The Middle Ear

Question 1

Tympanic Membrane

Answer 1

• thin
• semi transparent
• disc like
• separates ME from OE
• composed of 3 layers

Question 2

Layers of Tympanic Membrane

Answer 2

1. Lateral Surface
2. Middle Surface
3. Medial Surface

Question 3

Lateral Surface of TM

Answer 3

• AKA: epithelial layer
• Composed of thin layer of skin that is continuous from EAC

Question 4

Middle Surface of TM

Answer 4

• fibrous
• small triangular notch superiorly that is deficient in fibrous tissue (pars flaccida)
• pars tensa- rest of TM that keeps it tense
• Umbo- handle of malleus embedded in fibrous layer of TM
• Cone of light

Question 5

Medial Surface of TM

Answer 5

Formed by mucous membrane that lines the middle ear (tympanic) cavity

Question 6

Tympanic annulus

Answer 6

• Periphery of the TM ends in fibro-cartilaginous ring called the tympanic annulus
• It fits into a bony groove called the tympanic sulcus

Question 7

Quadrants of TM

Answer 7

1. Anterior superior
2. Anterior inferior
3. Posterior Inferior
4. Posterior superior

• Perforations on outer edges don’t heal well

Question 8

Otoscopic Examination

Answer 8

TM should appear smooth, pearly gray, and concave

Question 9

Otoscopic Landmarks

Answer 9

• Cone of light
• Umbo
• Manubrium of malleus
• Pars tensa
• Pars flacccida

Question 10

Function of TM

Answer 10

• Responds to acoustic events over a wide range of frequencies and intensities
• For frequencies up to 2400 Hz, the whole central portion of the TM works as a unit
• For frequencies above 2400 Hz, there is a phase lag and it moves in different segments

Question 11

Pathologies of TM

Answer 11

1. Perforation- result of a rupture, foreign object, loud explosion, head trauma, etc.
2. Tympanosclerosis- TM appears bright white

Question 12

Middle Ear Cavity

Answer 12

AKA: Tympanum or tympanic cavity

• Minute air filled chamber
• Upper portion, lying above TM, is the attic or epitympanic recess
• Opening in roof of ME is the aditus

Question 13

Walls of ME Diagram

Answer 13

Question 14

Superior Wall

Answer 14

• Roof of middle ear
• Formed by the mastoid portion of the temporal bone
• Tegmen Tympani**- **Thin layer of bone that separates the middle ear canvity from the meiinges and cranial cavity

Question 15

Inferior Wall

Answer 15

• Floor
• Jugular bulb- houses jugular vein
  
  • Located just beneath the floor

Question 16

Lateral Wall

Answer 16

Tympanic Membrane

Question 17

Medial Wall

Answer 17

• Oval window (top opening where stapes footplate is embedded)
• Round window (bottom)
• Promontory- basal turn of cochlea that just into middle ear cavity
• Part of facial nerve passes through
• Part of tensory tympani passes through

Question 18

Posterior Wall

Answer 18

• Small opening for chorda tympani to enter
  
  • Branch of facial nerve
  • Provides taste sensation to tongue
• Pyramid- houses stapedius muscle
• Mastoid process located behind this wall

Question 19

Anterior Wall

Answer 19

• Coratid wall
  
  • Carotid artery lies just in front
• Tensor tympani enters here
• Eustachian tube or pharygotympanic tube

Question 20

Eustachain tube

Answer 20

• Connects midle ear to nasopharyngeal cavity
  
  • Usually closed to prevent infection
• Allows air to enter middle ear and provides pressure equalization with atmospheric pressure to maximize TM mobility
• In adults, tube is closed, but can be opened by:
  
  • chewing
  • yawning
  • valsalva maneuver
• In infants, tube is shorter and more horizontal
  
  • Remains open until around 6 months of age
  • Makes them prone to infection

Question 21

Ossicular Chain

Answer 21

• 3 smallest bones in body
• Traverset the ME cavity

1. Malleus
   
   • largest in length
   • firmly embedded in middle layer handle of manubrium
   • head of malleus connected to the incus
   • club shaped
2. Incus
   
   • two cruara (short and long)
3. Stapes
   
   • smallest of the three
   • two cruara
   • footplate
   • neck and head

Question 22

Middle Ear Muscles

Answer 22

1. Stapedius
2. Tensor Tympani

Question 23

Stapedius

Answer 23

• Attached to head of stapes
• Moves stapes to the side and tenses the oval window
• Innervated by Facial Nerve
• Acoustic reflex
  
  • Contracts no matter what ear the sound is presented to

Question 24

Tensor Tympani

Answer 24

• Attached to manubrium of malleus
• Moves the malleus and tenses the TM
• Innvervated by the Trigeminal Nerve

Question 25

Middle Ear Impedance Matcher

Answer 25

• Acoustic stimulus is traveling from air filled to liquid filled space
• Without this, you would lose 30 dB
• Two things that happen
  
  1. Vibrating area of TM
     
     • Much larger than surface of oval window
     • Sound waves= pressure waves
     • Prevents loss of pressure (results in greater pressure at oval window)
  2. Lever action of ossicles
     
     • Smallest at oval window, largest at TM
     • Increases pressure gong from TM to oval window
     • Drives acoustic stimulus through fluid

Question 26

Pathologies of Middle Ear

Answer 26

1.

Question 27

Otitis Media

Answer 27

• Infection of the mucous membrane lining
• Most common in children
• Occurs more frequently during winter
• Occcurs more often in males
• Casued by poorly functioning Eustachian tube

Question 28

Stages of Otitis Media

Answer 28

1. Acute
2. TM loses landmarks
3. Superative (“puss producing”)

Question 29

Acute Stage

Answer 29

• TM swelling
  *