Movement Sensation

• What does the vestibular apparatus consist of?

  3 semi-circular canals (& their ampulla)

  Vestibule (utricle & saccule)
• Utrical & saccul both contain a macule, which contains hair cells.
• What do the utricle, saccule & semi-circular canals detect?

  Utricle -> detects horizontal movements

  Saccule - detects vertical movements

  Semicircular canals -> detect rotation
• What is vestibular sensation?

  Sense of balance/head position
• What is the vestibulospinal reflex?

  Stops you falling over by innervating spinal cord LMNs
• What is the vestibulocolic reflex?

  Keeps your head up by innervating cervical LMNs
• What is the vestibulo-ocular reflex?

  Keeps your gaze fixed by innervating cranial nuclei of III, IV & VI (extra-ocular nerves)
• Otolithic organs - vestibular sensation

  Tilt (linear) -> otolithic membrane moves due to gravity -> movement of stereocilia (within gelatinous cap) -> opening of K+ channels -> depolarisation -> opening of voltage-gated Ca+2 channels -> glutamate release -> afferent neurons project to vestibular nuclei in the brainstem -> vestibular nuclei project to multiple nuclei in the thalamus -> projects to distributed network of cortical areas involve in conscious vestibular sensation (lots of different areas which contribute to sense of self in space)
• Semi circular canals - vestibular sensation

  Tilt (rotational) -> endolymph moves due to gravity -> moves gelatinous cupula -> stereocilia detect the displacement of endolymph -> opening of K+ channels -> depolarisation -> opening of voltage-gated Ca+2 channels -> glutamate release -> afferent neurons project to vestibular nuclei in the brainstem -> vestibular nuclei project to multiple nuclei in the thalamus -> projects to distributed network of cortical areas involve in conscious vestibular sensation (lots of different areas which contribute to sense of self in space)
• Vestibulo-ocular reflex

  Vestibular information is transmitted dwon vestibulocochlear nerve to medial vestibular nucleus -> communicates with nuclei of CN III, IV & VI -> coordination of eye movement in order to counteract head movement (e.g. being able to focus on a single point whilst moving your head)
• Vestibulospinal & vestibulocollic reflexes

  Vestibular information if transmitted down VIII to the medial & lateral vestibular nuclei -> project to & from cerebellum & down the spinal cord (through lateral & medial vestibulospinal tracts)

  Tracts mediate the vestibulocollic & vestibulospinal reflexes
• Fill in the blanks

  A) Vestibulocochlear nerve

  B) Cochlear nerve

  C) Vestibular nerve

  D) Utricle

  E) Saccule

  F) Anterior semicircular

  G) Anterior ampulla

  H) Lateral semicircular

  I) Lateral ampulla

  J) Posterior semicircular

  K) Posterior ampulla

  L) Endolymphatic