Vestibular System - 56

Front 1

How many degrees of movement are there?

Back 1

There are usually 6 degrees of movement
Tranlational and rotational and rotational degrees of freedom of movement
There can be rotation around the vertical, nasal/occipital, and transverse axes

Front 2

What are 5 roles of the vestibular system?

Back 2

1. Compensatory eye movements
2. Postural control
3. Spatial orientation
4. Self-motion detection and perception
5. Cardio-vascular adjustement

NOTES:

Most of the time, we are unaware of the existence of our sense of balance.
We perceive our sense of balance only, when something goes wrong!
Examples: motion sickness, new glasses, Menière’s disease, influence of alcohol, vertigo, etc., etc.

Hint 2

Very = Cute Self PiCS

Front 3

Describe the labyrinth?

Back 3

Located in the petrosal bone. Part of the inner ear. Two components; the semicirular canals and the odoliths (sacculus and utricle)
Info sent via the vestibular nerve
3 semicirular canals:
Anterior semicircular
Horizontal semicircular canal
Posterior semicircular canal
Filled with endolymph
The receptor organs are located in the ampulla
Oriented in 3 dimensions in space: anterior and posterior are bilaterally symetric and are co-planer with the horizontal canal. When they turn the detect acceleration
When one canal gets excited, the other co-planer canal gets inhibited. They are all at 90 degree angles to each other

Front 4

What is the cupula and why is it important?

Back 4

Cupula is a gel-like structure that surround the hair cells and when the head is accelerated, the gel bends the cilia of the hair cells.

Front 5

Describe 2 mechanisms of adequate stimulation of vestibular receptors?

Back 5

Adequate stimulation of vestibular receptors:

A, B = Stimulation of the cupula-endolymph system.

A: resting condition.
B: displacement of the cupula by endolymph current. Thus, the hair cell cilia will be bent and stimulated.

C, D = Stimulation of the utriculus.

C: resting condition; pressure of the otoconia onto the hair cells does not constitute a
stimulus.
D: during head tilt, the otoconia slide across hair cells and thus exert a shear force (F) which constitutes the adequate stimulus.


NOTES:

Fluid stays stationary and presses upon the cupula that in turn presses on the hair cells
These are dynamic receptors, they only work when you move your head. Does not work with constant velocity
The odoliths are gravicepters; they detect the direction of gravity on the head
When you tilt your head the Ca crystals in the odoliths push on the hair cells and send a signal to the brain that the head is tilted

Front 6

1. What is involved in tip link structure?

2. Adaptation motor consists of what?

Back 6

1. Cadherin 23 = a cells adhesion protein + Ankryn (17 repeats?) are inolved in in tip link structure.

2. Adaptation motor consists of actin and myosin 1c

Front 7

Describe the hair cell membrane resting potential and the potential difference generated?

Back 7

-It is -140 mV in the endolymphatic space.
- It is -60 mV in the perilymphatic space

Due to high K+ concentration in endolymph, i.e., 140 mmol/l, but low in Na+ ions (15 mmol/l) [perilymph: Na+ 150 mmol/l, K+ 5 mmol/l]
Makes a potential differential of +80 mV between apex and basolateral pole of hair cells (so-called endolymphatic potential: driving force of receptor potential, because of constant inward K+ current; reversal potential for K+ is -2 mV) .

Front 8

What does this illustrate?

Back 8

Rotating chair give a velocity pusle and look at the cupula deflection. The cupula accelerate and then comes back to rest as the velocity become constant. When you deccelerate, the cupula deflects in the opposite direction.
The cupula only reacts to accelerations, not constant velociities

Front 9

Describe Postural reflexes?

Back 9

Postural reflexes
Tonic labyrinth reflexes (upon the extremities)
-Tonic neck reflexes (upon the extremities)
Righting reflexes = when you lie and animal down and it raises its head and the rest to the body follows
Stato-kinetic reaction

The pic above shows Tonic neck reflex = keeping your neck upright

Front 10

Differentiate between the detection of saccules and utricules?

Back 10

1. The utriculus are oriented horizontally and they detect side tilts (left/right acceleration)

2. The sacculus are oriented vertically and they detect up-down movement

Hint 10

Ur side

Front 11

What does this illustrate?

Back 11

Fencing posture: seen in newborns, a neck reflex
Not seen in adults

Front 12

Give an example of Tonic vestibular and neck reflexes?

Back 12

Tonic vestibular and neck reflexes
If you tilt the cat to the side and the head and neck are aligned it will lift its leg
If you tilt the trunk and leave the head, the cat’s neck will turn to align the head with the ground
If you rotate the neck only, the body will bend to stay on the ground
It is confusing

Front 13

What do these 2 images illustrate?

Back 13

Static kinetic reflex:
In the first pic, you want to have the reflex so you won’t fall and break your neck. When you are walking down the stairs you want to repress the reflex, so you can keep your balance while walking down the stairs.
In the pic with the baby, Lift reaction is a Static kinetic reflex.

Front 14

Describe how info from the vestibular system is transmitted?

Back 14

Info from vestbiular system is transmitted via the vestibular nerve to the scarpus ganglion and then to the vestibular nuclei.
There are several vestibular nuclei:
Superior vestibular nucleus
Lateral vestibular nucleus (does not usually get input from the vestibular nerve)
Medial vestibular nucleus
Inferior/descending vestibular nucleus

Front 15

Differentiate btw:

1. Lateral vestibulo-spinal tract

2. Medial vestibulo-spinal tract

3. Reticulo-spinal tract

Back 15

1. Lateral vestibulo-spinal tract (lateral vestibular nucleus “Deiters”) via ventrolateral medulla and spinal cord to ventral funiculus (lumbo-sacral segments).


2. Medial vestibulo-spinal tract (medial, lateral, inferior, vestibular nuclei), bilateral projection via descending medial longitudinal fasciculus to cervical segments.


3. Reticulo-spinal tract (medial ponto-medullary reticular formation), bilateral projection via funiculi lateralis and medialis to lumbar segments.

Front 16

What does this illustrate?

Back 16

Vestibular collic regions.
If you stimulate one of the semicircular canals, the animal will make movements in the plane of that canal
He cut the vestiubular canals and the observed movements animal does not make movements in the plane of the canal that was cut.

Front 17

What does this show?

Back 17

A. You rotate your head 10 degrees to the right and your eye moves an equal distance in the opposite direction (10 degrees to the left)

B. Top = movements of the cupula—head position, bottom = eye movements. The bottom graph for B. = the eye rotates as far as it can go in the orbit and then it resets (nystagmus)

C. The slow phase is the phase where the eyes are moving in the head in the opposite direction of rotation. The fast phase is the where the eyes reset to compensate and it is in the direction of rotation.

Front 18

1. What is the three-neuron arc?

2. Compare vestibular system and visual system?

Back 18

1. The semicircualar canals are connected with the eye muscles. There are 3 neurons connecting from the labyrinth to the eye muscles.

2. To get an eye movement after vestibular system 16 msec
To get an eye movement after visual stimulation 250 msec because it must go thru the retinal system and visual association cortex


NOTES:

You cannot separate visual and vestibular systems
A vestibular nucleus neuron does not know if it has a visual or vestibular input. It just gets excited/depolarized or hyperpolarized
when you turn the surround around the person and leave the person stationary after a while she will think that she is moving. The vestibular system cannot distinguish motion stimuli from visual stimuli

Front 19

What does this illustrate?

Back 19

This shows that visual input alters vestibular-derived postural information. Therefore, When the drum rotates people think that they are tilted…
This is a way to fool the odoliths (gravireceptors) into thinking they the head is tilted
.

Front 20

How are the eyes and neck related?

Back 20

Some of the axons from the vestibular system go to the eye and some to the neck so that eye and neck and head move together

Front 21

What does this show?

Back 21

This shows that Ipsilateral pathways are inhibitory,and contralateral pathways are excitatory .

Front 22

Describe the classical input of neurons from the vestibular system?

Back 22

Classical “vestibular” cortical areas, input via ventroposterior inferior nucleus of the thalamus. Therefore, these neurons send up collaterals to the thalamus (ventoposterior nucleus). The thalamus sends projections to the cortex (interparietal sulcus) and the VIP areas of the brain get lots of vestibular input.

Front 23

How is spatial hemineglect related to the vestibular system?

Back 23

Spatial hemineglect goes away when the vestibular system is stimulated

Front 24

The vestibular system develops from where?

Back 24

The vestibular system develops from the otic placode in the embryo

Front 25

What is important for the horizontal semicirular canals?

Back 25

The Otx 1 gene is important for the horizontal semicirular canals

Hint 25

HOt One

Front 26

Describe a hemi-labyrinthectomy
and its effect?

Back 26

If you take out one labyrinth, very dramatic things happen…
In a guinea pig, it would roll over continually. The head would tilt to one side and then it would roll over. After some time it would stop. The animal keeps trying to right itself because the one labyrinth that remains is telling the brain that the head is tilted to that side. The head will tilt towards the side of the lesion because of the righting reflex.
There would also be eye movement symptoms: nystagmus

Front 27

1. What happens if you push the brain to learn to adapt to a missing labyrinth?

2. Describe the Bechterew - Phenomenon?

Back 27

Eventully the brain will learn and the animal will stop turning. Disappearance of lesion symptoms is called compensation.

2. If the second labyrinth is lesioned after compensation, we observe a Bechterew-Phenomenon, i.e., similar lesion symptoms as in the case of the lesion of the first labyrinth, but now towards the side of the lesioned second labyrinth. This proves that tonic activity has been restored in the vestibular nuclei of the first labyrinthine lesion.

Front 28

What does this illustrate?

Back 28

It shows that the Vestibuluar system is important in navigation.
Place cells (in the hippocampus): fires when the rat moves in a certain position
Head direction cell: fires when the rat moves its head in a certain direction

Front 29

1. Describe Halmagyi-Curthoys head jerk?

2. What does the above picture illustrate?

Back 29

1. Halmagyi-curthoys head jerk = Have the patient hold an object in both both hand and fully extend the arms in front of them. Then have them walk

2. Induction of nystagmus with warm and cold water irrigation of the ear

Front 30

Describe vertigo?

Back 30

Vertigo: unpleasant sensation in connection with disorientation, misinterpretation of the direction of gravity and misinterpretation of passive and self-motion.
Per se not a disorder, but a consequence of many pathological processes

Front 31

What happens when there is Alcohol-nystagmus and –vertigo?

Back 31

After excessive alcohol intake, alcohol diffuses into the cupula, thus making it lighter than the endolymph. The now heavier endolymph deflects the cupula, effectively rendering it inot a graviceptor, leading to nystagmus and a sensation of self-movement.

Front 32

What are some movement disorders?

Back 32

Seasickness, airsickness, carsickness, space motion sickness

Front 33

What is perilymph fistula?

Back 33

Rupture of the otic capsule, usually at the oval or the round window, causing perilymph leakage and abnormal transfer of pressur changes.

Front 34

Differentiate between:

1. Tullio phenomenon

2. Tinnitus

Back 34

1. Tullio phenomenon:
Pathological sound-induced vestibular signs and symptoms in patients with perilymph fistula.


2. Tinnitus:
“Ringing” in the ear.

Front 35

Describe Menièr’s disease?

Back 35

It is caused by temporary leakage of endolymph from the labyrinth and acting upon vestibular nerve fibers: blockage of nerve impulses. Classical trias of fluctuating hearing loss, tinnitus and episodic vertigo.

Front 36

What is vestibular neuritis?

Back 36

Acute partial unilateral vestibular loss due to inflammation of the vestibular nerve with rotatory vertigo, nystagmus, postural imbalance, nausea and vomiting.

Front 37

What does this illustrate?

Back 37

-Benign paroxysmal positional vertigo where people have the sensation of falling backward when they get out of bed and they get nausea and nystagmus.

-Benign paroxysmal positional vertigo is due to an accumulation of loose otoconia in the posterior semicircular canal. Otoconia – movement of calcium carbonate within the ear, causes the feeling of falling down.
-Dix-Hallpike Test – tests for benign paroxysmal positional vertigo.

-There is a simple treatment for benign paroxysmal positional vertigo: just have the patient move in certain postions to get the debris to clear out of the posterior semicircular canal