Cerebellum and Motor System Anatomy

Cerebellum, Basal Nuclei & Extrapyramidal System

• Learning Outcomes: Describe cerebellar structure, mechanisms of balance and coordination, cerebellar disease related to region anatomy, identify basal nuclei parts, and relate anatomy to clinical problems (Parkinson's, Huntington's).

General Organization of Motor System

• The motor system involves cerebral cortex, brainstem, thalamus, basal ganglia, and cerebellum pathways connected via tracts.

Cerebellar Position in Cranium

• The cerebellum is located in the posterior cranial fossa, covered by the tentorium cerebelli.
• Key anatomical landmarks include grooves for sinuses and canals for nerves, foramina, and other structures.

Functional Connections of Cerebellum

• The cerebellum connects with the nervous system via peduncles.
• Superior peduncle connects to midbrain, middle peduncle to pons, and inferior peduncle to medulla oblongata.

Cerebellum

• Cerebellum consists of two hemispheres and a midline vermis.
• Anatomically, it has anterior, posterior/middle and flocculonodular lobes.

Divisions of Cerebellum - Multiple Ways

• Anatomical: Anterior, Posterior/Middle, Flocculonodular
• Functional: Vestibulocerebellum, Spinocerebellum, Cerebrocerebellum
• Evolutionary: Archicerebellum, Paleocerebellum, Neocerebellum

Functional Divisions

• FN (Vestibulocerebellum): Deep cerebellar nucleus (fastigial), interconnected with vestibular nuclei, controls posture, balance, and eye movements.
• Spinocerebellum: Deep cerebellar nuclei (globose & emboliform), input from spinal cord, maintains posture and muscle tone.
• Cerebrocerebellum: Deep cerebellar nucleus (dentate), primary input from cerebral cortex to lateral hemisphere. Coordinates, plans, and executes movements, gives feedback.

Summary of Major Efferents from Cerebellum

• Flocculonodular lobe via fastigial nucleus projects to vestibular nucleus & reticular formation, coordinates posture, and bilateral proximal/truncal muscle tone and eye movements.
• Inferior peduncle, coordinates posture, distal muscle tone, and eye movements.

Deep Cerebellar Nuclei

• Found in cerebellum's white matter.

• From medial to lateral:

  • Fastigial nucleus: associated with archicerebellum, balance & equilibrium.
  • Interposed nuclei (globose & emboliform): associated with paleocerebellum, walking & arm movements.
  • Dentate nucleus: most lateral, largest, part of neocerebellum, associated with highly skilled movements.

• Deep cerebellar nuclei receive input and modulate cerebellar influence throughout the nervous system.

Blood Supply to Cerebellum

• Supplied by the vertebrobasilar artery: superior cerebellar artery (SCA), anterior inferior cerebellar artery (AICA), and posterior inferior cerebellar artery (PICA).

Vascular Territories of Cerebellar Arteries

• SCA: Mostly pure cerebellar signs.
• PICA & AICA: Sensory and motor deficits, brainstem involvements.

Lesions

• Midline Lesions: Vestibulocerebellum/Spinocerebellum, nystagmus, balance/gait disturbances.
• Lateral Lesions: Cerebrocerebellum, incoordination/unsteady gait (ipsilateral), no sensory/muscular weakness.
• Bilateral Dysfunctions: Lack of coordination, intention tremor, unsteady gait.

Key Features of Cerebellar Lesion

• Ataxia: Incoordination of movements.
• Intention tremor: No tremor at rest, worsens with task approach.
• Dysmetria: Finger-nose & heel-shin test abnormalities.
• Dysdiadochokinesia: Difficulty performing alternating movements.
• Nystagmus: Oscillatory eye movements.
• Hypotonia & pendular knee jerks: Reduced muscle tone, exaggerated knee jerks.

Divisions of Cerebellum: Summary

• The table summarizes anatomical, phylogenetic, functional, and deep nucleus groupings of cerebellum.

Cerebellar Tonsil and Foramen Magnum Relation

• Cerebellar tonsils are located in the posterior fossa.
• Raised intracranial pressure can displace the tonsils through the foramen magnum, compressing the medulla.

Basal Ganglia: Major Components

• Basal ganglia are groups of gray matter embedded in the subcortical white matter.
• Components: Caudate, Putamen, Globus Pallidus, Subthalamic nucleus, and Substantia nigra.

Basal Ganglia: Major Components (Continued)

• Further details on the different components of the basal ganglia.

Basal Ganglia Connections

• Inputs: Primarily from cortex, thalamus, substantia nigra (pars compacta–dopamine-nigrostriatal pathway).
• Outputs: To globus pallidus (internal segment) and pars reticulata of substantia nigra
• Pathways to cortex (primary & supplementary motor region) and upper motor neurons (UMNs)

Parkinson's Disease

• Loss of dopaminergic neurons in substantia nigra (pars compacta/nigrostriatal pathway).
• Characterized by tremors (resting), rigidity, akinesia, posture/gait disturbances, slow/stooped posture, and shuffling gait.

Huntington's Disease (HD)

• Degenerative lesions in the caudate nucleus, neuronal loss in striatum and cortex (frontal & parietal).
• Progressive dementia and chorea (brief, sudden, purposeless jerks).
• Note: Caudate nucleus inputs from frontal association cortex.

Basal Nuclei Pathologies

• Parkinson's disease: Loss of dopamine-producing neurons in the substantia nigra leading to tremor, rigidity, akinesia.
• Huntington's disease: Neuronal loss in striatum (caudate and putamen), leading to progressive dementia and chorea.
• Hemiballismus: Damage to subthalamic nucleus leading to flailing movements of a limb.