Vestibular Function Flashcards
What is the vestibular system?
A sensory system essential in the control of posture and balance
Where is the vestibular system found and what is it made up of?
In the ear and is a series of fluid filled membranous tubes (labyrinths) which are embedded in the temporal bone
What does the vestibular apparatus consist of?
3 semi-circular canals
Utricle to which the semi-circular cannals all connect
Saccule
What do the semi-circular canals connect to?
Utricle
How are the 3 semi-circular canals positioned in relation to each other?
Right angles
What is found at the bases of the semi-circular canals?
Swellings called ampulla that contain hair cells
Where are hair cells found in the vestibular apparatus?
Ampulla
Utricle
Saccule
What are the utricle and saccule collectively known as?
Otolith organs
What parts of the vestibular apparatus detect linear acceleration?
Otolith organs (utricle and saccule)
What part of the vestibular apparatus detect rotational acceleration?
Semi-circular canals (SCCs)
What do the otolith organs do?
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 is back/front tilt detected by?
Utricle
What is vertical movement detected by?
Saccule
What does SCC stand for?
Semi circularcanals
What is A?
Superior semicircular canal
What is B?
Horizontal semi-circular canal
What is C?
Posterior semi-circular canal
What is D?
Cristae within ampulla
What is E?
Utricle
What is F?
Saccule
What is G?
Maculae
What is H?
Cochlea
What is the ampulla?
The senosry cells of the semi-circular canals which are embedded in swellings at the base of the bony canals
What are the sensory receptors called that are found with the ampulla?
Cristae
What does cristae consist of?
Flexible gelatinous structure called the capula
What does the capula stretch accross?
Entire width of the ampulla and responds to movement of the endolymph within the canals
What does the capula respond to?
Movement of the endolymph fluid within the canals
What is embedded within the gelatinous capula?
Cilia of hair cells which synapse directly with the sensory neurons of the vestibular nerve (CN VIII)
What do the hair cells detect that are found within the capula of the cristae?
Rotational acceleration
How does the capula detect rotational acceleration?
1) If the skull is rotated left or right from rest the endolymph does not move at first because of its inertia
2) But the ampulla moves instantly because it is embedded within the skull
3) Inertia of endolymph produces drag which bends the capula and consequently the cilia embedded in it in the opposite direction to movement
4) If rotate at constant velocity the endolymph catches up and rotates at the same speed removing the shearing force but this takes several seconds
5) Sudden stop will cause endolymph to continue to move due to momentum creating a sense of movement and dizziness
Why does the endolymph not move at first when the skull is rotated left or right?
Becuase of its inertia
What direction to movement does the capula bend due to the inertia of the endolymph producing drag?
The opposite direction to movement
Why does a sudden stop of skull rotation (left/right) produce the sense of movement and dizziness?
The endolymph carries on moving for a few seconds due to its momentum
What are the 2 types of cilia of the hair cells in the capula?
Single very large kinocilium
Progressively smaller sterocilia
What allows the brain to determine movement in space and time?
Distortion of the cilia in the direction of the kinocilium causes depolarisation and increased discharge of action potentials in the vestibular nerve
Distortion of the cilia away from the kinocilium leads to hyperpolarisation and decreased discharge of action potentials in the vestibular nerve
What does distortion of the cilia in the direction of the kinocilium cause?
Depolarisation and increased discharge of action potentials in the vestibular nerve
What does distortion of the cilia in the opposite direction of the kinocilium cause?
Hyperpolarisation and decreased discharge of action potentials in the vestibular nerve
How does the orientation of the capula compared from one to the next, and what does this allow?
Slightly different to one another
So the brain can build a 3D image of body position using the pattern of firing and inhibition recieved
Where does much of the integration of the sensory information from the capula take place?
Cerebellum
How does the direction of the shearing force on the capula compare to the start of rotation and once the head stops?
At the start is against the direction of head rotation
In the end is in the opposite direction to what it started (so same direction as initial rotation