What Aspects of Motor Function are under (Indirect) Cerebellar Regulation?
1) Synergy of movement: Collective coordination of elemental muscular contractions to create purposeful (perhaps highly complex) motoric output (e.g., walking).
2) Posture: Orientation of body parts relative to each other and the vector of gravity.
3) Muscular tone: Basal levels of contraction of muscles.
Describe the method of the indirect control that is being done by the cerebellum
- The cerebellum acts as a comparator
o Motor centers (e.g., primary motor cortex) transmit signals directly or indirectly to lower motor neurons to produce purposeful movement or simply to influence muscle tone or reflexive responsiveness
o Copies of such motor instructions reach the cerebellum
o The cerebellum compares sensory feedback with original motor instructions
o With mismatched motor instructions and outcomes, the cerebellum sends corrective signals to motor centers,
thereby influencing subsequent motor instructions
o Under the feedback-driven guidance of the cerebellum, the motor centers continually adjust output to facilitate
smoothly coordinated and posturally appropriate movements (this necessarily implies spatial and
temporal accuracy of movement)
Which side of the body does the cerebellum control?
Cerebellum indirectly regulates ipsilateral body
What occurs in acute cerebellar damage?
often yields pronounced motor deficits (ipsilaterally)
In what type of Cerebellar damage recovery possible?
Substantial functional recovery often occurs with long-standing but nonprogressive cerebellar damage
Describe embryological development of Cerebellum
emerged embryologically as a protuberance of the
metencephalon to occupy much of the posterior cranial fossa
Describe the General structure of the cerebellum
o The cerebellum is grossly hemispheric
o Hemispheres are separated by a midline vermis (worm)
A sagittal view of the vermis reveals an ornate complex of white matter (arbor vitae or tree of life) that penetrates
superficial gray matter
Name the Cerebellar lobes and their location
1) Anterior lobe: Superior to the primary fissure
2) Posterior lobe: Inferior to the primary fissure
3) Flocculonodular lobe: Mediolaterally oriented strip of tissue situated ventrally on the cerebellum, separated from the posterior lobe by the posterolateral fissure
Describe the somatotopic map of the cerebellum
o The trunk is functionally regulated by more medial cerebellar structures
o Limbs are functionally regulated by more laterally
What are the 3 functional zones of the cerebellum and describe their locations?
- Vestibulo-cerebellum- flocculonodular lobe
- Spino-cerebellum - anterior lobe
- Cerebro-cerebellum - posterior lobe
Function of the Vestibulo-cerebellum
afferents from vestibular apparatus to permit regulation of balance andeye movements
Function of the Spino-cerebellum
The spinal cord provides this region with sensory feedback regarding consequences of motor activity, thereby assisting with regulation of gross truncal and limb movements
Function of the Cerebro-cerebellum
Integrating motor with sensory feedback coordinates and
smoothes movements requiring precision of location and
timing
What forms the cerebellar peduncles?
Cerebellar efferents and afferents
Where are the fibers going from each of the cerebellar peduncles?
o Middle cerebellar peduncles largely carry information from the pons into the cerebellum
o Superior and inferior cerebellar peduncles carry bidirectional traffic, with the inferior cerebellar peduncle being the greater conductor of cerebellar afferents
o Superior cerebellar peduncles transmit cerebellar signals to the pons and midbrain (except those destined for the vestibular nuclei)
o Inferior cerebellar peduncles relay much information from
spinal levels into the cerebellum, although the superior cerebellar peduncle also contributes
o Communications with the olive, cranial nerve VIII and the vestibular nuclei also involve the inferior cerebellar peduncles
How does afferents allow cerebellum to act as a comparator?
- Motor systems (e.g., corticospinal system) advise the cerebellum of their impending influence on lower motor neurons
- Somatosensory systems (e.g., dorsal spinocerebellar system) advise the cerebellum of the results of motor system output
- Comparison of intended outcomes (motor instructions) with actual outcomes (somatosensory feedback) permit the cerebellum to transmit corrective instructions to motor systems
Describe the Cerebro-ponto-cerebellar Inputs (Copy of Motor Instructions)
o The precentral gyrus and anterior paracentral lobule of the frontal lobe emit large volumes of motor information, as part of the corticospinal and corticobulbar motor systems
o Other frontal areas along with parietal, temporal, and occipital lobes also contribute
o Copies of corticospinal and corticobulbar signals destined for lower motor neurons also terminate in the ipsilateral deep pontine nuclei
o Ponto-cerebellar (transverse) fibers then cross the midline to enter the cerebellar hemisphere opposite to the cortical site of origin via the middle cerebellar peduncle
Name 3 Examples of Spinal cerebellar Input (Sensory Feedback)
1) Dorsal spinocerebellar system
2) Ventral spinocerebellar system
3) Cuneocerebellar system
Describe the Dorsal spinocerebellar system input to the cerebellum
- Neuromuscular spindles and Golgi tendon organs transmit signals related to specific muscles (of the lower
body) into the spinal dorsal horn - The dorsal spinocerebellar pathway ascends ipsilaterally to enter the cerebellum via the inferior cerebellar peduncle
Describe the Ventral spinocerebellar system input to the cerebellum
- An array of receptors contributes to analysis of whole-limb movement, communicating with the spinal gray matter
- Spinal neurons send axons across the cord to ascend to the superior cerebellar peduncle, thereby entering the cerebellum
- Many of these same fibers cross a second time (within the
cerebellum) - Note that this pathway, which crosses the nervous system twice, is functionally similar to a pathway that does not
cross (i.e., one side of the cerebellum indirectly regulates the ipsilateral body)
Describe the Cuneocerebellar system input to the cerebellum
- Proprioceptors for the upper limbs contribute to the ipsilateral fasciculus cuneatus, which terminates in the
medullary nucleus cuneatus - External arcuate fibers enter the cerebellum through the ipsilateral inferior cerebellar peduncle as the cuneocerebellar pathway
Describe the histology of the cerebellum
- Beneath the meninges is the cerebellar cortex (analogous to cerebral cortex)
- Beneath the cerebellar cortex is subcortical white matter (analogous to cerebral white matter)
- Embedded within the subcortical white matter are deep cerebellar nuclei (analogous to the basal nuclei [ganglia] of the cerebrum)
Near the deep cerebellar nuclei is the ventricular system,
specifically the fourth ventricle (analogous to the lateral cerebral ventricles)
What are the 2 types of fibers that enter the cerebellum?
o Climbing fibers arise from the inferior olivary nuclei
o Mossy fibers constitute the remainder of cerebellar afferents
Describe the cerebellar cortical organization
The cerebellar cortex is organized as folia (little folds) and is laminated
o Closest to the white matter lie cortical granule cells,
o Between the molecular and granule layers is the Purkinje layer, occupied by the large Purkinje somata
o Outermost layer is Molecular layer
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