Cerebellum, Balance and Coordination Flashcards
Identify the main inputs and outputs for balance and coordination.
INPUTS
-Ete
-JPS, proprioception, superficial sensation
-Labyrinthe activity
-Cortex cerebellum, reticular formation, extra-pyramidal system inputs
These are integrated.
OUTPUTS
- Cortical awareness of head/body/motion
- Eye movement/control of oculomotor activity
- Control of posture
- Control of motor skills
Define vertigo.
Vertigo is the abnormal sensation of movement
What is the most common cause of vertigo ?
The commonest cause of vertigo is Benign Positional Vertigo (sometimes
called benign paroxysmal positional vertigo, BPPV), due to due to particles causing trouble in the posterior canal.
What are the main components of the inner ear ? Identify the function of each.
- Anterior, posterior and horizontal canal: semi-circular canals that detect angular motion (all linked up to cochlea)
- Utricle: Detect horizontal motion
- Saccule: Detect vertical motion
- Vestibule
- Cochlea
What are the main components of the inner ear ?
- Anterior, posterior and horizontal canal: semi-circular canals that detect angular motion (all linked up to cochlea)
- Utricle
- Saccule
- Vestibule
- Cochlea
Distinguish between the saccule, and utricle of the inne ear.
Vestibule has 2 otolith containing organs:
– Saccule macula (continuous with cochlea)
– Utricle macula (continuous with semi-circular canals)
Function: Both monitor position of head relative to force of gravity
– Saccule – monitors vertical movement (s for sky)
– Utricle – monitors horizontal movement
Describe the structure otolith containing organs, linking this to their structure.
- Hair cells, project hairs (stereocilia, kinocilium) into an otolithic (ear stone) containing gelatinous structure.
- Cilia + kinocilium – provide directional information
- Movement of otolithic membrane (from tilting or translational movement) bends the cilia/kinocilium in a very direction specific way
- A 0.5 micron movement of the kinocillium opens/closes the hair cell cation channels (allow potassium and calcium to come in so that otolitihic membrane moves across, changes kinocilium, to signal to brain that movement is occurring)
- “Shearing of the stereocilia toward the kinocilium causes a depolarization of the receptor potential and an increase in afferent action potentials (increased impulse frequency, i.e. excitation). There is an opposite effect on the other side – hyperpolarisation of the receptor potential and a decrease in afferent activity (decreased impulse frequency, i.e. inhibition). These counteracting bilateral changes in afferent activity affect the vestibular and oculomotor nuclei”
Identify a way in which structure of utricle/saccule can cause a pathology.
One of causes of benign positional vertigo is abnormal position of otoliths
How is rotational acceleration detected?
Detected in semi-circular canals:
- Monitor rotational acceleration and decelaration
- Three planes of orientation (at right angles of each other)
- Within each canal is semi-circular duct
- Within duct, ampulla
- In the ampulla there are supporting cells, hair cells, cilia, kinocilium
- Rotation directions are designated as Roll (around x axis) Pitch (around y axis) and Yaw (around z axis)
- The hair bundles extend out of the crista (sensory epithelium) into a gelatinous mass, the cupula, that bridges the width of the ampulla, forming a fluid barrier through which endolymph cannot circulate. As a result, the compliant cupula is distorted by movements of the endolymphatic fluid.
1) When the head turns in the plane of one of the semicircular canals, the inertia of the endolymph produces a force across the cupula, distending it away from the direction of head movement and causing a displacement of the hair bundles within the crista (which sends signal to the brain)
2) Linear accelerations of the head produce equal forces on the two sides of the cupula, so the hair bundles are not displaced.
-Signal transduction occurs (resting rate of transmitter release?), and AP will change depending on which wide fluid moves on (bending in one direction (towards the kinocilium) causes depolarisation and ↑AP rate
whereas other direction
causes hyperpolarisation and ↓AP rate i.e. one side of head depolarises; other hyperpolarises)
-This is detected bilaterally by vestibular nucleus in brainstem
Are otoliths ever found in semi-circular canals ?
In normal physiology, never
Pathologically (especially as a result of trauma), or sometimes as a result of age, otoliths from saccule and utricle move into posterior semi circular canal. Hence, every time you move, you feel as though room is spinning around (cupula and ampulla of semi circular canal are being stimulated every time move, by otoliths).
Describe Epley’s Maneuver, as well as its aim.
Aim: In patients with Benign Paroxysmal Positional Vertigo due to Canalithiasis, the partcile respositioning maneuver encourages the calcium carbonate debris to migrate towards the common crus of the anterior and posterior canals and exit into the utricular cavity (curative)
Procedure:
1) Patient is seated upright facing examiner, grasping examiner’s forearm with both hands for stability, then moved rapidly into supine position with head extending just beyond examining table, right ear downward
2) Examiner moves to head of table, repositioning hands as shown on step 2/3 of slide 17
3) Head is quickly rotated to the left, stopping with right ear upward. Position is held for 30 seconds
4) Patient rolls onto L side while examiner rapidly rotates head until nose is angled towards floor. Position is held for 30 seconds
5) Patient is rapidly lifted into sitting position. Entire sequence is repeated until no nystagmus can be elicited
BUT after maneuvre is done, tell patient that it may come back if lie down in bed tonight, so try to sleep sitting up, and also don’t bend down to tie shoelaces.
Describe Menière’s Disease.
- The vestibular apparatus is bathed in endolymph
- Normally drains to venous sinus
- Build-up of endolymph can cause Ménière’s disease (vertigo, nausea, tinnitus and hearing loss)
- Episodic (can last minutes, to hours)
- Can get progressive deafness over years
Identify a test used for brainstem lesions;
Caloric test in in comatose patients (tests for condition of brainstem):
- Putting warm water in the external meatus of a patient sets up calorically induced movements in the labyrinth system.
- Nystagmus pattern for a movement towards the irrigated ear with warm water is slow away from direction of rotation and a fast return in same direction of rotation
- Cold water does the opposite (COWS Cold Opposite Warm Same, refers to fast component)
- In comatose patients there is no fast saccade, only the slow component.
- Brain stem death, no vestibulo-ocular reflexes
Identify the main pathways which originate from the cerebellum, including their function.
Cerebellum receives sensory feedback from proprioceptors (muscle spindle and Golgi organ). Then, the following pathways form:
Spinocerebellar- simple movements
Cerebrocerebellar- complex movements
Vestibulocerebellar- posture and balance
All start in cerebellum, and go to the primary motor cortex in the brain.
What is the main function of the cerebellum ?
Modulates motor output based on integration of
- activity in the pre-motor and motor areas as well as spinal motor circuits (information about potential motor output)
- Sensory feedback from vestibular system, visual system, and ascending proprioceptive information (about real motor output)
Modulation by the cerebellum is effected at the motor cortex and brainstem.
