Cerebellum and Movement

Cerebellum

• latin for “little brain”

• interesting fact: 10% of brain’s volume

• part of the hindbrain (metencephalon)

• separated from cerebrum by tentorium cerebelli

• all cerebellar functions are unconcious

• does not initiate motor commands. instead, it: modifies movement (motor commands) output

• does not synapse directly on LMNs. Instead, it: regulates activity of UMN

Cerebellum General functions — all unconscious

Involved in complex functions:

• coordinating voluntary movements

• motor learning

• maintaining balance and adjusting posture

• cognitive functioning (not as well understood)

Coordinating voluntary movements

coordinates timing and force from different muscle groups to generate smooth limb and body movements

motor learning

• compares anticipated movement (intention) with actual movement output

• responsible for fine-tuning motor commands (trial-and-error)

maintaining balance and adjusting posture

adjusts commands to motor neurons to compensate for shifts in body position, and/or in changes of muscle load

Cognitive functioning (not as well understood)

language: helps with verbal fluency: grammar processing, correcting language mistakes (spoken or written)

Overview of Cerebellar input

*note: brainstem nuclei include: vestibular, pontine, reticular formation, inf. olivary nucleus

Overview of cerebellar input and Output

Surface Anatomy of the Cerebellum

• Cortex: three layers; has many tightly spaced folded layers of gray matter separated by parallel grooves. each gyrus = folium (plural: folia)

• Ventral surface of cerebellum = roof of 4th ventricle

• dorsal surface: separated from occipital lobe by dura mater

Cerebellum has 3 anatomical lobes

• anterior

• posterior

• flocculonodular

Cerebellum: Anterior Lobe

• mediates unconscious proprioception

• receives input from spinal cord via spinocerebellar tracts (unconscious proprioception)

• important in coordination of LE

• Also helps regulate muscle tone in LE

Cerebellum: Posterior Lobe

• important in fine motor coordination

  • via inhibition of involuntary movements (with GABA)

• receives input from brainstem and cerebral cortex (indirect)

Cerebellum: Flocculonodular Lobe

• maintains balance equilibrium and muscle tone

• has connections with vestibular nuclei (can use info about head movement to influence eye movements)

Cerebellum has 3 peduncles

• superior, middle, and inferior

• cerebellar peduncles convey input to cerebellum and/or output from cerebellum

Inferior Cerebellar Peduncles

• mostly afferents from spinal cord (post. spinocerebellar: proprioception of LE), medulla (inferior olivary nucleus), vestibular nuclei, vestibular apparatus

• some efferents to vestibular nuclei (vestibulospinal) and reticular formation (reticulospinal)

Middle Cerebellar Peduncles

afferents from pontine nuclei (cortico-ponto-cerebellar)

superior cerebellar peduncles

• mostly efferents from deep cerebellar nuclei to red nucleus and to the thalamus

• some afferents from ant. spinocerebellar tracts (proprioception of LE to anterior lobe of cerebellum)

Cerebellum has 3 vertical zones

vermis (midline)

paravermis/intermediate

lateral hemisphere

Note: flocculonodular lobe is not part of the vertical zones

Vertical Zone

each zone is associated with deep cerebellar nuclei located in the white matter of cerebellum

• vermis = fastigial nucleus

• paravermis = interposted nucleus (globose + emboliform)

• lateral hemisphere = dentate nucleus

Other Features

• cerebellar cortex (3 layers)

• cerebellar white matter

  • contains afferent and efferent fibers associated with cerebellar cortex

• deep cerebellar nuceli (within white matter)

  • receive most output from cerebellar cortex (via Purkinje cells)

  • send efferent output from cerebellum to other supraspinal area mostly by way of superior cerebellar peduncle

Cerebellar Cortex (grey matter): 3 layers

• molecular layer (outer)

  • dendrites of purkinje cells (look like a flat tree)

  • parallel fibers of granule cells (run perpendicular to purkinje dendrites)

  • stellate and basket cells

• purkinje layer (middle)

  • cell bodies of purkinje cells

• granule cell layer (inner)

  • numerous small tightly packed granule cells (interneurons)

  • golgi cells (interneurons)

Input to cerebellum

• mossy fibers (main input):

  • from pontine nuclei: spinal cord, reitcular formation, and vestibular nuclei

  • send excitatory projections to

    • deep cerebellar nuclei

    • granule cells

• Climbing fibers

  • from inferior olivary nucleus

  • send excitatory projections to

    • deep cerebellar nuclei

    • purkinje cells

output from cerebellum

• purkinje cells

  • only source of output form the cerebellar cortex

  • send inhibitory proejctions to deep cerebellar nuclei (in white matter)

  • use GABA

• deep cerebellar nuclei

  • from white matter of cerebellum to other CNS regions

Note:

• mossy and climbing fibers synapse directly on deep cerebellar nuclei to provide

  • coarse adjustment output from cerebellum to UMNs

• purkinje cells synapse on deep cerebellar nuclei to provide:

  • fine adjustments output to from cerebellum to UMNs

Cerebellar White Matter

afferents and efferents

deep cerebellar nuclei

• provides most output from cerebellum (exception: flocculonodular lobe)

• fastigial nucleus: most medially located: associated with vermis

• interposed nuclei (globose + emboliform): associated with the paravermis

• dentate nucleus: largest cerebellar nucleus

  • associated with the lateral hemisphere

General Overview of Functional Regions

• Vestibulocerebellum:

  • flocculonodular lobe

  • vestibular apparatus

• Spinocerebellum:

  • vermis and paravermis zones

• Cerebrocerebellum: lateral hemispheres

Vestibulocerebellum

• functional part of the flocculonodular lobe

• regulates balance via vestibular system (eyes/head/neck movements)

Spinocerebellum

• functional part of vermis & paravermis

• coordinates posture & gross limb movements

Cerebrocerebellum

• functional part of lateral hemispheres

• coordinates precise, distal voluntary movements

Example: Reaching for a book on the top shelf

• vestibulocerebellum

  • keeps body/trunk steady (prior to reaching for book)

• spinocerebellum

  • coordinates timing of proximal & gross limb movements (as we start reaching for book)

• cerebrocerebellum

  • coordinates precise, voluntary movements of hands and fingers (to grab & pull book with fingers from top shelf)

Functional cerebellum and deep nuclei

Inputs and Outputs of the three functional divisions of the cerebellum

Vestibulocerebellum output

• axial muscles control & vestibular reflexes

• from flocculonodular lobe to vestibular nuclei then vestibulospinal

• Not shown: tracts that transmit signals for eyes and head movements

Spinocerebellum output: medial and lateral activating systems

• Fastigial nucleus (M):

  • axial & proximal muscles control via:

    • vestibulospinal tracts

    • reticulospinal tract (pons)

    • thalamus (thalamocortical tract; medial corticospinal)

• interposed nucleus (L):

  • control of gross limb movements via:

    • rubrospinal and lateral corticospinal

Cereberocerebellum output: Lateral activating system

• planning of movements

• initiation of coordination of movements

• timing of movements

• precise distal motor control (fractionation)

• ongoing execution of movements