L9.3 Ear

Question 1

Auricle & Tragus

Answer 1

• Auricle - mostly cartilaginous
  
  • Lobe does not have cartilage
• Tragus - little flap directly ANT to ear canal

Question 2

Features of the external acoustic meatus?

Answer 2

• Sound transmission
• Supported by:
  
  • LAT: Cartilage (1/3)
  • MED: bone
• Lines by cerumen glands → produces earwax
  
  • Helps prevent masceration when it comes in contact with water

Question 3

NS of the ear

Answer 3

• POS/INF surface innervated by vagus
• ANT/SUP Surface innervated by auriculotemporal N (mandibular division of the trigeminal N)
  
  • Also stimulates the tympanic membrane
  • Refer pain to other areas of the mandibular N innervation (May be to the teeth)

Question 4

Tympanic membrane (LAT view)

Answer 4

• Indentation form by handle of malleus
• Concave LAT
  
  • Concavity depends on pressure that exists in the middle ear
• Cone of light in ANT-INF quadrant
  
  • Light shown due to concavity of the membrane
  • If light changes position → may have problem with middle ear

Question 5

Middle ear

Answer 5

• Space b/w tympanic membrane and petrus part of temporal bone

Question 6

What does the middle ear split into?

Answer 6

• Tympanic cavity proper (MED to the tympanic membrane)
• Epitympanic recess (projects up above)
  
  • Communicates with the mastoid air cells

Question 7

Communication of middle ear to the nasopharynx

Answer 7

• Via Auditory tube (aka: pharyngotympanic tube)
  
  • Projects ANT and INF to nasopharynx
  • Cartilaginous part towards the pharynx
  • Embedded in bone in the tympanic part

Question 8

Ossicles of the ear

Answer 8

• Malleous - shaped like hammer
• Incus - shaped like a anvil
• Stapes - shaped like a steer
  
  • Stapes sits on the oval window opening to the inner ear
  • Transmit the energy to the inner ear

Question 9

What happens if the auditory tube is blocked?

Answer 9

• If auditory tube is blocked → impacts on the movement of the ossciles → impact energy into the inner ear → problems with hearing

Question 10

Difference in auditory tube of adults and infants? What is the significance?

Answer 10

• Vertical in adults → drains down → prevents infections
• More horizontal and shorter in infant (bacteria may move from nasal cavity through the nasal cavity and infect inner ear
  
  • More difficult to drain infection as well
• Infection may interrupt movement of small bones which interrupts hearing and damage the tympanic membrane

Question 11

Tensor tympani

Answer 11

• ANT wall → malleolus
• Innervated by 5th cranial N

Question 12

Stapedius

Answer 12

• Attaches to stapes
• Innervated by the 7th cranial N
  
  • Reduced reflex response when there is a problem with this facial N
    
    • Increases hearing in these people

Question 13

Why is there a reflex contraction of the ear muscles?

Answer 13

• When sound is too loud
• When the muscles contract the dampen the vibration amplitude of these bones → prevent damage

Question 14

LAT view of ear with tympanic membrane removed

Answer 14

• Muscles
• Round window
  
  • Another opening of the inner ear
• Promontary (basal turn of the cochlear → makes an impression)
• Chorda tympani
  
  • Runs through the middle ear (but doesn’t innervate the middle ear)
  • Branch of the facial N
  • Runs a tortous path to the ANT 2/3 of tongue

Question 15

Association of internal carotid artery with the middle ear

Answer 15

• Internal carotid artery
  
  • Close association with the tympanic cavity and middle ear
  • Infection dev in middle ear
    
    • Energy from pulse → transmitted to the ossicles → able to hear your pulse

Question 16

Inner ear

Answer 16

• Inner ear is a system of spaces and membrane imbedded in the petrous part of the temporal bone
  
  • Bony labyrinth filled with periplymph (white bits)
  • Suspended inside → membranous labyrinth contains endolymph
    
    • Also sensory for hearing and equilibrium
• Round window → provides escape of the transmitted energy

Question 17

Features of the bony labyrinth

Answer 17

• Cochlea
• Vestibule - connect cochlea to canals
  
  • Opening of round and oval window relative to vestibule

Question 18

Membranous labyrinth

Answer 18

• Suspended in the bony labyrinth
• One twisted sac that approximates space that sits in the bony labyrinth

Question 19

Cochlear

Answer 19

• Contains sensory R for hearin
• Cochlear N (8th cranial N) connected to cochlear

Question 20

Semicircular ducts

Answer 20

• Sits in semicircular canals
• ANT/POS/horizontal

Question 21

Ampulla

Answer 21

• Has sensory R for dynamic equilibrium
• Information for our head MOVEMENT

Question 22

Vestibule

Answer 22

• Has Utricle & saccule for static equilibrium
• Information for our head POSITION

Question 23

What forms the 8th cranial N

Answer 23

• Vestibule + Ampulla gives information → forms the 8th cranial N

Question 24

Vibration of tympanic membrane relative to freq and loudness

Answer 24

• Tympanic membrane vibrates relative to freq and loudness → ossicles → oval window → perilymph → membranous labyrinth → endolymph → vibrates sensory R on membrane (along the organ of corti in the cochlea)

Question 25

How does the brain code for high freq and low freq sound?

Answer 25

• Sensory neurons for:
  
  • High freq = base of cochlear
  • Low freq = apex of cochlear

Question 26

Organ of corti

Answer 26

• Vibrates → pulls on hair → activate sensory R.

Question 27

Dynamic equilibrium

Answer 27

• Rotate in 1 direction → endolymph in horizontal semi-circular canal is heavy → lags behind → moves in opposite head direction
  
  • Cupula deflected and activates hair cells
  • Brain decodes which ampulla is most active

Question 28

Static equilibrium

Answer 28

• Otoconia (crystals) move with head by gravity → stays in one position → activates hair cells in that position