UMass Amherst KIN 460 - 12- Vestibular system (25 pages)

Kinesthetic Organs Overview What is the function of the vestibular system How is motion detected in the vestibular system How does the vestibulo ocular reflex work The vestibular system 3 semicircular canals anterior posterior horizontal 2 otoliths utricle and saccule Vestibular System in 2 minutes https youtu be P3aYqxGesqs Vestibular apparatus Semicircular canals Angular accelerations Otolith organs utricle and saccule Linear accelerations Static head position Box 14A A Primer on Vestibular Navigation Overview What is the function of the vestibular system How is motion detected in the vestibular system How does the vestibulo ocular reflex work Sensory receptors of the vestibular system Sensory receptors hair cells located in the ampullae utricle and saccule Part 1 Cross section of hair cells with kinocilia of a group of hair cells located on the same side of the hair cell Top view of hair cells Stereocilia move toward kinocilium depolarization neurotransmitter release excitation of vestibular nerve Morphological polarization of hair cells in the utricular and saccular maculae Response from a otolith afferent fiber in a monkey seated in a tilting chair Prior tilt high firing rate above zero firing rate increases or decreases depending on the direction of tilt Firing rate remains constant as long as tilting force remains constant encoding static forces applied to the head Forces acting on the head displace the otolithic membrane of the utricular macula Schematic representation of the action of otolith at rest left when the head is tilted centre and during linear acceleration right The action of otolith is similar both during tilting of the head and during linear acceleration Orientation of the utricular and saccular maculae in the head Arrows orientation of kinocilia Range of orientations signal linear forces in every direction the head might move Utricle and saccule Utricle Oriented horizontally responds to lateral displacement of the head Saccule Oriented vertically responds to up down and forward backward displacements of the head The ampulla of the posterior semicircular canal Semicircular canals Sensory receptors hair cells in the ampulla Sense head rotations Functional organization of the semicircular canals Canals and ampullae full of endolymph Hair bundles involved in into the cupula gelatinous mass is a barrier for endolymph Head turns in the plane of one semicircular canal inertia of endolymph force across the cupula cupula and hair cells displacement in opposite direction of head movement depolarization or hyperpolarization Response of a vestibular nerve axon from semicircular canal to angular acceleration Prior acceleration high firing rate above zero baseline Initial acceleration firing rate increases cupula deflection despolarization Constant velocity return to baseline cupula returns to non deflected state Deceleration decreased fing rate cupula defletion in opposite direction Benign paroxysmal positional vertigo Unpleasant sensation of head spinning when head moves due to otoconia debris creating currents in endolymph fluid Many causes concussions Overview What is the function of the vestibular system How is motion detected in the vestibular system How does the vestibulo ocular reflex work Functional organization of the semicircular canals 2 sets of semicircular canals Dynamic contributions Vestibular nystagmus Rotating chair Head motion results in smooth counter rotation of the eyes in opposite direction to head motion slow phase interrupted at more or less regular intervals by a quick flick in the other direction quick phase giving rise to a sawtooth like eye movement Initiated by semicircular canals Connections underlying the vestibulo ocular reflex 1 Head turns left 2 Eyes turn right 3 Activate left medial rectus and right lateral rectus Galvanic Vestibular Stimulation GVS Application of weak electrical stimulation to mastoid bones that carries through the head and interferes with vestibular system Leads to postural sway responses When seated leads to illusion of moving GVS elicits sway in the direction opposite to the negative electrode the side the person perceives they are tilting to This response is automatic and involuntary https youtu be Px6sOkjj ZE t 2m35s