Vestibular Function Flashcards
Which bone contains the vestibular system?
Temporal bone
What do the three semicircular canals all connect to?
All connect to the utricle
What is the name given collectively to the utricle and the saccule?
Otolith organs
What do the utricle and the saccule do?
They detect linear acceleration and encode information about the position of the head in space; back/front tilt is detected by the utricle, vertical movement is detected by the saccule.
What do the semicircular canals detect?
They detect rotational acceleration
Where are the sensory cells of the semicircular canals located?
The sensory cells of the semi-circular canals are embedded in swellings at the base of the bony canals called ampulla.
What are the sensory receptors in the swellings? What are they composed of?
Cristae - consist of flexible gelatinous structure called the cupula
Describe the cupula
Stretches across the entire width of the ampulla and responds to movement of the endolymph fluid within the canals.
How does the cupula make a connection with the vestibular nerve?
Cilia of hair cells are embedded in the gelatinous cupula, these cilia synapse directly with the sensory neurons of the vestibular nerve
What do the hair cells detect?
Rotatinoal acceleration
How is rotational head movement detected?
Endolymph at first does not move during rotation because of inertia, ampull moves instantly because it is embedded in the skull.
Resultant bend in cupula and the cilia embedded in it.
How do you become dizzy?
If rotate at constant velocity, the endolymph catches up and rotates at the same speed, removing the shearing forces, but this takes several seconds.
Sudden stop will cause endolymph to continue to move due to momentum creating a continuing sense of movement and dizziness.
What are the different types of the cilia of the hair cells?
There is a single very large kinocilium and a set of progressively smaller stereocilia
How is the rate of discharge of AP’s in the vestibular nerve increased / decreased?
If the cilia are distorted in the direction of the kinocilium - depolarization and increased discharge of AP’s
If the cilia are distorted away from the direction of the kinocilium - hyperpolarization and decreased discharge of AP’s
What is the sensory apparatus of the utricle and saccule collectively known as?
The maculae
How are the macula orientated in the utricle and the saccule?
The macula in the utricle are orientated on the horizontal plane, those in the saccule on the vertical plane.
What is the structure of the maculae?
Have a set of cilia (one kinocilium and a series of stereocilium) which protrude into a gelatinous mass called the otolith membrane. Embedded in the otolith membrane are CaCO3 crystals called otoliths.
How is the increase rate of action potential firing achieved during a backwards head tilt?
Head tilt detected by utricle
Otoliths have a greater density than endolymph, more affected by gravity
Tilt of the head moves the otoliths and the otolith membrane inwhich they are embedded - distorts jelly and moves the cilia.
Otoliths move in the direction of the kinocilium during backwards head tilt causing depolarisation and increased discharge of APs. Opposite for forward tilt.
What forces does the saccule respond to?
Vertically orientated macula in the saccule respond to vertical forces e.g. movement in a lift, and provide information on orientation of head when lying down.
Where do many of the sensory afferents of the vestibular nerve terminate?
Vestibular centres of the medulla
Vestibular centres of the medulla have strong connections with which brain structure?
Cerebellar centres - which co-ordinate the postural muscles required to maintain balance.
How do projections from the vestibulat nuclei reach the descending motor-pathways?
Projections from the vestibular nuclei on one side project ipsilaterally, bilaterally and contra-laterally to descending motor pathways (and also the extraocular nuclei (extraocular muscles)
Where do proprioceptors signalling limb and body position, neck and eye muscles send their sensory information?
TO vestibular nuclei
How is kinaesthesia achieved?
Vestibular nuclei project via the thalamus to the cerebral cortex - perception of movement and body position
