Ear

• Embryonic development

  1. Development of inner ear

  2. Development of external and middle ear

  3. Pinna

  4. Great Auricular (Cervical Plexus), Auriculotemporal (CN V), Arnold’s Nerve (CN X)
• Inner Ear

  1. Tympanic/Jacobson’s Nerve

  2. Eustachian Tube and Pharynx

  3. Inner Ear Cochlea

  4. Otoacoustic Emission
• Middle Ear


  Middle Ear and Mastoid Cavity
• Cartilage in the pinna can be modified. Cartilage from the pinna can be used in plastic surgery for the nose
• When a hematoma develops, the ear becomes devascularized. This can be seen in UFC fighters
• Causes of ear pain


  • Toothache, periapical abscess in lower jaw, odontogenic tumor, impacted tooth, neck problems, tonsillitis, laryngitis/sore throat, singaw, tongue ulcer, oral ulcer, cancer of the throat, cancer of the tongue, ear wax, ear infection in the middle or outer ear
• Facilitate drainage but not sacrifice the ability to collect sound
• If the pressure underneath the tympanic membrane is different from the external environment, the tympanic membrane would be tensed
• A person without a pinna may still be able to hear but may have other maxillofacial problems because the ear has the same embryologic origin as the jaw
• Some patients with microtia have very small ears because the pinna did not develop properly
• How to see the ear by direct line of sight

  For adults, pull the pinna upwards and backwards. For children, just backwards
• Problems associated with pinna will cause hearing-related problems. Along with these are cosmetic issues
• Congenital issues with the pinna do not translate to issues with the inner ear nor middle ear. Patients can still hear even without pinna
• Problems in the mid-face (e.g. cleft palate) may manifest as middle ear issues
• When punched on the ear and a hematoma develops, it may result in cauliflower ears
• Cleaning the ear can make us cough due to stimulation of portions of the larynx, which is innervated by the Vagus nerve (CN X)
• Insults in the structures of the pinna may result in a deformed pinna, called microtia
• Incus


  • Has a body, short process, long process, and lenticular process
  • The lenticular process is attached to the neck of stapes
• Contents of Middle Ear

  • Laterally bounded by the tympanic membrane
  • Tympanic membrane is attached to the malleus handle
  • Ossicular chain: Malleus handle → malleus head → Incus long process → Incus lenticular process of incus → neck of stapes
  • 3 famous bones: Malleus, Incus, and Stapes are there to amplify the sound
  • The lever mechanism of the malleus handle and long process of incus will try to add amplification to the sound
• Footplate

  • Connected to your oval window
  • Compare the diameter of tympanic membrane with the footplate
  • The diameter of the tympanic is much larger so this adds to the amplification of the sound aside from the lever mechanism of your ossicular chain
• Stapedius Muscle


  • Innervated by CN VII
  • Attached to the stapedius neck/stapes neck
  • Another muscle that tenses the ossicular chain via the stapes neck in order to bounce off excess energy. This is called stapedial reflex
• Chorda Tympani

  • Branch of facial nerve that innervates the anterior 2/3 of the tongue
  • For taste
  • Branches from facial nerve (CN V) that will exit the temporal bone, going into the infratemporal fossa, then join the lingual nerve and go towards the tongue to innervate the anterior 2/3 of the tongue
• Middle Ear and Mastoid Cavity

  • Middle Ear: Tympanic cavity or cavity of the middle ear is the narrow air-filled chamber in the petrous part of the temporal bone
  • Cavity has two parts: the tympanic cavity proper, the space directly internal to the tympanic membrane, and the epitympanic recess, the space superior to the membrane
  • Posteriorly, it has an opening (aditus) and behind that is the mastoid bone which has air cells
• Stapes


  • The smallest ossicle
  • Has a limb, footplate, and neck
  • Its head, directed laterally, articulates with the incus
• Tensor Veli Palatini


  • CN V
  • Muscle that opens the eustachian tube and elevates the palate
• Malleus Bone


  • Has a head that is suspended superiorly by ligaments
  • Attached to the incus
  • The rounded superior head of the malleus lies in the epitympanic recess
• Tensor Tympani


  • Innervated by CN V
  • Muscle that tenses the malleus whenever there are too loud sounds
• Jacobson’s Nerve

  • Tympanic branch of CN IX or Glossopharyngeal nerve from its inferior ganglion
  • Will enter the temporal bone to join CN V to innervate the parotid gland
• Each semicircular canal is responsible for sensing a particular head direction
• Membranous labyrinth


  • Suspended within the bony labyrinth, a closed system of ducts and chambers filled with endolymph
• Parts of the inner ear

  • Bony labyrinth
  • Membranous labyrinth
• Bony labyrinth

  • Contains the cochlea (for hearing), vestibule (for balance), and 3 semicircular canals (for balance)
• Inner ear

  Contains the vestibulocochlear organ concerned with the reception of sound and the maintenance of balance
• Organs in the Inner Ear

  • Cochlea
  • Vestibule
  • Semicircular Canals
  • Cochlear duct
  • Saccule
  • Utricle
  • 3 semicircular ducts
• When displacement of fluid occurs within the canal, nerve signals are sent to the brain informing which direction the head just turned
• Superior/Anterior Semicircular Canal (SSCC)


  • Detects head nods up and down, rotation in the sagittal plane
• Lateral Semicircular Canal (LSCC)


  • Detects side-to-side head movement, rotation in the transverse plane, involved in Vestibulo Ocular Reflex
• Stimulating the LSCC

  Can be done by sudden head movement to the left
• The cochlea consists of three tubes: Middle, Superior, and Helicotrema connecting scala vestibuli and scala tympani
• Stimulating the PSCC


  Occurs when jerking the head to the posterior left