CNS: Vestibular system Flashcards
Where does the sensory info travel to the CNS?
- along the vestibular portion of the vestibulocochlear nerve, CN VIII
where are sensory receptors of the vstibular system?
- The labyrinths of the inner ears (as is cochlear)
Where does the sensory info travel to the CNS?
What is vestibular input used for?
- along the vestibular portion of the vestibulocochlear nerve, CN VIII
- For conscious perception of balance as well as for maintenance of balance through a number of reflexes
What is the name of the reflex that stabilises the retinal image during rapid rotations and accelerations of the head?
What is occuring?
- The vestibulo-ocular reflex
- 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
What is the structure of the labyrinth
- Inner ear consists of the bony labyrinth
- Which contains the membranous labyrinth
- ML consists of thin epithelial membranes and comprises both vestibular organs and cochlea
- Inside ML is fluid called endolymph
- Between ML and BL is fluid called perilymph
What is the structure of the labyrinth
- Inner ear consists of the bony labyrinth
- Which contains the membranous labyrinth
- ML consists of thin epithelial membranes and comprises both vestibular organs and cochlea
- Inside ML is fluid called endolymph
- Between ML and BL is fluid called perilymph
- Labyringth in terms of vestibular organs, forms itself into 3 semicircular camals = what they’re called
- Orientated in 3 different planes, all communicate with eachother via widened area at bottom = the utricle and saccule
So what actually “house” the vestibular organs?
- Semicircular canals
- utricle
- saccule
Within the semicircular canal, where is the actual organ of sense?
- in swellings called the Ampullae at the end of each semicircular canals
- The organ is the cristae ampularis (the sensory bit). These detect rotational movement of the head about its axis
Why are the semicircular canals arranged into three planes?
- To ensure that rotation of the head in any direction can be detected
What sensory organ is located in the utricle and saccule?
What does this detect?
How are they orientated
- Maculae/ otolith organ
- Detects linear acceleration/ deceleration and tilting of the head
- Orientated wither vertically or horizontally
What happens to endolymph when head moves
- 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
- This bends the hair cells of the crista, causing receptor potential to be generated
- Circulating stimulates sensory organs in the various planes to inform brain as to where head is at.
When are cristae activated?
- Only during acceleration or deceleration as these change rotational movmeent
What are hair cells
- The sensory of the vestibular organ
- modified cell membrane = microvilli, each hair cell has one cillium
- hair cell in contact with dendrites of vestibular cochlear nerve
- When hair cells are stimulated, causes a change in action potentials coming down the vestibular cochlear nerve
- Diagram of hair cells in situ in cristae ampularis. How does endolymph cause an action potential?
- Hair cells project up from membranous labrynth membrane
- 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
- when endolymph swooshes past, causes cupula of jelly (jelly hat) to bend cilia and microvilli of hair cells = action potnetial
How does endolymph cause action potential with regards to ahri cells in macula
- Hair cells project up from membrane of ML up into jelly cap
- Jelly doesn’t stick to opposite wall = free in utricle and saccule
- instead CaCO3 crystals in cap which gives cap weight
- Means that as move head jell moves, and lags = bends hair cells
When microvilli and cilia of hair cells bend what does this cause
- change in depolarisation of vestibular cochlear nerve
- At rest. VC nerve depolarises at normal given resting rte
- If micro villi bend towards cilium = inc rate of dep = freq AP
- If microvilli bend away from cilium = dec freq of AP:. rate of depolarisation
Talk about cristae
- Sit in ampulla of semicircular canals
- Gel cap over hair cells = cupula
- Cupula is attached to roof of ampulla
- when endolympth moves, so does cupulla = bends hair cells = change in CNVIII depolarisation (inc is bend towards cilium, dec is away)
- Detects rotatory movement = input from dynamic balance
- Only during acceleration or deceleration when endolymph is moving
Talk about maculae
- In utricle (horizontal) and saccule (verticle)
- Hair cells orientated in lots of directions within a macula
- Gel caps containing otoliths covers hari cells (otolith organs)
- Otoliths are heavy so gravity drags them = bends hair cells = changes CNVIII input
- Detects linear acceleration/ deceleration and tilt of the head = input for static balance
Where does the vestibular cochlear come into the brain and then travel?
- Come into brain stem on same side as it originates from = ipsilateral
- vestibular nuclei in medulla oblongata and pons
- from there = several different connections
To be aware of balance, where does info have to get from and to for you to perceive it?
- From vestibular nuclei
- decussates through contralateral thalamus
- to contralateral cerebral cortex
What enables coordination of eye movements with head position
- From vestibular nuclei
- decussates
- to cranial nerves that supply the extraocular muscles (6 muscles that control movement of the eye)
- These are oculomotor nerve [CN III], trochlear
nerve [CN IV] and abducens nerve [CN VI]
What enables neck muscle movement to maintain appropriate head position?
- From vestibular nuclei
- decussates
- to accessory nerve CN XI
What enables the cerebellum to fine- tune postural and ocular reflexes?
- The reciprocal connection between the vestibular nuclei and cerebellum
- cerebellum receives input from, and sends input to the vestibular nuclei
What enables the direct affect of limb and body position in response to vestibular input?
- From vestibular nuclei
- decussates
- to vestibulospinal tract which is an upper motor neurone tract and hence directly affects limb and body position
What three major postural reflexes is the vestibular system involved in for our species and the one for maintaining stable visual image
- Vestibular reflex
- Tonic neck reflex
- Righting reflex
- Vestibulo-ocular reflex
What is the difference between the vestibular reflex and tonic neck reflex
- Vestibular reflex = Head- neck angle hasn’t changes
2. tonic neck reflex = Head neck angle changes
Tonic neck reflex
not vestibular but closely related in function
- Use input from the muscle spindles of the neck to enable postural adjustments in response to changes in the head: neck angle
- change in the angel activates muscle spindles in neck
- dog downhill, lifts head p to see better = extends fore and flex hind to reduce head neck = reduce head neck angle
How does an animal manage to stand still and move its head up?
- tonic neck reflex = change head nec angle by decreasing it = extends forelimbs
- Vestibular reflex = changes angle of head with respect to gravity = head bent up. If imaging bent up because of slope = upwards hill = forelimbs flex
- so 2 reflexes counteract each other so animal is able to stand still
Righting reflex
- way cat is able to land of feet if dropped from upside down
- first use vestibular organs to correct head with respect to gravity
- use tonic neck reflex to sort rest of body out relative to head
- otolith organs detect linear acceleration towards ground = as get close to ground, limbs extend so land on feet
- also skin pressure receptors and vision
What is the sensory input for the Vestibulo ocular reflex?
- VESTIBULAR
2. NOT OCULARRRRR as blind animals and animals in the dark do this
Which vestibular organs are involved in the vestibulo ocular reflex?
- CRISTAE = semi circular canals = rotation
- = response to input from semi ciruclar canals
- motor out put = Oculomotor nerve, trochlear nerve and abducens nerve (3, 4, 6)
Vestibular disease
what forms and clinical signs
- common
- 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
- 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
Which central connections from the vestibular nuclei cause the motor actions seen in the vestibular reflex
- vestibular reflex = tilt animal with respect to gravity and they move limbs accordingly soooo
- Vestibulo spinal tract
What does the thalamic relay too the cerebral cortex allow?
- conscious perception
How does bending hair cells affect the function of the vestibular portion of the vestinulocochlear nerve?
- bend towards cilium = inc rate of depolarisation
2. micro villi away = hyperpolarises = dec rate of AP
What is the purpose of the vestibulo-ocular reflex and how is this achieved?
- stops vision from becomming blurred as fixed image on retina
- VESTIBULAR INPUT!!
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?
- get motion sick as eyes telling something different from vestibular
- look out of window = corrects imbalance
