112. Anatomy | Special Afferents of the Head and Neck

A 28-year-old male presents with complete loss of smell following a head trauma in which he struck the frontal region of his skull. He reports that food now tastes “bland,” and he recently had an episode of food poisoning. Imaging shows small fractures in the cribriform plate. Which structure was most likely sheared during the injury?

A. Mitral cells
B. Olfactory tract
C. Olfactory nerves passing through cribriform plate
D. Superior concha epithelium
E. Lateral olfactory stria

C

• A. Mitral cells ❌
  Located inside the olfactory bulb, not traversing the cribriform plate. Trauma to the bulb occurs, but shearing is classically at the tiny nerves.

• B. Olfactory tract ❌
  This is the CNS extension along the brain base; it does not pass through the cribriform plate and is not the structure that shears during trauma.

• C. Olfactory nerves passing through cribriform plate ✅
  These ~10 small fibers descend through the “cheese-grater–like” cribriform plate (slide 3). Head trauma shears these → anosmia, loss of smell→ reduced flavor→ increased risk of food poisoning (slide 8).

• D. Superior concha epithelium ❌
  This houses olfactory epithelium but is not the part sheared in trauma.

• E. Lateral olfactory stria ❌
  A CNS pathway from the bulb to the cerebrum; not vulnerable to cribriform fractures.

A 64-year-old female complains of difficulty reading unless she holds the page far away from her face. She denies pain or redness. Ophthalmologic exam shows decreased lens elasticity. Which muscle is responsible for the accommodation process she is failing to perform effectively?

A. Sphincter pupillae
B. Dilator pupillae
C. Ciliary body
D. Superior rectus
E. Orbicularis oculi

C

• A. Sphincter pupillae ❌
  Parasympathetic constrictor muscle of iris, irrelevant to lens accommodation.

• B. Dilator pupillae ❌
  Sympathetic radial muscle, also unrelated to lens shape.

• C. Ciliary body ✅
  Lecture 112: Ciliary body contracts → zonular fibers loosen → lens becomes round for near vision.
  Presbyopia = loss of lens elasticity → difficulty with near vision (slides 40–41).

• D. Superior rectus ❌
  Extraocular muscle; moves eye upward.

• E. Orbicularis oculi ❌
  Closes eyelids; no role in vision refraction.

A 6-year-old child presents with loss of taste on the anterior 2/3 of the tongue following otitis media complicated by damage within the middle ear cavity. Which nerve was most likely affected?

A. Lingual nerve (CN V3)
B. Glossopharyngeal nerve (CN IX)
C. Chorda tympani (CN VII)
D. Internal laryngeal nerve (CN X)
E. Greater petrosal nerve (CN VII)

C

• A. Lingual nerve (CN V3) ❌
  Carries general sensation to anterior 2/3 — NOT taste.

• B. Glossopharyngeal nerve (IX) ❌
  Taste to posterior 1/3.

• C. Chorda tympani (VII) ✅
  Lecture: Travels through the middle ear cavity (video transcript) → exits petrotympanic fissure → taste anterior 2/3. Otitis media can damage it.

• D. Internal laryngeal (X) ❌
  Taste from epiglottic and posterior mucosal fields.

• E. Greater petrosal (VII) ❌
  Parasympathetic to lacrimal gland; no taste fibers for tongue.

A 55-year-old man develops sudden, debilitating vertigo lasting several minutes after rolling over in bed. He describes a spinning sensation accompanied by nausea. Examination suggests misplaced otoliths stimulating an inappropriate canal. Which structure most directly detects rotational head movements under normal conditions?

A. Utricle
B. Saccule
C. Semicircular canal ampulla (crista ampullaris)
D. Otolith membrane
E. Organ of Corti

C

• A. Utricle ❌
  Detects horizontal linear acceleration, not rotation.

• B. Saccule ❌
  Detects vertical acceleration.

• C. Semicircular canal ampulla (crista ampullaris) ✅
  Lecture 112: SCCs detect rotational acceleration → endolymph bends cupula → depolarization (slides 52–54).

• D. Otolith membrane ❌
  Used in utricle/saccule for linear acceleration.

• E. Organ of Corti ❌
  Hearing, not balance.