Lecture 25: Ear & Auditory Canal

Question 1

What makes up the outer ear and what are its features?

Answer 1

Auricle - collects sound and is supported by cartilage

Question 2

Where is the tragus?

Answer 2

Anterior to the ear canal/external auditory meatus

Question 3

What supports the external acoustic meatus?

Answer 3

Laterally supported by cartilage and medially supported by bone (temporal)

Question 4

What lines the external acoustic meatus?

Answer 4

Cerumen glands and hairy skin

Question 5

What do the cerumen glands present?

Answer 5

Produce wax to prevent maceration of skin and water

Question 6

What is the nerve supply to the outer ear?

Answer 6

Posterior and inferior surface is innervated by vagus and anterior superior surface of external auditory meatus is innervated by the auriculotemporal nerve (branch of mandibular/V3 branch of trigeminal nerve

Question 7

Where is pain in the outer ear referred?

Answer 7

Lower teeth - mandible

Question 8

What forms the indentation of the tympanic membrane?

Answer 8

Small bone in the middle ear (malleolus)

Question 9

What is the shape of the tympanic membrane?

Answer 9

Concave laterally - dependent on the pressure that exits medial to it in the middle ear

Question 10

What is the cone of light?

Answer 10

Position of light when you shine light into the anterioinferior quadrant - if light is in a different position there has been a pressure change

Question 11

What is the middle ear?

Answer 11

Space between tympanic membrane and petrous part of temporal bone

Question 12

What is the middle ear split into?

Answer 12

Tympanic cavity proper and epitympanic recess

Question 13

What does the epitympanic recess communicate with?

Answer 13

Mastoid air cells - openings from middle ear to spaces in mastoid bone

Question 14

How do the middle ear and nasopharynx communicate?

Answer 14

Auditory tube

Question 15

What is the position of the auditory tube?

Answer 15

Projects anterior and inferior towards the nasopharynx

Question 16

What is the auditory canal made up of?

Answer 16

Cartilaginous where it opens into the nasopharynx and embedded in bone near the tympanic cavity

Question 17

What happens due to the auditory canal opening downwards?

Answer 17

Migratory pathway for bacteria

Question 18

What does infection in the ear cause?

Answer 18

Disrupted movement of the ossicles, reduced sound transport, impaired hearing

Question 19

What are the ossicles and where do they attach?

Answer 19

Little bones in the middle ear. Malleus is shaped like a hammer, incus is shaped like an anvil and stapes is shaped like a stirrup (lateral to medial). Attach laterally to tympanic membrane.

Question 20

How does the auditory tube change from infancy to adulthood?

Answer 20

Tube starts out short and horizontal (lots of ear infections) and becomes more vertical and longer

Question 21

What innervates tensor tympani and what does it attach to?

Answer 21

Trigeminal nerve, anterior wall to malleus

Question 22

What innervates stepedius and what does it innervate?

Answer 22

Facial nerve - stapes and posterior wall

Question 23

What is the function of the small muscles in the middle ear?

Answer 23

When muscles contract they dampen the amplitude of vibration of the bones - reflex response to loud sounds. If energy is too large - amplitude will be too loud and damage sensory auditory structures. Reflex contraction of muscles to stop vibration of ossicles when we hear a really loud sound. Same frequency of sound but reduced amplitude.

Question 24

What happens to hearing in facial nerve palsy?

Answer 24

Stapedius muscle function disrupted - less reflex to reduce loud noise - increased sensitivity to hearing

Question 25

What is the round window?

Answer 25

Opening related to big swelling on medial wall – promontory – basal turn of cochlear

Question 26

What is chorda tympani?

Answer 26

Small nerve in the ear, a branch of the facial nerve (intermediate division), takes tortuous path and ends up on anterior 2/3 of the tongue (info on taste), branch of facial nerve in petrous portion of temporal bone, runs through middle ear to get there, continues with linguinal branch of trigeminal nerve to reach tongue

Question 27

What is the relationship of the internal carotid artery and the ear?

Answer 27

Runs close by - when there is fluid near the tympanic membrane mechanical energy is formed and you can hear the artery pumping

Question 28

What is the inner ear?

Answer 28

System of spaces and membranes imbedded in petrous part of temporal bone

Question 29

What is the bony labyrinth and what fluid is it filled with?

Answer 29

System of spaces in temporal bone - perilymph

Question 30

What is the membranous labyrinth and what fluid is it filled with?

Answer 30

Single closed sac within boy labyrinth - endolymph

Question 31

What does the vestibule connect?

Answer 31

Cochlea to semicircular canals

Question 32

What are the semicircular ducts?

Answer 32

Ducts that sit within canals

Question 33

What is at the base of each duct?

Answer 33

Ampulla - sensory fibres for dynamic equilibrium

Question 34

What are the swellings in the vestibule?

Answer 34

Utricle and saccule - sensory receptors for static equilibrium

Question 35

What nerves come together to form the vestibulocochlear neve?

Answer 35

Vestibular and cochlear nerves

Question 36

How is sound transmitted?

Answer 36

Sound transmitted onto vibrations of tympanic membrane; vibrate with frequency with amplitude relative to sound, transmitted through ossicles to inner ear via oval window. Once in perilymph transferred into membranous labyrinth into the endolymph and vibrates sensory receptors that sit on a membrane that forms part of the organ of corti (complex that contains sensory receptors for hearing)

Question 37

Where do high and low frequency receptors sit?

Answer 37

High - base of cochlea

Low - apex of cochlea

Question 38

What happens in static equilibrium?

Answer 38

Put head in any one position, otolithic membrane flops down due to gravity and stays in one spot - deflect hair cells in direction affected by gravity