L3-Contributions of Cerebellum to Motor Function Flashcards
general functions of cerebellum
- the cerebellum plays major roles in the timing of motor activities and in rapid, smooth progression from one muscle movement to the next
- its not essential for locomotion
- helps sequence motor activities
- monitors and makes corrective adjustments to motor activities while they are being executed
true or false: electrical excitation of the cerebellum causes conscious sensation and motor movement
false; does not cause any conscious sensation and rarely causes any movement
what happens if the cerebellum is removed?
it causes the body to become highly abnormal
describe what the cerebellar functions are:
- compares actual movements with intended movements
- aids cortex in planning next sequential movement
- learns by its mistakes
- functions with SC to enhance stretch reflex
- functions with brain stem to make postural movement
- functions with cerebral cortex to provide accessory motor functions
- turns on antagonist at appropriate time
- helps program muscle contraction in advance
- functions mainly when muscle movements have to be rapid
what is the anatomical organization of the cerebellum
- two hemispheres separated by vermis: each divided into an intermediate zone and a lateral zone.
what 3 loves is it divided into?
anterior lobe
posterior lobe
flocculondular lobe (associated w vestibular system)
describe the vermis
location for control functions for muscle movements of the axial body, neck, shoulders, and hips
describe the intermediate zone
concerned with controlling muscle contractions in the distal portions of the upper and lower limbs, especially hands, feet, fingers, and toes.
describe the lateral zone
associated with cerebral cortex with planning of sequential motor movements
describe the gray matter of the cerebellum
cortex: consists of cells, dendrites and synapses
describe the intracerebellar nuclei
these make up an inner layer of gray matter and include the following:
dentate
emboliform
globose
fastigial
describe the dentate, emboliform, and globose nuclei
- lesions in these nuclei = extremity ataxia
- these fibers project to the red nucleus
- related to limb musculature and fine manipulative movement
describe the fastigial nuclei
- lesion in this nucleus –> trunk ataxia
- fibers project to reticular formation and vestibular nuclei
- related to postural activity and limb movements via reticulospinal and vestibulopsinal tracts
what are the layers of the cerebellar cortex?
granular layer
purkinje cell layer
molecular layer
describe the granular layer
- innermost layer
- made up of granule cells, golgi type II cells, and glomeruli
- axons of mossy fibers synapse with granular cells and golgi type II cells in the glomeruli
describe the purkinje cell layer
- middle layer
- contains purkinje cells
describe the molecular layer
- outermost layer
- contains stellate cells, basket cells, purkinje dendrites, golgi type II cells, and axons of granule cells (parallel fibers)
what are the cells in the cerebellar cortex
- granular cells: axons from parallel fibers in cortex (+)
- golgi cells: from parallel fibers to granular cell bodies (-)
- basket cells: from parallel fibers to purkinje axon hillock (-)
- stellate cells: from parallel fibers to purkinje dendrites (-)
whats something to note about basket cells and stellate cells?
they provide lateral inhibition on adjacent purkinje cells to provide damping
describe the purkinje cells
- extensive dendritic branching
- receives input from parallel fibers (20K between parallel fibers and one purkinje cell)
- project to intracerebellar nuclei (-)
- ONLY output from cortex
- OUTPUT IS ALWAYS INHIBITORY
what are the afferent, in cerebellar cortex?
climbing fibers and mossy fibers
describe the climbing fibers
- originate from medullary olives
- make multiple synapses with purkinje cells
- provide high frequency bursts (complex spikes)
- “condition” the purkinje cells
- play a role in motor learning
describe the mossy fibers
- originate from multiple centers in brainstem and spinal cord, including vestibulocerebellar, spinocerebellar, and pontocerebellar tracts
- make multiple synapses on Purkinje cells and result in simple spikes
- synapse on granule cells in glomeruli
which ones are the efferent neurons in cerebellar cortex? describe them
purkinje cell axons
- only output from cerebellar cortex
- output is always inhibitory
- GABA
- projects to deep cerebellar nuclei and vestivular nucleus
- modulates output of cerebellum and provides synergy (regulates rate, range, and direction of movement)
describe the functional units of the cerebellar cortex
- 30 million functional units in cerebellar cortex
- each functional unit is centered on a purkinje cell and a corresponding deep nuclear cell
- output from a functional unit is from a deep nuclear cell
- afferent inputs to the cerebellum are mainly from the climbing and mossy fibers
- all climbing fibers originate from the inferior olives
in regards to the cerebellar cortex, what do the mossy fibers do?
mossy fibers enter cerebellum from a variety of sources (send excitatory collaterals to deep nuclear cells and then synapse in granular layer with thousands of granule cells
what about granule cells?
they send axons to the outer cerebellar surface; axons branch in two directions parallel to folia
where do purkinje dendrites project to?
parallel fibers
what excites and inhibits nuclear cells?
- direct stimulation by climbing and mossy fibers excites deep nuclear cells
- purkinje cell signals inhibit deep nuclear cells
what else functions are inhibitory cells?
basket cells and stellate cells
what does the nervous system use cerebellum for?
to coordinate motor control functions at three levels:
- vestibulocerebellum
- spinocerebellum
- cerebrocerebellum
what does the vestibulocerebellum consist of? whats its functions?
- consists of flocculonodular lobes and vermis
- functions in control of balance and eye movements
further describe the vestibulocerebellum
- receives fibers from vestibular system and oculomotor system (pontocerebellar fibers)
- sends output pimarily to vestibular system
what happens if theres loss of flocculonodular lobes?
extreme disturbance of equilibrium and postural movements
desribe the relationship of vestibulocerebellum to pendular movements
- most body movements are pendular
- all pendular movements tend to overshoot (why?)
- appropriate learned subconscious signals from intact cerebellum can stop movement precisely at intended point (=damping system)
what changes occur when cerebellum is removed?
- movements are slow to develop
- force developed is weak
- movements are slow to turn off
describe vestibulocerebellar syndrome
- starts with abnormal eye movement, including nystagmus
- progressive genetic disease of flocculondular lobe
- vertigo, tinnitus
- ataxia
- eventually fine motor skills are lost
what is the general function and what does the spinocerebellum consist of?
- consists of mostly vermis and intermediate zone
- functions in synergy: control rate, force, range, and direction of movement
where does the spinocerebellum receive info from?
- receives info from motor cortex and red nucleus telling cerebellum intended sequential plan of movemebt for the next few fractions of a second
- feedback information from periphery telling cerebellum what actual movements result
what two sources of info does it compare and where does it send corrections to?
- motor cortex via thalamus
- magnocellular portion of red nucleus
what are the functions of the cerebrocerebellum?
- consists of lateral parts of hemisphere
- mostly associated with the premotor and the primary and association somatosensory areas of the cerebral cortex
- receives corticopontocerebellar projections
- involved in coordination of skilled movement and speech
- plans as much as tenths of a second in advance of actual movements: referred to as “motor imagery”
what are the afferent tracts to cerebellum?
- corticopontocerebellar
- vestibulocerebellar
- reticulocerebellar
- spinocerebellar (dorsal and ventral)
- all these tracts form the mossy fibers that terminate on the granule cells in the cerebellar cortex (+)
- olivocerebellar
describe the corticopontocerebellar
- motor and premotor cortices/ somatosensory cortex –> pontine nuclei –> lateral divisions of cerebellum
- main link between cortex and cerebellum
where do the vestibulo- and reticulocerebellar terminate?
- flocculonondular lobes
- primarily in the vermis
describe spinocerebellar
- dorsal and ventral
- transmits signals at 120 m/sec
describe the dorsal spinocerebellar
- muscle spindles –> ipsilaterally in vermis and intermediate zones
- apprise cerebellum of momentary status of:
muscle contractions
degree of tension on the muscle spindles
positions and rates of movements of body parts
forces acting on surfaces of the body
describe the ventral spinocerebellar
- terminates both ipsilaterally and contralaterally
- excited by signals coming from: cortex via corticospila and rubrospinal tracts; internal motor pattern generators within spinal cord
what does the ventral spinocerebellar tell the cerebellum?
- which motor signals have arrived at the anterior horns
- this feedback = efference copy of the anterior horn motor drive
describe the olivocerebellar tracts
- neurons project from inferior olivary nuclei (in medulla) to purkinje cell dendrites (+) and to intracerebellar nuclei
- axons form climbing fibers
- climbing fiber causes a single, prolonged action potential to each purkinje cell with which it connects (one climbing fiber per 5-10 Pc’s)
what is a complex spike?
each signal starts out as a strong spike and is followed by a series of weak secondary spikes
true or false: mossy fibers send (+) signals to granule cells
T
list and describe the efferent tracts from cerebellum
- cerebelloreticular: fastigial nuclei –> reticular nuclei in pons and medulla
- cerebellothalamocortical: dentate, emboliform, globose nuclei –> thalamus –> motor cortex
- cerebellorubral: dentate, emboliform, globose nuclei –> red nucleus
- cerebellovestibular: cerebellum –> vestibular nuclei
what can damage to the cerebellum lead to?
- dysmetrai (inability to judge distance and when to stop)
- ataxia (uncoordinated movement)
- adiadochokinesia ( inability to perform rapid alternating movements)
- past pointing
- movement tremors
- cerebellar lesion gait (staggering, widebase walk)
- falling
- cerebellar hypoplasia (weak muscles)
- ataxic dysarthria (slurred speech)
- nystagmus (abnormal eye movement)
- ballistic movemebts (dystonia)
what are the symptoms of cerebellum disorders?
- lack of muscle control and coordination
- ataxia
- slurred speech and difficulty talking
- abnormal eye movement
- headaches
what are the causes?
- genetic
- tumor,
- poisons
- injury
- cerebral palsy
- MS
- stroke
- infections
