Lec 5: Cerebellum Flashcards
Motor Pathways Overview
-Cerebellum receives from cerebral cortex (1) and spinal cord (2) for motor coordination and correction
-Cerebellum sends to cortex (via thalamus VPL) and to SC (via brain stem)
-Cortex receives from thalamus
-Cortex sends to SC (via brain stem), BG, and cerebellum
Motor Control and Cerebellum
- maintenance of balance and posture (via vestibular info/proprioception)
- coordination of multiple motor groups/movements
- Proprioception input from MS feedback
- Postural adjustments (based upon load) unconsciously from GTO
- Sensory processing
- Adaptability
- Automaticity (esp. in posture)
- Motor commands not initiated in cerebellum (modifies motor activity for accuracy
Cerebellum role in motor learning
-adapting and fine tuning motor programs to make accurate movements via trial and error process
Cerebellum role in cognitive functions
-functions (like language), extend beyond motor control but not yet understood
Cerebellum requires…
proprioception from muscle spindles and vestibular information for control of balance and equilibrium
Anticipatory function of cerebellum
Anticipates output of motor command (especially in coordination of multiple muscles across several joint
Cerebellum function in eye reflex
Fixation on target and eye coordination
Cerebellum sensorimotor coordination
-predicts the sensory outcome of our movements/actions
-creates replica of our movement in time and produces :likeness of pattern”
-if motor performance has errors (cerebellum corrects via error based learning)
-timing is critical, onset and offset of muscle activation, direction of movement
Cerebellum volume
contains over 50% of total number of neurons in brain
Cerebellum input and modulation
Input: from vestibular receptors and muscle proprioceptors (MS and GTO)
Modulates: to motor neurons (to compensate for shifts in body position or changes in load upon muscles)
Flocculonodular Lobe
-major transport for vestibular information to cerebellum
-Equilibrium, balance, posture
Cerebellum Regional Function
Lateral hemispheres: motor planning for extremities, planning and initiating of movements
Intermediate hemispheres: distal limb coordination
Vermis: proximal limb and trunk coordination
Flocculonodular lobe: balance and vestibulocular reflexes
Deep cerebellar nuclei input to and output from cerebellum
Output: Purkinje cells
Input: Climbing fibers and mossy fibers
Main Cerebellar Input Pathways
UNCONSCIOUS INPUT, DIRECT
1. Vestibular inputs: Balance and equilibrium
2. Motor, sensory, and visual inputs: from all regions (corticopontine fibers)
- Vestibular-Cerebellar Connections
-DIRECT connection from vestibular receptors to flocculonodular lobe of cerebellum
-Vestibular receptors –> Vestibular ganglion –> Vestibular complex in Rostral Medulla –> Cerebellum
- Periphery (LL and trunk) Connections
1a: Dorsal Spinocerebellar Tract: from L2 and below, stays ipsilaterally, large myelinated axons carrying proprioceptive, touch, and pressure from LL and trunk
1a: Cuneo Spinocerebellar Tract: from C8 and above, stays ipsilaterally, large myelinated axons carrying proprioceptive, touch, and pressure sensation from LL and trunk
1b: Ventral Spinocerebellar Tract: from L2 and below, double crosses over, carrying info for coordinated movement and posture of entire LL
1b: Rostral Spinocerebellar Tract: from C8 and above, stays ipsilaterally, carrying info for coordinates movement and posture of entire LL
Cerebellum Output Pathways
INDIRECT connections to motor system
1. DCN –> red nucleus –> SC
2. DCN –> VLN –> cortex (pre motor, supplementary, and pre frontal association area)
Spinocerebellar Tract Origin of Input
Dorsal SCT: Leg proprioceptors
Ventral SCT: Leg interneurons
Cuneal SCT: Arm proprioceptors
Rostral SCT: Arm interneurons
Vestibular Input Origin
Vestibular system
Lesions of cerebellum
-remain ipsilateral to side of lesion (Ventral SCT crosses twice)
(Dorsal, cuneo, and rostral stay unilateral)
Deficits of patients with cerebellar dysfunction
-uncoordinated voluntary movements and problems maintaining balance and posture
-decomposition of movement
-intention tremor
Decomposition of Movement
-unable to produce coordinated, smooth movements
-loss of feedforward mechanism (input from spindle ab speed and GTO ab force) does not allow for temporal/timing of activated muscle sequence of activation, force or awareness in space
Intention Tremor
-when making movement to a target pt produces involuntary movement tremor
-tremor increases as they approach closer to target
-e.g. starts out direct and is it gets closer hand moves back and forward
Cerebellar Exams: Speed, coordination, timing
e.g. heel to shin and finger to nose
Dysrhythmia: abnormal timing
Dysmetria: overshoot or past pointing
Cerebellar Exams: Rapid Alternating movements
Dysdiadochokinesia: RAM (sup/pro)
Overshooting: holding a test position and suddenly letting go
Action tremor or Intention Tremor
Truncal Ataxia
Cerebellar Disorder Deficit
Postural Dysfunction
-high fall risk
-loss of automatic movements
-loss of ankle, hip strategies
-static and dynamic posture, especially
Deficits in cerebellar function
Hypotonia: low tone from loss of MS and GTO input
Slow generation of force: unable to produce timely force generation (5/5 strength t/o)
Loss of RAM: inability to produce RAM patterns and alternating mvmt patterns
Deficits in Motor Learning: loss of ability to anticipate (feedforward) or correct (feedback) bc loss of proprioceptive, sensory, and muscular force
