Lecture 14: Vestibular System

• What sensory function do the ears maintain aside from hearing?

  Equilibrium
• What are the two main sections of the inner ear?

  Membranous labyrinth and bony labyrinth
• What are the three areas of the bony labyrinth?

  Semicircular canals, vestibule, cochlea
• Which structures contain receptors for equilibrium?

  Semicircular canals and vestibule
• What is the collective name for the receptors in the semicircular canals and vestibule?

  Vestibular system
• What does the vestibular system maintain in response to head positioning?

  Stable eye and body position
• What is part of the bony labyrinth?

  Vestibule
• What are the parts of the membranous labyrinth found within the vestibule?

  Utricle and saccule
• What sensory receptor area is found in the utricle and saccule?

  Macula
• What do the maculae in the utricle and saccule contain?

  Receptor hair cells
• What is the otolithic membrane made of?

  Gelatinous material covered by glycoprotein
• What are otoliths also known as?

  Otoconia
• How do otoliths affect hair cells in the maculae?

  They apply shearing stresses to hair cells
• What does the weight of the otoliths provide to the otolithic membrane?

  Sufficient inertia
• What do the utricle receptors lie in?

  Horizontal plane
• What do the saccule receptors lie in?

  Vertical plane
• What do the semicircular canals detect?

  Rotational acceleration or deceleration
• What is the swollen area at the end of each semicircular canal called?

  Ampulla
• What are the sensory receptors in the ampullae called?

  Crista
• What structures comprise the sensory hair cells in cristae ampullaris?

  Kinocilium and stereocilia
• What connects each stereocilium to its neighbor?

  Tip link
• What encapsulates the stereocilia in the crista?

  Gelatinous structure called cupula
• How is rotational acceleration detected by the ampullary crista?

  Through mechanical movement in endolymph
• What happens to the cupula when the head is moved?

  It is pushed to one side
• What effect does bending the stereocilia have?

  Affects firing rate of vestibular nerve fibers
• What are the main components of the vestibular system?

  • Utricle and saccule (maculae)
  • Semicircular canals (ampullae and cristae)
  • Otolithic membrane and otoliths
• How do the utricle and saccule differ in their orientation and function?

  • Utricle: Horizontal orientation, detects horizontal movements
  • Saccule: Vertical orientation, detects vertical movements
• What is the role of the cupula in the vestibular system?

  • Encapsulates stereocilia
  • Moves with endolymph displacement
  • Affects hair cell stimulation
• What is the relationship between hair cell movement and vestibular nerve firing?

  • Hair cell movement alters firing rate
  • Increased movement leads to increased firing
  • Decreased movement leads to decreased firing
• What mediates the vestibular control of skeletal muscles?

  Descending vestibulospinal tracts
• How do the descending vestibulospinal tracts affect motor neurons?

  They modulate alpha and gamma motor neurons
• What is the role of the vestibulospinal tracts in maintaining balance?

  They facilitate extensor muscles and inhibit flexor muscles
• Where do the vestibulospinal tracts descend in the spinal cord?

  In the ventral funiculus
• What mediates the vestibular control of extraocular muscles?

  Ascending medial longitudinal fasciculus
• Where does the medial longitudinal fasciculus originate?

  In the vestibular nuclei
• What is the function of the vestibulo-ocular reflex?

  It maintains a steady gaze during head movement
• How does the vestibulo-ocular reflex help an animal?

  By moving eyes opposite to head movement
• What types of head movement does the vestibulo-ocular reflex compensate for?

  Linear, rotational, or a combination of both
• What are the key functions of the vestibulospinal reflex and vestibulo-ocular pathway?

  • Vestibulospinal reflex:
  • Controls skeletal muscles for balance
  • Modulates alpha and gamma motor neurons
  • Vestibulo-ocular pathway:
  • Controls extraocular muscles for gaze stability
  • Compensates eye movement during head motion