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Cerebellar Connections

Motto: Qui bene distinguit, bene docet

Memorize on tracts: origin, target, laterality, positions, main function, synapses and transmitters (if characteristic).

Cerebellar connections 
by dr. Mihály Kálmán

(based on the handouts of Prof. Réthelyi and Dr. Hajdu, completed with data of Gray’s Anatomy).

Afferent pathways:

  • from the vestibular system to the archicerebellum (most ancient)
  • from the spinal cord and brainstem to the paleocerebellum
  • from the cortex to the neocerebellum (only in mammals)

Each of them represented by both mossy fibers and climbing (olivocerebellary) fibers.

Supposed inputs to the cerebellar nuclei: by the collaterals of the inputs of the cerebellar cortex.

Principle: there is no primary sensory input but secondary or tertiery inputs via “precerebellar nuclei” (see below underlined), there is only one exception.


With mossy fibers:

  • Vestibulocerebellar (ipsilateral, archi)- vestibular organ, via the med. and inf. vestibular nuclei (secondary) and directly from the vestibular ganglion (exception: primary).
  • Dorsal spinocerebellar (Flechsig, ipsilateral, paleo) – lower limb and trunk, via the dorsal spinal nucleus (Clarke). This and the next four carry mainly propriceptive informations.
  • Ventral spinocerebellar (Gowers, mainly ipsilateral, paleo) – lower limb and trunk, via the spinal grey matter, crossing in the spinal cord, re-crossing in the brain stem.
  • Cuneocerebellar (ipsilateral, paleo) – upper limb and trunk (corresponds to the Flechsig), via accessory cuneate nucleus and ext. dors. arcuate fibers.
  • Rostral ventral spinocerebellar – upper limb and trunk (corresponds to the Gowers), hardly known in human.
  • Nucleocerebellar (ipsilateral, paleo) from proprioceptive receptors (head), via principal sensory trigeminal nucleus (also called simply trigeminocerebellar).
  • Reticulocerebellar (ipsilateral, paleo) – via the lateral reticular nucleus.
  • Tectocerebellar (contralateral, neo/paleo) from the auditory and visual systems via the inf. and sup. collicles (its being separate tract is challenged, possibly via reticular formation and reticulocerebellar tract).
  • Corticopontocerebellar (contralateral, neo) from the cortex, via the parapyramidal tracts (Türck, Arnold), pontine nuclei.
  • Arcuatocerebellar (ipsilateral, neo) from the cortex, via the pyramidal tract, arcuate nucleus, ext. ventr. arcuate fibers.
  • Diffuse input: Hypothalamocerebellar, raphecerebellar (serotonine), coeruleocerebellar (norepinephrine).


With climbing fibers:

  • Olivocerebellar (contralateral, archi, paleo, neo)

To the hemispheres: principal nucleus of inf. olive.

To the nodulus and flocculus: a minor part of the medial accessory olive (dorsal cap)

To the vermis and paravermis: the dorsal and medial accessory olives.

(paravermis: intermedier zone of the hemisphere beside the vermis).

Input to the inf. oliva (all ipsilateral):

Centr. tegmental fasc. (mainly parvicellular red nucleus, tectum, other subcortical motor centers)

Corticoolivary, spinolivary, vestibuloolivary tract

 

Efferent pathways:

Principle: there is no direct output from the cerebellar cortex, only (inhibitorily) via cerebellar nuclei (see below underlined). There is only one exception.

Cerebellar cortex to cerebellar nuclei

Vermis – to the fastigial nucleus,

Medial (intermediate) part of the hemisphere – to the globosus and emboliform nuclei

Lateral major part of the hemisphere – to the dentate nucleus from the, the other nuclei to the

Exception: there are direct fibers from the archicerebellum to the lat. vestibular nucleus.


Cerebellar nuclei to extracerebellar nuclei

  • Cerebellovestibular (ipsilateral) via the fastigial nuclei to the lat. vestibular nucleus.
  • Cerebelloreticular (ipsilateral), via the fastigial nucleus to the reticular formation.
  • Fastigiobulbar (“hook” of Russel, contralateral) via the fastigial nucleus to the vestibular nuclei and reticular formation).
  • Cerebello(dentato)rubral (contralateral) via the globosus and emboliform nuclei to the posterior, magnocellular part of the red nucleus (paleorubrum) and via the dentate nucleus to the anterior, parvocellular part of the red nucleus (neorubrum).
  • Cerebello(dentato)thalamic (contralateral) via the dentate nucleus to the thalamus (VA,VL nuclei), and then to the cortex, also to the striatum via the centromedial thalamic nuclei (latter starts from fastigial nucleus??).

The cerebellum is multiply involved in the reverberation circles of the motor system (see extrapyramidal tracts). It effects indirectly via:

  • vestibulospinal tract – postural reflexes,
  • reticulospinal tracts (lat., ant.) – postural reflexes, muscular tone
  • rubrospinal tract? – (negligible in human, important in non-mammals)
  • medial longitudinal fasciculi – eye and head movement coordination
  • thalamocortical feedback – motocortical functions.


Summarized: cerebellar cortex to extracerebellar nuclei:

Lateral hemispherium – (dentatus nucl.) – neorubrum, thalamus, then cortex, striatum.

Intermediate hemispherium – (globosus, emboliform nuclei) – paleorubrum, tegmentum (rubro-, reticulospinal tracts;

Vermis – (fastigial nucl.) – reticular formation, nu. vestibulares (med. long. fasc., reticulospinal tract);

Archicerebellum direct to the lat. vestibular nucleus vestibulospinal tract

The cortical representations of the output and input overlap only in a part.


According to the peduncles:

SPC:

spinocerebellaris ventr.,

tectocerebellar,

cerebellothalamic,

cerebellorubral,

reticulocerebellar (in part)?

hypothalamo-, coeruleocerebellar?

MPC:

(cortico)pontocerebellar

arcuatocerebellar?

raphecerebellar?

ICP:

everything else