CVT Vestibular System Anatomy & Physiology Techniques 3 — Questions and Answers
Question 1: The posterior semicircular canal is most sensitive to head movements in which plane?
- Horizontal plane
- Sagittal (pitch) plane (Correct answer)
- Frontal (roll) plane
- Oblique plane at 45° to sagittal
Correct answer: Sagittal (pitch) plane
The posterior semicircular canal lies in a plane roughly parallel to the sagittal plane and responds primarily to pitch (nodding) head movements.
Question 2: Which of the four vestibular nuclei is primarily involved in the vestibuloспinal reflex controlling trunk and limb muscles?
- Superior vestibular nucleus (Bechterew)
- Medial vestibular nucleus (Schwalbe)
- Lateral vestibular nucleus (Deiters) (Correct answer)
- Inferior vestibular nucleus (Roller)
Correct answer: Lateral vestibular nucleus (Deiters)
The lateral vestibular nucleus (Deiters' nucleus) gives rise to the lateral vestibulospinal tract, which facilitates ipsilateral extensor muscles for postural stability.
Question 3: Otoconia are primarily composed of:
- Calcium phosphate crystals embedded in a protein matrix
- Calcium carbonate (calcite) crystals in a glycoprotein gel (Correct answer)
- Magnesium sulfate crystals in endolymph
- Silica crystals attached to stereocilia tips
Correct answer: Calcium carbonate (calcite) crystals in a glycoprotein gel
Otoconia are dense calcium carbonate crystals embedded in a gelatinous glycoprotein matrix (otolithic membrane) overlying the macula.
Question 4: The medial vestibulospinal tract primarily coordinates:
- Lower limb extensor tone for standing balance
- Neck and upper limb muscles for head stabilization (Correct answer)
- Ipsilateral limb flexion reflexes
- Abdominal muscle activity during respiration
Correct answer: Neck and upper limb muscles for head stabilization
The medial vestibulospinal tract descends in the MLF to cervical and upper thoracic levels, coordinating neck and upper limb muscles to stabilize the head.
Question 5: In BPPV of the posterior canal, the Dix-Hallpike maneuver typically elicits nystagmus that is:
- Horizontal and persistent, lasting more than 1 minute
- Torsional-upbeat, geotropic, and fatigable (Correct answer)
- Pure vertical downbeat and non-fatigable
- Purely horizontal toward the affected ear
Correct answer: Torsional-upbeat, geotropic, and fatigable
Posterior canal BPPV produces torsional-upbeat (geotropic top pole beating toward affected ear) nystagmus that is fatigable with repeated testing due to canalith repositioning.
Question 6: Which structure regulates endolymph volume and composition through active ion transport?
- Round window membrane
- Stria vascularis (in cochlea) and dark cells (in vestibule) (Correct answer)
- Helicotrema
- Spiral ligament only
Correct answer: Stria vascularis (in cochlea) and dark cells (in vestibule)
The stria vascularis in the cochlea and analogous dark cells in the vestibular labyrinth actively pump ions to maintain the high-K⁺ endolymph composition.
Question 7: The tilt of the head to one side causes the utricle macula to detect gravity because otoconia deflect the:
- Cupula toward the helicotrema
- Striola, causing stereocilia to bend away from the kinocilium
- Stereocilia toward or away from the kinocilium depending on tilt direction (Correct answer)
- Endolymph to flow into the semicircular canals
Correct answer: Stereocilia toward or away from the kinocilium depending on tilt direction
Head tilt shifts the weight of otoconia, bending stereocilia either toward or away from the kinocilium depending on the direction of tilt, resulting in excitation or inhibition.
CVT Vestibular System Anatomy & Physiology Techniques 3
The posterior semicircular canal is most sensitive to head movements in which plane?