CNS: Vestibular system

Question 1

Where does the sensory info travel to the CNS?

Answer 1

1. along the vestibular portion of the vestibulocochlear nerve, CN VIII

Question 2

where are sensory receptors of the vstibular system?

Answer 2

1. The labyrinths of the inner ears (as is cochlear)

Question 3

Where does the sensory info travel to the CNS?

What is vestibular input used for?

Answer 3

1. along the vestibular portion of the vestibulocochlear nerve, CN VIII
2. For conscious perception of balance as well as for maintenance of balance through a number of reflexes

Question 4

What is the name of the reflex that stabilises the retinal image during rapid rotations and accelerations of the head?
What is occuring?

Answer 4

1. The vestibulo-ocular reflex
2. The extraocular muscles move the eyeball in response to the vestibular input so that as the head turns, the eyes remain fixed on one point for as long as possible before “flicking” to fix on a new point of focus

Question 5

What is the structure of the labyrinth

Answer 5

1. Inner ear consists of the bony labyrinth
2. Which contains the membranous labyrinth
3. ML consists of thin epithelial membranes and comprises both vestibular organs and cochlea
4. Inside ML is fluid called endolymph
5. Between ML and BL is fluid called perilymph

Question 6

What is the structure of the labyrinth

Answer 6

1. Inner ear consists of the bony labyrinth
2. Which contains the membranous labyrinth
3. ML consists of thin epithelial membranes and comprises both vestibular organs and cochlea
4. Inside ML is fluid called endolymph
5. Between ML and BL is fluid called perilymph
6. Labyringth in terms of vestibular organs, forms itself into 3 semicircular camals = what they’re called
7. Orientated in 3 different planes, all communicate with eachother via widened area at bottom = the utricle and saccule

Question 7

So what actually “house” the vestibular organs?

Answer 7

1. Semicircular canals
2. utricle
3. saccule

Question 8

Within the semicircular canal, where is the actual organ of sense?

Answer 8

1. in swellings called the Ampullae at the end of each semicircular canals
2. The organ is the cristae ampularis (the sensory bit). These detect rotational movement of the head about its axis

Question 9

Why are the semicircular canals arranged into three planes?

Answer 9

1. To ensure that rotation of the head in any direction can be detected

Question 10

What sensory organ is located in the utricle and saccule?
What does this detect?
How are they orientated

Answer 10

1. Maculae/ otolith organ
2. Detects linear acceleration/ deceleration and tilting of the head
3. Orientated wither vertically or horizontally

Question 11

What happens to endolymph when head moves

Answer 11

1. Endolymph inside the semicircular canals shifts and drags the cupula (gelatinous mass that the cristae are embedded within) in the opposite direction to the rotation of the head
2. This bends the hair cells of the crista, causing receptor potential to be generated
3. Circulating stimulates sensory organs in the various planes to inform brain as to where head is at.

Question 12

When are cristae activated?

Answer 12

1. Only during acceleration or deceleration as these change rotational movmeent

Question 13

What are hair cells

Answer 13

1. The sensory of the vestibular organ
2. modified cell membrane = microvilli, each hair cell has one cillium
3. hair cell in contact with dendrites of vestibular cochlear nerve
4. When hair cells are stimulated, causes a change in action potentials coming down the vestibular cochlear nerve

Question 14

1. Diagram of hair cells in situ in cristae ampularis. How does endolymph cause an action potential?

Answer 14

1. Hair cells project up from membranous labrynth membrane
2. stick up micro vili and cilia into special cap of jelly that sits on top of them and extends across to other side of ampulla and sticks to oppo wall
3. when endolymph swooshes past, causes cupula of jelly (jelly hat) to bend cilia and microvilli of hair cells = action potnetial

Question 15

How does endolymph cause action potential with regards to ahri cells in macula

Answer 15

1. Hair cells project up from membrane of ML up into jelly cap
2. Jelly doesn’t stick to opposite wall = free in utricle and saccule
3. instead CaCO3 crystals in cap which gives cap weight
4. Means that as move head jell moves, and lags = bends hair cells

Question 16

When microvilli and cilia of hair cells bend what does this cause

Answer 16

1. change in depolarisation of vestibular cochlear nerve
2. At rest. VC nerve depolarises at normal given resting rte
3. If micro villi bend towards cilium = inc rate of dep = freq AP
4. If microvilli bend away from cilium = dec freq of AP:. rate of depolarisation

Question 17

Talk about cristae

Answer 17

1. Sit in ampulla of semicircular canals
2. Gel cap over hair cells = cupula
3. Cupula is attached to roof of ampulla
4. when endolympth moves, so does cupulla = bends hair cells = change in CNVIII depolarisation (inc is bend towards cilium, dec is away)
5. Detects rotatory movement = input from dynamic balance
6. Only during acceleration or deceleration when endolymph is moving

Question 18

Talk about maculae

Answer 18

1. In utricle (horizontal) and saccule (verticle)
2. Hair cells orientated in lots of directions within a macula
3. Gel caps containing otoliths covers hari cells (otolith organs)
4. Otoliths are heavy so gravity drags them = bends hair cells = changes CNVIII input
5. Detects linear acceleration/ deceleration and tilt of the head = input for static balance

Question 19

Where does the vestibular cochlear come into the brain and then travel?

Answer 19

1. Come into brain stem on same side as it originates from = ipsilateral
2. vestibular nuclei in medulla oblongata and pons
3. from there = several different connections

Question 20

To be aware of balance, where does info have to get from and to for you to perceive it?

Answer 20

1. From vestibular nuclei
2. decussates through contralateral thalamus
3. to contralateral cerebral cortex

Question 21

What enables coordination of eye movements with head position

Answer 21

1. From vestibular nuclei
2. decussates
3. to cranial nerves that supply the extraocular muscles (6 muscles that control movement of the eye)
4. These are oculomotor nerve [CN III], trochlear
   nerve [CN IV] and abducens nerve [CN VI]

Question 22

What enables neck muscle movement to maintain appropriate head position?

Answer 22

1. From vestibular nuclei
2. decussates
3. to accessory nerve CN XI

Question 23

What enables the cerebellum to fine- tune postural and ocular reflexes?

Answer 23

1. The reciprocal connection between the vestibular nuclei and cerebellum
2. cerebellum receives input from, and sends input to the vestibular nuclei

Question 24

What enables the direct affect of limb and body position in response to vestibular input?

Answer 24

1. From vestibular nuclei
2. decussates
3. to vestibulospinal tract which is an upper motor neurone tract and hence directly affects limb and body position

Question 25

What three major postural reflexes is the vestibular system involved in for our species and the one for maintaining stable visual image

Answer 25

1. Vestibular reflex 2. Tonic neck reflex 3. Righting reflex 4. Vestibulo-ocular reflex

Question 26

What is the difference between the vestibular reflex and tonic neck reflex

Answer 26

1. Vestibular reflex = Head- neck angle hasn't changes | 2. tonic neck reflex = Head neck angle changes

Question 27

Tonic neck reflex | not vestibular but closely related in function

Answer 27

1. Use input from the muscle spindles of the neck to enable postural adjustments in response to changes in the head: neck angle 2. change in the angel activates muscle spindles in neck 3. dog downhill, lifts head p to see better = extends fore and flex hind to reduce head neck = reduce head neck angle

Question 28

How does an animal manage to stand still and move its head up?

Answer 28

1. tonic neck reflex = change head nec angle by decreasing it = extends forelimbs 2. Vestibular reflex = changes angle of head with respect to gravity = head bent up. If imaging bent up because of slope = upwards hill = forelimbs flex 3. so 2 reflexes counteract each other so animal is able to stand still

Question 29

Righting reflex

Answer 29

1. way cat is able to land of feet if dropped from upside down 2. first use vestibular organs to correct head with respect to gravity 3. use tonic neck reflex to sort rest of body out relative to head 4. otolith organs detect linear acceleration towards ground = as get close to ground, limbs extend so land on feet 5. also skin pressure receptors and vision

Question 30

What is the sensory input for the Vestibulo ocular reflex?

Answer 30

1. VESTIBULAR | 2. NOT OCULARRRRR as blind animals and animals in the dark do this

Question 31

Which vestibular organs are involved in the vestibulo ocular reflex?

Answer 31

1. CRISTAE = semi circular canals = rotation 2. = response to input from semi ciruclar canals 3. motor out put = Oculomotor nerve, trochlear nerve and abducens nerve (3, 4, 6)

Question 32

Vestibular disease | what forms and clinical signs

Answer 32

1. common 2. can be peripheral = disease or damage to sensory organs = disease of (mainly) cristae (in ampula of semi circular canal) AND maculae (in utricle and saccule) of inner ear 3. Central = disease or damage to vestibular nuclei (in pons and medulla oblongata) and/ or central connections (CNS). Disease of thalamus, and cerebellum disease = recriprocal exchange of info with vestibular nuclei = no balance, nastagmas, loss of vestibular reflex, vomiting, head tilt

Question 33

Which central connections from the vestibular nuclei cause the motor actions seen in the vestibular reflex

Answer 33

1. vestibular reflex = tilt animal with respect to gravity and they move limbs accordingly soooo 2. Vestibulo spinal tract

Question 34

What does the thalamic relay too the cerebral cortex allow?

Answer 34

1. conscious perception

Question 35

How does bending hair cells affect the function of the vestibular portion of the vestinulocochlear nerve?

Answer 35

1. bend towards cilium = inc rate of depolarisation | 2. micro villi away = hyperpolarises = dec rate of AP

Question 36

What is the purpose of the vestibulo-ocular reflex and how is this achieved?

Answer 36

1. stops vision from becomming blurred as fixed image on retina 2. VESTIBULAR INPUT!!

Question 37

Why do animals get motion sick? what circumstances make this more likely to happen and how can you help yourself if you feel motion sick?

Answer 37

1. get motion sick as eyes telling something different from vestibular 2. look out of window = corrects imbalance