Vestibular system

Question 1

vestibular system

Answer 1

• The vestibular system is essential for maintaining the position of the body in space, which, in turn, is important for coordination of motor responses, eye movements, and posture.
• It consists of:
  • Otolith organs: saccule and utricle  linear acceleration
  • Three semicircular canals (anterior, posterior and lateral) angular acceleration

Question 2

otolith organs

Answer 2

• for translations (linear accelerations) and tilt
• The saccule is an ovoid sac-like structure that is connected to the cochlea (through the canal reuniens) and to the utricle (through the utriculosaccular duct)
• A small area containing hair cells and supporting cells is located within the saccule and constitutes the sensory organ of the saccule –> the macula of the saccule
• The utricle is also an ovoid sac-like structure
• Its sensory organ, the macula of the utricle, is similar to that of the saccule
• The macula of the saccule is almost at a right angle to the macula of the utricle
• When the head is in an upright position, the macula of the utricle is in the horizontal plane, while the macula of the saccule is in the vertical sagittal plane
• the maculae contain hair cell embedded in a gell on which lay the heavy otoliths which make the gal and cilia of the hair cells move when the body moves

Question 3

semicircular canals

Answer 3

• There are three semicircular canals that lie in different planes and are perpendicular to each other to measure angular acceleration
• Each of these canals is continuous with the utricle at each end.
  • Each of the canals ends is dilated, and this dilation is called the ampulla.
  • Inside the ampulla, a cone-shaped structure called the crista ampullaris  here the receptor cells reside
  • A gelatinous mass (the cupula) extends from the surface of the hair cells to the roof of the ampulla and contains the cilia of the hair cells
• In the ampullae of the semicircular canals, when the head turns in the plane of one of the semicircular canals, the inertia of the endolymph generates a force across the cupula, moving it away from the direction of head movement, which results in a displacement of the hair cells within the crista

Question 4

Vestibular sensory receptors

Answer 4

• The receptors in the vestibular system (maculae of saccule and utricle and ampullae of semicircular canals) are the hair cells.
• The hair cells of the vestibular system are of two types:
  1. Type I hair cells are goblet shaped,
  2. Type II hair cells are cylindrical in shape.
• Stereocilia in large numbers project from the apical surfaces of all hair cells.
  • A single kinocilium is present at the edge of the apical surface.
  • The stereocilia are relatively shorter than the kinocilium, and their length increases as they approach the kinocilium.
• When the stereocilia are displaced toward the kinocilium, the hair cell is excited.
• When the stereocilia are displaced away from the kinocilium, the hair cell is inhibited
• Excitation is stronger response than inhibition
• The orientation of the hair cells exploits this
• Left vestibular organ more sensitive to movements to the left and vice versa

Question 5

alcohol and vestibular system

Answer 5

• The capula is in direct connection to blood and thus becomes less viscous when alcohol was consumed while the endolymph remains as thick as before consumption causing a disbalance –> stronger reactions to rotations
  - the endolymph enventually also becomes thinner which the morning after can cause dizziness again since the capula is thicker again

Question 6

BPPD

Answer 6

• Debris floating in canals causing a current in the endolymph
• Debris results from breakdown of the otolith organs (utricle)
• The debris can attach to the capula which sensitizes it to gravity

Question 7

visual system and balance

Answer 7

• when the vestibular system is impaired the visual system can compensate (together with proprioception)
• The vestibulo-ocular reflex (VOR) is a reflex acting to stabilize gaze during head movement, with eye movement due to activation of the vestibular system.
  • Gaze is held steadily on a location by producing eye movements in the direction opposite that of head movement.
• the vestibular system provides 2 more reflexes: vestibulospinal and colic reflex (balance)

Question 8

loss of vestibular organ

Answer 8

• Acute loss of vestibular organs causes disbalance between the two organs
• The body will receive wrong info all forces will feel as if they are angled so your reflexes will occur without them being needed
• Central compensation –> the brain will adapt to the loss of a vestibular organ
  • The vestibular nuclei will start be become more active in the absence of signal to be more balanced to the other vestibular organ when there is no movement
  • When there is movement there will be a disbalance once again
  • This can be tested by moving the head fast to left and right if the eyes lag behind (no vestibulo ocular reflex) when moving to one side the issue is with the organs on that side of the head
• Sensoric substitution –> depend more on other senses
  • Adaptation
  • habituation

Question 9

limitation of vestibular system

Answer 9

• At low frequencies the otolith organs think your moving but the canals don’t –> conflict
• The visual system is effective at low frequencies so this can compensate
• However at 0.2Hz there is a conflict since the otoliths and think there is movement while the canals and visual system are uncertain (you move once every 5 seconds like on a boat –> motion sickness)