Vestibular System

Question 1

Function of the Vestibular Apparatus:

Answer 1

• Maintain upright posture
• Adjust head position in response to changes in posture
• Coordinate eye movements with each other
• Coordinate eye movements to compensate for head movements

Question 2

1. Linear Acceleration:
2. Angular acceleration:

Answer 2

1. head movement along a single plane
2. head rotation in a single plane or simultaneous change in velocity and direction

Question 3

Anatomy of Vestibular Apparatus:

Answer 3

• Bony labyrinth
• Membranous labyrinth
• Sensory receptors

Question 4

What lies in between the gap of the bony labyrinth?

Answer 4

perilymph

Question 5

Maculae (N=2):

Answer 5

• Utricle and saccule
• Mechanoreceptors that detect linear acceleration
• Hair cells in the macula epithelium are covered by a gelatinous otolithic membrane
• responds to head tilt

Question 6

1. The macula in the utricle is oriented in the _____________ and is most sensitive to movement in this plane (e.g. forward-backward or side to side)
2. The macula in the saccule is oriented in the __________ and is most sensitive to movement in the sagittal plane (e.g. forward-backward or up-down)

Answer 6

1. horizontal plane
2. vertical plane

Question 7

Semicircular canal (N=3):

Answer 7

• Movement of endolymph within the semicircular canals deflects the gelatinous cupola
• Respond to changes in angular acceleration

Question 8

Functional Pairs of Semicircular Canals:

Answer 8

1. Right Horizontal / Left Horizontal
2. Right Superior / Left Posterior
3. Right Posterior / Left Superior

Question 9

Special Sensory information is transmitted via the __________________ to the brainstem

Answer 9

vestibulocochlear nerve (CN VIII)

Question 10

Vestibular Nuclei (N=4):

Answer 10

• Caudal Pons (superior and lateral)
• Rostral Medulla (medial and inferior)

Question 11

Lateral Vestibulospinal Tract

1. Function:
2. Route:
3. Mechanism:

Answer 11

1. Function: Maintains balance and posture
2. Route: Pathway descends ipsilaterally from lateral vestibular nucleus to all spinal cord levels
3. Mechanism: Excites extensor muscles of the neck, back and lower limbs (antigravity muscles)

Question 12

Medial Vestibulospinal Tract
Functions:

Answer 12

1. Adjusts head position in response to postural changes
   
   1. Pathway descends bilaterally from medial vestibular nucleus to cervical spinal cord levels
2. Coordinates eye movements with each other
   
   1. Pathway projects superiorly and bilaterally along medial longitudinal fasciculus (MLF)
   2. Vestibular nuclei ⇒ paramedian pontine reticular formation (PPRF)
   3. PPRF projects to the ipsilateral abducens nucleus which, in turn, projects to the contralateral oculomotor nucleus
   4. Eyes are yoked together resulting in conjugate horizontal gaze
3. Coordinates eye movements to compensate for head movements
   
   • vestibuloocular reflex - VOR
   • _​_VOR maintains eye position during head turning

Question 13

Nyastagmus:

Answer 13

• Rhythmic oscillations of the eyeballs
  
  • Involuntary to-and-fro, up-and-down, or rotary movements on one or both eyes
• Nystagmus may be produced by:
  
  • Rotation of the head (rotary nystagmus)
  • Observing a moving object when the head is stationary (optokinetic nystagmus)
  • Temperature-generated convection currents in semicircular canal endolymph (caloric nystagmus)

Question 14

Application of warm water into left ear canal ⇒ warmed endolymph “rises” simulating head turning toward ____ and inducing a ___________

Answer 14

left; left-beating nystagmus

Question 15

Application of cold water into left ear canal ⇒ cooled endolymph “sinks” simulating head turning toward _____ and inducing a ______________.

Answer 15

right; right-beating nystagmus