Smooth execution and appropriate completion of ongoing movements, particularly those guided by vision.
Other possible functions: participation in cognitive and language functions.
Three subdivisions of the cerebellum
distinct anatomic regions separated on basis of physiologic function, phylogenetic origin, and anatomic connections with other major structures
(1) Vestibulocerebellum
– Functions in control of balance and head-and-eye movements. Has extensive connections to the brainstem vestibular nuclei, receives primary afferent input from semicircular canals, receives input from and sends output to the vestibular nuclei.
(2) Spinocerebellum
– Functions to adjust ongoing movements especially smoothing their execution. Receives extensive somatosensory input from the spinal cord and from the brainstem and sends output back to the spinal cord via brainstem nuclei. Output can also go to the motor cortex via the thalamus.
(3) Cerebrocerebellum
(Neocerebellum) – Thought to coordinate and plan limb movements. Receives input from wide areas of the cerebral cortex via the brainstem (pontine nuclei) and sends output via the thalamus to extensive area of the cortex.
Cerebellar Anatomy
Located in posterior fossa, separated from cerebral cortex by tentorium, overlies 4th ventricle posterior to brainstem.
Major Subdivisions:
Sagittal Subdivisions
: Vermis (midline) – fastigial nucleus; Intermediate – interposed nucleus; and Lateral hemispheres (paired and lateral to vermis) – dentate nucleus
Spinocerebellum is somatotopically organized like the ventral horn (medial=axial muscles, lateral=distal muscles)
Vermis
INPUT: through ipsilateral inferior and superior cerebellar peduncles
somatosensory input from axial musculature (cranial, cervical, thorax, lumbar and sacral)
"efference copy"
vestibular and visual inputs
OUTPUT: bilaterally through superior cerebellar peduncle
Purkinje cells project to Fastigial nucleus.
Fastigial nuclei project bilaterally through superior cerebellar peduncle to brainstem reticular and vestibular nuclei
Reticulo- and Vestibulo-spinal tracts project anteromedially to control axial musculature
Note: Secondary output through superior cerebellar peduncle decussates and synapses in the contralateral ventrolateral (VL) nucleus of the thalamus and then projects to the motor cortex controlling axial musculature, thus decussating two times
Effect of Lesions:
posture
broad-base gait with alcoholic degeneration of anterior lobe
Intermediate Hemispheres
INPUT: through ipsilateral inferior and superior cerebellar peduncle
somatosensory input from distal musculature (cervical and lumbar)
"efference copy"
vestibular and visual inputs
OUTPUT: through superior cerebellar peduncle
Purkinje cells project to Interposed nuclei.
Interposed nuclei project through superior cerebellar peduncle to contralateral red nucleus (Magnocellular Division) and contralateral ventrolateral nucleus of the thalamus
Rubrospinal tract decussates in the midbrain and projects posteriolaterally in the spinal cord.
Ventrolateral (VL) nucleus of the thalamus projects to motor cortex controlling distal musculature. The corticospinal tract crosses at the pyramidal decussation then projects to distal muscles.
Both rubro- and cortico-spinal tracts control distal musculature.
Note: OUTPUT crosses twice – decussation of superior cerebellar peduncle, and of rubrospinal tract or of corticospinal tract at the pyramidal decussation.
Effect of Lesions: all ipsilateral
tremor (involuntary rhythmic oscillation of limbs)
dysmetria (overshooting target)
hypotonia (decreased muscle tone)
ataxia (staggering of movement, distortion of muscular coordination)
(3) Cerebrocerebellum
– gets info from cerebral cortex and participates in planning of movement
Lateral Hemispheres
(Figure 4)
INPUT: through middle cerebellar peduncle
Pontine nuclei, pontine cell bodies are contralateral to their cerebellar targets. Thus, axons from the pontine cells decussate on the anterior surface of the pons.
Pontine nuclei receive their input from ipsilateral cerebral cortex (motor, premotor, and association cortex).
OUTPUT: through superior cerebellar peduncle
Purkinje cells of the lateral hemispheres project to the Dentate nucleus which projects through the superior cerebellar peduncle to the contralateral ventrolateral nucleus of the thalamus, and the contralateral red nucleus (parvocellular division)
Ventrolateral (VL) nucleus of the thalamus projects to motor cortex controlling distal musculature. The corticospinal tract crosses at the pyramidal decussation then projects to distal muscles.
Parvocellular division of the red nucleus projects ipsilaterally to the inferior olive whose output decussates and loops back to the lateral hemisphere of the cerebrocerebellum.
Effect of Lesions: (Note: hard to distinguish effects of Intermediate and Lateral hemispheres)
Dysdiadokinesis: slowness in reversing rapid alternating movements