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Other parts of the brain involved in the control of movement.
   The cerebellum: its parts and their connections.


The cerebellum has three functional divisions, based on the principal sources of afferent fibres. The vestibulocerebellum (salmon pink, surrounded by a thin yellow line on the diagram) consists of the nodule and the two flocculi. Afferents are from the vestibular ganglion and nuclei. The spinocerebellum (light beige on diagram, and demarcated by a thick yellow line) consists of the vermis and adjacent cortex of the anterior lobe and of part of the posterior lobe. The dorsal and ventral spinocerebellar tracts terminate in these regions.
[ The textbook (Crossman & Neary) assumes there is a significant human rubrospinal tract (eg diagram of spinocerebellar circuitry on p.122). This is wrong. Use the lecture and these web notes for guidance. ]
The pontocerebellum is the largest division, comprising most of the cerebellar cortex (pale cream colour, almost white, in the diagram). Afferent fibres are from the pontine nuclei.
Divisions and landmarks of the cerebellum. Click here to view.
In addition, all parts of the cerebellum receive fibres from the contralateral inferior olivary complex of nuclei in the medulla.

Each functional division of the cerebellar cortex has its own nucleus, embedded in the white matter of the core of the cerebellum.
  • Vestibulocerebellum  -  Fastigial nucleus
  • Spinocerebellum        -  Interposed nucleus
                                       (= globose and emboliform nuclei)
  • Pontocerebellum        -  Dentate nucleus
Click here for a diagram showing the positions of the cerebellar nuclei.
(The spinocerebellum also has some connections with the fastigial nucleus.)
Note on terminology.  Alternative names for the divisions of the cerebellum are derived from phylogeny. Although the functional and phylogenetic divisions are not exactly equivalent, it is "almost true" to say that:
Vestibulocerebellum  =  Archicerebellum
Spinocerebellum  =  Paleocerebellum
Pontocerebellum  =  Neocerebellum

Intrinsic circuitry.   (  Diagram  )  The cerebellar nuclei are the sources of the efferent fibres. Every axon that enters the cerebellum gives a collateral branch in one of the deep nuclei before continuing to the cortex. The cerebellar afferents are all excitatory. The principal cells of the cerebellar cortex (Purkinje cells) send their axons to the cerebellar nuclei, where their action is inhibitory.

Extrinsic neuronal circuits of the cerebellum.
The best understood function of the cerebellum is to ensure that movements are made smoothly by proper timing of contractions of different muscles, each with the required changes in length and force. You may wish, at this point, to review a general plan of all the motor pathways. Remember that the basal ganglia are also importantly involved in programming the patterns of signals that are sent to motor neurons.

The connections of the cerebellum are with the same side of the body and with the opposite cerebral hemisphere.  Consequently some of the tracts of fibres going to and from the cerebellum cross the midline, whereas others do not.

In this Diagram of all cerebellar connections the decussations are shown as orange crosses. From your studies of the spinal cord and brain stem you should already know the levels of most of these decussations, but they are repeated here for revision. (Nearly everything in a neuroanatomy course is done at least twice!)
  • Vestibular connections are all uncrossed.

  •    (They hardly involve the cerebral hemisphere.)
  • Olivocerebellar fibres cross in the

  •    reticular formation at mid-medullary levels.
  • Cerebellothalamic fibres cross as the

  •    decussation of the superior cerebellar,
    , at the level of the inferior colliculi.
  • Pontocerebellar fibres cross in the ventral pons.
  • Corticospinal fibres cross in the decussation

  •    of the pyramids
    at the caudal end of the
       medulla. (A minority descend ipsilaterally
       in the ventral funiculus and cross at
       segmental levels in the cord.)
Finally, you should know which populations of fibres are in the three cerebellar peduncles:
  • Superior cerebellar peduncle contains all

  •    the cerebellothalamic fibres. (It also contains
       fibres from the ventral spinothalamic tract.)
  • Middle cerebellar peduncle contains only

  •    pontocerebellar fibres.
  • Inferior cerebellar peduncle contains

  •    olivocerebellar fibres,
       the dorsal spinocerebellar tract,
       and all the fibres connecting with
       the vestibulocerebellum.

Effects of diseases on cerebellar function.
Much clinical jargon here!  Consult a glossary or a medical dictionary for words you don't know.

The functions of the vestibulocerebellum are inseparable from those of the vestibular system. The symptoms are vertigo, nystagmus and an unsteady gait.

The spinocerebellum responds to proprioceptive input. Diseases include hereditary spinocerebellar degenerations (such as Friedrich's ataxia) and degenerative disease due to too much ethanol imbibition. Alcoholic cerebellar disease affects midline structures, which include parts of both the spino- and the vestibulo-cerebellum. The principal consequence is ataxia that affects gait (broad-based, staggering) and keeping the back and head upright ("truncal ataxia").

Pontocerebellar symptoms are typically unilateral, because a single lesion is unlikely to involve the lateral parts of both cerebellar hemispheres.  They are ipsilateral (same side of the body). The ataxia is seen in limb movements, and can be detected by simple clinical tests. Buzz-words from the 1890s  still in use today:  Finger-nose test. Past-pointing. Heel-shin test. Dysdiadochokinesis.
These can indicate damage in a cerebellar hemisphere or in a connected region. Pontocerebellar disorder may be due to multiple sclerosis, with a large plaque of demyelination in a superior cerebellar peduncle (SCP), disrupting the dentato-thalamic projection. Will a lesion in the right SCP cause ataxia in the right or the left limbs?

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