Neuro 101: Cerebellum and Basal Ganglia

The Cerebellum and Basal Ganglia

The primary role of the cerebellum is to modulate the descending fibres of the corticospinal tract. It regulates muscle tone and coordination and controls posture and gait.

Cerebellar Lobes
Cerebellum lobes

The cerebellum is divided into three lobes:

Anterior lobe

  • Controls posture and muscle tone
  • Receives input from the spinal cerebellar tracts
  • Damage might produce ataxia of the limbs

Posterior lobe

  • Controls coordination in skilled activities
  • Receives input from the cortex
  • Damage produces hypotonia and truncal ataxia

Flocculonodular lobe

  • Concerned with equilibrium
  • Receives input from the vestibular nuclei
  • Damage produces nystagmus, vertigo, and difficulty with equilibrium
Functional Regions
cerebellum functional zones

The cerebellum is also divided into three functional zones:

Medial

  • Controls proximal and trunk muscles
  • Controls vestibulo-ocular reflexes
  • Damage causes gait unsteadiness and nystagmus with vertigo

Intermediate

  • Controls distal muscles of appendages
  • Damage causes appendicular ataxia

Lateral

  • Controls motor planning for extremities
  • Damage may affect fine motor skills
Cerebellar Connections

Three pairs of peduncles (inferior, middle, superior) connect the cerebellum to other parts of the nervous system.

Cerebellar connections

Input

  • Mostly through inferior and middle peduncles
  • Sensory input from brainstem, midbrain, and spinal cord
  • Modulates cerebellar output

Output

  • All arises from deep cerebellar nuclei
  • All output is inhibitory
  • Travels via superior cerebellar peduncle to cortex
Cerebellar Dysfunction

Signs include:

  • Ipsilateral ataxia
  • Decreased muscle tone
  • Decreased reflexes
  • Horizontal nystagmus
  • Cerebellar dysarthria
  • Intention tremor
Common Cerebellar Afflictions

Tonsillar Herniation
Increased intracranial pressure causes cerebellar tonsil herniation through foramen magnum → brainstem compression → coma and death.

Chiari Malformation (Type I)
Cerebellar tonsils displaced below foramen magnum. May develop syringomyelia. Symptoms: headache, high ICP, spinal cord signs, ataxia, vertigo, downbeat nystagmus.

Toxins (Ethanol)

  • Acute: postural instability
  • Chronic: vermis damage → truncal ataxia
  • May be worsened by thiamine deficiency

Neoplasms

  • Medulloblastoma (children)
  • Astrocytoma
  • Metastases
  • Meningiomas
    Signs: headache, vomiting, vision changes, ataxia, personality and cognitive changes, increased head size in children

Cerebellar Stroke

  • AICA/SCA: appendicular ataxia, nystagmus, nausea
  • PICA (Wallenberg): vertigo, nystagmus, facial (ipsi) and body (contra) sensory loss
Cerebellar circulation

Other Pathologies

  • Hypertensive haemorrhage: rapid ICP increase → herniation
  • Degenerative: Friedreich’s ataxia, OPCA/MSA

The Extrapyramidal System

Not a true separate system, but refers to indirect control of movement via cerebellum and basal ganglia. Modulates corticospinal tract activity.

Basal ganglia
Basal Ganglia Structures
  • Caudate + putamen = corpus striatum
  • Thalamus is adjacent but not part of basal ganglia
Motor Pathways

There are two pathways in the basal ganglia made up of interconnections, which form a series of feedback loops, all of which modulate motor activity.

Direct Pathway

  • Globus pallidus internus inhibits thalamus
  • Striatum suppresses this inhibition → increases motor activity

Indirect Pathway

  • Striatum inhibits globus pallidus externus
  • → less inhibition of subthalamic nucleus → more GPI activity → decreased movement
Dopaminergic System
  • Substantia nigra → striatum (dopamine) → disinhibition of movement
  • Acetylcholine has opposite effect (inhibits movement)
  • Normally balanced with dopamine

Extrapyramidal Disorders
Hypokinetic Movement Disorders (Parkinsonism/Parkinson’s disease)
  • Caused by loss of dopamine neurons in substantia nigra
  • Indirect pathway becomes dominant → suppressed movement

Classic Signs

  • Rigidity (cogwheeling)
  • Rest tremor (pill-rolling)
  • Postural tremor
  • Bradykinesia
  • Postural instability
  • Festination

Examination

  • Gait and facial expression
  • Resting tremor (4–8 Hz)
  • Cogwheeling on passive movement
  • Retropulsion (pull test)
Hyperkinetic Movement Disorders
  • Excessive movement: chorea, ballism, tics, dystonia
Huntington’s Disease
  • Genetic, progressive
  • Chorea, cognitive decline, psychiatric changes
  • Loss of striatal neurons → favours direct pathway → increased movement
  • Loss of GPI inhibition → thalamocortical hyperactivity

This is an edited excerpt from the Medmastery course Clinical Neurology Essentials by Robert Coni, DO, EdS, FAAN. Acknowledgement and attribution to Medmastery for providing course transcripts.

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LITFL author Robert Coni DO EdS

Robert Coni, DO, EdS, FAAN. Vascular neurologist and neurohospitalist and Neurology Subspecialty Coordinator at the Grand Strand Medical Center in South Carolina. Former neuroscience curriculum coordinator at St. Luke’s / Temple Medical School and fellow of the American Academy of Neurology. In my spare time, I like to play guitar and go fly fishing. | Medmastery | Linkedin |

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