with utricle
-Each duct contains an ampulla (swollen region containing sensory receptors)
-Hair cells are clustered together on parts of the ampulla (crista ampullaris)
-Sensory hair cells embedded in gelatinous mass called cupula

*innervated by vestibular branches of CN VIII

Question 18

Sensing Rotational Movement- Semicircular Canals (4)

Answer 18

1. Head rotates and causes movement of endolymph
2. Semicircular canal rotates with head and endolymph sloshes against cupula
3. Displacement of cupula distorts sensory hair cells
4. Nerve impulses are transmitted during this displacement

Question 19

Vestibule- Saccule and Utricle

Answer 19

Membranous sacs filled with endolymph
-Each sac contains a macula (hair cells are in this macula)
-Macula contains otoliths which are crystals that are heavy and lag behind (involved with gravity and velocity detection)

Utricle= horizontal acceleration (ex. car)
Saccule= vertical acceleration (ex. elevator)

*innervated by vestibular branches of CN VIII

Question 20

Otoliths

Answer 20

Sense gravity, linear acceleration and head position
-Movement of dense otoliths stimulates hair cells
-Hair cells release neurotransmitters and send neural signal

Question 21

Clinical Connection: Vertigo

Answer 21

Vertigo happens when otoliths stay tilted over (ex. get hit) when the head is in normal position, which messes up balance and makes sense not be aligned (sight not the same as balance) so you feel nauseous and dizzy