Vestibular System Flashcards
What is the function of the vestibular labrynths?
Sense head motion (each canal detects one of three different rotational movements)
What are otoliths?
Utricle and saccule
What aspects of motion do the vestibular labrynths detect?
Acceleration of the head and intertial forces
What does info from the the vestibular system used to generate?
Vestibulo-ocular reflex (VOR)
What is the purpose of the VOR?
To keep the visual scene steady on the retina during head movements
The output of the vestibular system is proportional to what?
Head velocity
Example:
Head accelerates from 1-10 deg/ sec. The vestibular system detects the acceleration and it integrates over time to determine the head velocity. It then sends a signal to the eye muscles to counter rotate the eyes with a velocity of 10 deg/sec
What are the components of the vestibular apparatus?
Ampulla of the superior canal, Saccular macula, Utricular macula
Describe the orientation of the hairs in the ampulla:
Hairs are all oriented in the same direction
Describe the orientation of the hairs in the saccular macula:
Striola sperates hairs with opposite polarity. Vertical organization
Describe the orientation of the hairs in the utricular macula:
Striola sperates hairs with opposite polarity. Horizontal organization.
Polarization of what hair cells gives the vestibular aparatus is directional sensitivity?
all three…Ampulla of the superior canal, Saccular macula, Utricular macula
What is the significance of the striola?
Orientation of the hair cells relative to the striola in each structure gives continuous representation of ALL body movement directions
What are hair cells connected to?
Primary afferent fiber and an efferent fiber
Where do apical hair cells of the utricle and sacculus project to?
They project into the otolithic membrane (gelatinous mixture)
Is the method of stimulating the hair cells in the ampulla the same as the utricle and sacculus?
No the mechanism is different.
What is the otoconia?
Calcium carbonate that gives the gelstinous mixture weight
What forces depolarize the hair cells?
Backward head tilt or forward acceleration
Hairs bend toward the kinocilia
What forces hyperpolarize the hair cells?
Forward head tilt and forward deceleration
hairs bend away from the kinocilia
When considering inertial forces….what directions do the hear cells move?
Displacement of the otolithic membrane and hair cells is in the OPPOSITE direction of the inertial force
What does depolarization of hair cells produce?
Increase impulse frequency…this increases the response of the innervating CN 8 fiber
What does hyperpolarization of hair cells produce
decrease impulse frequency…this decreases the response of the innervating CN 8 fiber
What is kinocilia and steriocilia
the endings of the hair cells. Kinocilia is the tall cilia and it is singular. There are many, smaller sterocilia.
What are the three degrees of rotation?
Yaw: z axis
Roll: x axis
Pitch: y axis
How do the three degrees of rotation help in the vestibular system?
This is how we detect acceleration and deceleration….it is a very sensitive system
The left anterior canal works with……
the right posterior canal
The right anterior canal works with….
the left posterior canal
What is the cupula?
a gelatinous membrane extending from the ampullary crest to the top of the ampulla
Whta displaces the cupula?
the cupula is displaced by the inertia of the fluid in the semicircular canals due to angular acceleration or deceleration of the head
If you move your yead to the right…which way does the fluid/ cupula move?
to the left
Where do the cilia of hair cells project in the canals?
Into the cupula
Why do pairs of canals on opposite sides of the head work together?
To provide bilateral information about rotation
Does left rotation excite or inhibit left CN 8 and vestibular nuclei?
Excite (and it inhibits the right CN8 and VN)
When you turn your head left and the left vestibular nuclei gets excited…what does the left VN then excite?
- The right abducens nuclei (which then activates the right lateral rectus muscle
- the MLF (which then excites the left oculomotor nucleus –CN 3)
When resting, what are the vestibular nerves doing?
maintaining a resting discharge when there is no head movement
What happens in pathologic conditions?
No activity is coming from one of the canals and when there is comparison of the activity from the two canals, it is interpreted as rotation to the side that is firing as normal (away from the silent side)
Describe the nystagmus that results in a pathologic condition?
Slow eye movements toward the silent side and then a quick reset to the normally firing side (the side your brain thinks you are rotating towards)
