C18 - External ear, cavum tympani

Question 1

Give the subdivision of the ear

Answer 1

• External ear
• Middle ear
• Internal ear
• Temporal bone houses all three parts of the ear

Question 2

External ear

What is the extenal ear composed of?

Answer 2

• Auricle
  
  • ​Auricular cartilage
  • Scutiform cartilage
  • Auricular muscles
• Meatus acusticus externus
• Tympanic membrane

Question 3

External ear

Auricle

Answer 3

• Funnle shaped
• Sound gathering structure
  
  • Muscles will work to gather sound waves
• Connected with meatus acusticus externus
• Several auricular muscles arise from the scutiform cartilage

Anatomical features of the auricle:

• Apex auriculae
• Rostral and caudal margins
• Convex surface
• Concave surface
  
  • ​Scapha
  • Concha

Question 4

External ear

Meatus acusticus externus

Answer 4

• Also called ear canal
• Begins with the narrowed part of the auricular cartilage and ends at the eardrum
• Bone: pars tympanica of temporal bone (riktig???)
• Divided into:
  
  • Distal cartilagenous part (long and curved)
  • Proximal osseous part (short, attached to the basal portion of the concha by annular cartilage)
• Sebaceous and tubular ceruminous glands secrete earwax
  
  • Eq, ru: located within the cartilagenous part
  • Car: located along the whole meatus acousticus externus

Question 5

External ear

Tympanic membrane

Answer 5

• Also called eardrum
• Innervation: sensory nerve fibers
• Highly vasculized
• Separates the middle ear from meatus acousticus externus
• Transmits sounds onto the auditory ossicles of the middle ear
• Suspended within the tympanic ring
• Pars tensa: the part of the membrane that attaches to the tympanic ring
• Pars flaccida: the part that covers the noctch of the tympanic ring

Question 6

Middle ear

What is the middle ear composed of?

Answer 6

• Cavum tympani
• Ossicula auditus
• Tuba auditiva
  
  • ​Eq: forms a large diverticulum: guttural pouch

Question 7

Middle ear

Cavum tympani

Answer 7

• Bone: housed within pars petrosa of os temporale
• Parts:
  
  • Epitympanicus​
    
    • ​Dorsal
    • Contains auricular ossicle
  • Mesotympanicus
    
    • ​Middle
    • Includes tympanic membrane in its lateral wall
    • Opens rostrally into nasopharynx via tuba auditiva
  • Hypotympanicum / bulla tympanica
    
    • ​Enlarged bulbous expansion of os temporale
    • Floor and part of lateral wall of cavum tympani

1. Dorsal part
   
   • ​Epitympanicum
2. Middle part
   
   • ​Mesotympanicum
   • Tympanic membrane
3. Ventral part
   
   • ​Hypotympanicum / bulla tympanica
4. Lateral wall
   
   • ​Hyotympanicum / bulla tympanica
   • Tympanic membrane
5. Middle wall
   
   • 2x windows:
     
     • Oval vestibular window
       
       • ​Occupied by the base of the stapeds
       • Connects cavum tympani with the internal ear
     • Cochlear window​ / for. cochleae
       
       • ​Leads to cochlea
       • Closed by the secondary tympanic membrane
6. Cochlea
   
   • ​Located within promontorium (bony prominence)
   • Protrudes the medial wall of cavum tympani
7. Auditory ossicles
   
   • ​Malleus
   • Incus
   • Stapes

Question 8

Middle ear

Cavum tympani: auditory ossicles

Answer 8

• The transmission of vibrations from the typmanic membrane across the tympanic cavity to the inner ear is mediated by the three auditory ossicles:
  
  • ​Malleus​
    
    • ​The manibrium is embedded within the tympanic membrane
  • Incus
  • Stapes
    
    • ​Basearticulates with thefibrocarilagenous ringthat surrounds thevestibular window

Question 9

Middle eart

Tuba auditiva

Answer 9

• Connects the cavum tympani with nasopahrynx
• Role: equalise atmospheric pressure on the two sides of the tympanic membrane

Horse have guttural pouchs:

• Fomed by outpouching of the mucosal lining of the tuba auditiva through the ventral slit of the supporting cartilage
• Can hold 500 ml
• Location:
  
  • Dorsal: between basis cranii → atlas
  • ventral: between pharynx → esophagus
• Os stylohyoideus incompletely divides the pouch into medial and lateral compartments
• Closely related anatomical structures:
  
  • A. carotis externa
  • A. carotis interna
  • N. vagus
  • N. glossopharyngeus
  • Ggl. cervicale cranaiale
  • Ln. retropharyngeus
• Clinical importance of the closely related structures: infection may spread onto them

Question 10

Innervation

Too much info, from topic C13

Answer 10

• ​N. facialis​ (VII):
  
  • ​​Porus acusticus internus → canalis facialis → for. stylomastoideum
• N. facialis branches into:
  
  1. N. petrosus major:
     
     • Parasympathetic
     • ​Regulates secretion of nasal and lacrimal gland
  2. Chorda tympani:
     
     • Parasympathetic
     • Originates from taste buds of the tongue, runs through middle ear and carries taste messages to the brain
     • ​From n. facialis to join n. lingualis
     • Leaves through fissura petrotympanica
  3. N. stapedius:
     
     • ​Motor
     • To m. stapedius