Unit 7: The vestibular system

what are the roles of vestibular information in our daily life?

involved in a series of reflexes:

• balance & postural control

• visual stability

• regulation of blood pressure

what is the vestibulo-spinal reflex?

involved inbalance & postural control

what is the vestibulo-ocular reflex?

visual stability, reflex of vestibular organs responding to our eyes

• when we move our head, our eyes compensate for the head movement

what is the vestibulo-autonomic reflex?

regulates blood pressure and involuntary actions that are important for our survival

• our ability to change positions: laying down and standing up

  • healthy: slight decrease in blood pressure but has no change

  • damaged: oxygen level to the brain is not optimal, blood pressure decreases (potential black out)

what information does the vestibular system provide?

• provides an accurate measure of where we are in space and position of ourselves in space (balance and spatial orientation)

where is the vestibular system in the human body located?

• vestibular organs are located in the inner ear

• vestibular organs and cochlea form the labyrinth of the inner ear

what are vestibular organs?

two kinds in each ear:

1. three semicircular canals, sense rotational movements (turning head to the right or left)

2. a utricle and a saccule that form the otolith organs, sense linear acceleration and gravity (when we are in a car moving forward)

how are the vestibular organs sensitive to change?

they detect changes in acceleration, movements of any amplitude in any direction will be detected (forward, backward, sideways, upward, downward)

• do not respond to constant velocity

what is the function of hair cells in the vestibular organ?

transduce the mechanical movements into neural energy

• tallest stereocilia is the kinocilium

how do vestibular organs work when the head is moving?

when we move our head, the movements cause the sterocilia to bend, which causes a change in voltage

• cells are depolarized

how do vestibular organs work when the head is not moving?

when the head is not moving, we are in a resting state

what is the resting state?

observed when stereocilia are not bent (sitting upright and still responding)

what is depolarization (excitation)?

observed when the cell increases its firing rate, stereocilia bend more in the direction of the kinocilium

what is hyperpolarization (inhibition)?

head movement still bends, and causes a change in voltage

observed when stereocilia bend in the direction opposite to the kinocilium

• cell decreases it’s firing rate

what is the definition and function of otolith organs?

sense linear acceleration and gravity

what are the utricles and saccules?

form the otolith organs

utricles: contains 30,000 hair cells that detect changes in acceleration along the horizontal plane (tells brain we are moving forward)

saccules: contains 15,000 hair cells that detect changes in acceleration along the vertical plane (feeling of upwardness in elevator)

what is otoconia?

crystals lying on top of a gelatinous layer

• as we accelerate, they drag behind

• linear acceleration and gravity cause a displacement of the otoconia (causes a deflection of the hair cells)

what is striola?

band that determines the direction of the kinocilium

• divides the organ into two sections

• brain understands the direction of our accelerations because of patterns of responses

what are hair cells?

embedded in the gelatinous layer, pulled by crystals in one direction

what are the functions of semicircular canals?

sense rotational movements, moving our head up or down or side to side

what are the three semicircular canals?

anterior

posterior

horizontal

• each canal is filled with perilymph and contains a smaller canal that is filled with endolymph

• canals are oriented along different axes

• as the head is rotated, the fluids move in one or more canals

what are the structures of semicircular canals?

ampulla: where tubes connect, each canal has one containing a cupula

cupula: a gelatinous membrane, the bottom part of the cupula (crista) contains the hair cells involved in process of transduction

hair cells: as fluids move in canals, they push on the cupula (like wind) and hair cells’ stereocilia will bend

what is the direction of rotational movements?

different rotational movements cause hair cell’s deflections in one or more canals

how can we tell different rotational movement cause changes in semicircular canals?

Push-pull effects

what are the push-pull effects in the two ears?

arrangement of the hair cells within the two ears are such that when one ear is depolarized, the other is hyperpolarized (tells use direction of the rotation and movement in our head)

what is the difference between low vs high amplitude movements?

the more the hair cells bend, the larger the change in the voltage

• high amplitude movements = larger change in voltage than small amplitude movements

what are the sinusoidal changes in angular acceleration?

moving our head right(+) and left(-) and 0 represents

• measures how the neurons fire when we move our head

• as you move your head, neurons start to signal our brain about the movements

what is the deflection of the cupula after acceleration and deceleration?

• as the rotation starts the cupula bends in one direction, once reaching angular acceleration it goes back to it’s position

• when the rotation is stopped abruptly, the fluids keep moving and the cupula deflects in the opposite direction

what is the experienced speed of turning?

as the chair rotates, the increase in our experience is represented and we experience the feeling that we stopped rotating (even though we are)

• semicular canals respond to changes and not constant velocity

• when the chair stops, we have the feeling that we are rotating in the opposite direction

what is the exponent for turning sensation?

magnitude of estimation method so that the participants can give us values

exponent of about 1.3

what is passive translation?

when we are in the dark and sitting in a chair, what our experience will be

• we are good at saying which direction we are moved or how fast or far they moved you

what is the perception of tilt works?

tells us that we are very precise at reporting the amount that we are tilted at any direction, even in the dark

what do dysfunctions of the vestibular sense cause?

• visual instability (blurred vision, eye and head not coordinated)

• spatially disoriented

• postural inability, dizziness, vertigo, imbalance, blood pressure dysregulation, illusory self-motion

what is vertigo?

symptoms: sensation of feeling off balance, dizzy, feel like they are spinning, nausea, difficulty with vision, no change in hearing

cause: commonly BPPV, small calcium particles accumulate in the canals

• can be treated, use of exercise to move particles in canals

what is vestibular neuritis?

symptoms: sensation of feeling off balance, dizzy, feel like they are spinning, nausea, difficulty with vision, no change in hearing

cause: inflammation of vestibular nerve

• treatment for inflammation

what are labyrinths?

symptoms: vestibular symptoms and issues with hearing

cause: inflammation of the vestibular and cochlear nerve

• in addition to vertigo, tinnitus and or hearing loss (noises that they hear)

what is motion sickness?

symptoms: feeling sick while in motion because of signals that we are not moving (vestibular) but that we are (visually)

• occurs in people when they travel by car, train, airplane or boat

cause: disagreement between vestibular organs and vision

what is the illusion of self-motion?

aka vection, stationary but we get the feeling that we are moving when we see that something else is moving