cerebellum: the motor modulatory system

direct motor pathway

pyramid pathway

corticospinal tract, rubrospinal tract, reticulospinal tracts

indirect motor pathways

the cerebellum and basal ganglia

cerebellum

coordinate of movement, maintenance of upright posture (in humans), maintenance of the tension or firmness of the muscles

overall coordinate sequence of muscle contractions

ataxia

uncoordinated and inaccurate movements

dysnergia

decomposition of synergistic multi-joint movements

dysmetria

overshoot or undershoot targets

deep cerebellar nuclei

relay cerebellar cortical output to brainstem structures

embedded in the cerebellar white matter

vermis

axial musculature control, contributes to ventromedial pathways

cerebellar hemispheres

limb movements, contributes to lateral pathways

anterior lobe

muscle tone (axial muscles), posture

posterior lobe

motor movements of limbs

flocculonodular lobe

posture, balance, equilibrium, vestibular system and eye movements

inputs of cerebellum

cerebral cortex, vestibular system, visual and auditory systems, spinal cord

outputs of cerebellum

cerebellar deep nuclei → brainstem, thalamus, other CNS areas

lateral cerebellum

motor loop responsible for the proper execution of planned, voluntary, multi-joint movements

corticopontocerebellar projection

20 times larger than the pyramidal tract

sensorimotor cortex → pons (pontine nuclei) → cerebellum

anterior lobe syndrom

midline damage, causing postural instability

broad-based staggering gait, because the control of the legs are affected

ataxia (general incoordination) of leg movements

neocerebellar syndrom

lateral damage, causing limb ataxia, manifestations occur on the ipsilateral side of lesion

hypotonia

decrease in muscle tone

hyporeflexia

decreased stretch reflexes

pendular reflexes

a limb may swing back and forth after a reflex contraction

intention tremor

when a patient approaches a target and has the appearance of a tremor

tremor in voluntary movement

dysdiadochokinesia

rapid alternating movements become difficult

decomposition of movement

when complex movements involving more than one joint are performed, the timing of different parts is defective in different ways

scanning speech

normal flow and rhythm of speech is disrupted, successive syllables may emerge slowly and separated from each other

flocculonodular syndrome

damage to flocculus affects eye movements

loss of balance, but no tremor or change in reflexes and muscle tone

medulloblastomas

tumors on medulla (below flocculus/nodulus) which are the most common cause of damage of the flocculonodular lobe

happens a lot in children

purkinje cells

make up a layer of the cerebellum

the only neurons whose axons leave the cerebellar cortex and synapse with the cerebellar deep nuclei

granule cells

make up a layer of the cerebellum

each sends its axons to molecular layer → bifurcates → form parallel fibers → synapse with purkinje cells

inferior olivary nucleus

input (afferent) fibers into the cerebellar cortex

send climbing fibers → synapse onto purkinje cells of cerebellar cortex (both anterior and posterior lobes)

mossy fibers

input (afferent) fibers from other parts of the CNS into the cerebellar cortex

synapse onto granule cells → parallel fibers → synapse onto Purkinje cells

long term depression (LTD)

when parallel or climbing fibers are stimulated repeatedly, they elicit enhanced inhibitory responses of Purkinje cells (release GABA)

enhanced inhibitory response lasts a long time even under normal stimulation