Sensory systems L3: Vestibular System

Question 1

What are 6 characteristics of equilibrium?

Answer 1

1. Sense of body orientation and motion
   
   • Walking; side ways; backways
2. Body orientation with respect to gravity
   
   • Eg. do on roller coaster –> system gets overloaded (in a situation that is not “normal” or when taking off in plane) –> change in sensation and gravity
3. Discriminate self-generated movements from external forces
   
   • System realises that is not an internal change –> external force stops something (awareness of situation)
4. Activates reflex pathways – compensatory body movements- Eg. Don’t have to think to put one foot in front of other when walking or learning to driver (new driver) VS old driver –> don’t need to think)
5. Also activates pathways that project to the cortex;
6. Other senses help maintain equilibrium: vision and proprioception.

Question 2

What happens when equilibrium is out of place? (eg. balance is out of balance)–> What does your system do for you?

Answer 2

• Reacts to prevent you from falling
• If you let yourself go forward, don’t need to tell your leg to move
• The moment you do this –> autonomically leg will move
  
  • Not the cortex
  • Cerebellum detects movement and sends information done

Question 3

Semi-circular canals are responsible for the ____ space (when you move your head its because something is happening) EXAM

Answer 3

3D

Question 4

____ and ____ are responsible for the movement (eg. horizontal, forward and back and vertical) EXAM

Answer 4

Utricle; saccule

Question 5

What is endolymph?

Answer 5

Thick glutinous substance

Question 6

Each SSC has its own ______ (where hair cells are found = connect with nerves) Once cells are activated they send signals towards the nerve

EXAM QUESTION

Answer 6

ampulla

Question 7

What do 2 vestibular apparatus consist?

EXAM QUESTION

Answer 7

1. Semicircular canals – they detect rotational or angular acceleration or deceleration of the head (rotational equilibrium)
2. Otolith organs – they detect changes in the rate of linear movement and provide information about head position relative to gravity (gravitational equilibrium). When you walk forward

Question 8

What are 5 characteristics of semicircular canals?

Answer 8

1. Fluid filled canals (endolymph)
2. Detect rotational or angular acceleration or deceleration;
3. Canals are perpendicular to each other (map 3D space)
   
   • Why is this important? –> because we live in a 3D world –> not helpful if could only detect 2D (missing other rotation)
4. Receptors (hair cells) are located in the cristae ampullaris within the ampulla of each canal
5. Hairs are embedded in gelatinous material called the cupula. Different activation will have specific neurons present in the inner cortex

Question 9

What are receptor cells in ampulla of semi-circular canals?

Answer 9

Cells present on RHS = hyperpolarised (deactivated/less AP)

Cells present on LHS = depolarised

Movement of the liquid and which side of the ampulla is actually activated that will determine the 3D space of movement (rotation)

Question 10

Move our head to the right hand side, the fluid will move the opposite way (to the left hand side) Will activate one side and deactivate the other side. Why?

Answer 10

• Need to tell head that moving to the right
• Activate R (more AP) and deactivated L (less AP) = brain will detect
• Even when head is still –> AP will always be generated (always have background activity –> not all or nothing –> it is graded)
• Once head has moved and the fluid has returned to the speed it was originally at = goes back to same amount of AP
• System needs to be informed that movement has stop (not longer doing it)
  
  • Eg. when walking there is movement but when you stop there is not point to send the same signals to the brain = already stopped
  • Go back to base-line and then start to send signals again It is not continuous

Question 11

What are 4 characteristics of transduction?

Answer 11

1. When head is turned, endolymph lags behind due to inertia
2. Endolymph (in the canal that is in the same plane as the movement) pushes on cupula and bends hair cells in the opposite direction of head movement = appropriate signal)
3. If head movement continues in same direction, the endolymph moves at the same speed as the head movement, no force in the cupula = hair cells are not longer bent
4. If head movement stops, the reverse happens.

Question 12

What is the major difference of sterocilium and kinocilium?

Answer 12

Longest stereocilium on top of hair cell = kinocilium

Question 13

What are 4 characteristics of hair cells?

Answer 13

1. Hair cell - separate receptor cell
2. Hair cell consist of 1 kinocilium and 20-50 stereocilia (microvilli)
3. Hairs are connected by tip links- Connect to the longest = kinocilium (activation) when the hair cells bend
4. Mechanically gated ion channels open/close depending on direction of bending.

Question 14

______ (Depolarisation/hyperpolarisation) in hair cell induces increased neurotransmitter released and the consequent increased in frequency of action potentials

Answer 14

Depolarisation

Question 15

Semicircular canals work in ______: depolarisation on one side/ hyperpolarisation on the other head and vice versa

Answer 15

pairs

Question 16

When fluid stops moving, hair cells straighten = state of no signal, which is the ____ membrane potential. Axons of afferent neurons from the ____ nerve

Answer 16

resting; vestibular

Question 17

When is there no signal for transduction?

Answer 17

No signals when head keeps turning at a constant speed or when head is motionless

Question 18

The _____ nerve combined with the auditory nerve from cochlea form the vestibulocochlear nerve (VIII cranial nerve).

Answer 18

vestibular

Question 19

Which cortex is important for the auditory system? EXAM- what part of the cortex is responsible for what? Eg. which part of the auditory sends signals to?

Answer 19

Temporal lobe

Question 20

What are 7 characteristics of otolith organs?

Answer 20

1. Information about position of the head relative to gravity and changes in rate of linear motion- Eg. starts walking = something happens (has hair cells involved but are a bit different –> not within ampullas)
2. Otolith organs: Utricle and Saccule
3. Sack like structures in bony capsule between semicircular canals and cochlea
4. Receptors: hair cells arranged in maculae
5. Overlying the hair cells is a gelatinous sheet with many calcium carbonate crystals (otoliths)- Crystals will impact the gelatine and cause changes in cilia = changes in AP generation
6. Added weight of otoliths increases inertia
7. When in upright position, hairs of utricle are oriented vertically and those in saccule horizontally.

Question 21

What is receptor cell in utricle?

Answer 21

Go forward = will move hair cells back Semi-circular canals Endolymph (liquid) movements due to 3D movements has an impact on ampulla and will bend hair cells and will activate one side and deactivate the other side Otolith organs: Gelatine sitting on hair cells and crystals on top of that = change of shape and activation

Question 22

What are 5 characteristics of utriculus?

Answer 22

1. Gravitational forces on the otoliths cause bending of the hair cells = appropriate signal
2. Depending on the direction of the head tilt (up or down), hair cells depolarise or hyperpolarise
3. The utriculus also responds to changes in horizontal linear motion (moving forwards, backwards or sideways)- Change in direction of head (changing gravitation)
4. Heavy otoliths lag behind as movement starts, which cause hair cells to bent = appropriate signal
5. No signals are detected when movement constant.

Question 23

What does the activation of utriculus by change in head position look like?

Answer 23

Question 24

What does the activation of utriculus by horizontal linear acceleration look like?

Answer 24

Question 25

What are 4 characteristics of sacculus?

Answer 25

1. Responds if head is tilted away from horizontal position (getting up from bed)
2. Also responds to vertically directed linear acceleration (jumping up and down)
3. Depending on the direction of the head, hair cells depolarise or hyperpolarise
4. No signals are detected when movement is constant.

Question 26

SUMMARY SCC = ____ movements Utricle= _____ movement Saccule = _____ movements going from horizontal to vertical

Answer 26

3D; linear; gravitational

Question 27

What are 6 Signal transduction- comparison with cochlea? EXAM

Answer 27

1. Many similarities with cochlea
2. Neural signals are generated as fluid moves with vestibular sense organs
3. Mechanical deformation of hair cells occurs in response to this movement
4. This bending produces depolarizing or hyperpolarizing potentials depending on the direction of the movement;
5. Hair cell orientation differs between organs
6. Unlike information from the cochlea, much vestibular information does not reach the level of conscious awareness.- Usually sent to the cerebellum to integrate signals not cortex (will reach eventually)

Question 28

What are 3 Vestibular projections?

Answer 28

1. Signals from the vestibular apparatus are carried through the vestibulocochlear nerve to the vestibular nuclei (brain stem) and then to the cerebellum- Not under conscious awareness
2. Cerebellum integrates information from eyes, skin surface, joints and muscles.- Make changes happen
3. Information is used to maintain balance and posture, controlling eye movement and perceiving motion and orientation.

Question 29

What is the overview for vestibular system?

Answer 29

Question 30

If you turn your head –> eyes will autonomically follow the direction (without telling them). Why is this important?

Answer 30

Vision is what we rely on - eye muscles

Question 31

What are different lobes of the cortex?

Answer 31

Question 32

What happens when the vestibular system goes wrong?

Answer 32

1. Benign paroxysmal positional vertigo
2. Menier’s disease

Question 33

What are the 3 symptoms of BPPV?

Answer 33

1. Sudden sensation of spinning when head is moved
2. Mild to intense dizziness
3. Triggered by specific changes in head position – lying down

Question 34

What are 2 causes of BPPV?

Answer 34

1. Hard to determine
2. Otoliths can become dislodged and move into one of the semicircular canals = sensitivity to additional changes = dizziness

Question 35

What are 4 symptoms of Menier’s disease?

Answer 35

1. Spontaneous recurring episodes of vertigo and nausea;
2. Fluctuating hearing loss
3. tinnitus
4. Feeling of fullness in the ear;

Question 36

What are 3 causes of Menier’s disease

Answer 36

1. Abnormal volume or composition of fluid in the inner ear thought to be responsible
2. Various triggers have been proposed, such as improper fluid drainage, head trauma, genetic predisposition, migraines
3. No single cause has been identified, disease is probably caused by combination of factors;

Question 37

What are the 2 treatments of Menier’s disease, while there is no cure?

Answer 37

1. Anti-nausea drugs
2. Surgery in extreme cases

Question 38

What are 6 steps in vestibular system problems?

Answer 38

1. Endolymphatic membrane starts to stretch due to increase fluid = rupture of membrane = mixing of fluid from different chambers= symptoms
2. Over time the membrane will grow back = separation of fluid back into chambers = symptoms stop
3. Patients should avoid salt, caffeine and alcohol (diuretics helps to reduce fluid build up)
4. Surgery can be performed if conservative management fails (eg. endolymph sac decompression surgery or endolymphatic duct blockage)
5. Last resort –> nerve going to inner ear for balance can be dissected or special drugs can be chemically destroy the imbalance
6. Different levels of surgery due to different severity/symptoms (eg. don’t cut nerve if only mild symptoms)

Question 39

What is a symptom of motion sickness?

Answer 39

Nausea, vomiting, pale skin, dizziness

Question 40

What are 3 causes of motion sickness?

Answer 40

1. Conflict of information between sense, in particular visual and vestibular information
2. When travelling in car along windy road and reading a book = vision system reports no movement, vestibular system reports movement
3. It is possible that vomiting response is caused to get rid of a perceived poison

Question 41

What are 3 treatment for motion sickness?

Answer 41

1. Minimize movement
2. Fix vision on stable object – horizon
3. Various medications.