Physiology Of Balance Flashcards
What is the vestibular system & where is it located
Sensory apparatus of balance located in the inner ear
What are the five key end organs of the vestibular system
The two otolith organs (urticaria & saccule)
The three semicircular canals
What structure(s) are involved in sensing head position (linear movement)
The otolith organs - urticle & saccule
Where are the otolith organs located
In the vestibule
What otolith organ detects horizontal movement of the head
Urticle
What otolith organ detects vertical movement of the head
saccule
What is the sensing organs of the otolith organs called
The macule
What does the macule of otolith organs contain
Stereocilia & their supporting hair cells
Gelatinous matrix with otoconia
What are otoconia
‘Ear stones’
Kinocilium vs stereocilia
Kinocilium - the largest hair-like projection on hair cells that serves as a reference for stereocilia movement
Stereocilia - all other hair-like projections that move on the hair cells and cause release of neurotransmitters
What would increase the rate of action potential firing from the hair cells
Deflection of stereocilia towards the Kinocilium
What would decrease the rate of action potential firing from the hair cells
Deflection of stereocilia away from the Kinocilium
How are the macula’s of the saccule & utricle located with respect to each other & why is this important
They are oriented 90 degrees to one another so that they respond to positions in different planes
Describe the steps that initiate an action potential in the vestibular nerve as a result of linear head movement
- When the head moves, gravity causes the stones in the membrane of the macula to move
- The movement of the stones causes stereocilia to bend
- This initiates an action potential in the vestibular nerve fibers
What end organs of the vestibular system detect head movement
semicircular canals
What are the three semicircular canals
Anterior
Lateral
Posterior
(Two in horizontal plane, one in vertical plane)
(90 degree orientation)
What is the name of the region at the base of the semicircular canal where it meets the vestibule
Ampulla
What does the ampulla contain
Crista ampullaris (cupula, hair cells & sensory nerve fibres)
How does head movement lead to CN VIII firing
Deflection of the stereocilia caused by motion of the endolymph in the semi circular canal
This results in an opening (or closing) of the transduction channels of hair cells
This changes the membrane potential of the hair cells resulting in release of neurotransmitters & CNVIII firing
What part of the vestibular system is responsible for sensing head position
The otolith organs (urticle & saccule) in the vestibule
What otolith organ senses horizontal movement
Urticle
What otolith organ senses vertical movement
Saccule
What is the name of the sense organ of each otolith organ
Macula
What is found in the macula
Stereocilia that project upwards into the gelatinous matrix with otocania
Kinocilium vs sterocilia
Kinocilium is the largest hair-like projection on hair cells that serves as a reference point for the surrounding sterocilia
What would increase the action potential firing rate of the hair cells
deflection of stereocilia towards the kinocilium
What would decrease the action potential firing rate of the hair cells
deflection of stereocilia away from the kinocilium
Vestibule-ocular reflex vs nystagmus
Vestibule-ocular reflex - Reflex that helps stabilise vision during head movements by automatically adjusting eyes to counteract head movement. Is a physiological nystagmus
Nystagmus - Involuntary eye movement. Can be physiological (VOR) or pathological.
What would happen to the firing rate of the left & right horizontal (aka lateral) semicircular canals if you were to turn your head to the left
Excitation on left hand side,
Inhibition on right hand side
What would happen to firing rate of the left & right horizontal (aka lateral) semicircular canals if you were to turn your head to the right
Inhibition on left hand side,
Excitation on right hand side
What would happen in right vestibular damage
The right semicircular canal is not working/ firing ⇒
The left hand side is firing more than the right ⇒
The brain perceives this as turning left ⇒
Vertigo & nystagmus
=> This is similar for left vestibular damage
What movements are detected by the three different semicircular canals
Left & right rotation ⇒ lateral (horizontal) semicircular
Right & left lateral flexion ⇒ posterior semicircular canals
Flexion & extension ⇒ anterior semicircular canal
What are the three central pathways of vestibular nuclei
- Vestibulospinal tract - motor output to neck, back and leg muscles
- Medial longitudinal fasciculus & ocular muscles - eye motor output
- Medial lemniscus and thalamus to cerebrum
