Physiology 3120 Lecture 8: Neuro1
9 May 2018
School
Department
Course
Professor
Physiology 3120
Dr. Pruszynski
Lecture 8
Vestibular System and eye movements
Vestibular System
- Position and motion of head in space
- provide info about both rotational and linear movement
- located in the inner ear (right about the cochlea)
- you have 3 semicircular canals
o tell you about rotational sense of motion
o located above the cochlea
o anterior, lateral and posterior
- you have 3 otoliths (utricle, saccule etc)
o tell you about the linear sense of motion
- this pic is one of the 3 semicircular canals
o similarities to auditory system: the transduction elements are hair cells
o movement of hair cells transduce your motion through space
o for semicircular canal, if you move your head, the canal itself is filled with
endolymph fluid (same fluid that is in cochlea) and bc the canal is rigidly
attached to skull, it will move immediately with head
o but bc of the intertia of the fluid (the fluid is not rigidly attached) its going to lag
your movement
o the net effect is that the fluid relative to the skull is lagging (moving in opposite
direction of movement) and exerting a force on the cupula
o the cupula is a gelatinous wedge that blocks the fluid from moving – so the
gelatinous wedge gets pushed and the hair cells get moved
- this pic shows 2 of the 3 otoliths
o otoliths sense linear motion
▪ within the gelatinous wedge you have otoconia (crystals of CaCO3
embedded in the gelatinous material)
▪ these provide mass to these wedges, so that if you accelerated and
started to move, the inertia of the otoconia will cause deflection of the
hairs while the gelatinous wedge moves (bc its forced to move)
o the saccule (the vertical otolith)
▪ bc it has otoconia in it, it is always being pushed down by gravity when
you stand up right
▪ provides you info about your orientation relative to gravity
o this is also true about the other otoliths
o together, the 3 otoliths provide you a continuous info about the orientation of
your head in space
o the semicircular canal is diff
▪ if you start to spin head, you get inertia and activate your hair cells
▪ if you continue to spin your head at a constant velocity, eventually the
endolympth fluid will begin to catch up and there would be no forces
exerted on the hair cells
▪ so in semicircular canals, you don’t have a mechanism to sense your
constant rotation but in otoliths, you have the ability to sense your
constant head tilt relative to gravity
Semicircular canals (rotation)
- Three orthogonal fluid-filled structures
- Ampula - swelling in the canals.
- Cupula - Gelatonous wedge that interrupts the canal.
- Hair cells are embedded in the gelatinous cupula and attached to basal layer.
- When the head moves (acceleration), the endolymph lags behind and thus pushes on
the cupula, which in turn moves the hair
- If you keep moving, eventually the fluid catches up and the hair cells no longer have
forces exerted on them and you no longer get any signaling info about the rotation of
your head – hair cells return to straight. (can only signal changes in head orientation)
Otoliths (linear)
- Utricle
o 2 of these
o oriented horizontally
- saccule
o oriented vertically
- Have gelatanous mass, this time filled with Otoconia (calcium carbonate)
o So it’s the CaCO3 that causes the inertia here
- The gelatanous mass again filled with hair cells.
- If moving, the otoconia lag behind and thus deflect the hair cells.
- Because of the otoconia, the hair cells in the saccule can provide constant information
about gravity.
- Although the saccule is orientated vertically, which is important when you are standing
up right, it is the combination of information from all of the otoliths that you give you
the full info about how your head is oriented
- Bc as soon as you deviate a little bit in one direction, now all 3 of them are signaling info
about the orientation of your head your head in one way or another
- This is same for the semicircular canals, each one individually works in a particular
direction so you have to integrate info from all of them to gain a whole percept of how
your head is rotating in space
Benign positional vertigo
- Commonly occurs after head trauma or infection of vestibular apparatus.
- Characterized by sudden attacks of vertigo and nausea produced by turning the head to
certain positions.
- Due to distortion of endolymph flow by debris in semicircular canals (e.g. otolith
crystals).
- Can be cured (at least temporarily) but moving the person through a series of
maneuvers that clear the debris.
- The crystals in the otolith can break off –stones flowing around in our endolympth fluid
o This happens to all of us constantly – they are being constantly removed
o But sometimes, for ex: bc of an infection or head trauma, a big chunk of it falls
off and it migrates into semicircular canal, it changes the intertial properties of
the fluid in that semicircular canal
o So when you move your head in particular way, these crystals are adding or
changing the forces impacted on the hair cells within the semicircular canal
Document Summary
Position and motion of head in space. Provide info about both rotational and linear movement. You have 3 semicircular canals located in the inner ear (right about the cochlea: tell you about rotational sense of motion, anterior, lateral and posterior located above the cochlea. Cupula - gelatonous wedge that interrupts the canal. Hair cells are embedded in the gelatinous cupula and attached to basal layer. When the head moves (acceleration), the endolymph lags behind and thus pushes on the cupula, which in turn moves the hair. Utricle: 2 of these, oriented horizontally saccule, oriented vertically. Have gelatanous mass, this time filled with otoconia (calcium carbonate: so it"s the caco3 that causes the inertia here. The gelatanous mass again filled with hair cells. Because of the otoconia, the hair cells in the saccule can provide constant information. If moving, the otoconia lag behind and thus deflect the hair cells. about gravity.
