Vestibular Physiology 1 Flashcards
The ear detects _______, whereas the vestibular organs detect ______.
The ear detects vibration, whereas the vestibular organs detect movement.
What is balance?
- Maintenance of steady position, requiring the coordination of many motor responses, eye movement and posture. ((We take it for granted!))
- There is both dynamic and static equilibrium
- Highly sophistiated integrated system
Balance involves intergration of?…
Visual, vestibular, proprioreceptive input (joint receptors) and superficial sensory information.
You can do without one of these (eg, no vestibular system in space)
Vestibular → input on head movement
Visual → input on sight
Proprioreceptive → input on touch
SENSORY INPUT → INTEGRATION OF INPUT → MOTOR OUTPUT → BALANCE
What is the vestibular/balance systems role in cognition?
- Self-motion perception
- Bodily awarness/self-consciousness
- Spatial navigation: to move through the world
- Spatial memory and object recognition: as if the vestibular system goes, the hippocampus will atrophy, therefore is there a link between vestibula function and dementia?
- Spatial learning
What does the Vestibular System and balance detect?
- Dynamic and static head position.
- Linear and angular acceleration of the head
- Conscious/constant awarness of head position and controls reflex eye-movements
**Vestibular organs only sense acceleration!! If you were moving at a constant velocity you would not know (eg; sitting in an airplane)
The vestibular system is ________ and finely ________.
Minor, acute derangements have catastrophic effects on balance, causing ______. (describe this word), as well as disorientation and nausea.
The vestibular system is sensitive and finely balanced.
Minor, acute derangements have catastrophic effects on balance, causing VERTIGO. (sense of losing balance, movement), as well as disorientation and nausea.
What is the difference between acute and chronic loss of vestibular function!
Chronic/gradual loss may have limited symptoms due to compensation at central nuclei.
Just say you lost one side, your brain could pretend to/compensate so you barely notice!
Symptoms of Vertigo and how do you define it?
Perception of motion, person or environment (room spinning), when there is none.
- Differs from lightheadedness or dizziness (has a direction).
- Accompanied by visceral Autonomic symptoms: pallor, sweating, nausea, vomiting
WHy do we get Motion Sickness?
Due to conflict between the sensory inputs (vestibular, visual, proprioceptive) compared with an expected internal model.
This mismatch of inputs promotes symptoms associated with vertigo and motion sickness.
Eg; reading in the car!
What’s the effect of microgravity; ‘space travel’ on vestibular function?
In space you have no vestibular function due to the lack of gravity.
Due to no stimulation the vestibular system begins to atrophy so they come back with balance issues.
Thought (due to the connection of the vest. system to the hipocampus) that some may also develop memory problems
Astronauts become incredibly reliant on their visual and proprioreceptive systems to balance/move!
What are the inputs and out puts of the vestibular organs
Sensory organs in inner ear project via the VIII cranial nerve (vestibulocochlear) to vestibular nuclei in brainstem. These are close to the facial and cochlear nucleus.
The vestibular nuclei has outputs to the
- cerebral cortex
- motor cortex
- cerebellum
- ANS
- Nuclei III, IV and VI (oculuomotor muscles)
Describe the Sensory Vestibular Apparatus…
The inner ear is a series of tubes within a block of bone. Within this bone is
- The cochlear: auditory portion
- Atrium ‘vestibule’ with 3 semi-circular canals coming off the side: vestibular portion or “Sensory Vestibular apparatus”
- Each Semi-circular canal lies in a different plane, all at right angles to each other and each contain a sensory organ. Hence detect motion in each plane. Filled with endolymph
- Within the vestibule is the membranous labyrinth filled with endolymph, and contains two sensory organs
Describe the semi-circular canals, what is in them and how they detect movement.
The semi-circular canals go in 3 seperate directions/planes; ‘Anterior, posterior and lateral’.
Within the ampullae of each semi-circular canal is a cristae ampullaris; a sensory organ that detects angular accelertion.
Cristae Ampullaris: specialised endothelial ridge that contains vestibular sensory cells innervated by the sensory nerve.
Covered by the gelatinous cupula thst stretches to the roof of the ampulla, and the displacement of this due to endolymph flow is wat stimulates vestibular sensory cells.
What lies within the vestibule?
Two Otolithic Sensory organs
- Utricle
- Saccule
These both detect linear acceleration and static head position (relative to gravity)
What innervates the vesitbular organs?
Superior and inferior vestibular nerve with cell bodies Scarpa’s ganglion exits as part of the vestibulocochlear nerve in the internal auditory meatus.
Superior division innervates: utricle, anterior saccule, lateral + anterior semi-circular canals
Inferior Division Innervates: posterior saccule and posterior SC canal
How are the ear canals paired?
- Lateral (horizontal) canals of each ear are paired.
- Anterior canal is paired with posterior canal of opposite ear.
The anterior and posterior canals are at 45 degrees above and below the midline. Paired Ant. to Post so that when you move your head one part wil be excited whilst the others inhibited and it’s that mismatch that give information to the brain!
How do the cristae ampullaris of the semi-circular canals organised?
Within the SCC (containing endolymph, remeber perilymph is extracellular), where the swelling of the ampulla is, is the cristae ampullaris, a dam-like structure.
This is a piece of epithelial tissue that extends into the tube, and sitting atop it is a gelatinous ‘cupula’ that extends almost to the top of the roof.
On the bottom of the dam the sensory hair cells extend into the cupula, all orientated with their kinocilium hair cells in the same plane, polarised in the same direction. They are surrounded by supporting cells in an epithelium ridge
How do the otolithic organs (saccula and utericle) work within the vestibule?
Hair cells in otolithic organs arranged in “button like” macula sheets.
Stereocilia project into otolithic membrane (instead of cupula), which have otoconia (Calcium carbonate crystals) embedded.
The otoconia has weight to it unlike the cupula
Remember that the hair cells of the vestibular organs are polarised and arranged so they’re aligned in the same direction!
Only differene is the in the
sacculus they are pointing away from the centre
Utricle towards the midline
Ampulla all in the same direction
How do the vestibulare hair cells change due to the direction they move?
Movement/stimulation towards kinocilium → depolarisation + increased nerve activity
Movment/stimulation away from kinocilium → hyperpolarisation and decreased vestibular nerve activity.
There’s always a constant low-level current flowing through the hair cells (like in the cochlear), causing a resting discharge.
How do the ampullae sense anglar acceleration
If the head and therefore the bony structure of the inner ear moves in any give direction, then the endolymph remains stationary for a movement due to its inertia.
There is therefore an apparent flow of endolymph relative to the bony canal that causes a deflection of the cupular and hair cell cilia in the opposite direction to the movement.
**cristae detects acceleration via increased firing, BUT inertia is overcome in steady-state and firing returns to rest during constant velocity!
How do the otolithic organs deteect movement?
As they are under the control of gravity, so as you move your head the weight of the calcium carbonate crystals will pull the stereocilia hairs down under the force of gravity, in a polarising or hyperpolarising direction.
They stay on for the duration of the tilt ⇒ constant discharge
Why do you get vertigo from acute peripheral damage
the brain takes that resting discharge as being ‘at rest’.
As i move my head, firing increases in one side and decreases in the other. This differential input to the brain tells about the rate and direction of movement.
If the inner ear ion one side is damaged, the firing discharge goes to zero, there is now a differential, and the brian senses you are moving in the direction opposite to the injury ⇒ VERTIGO
If the brain senses this and can compensate but increases the firing so you don’t feel vertigo anymore
What nerves are involved in Vestibulo-ocular reflex?
Comes in through CN III, IV and VI, these are ‘hard-wired. Also the vestibular nerve is involved.
If injured cause Nstagmus.
- the idea that we as humans can ‘keep gaze’, and as we move we can remain a steady view on an object.
