Basal Ganglia and Cerebellum Notes

Learning Objectives

• Identify the subcortical nuclei of the basal ganglia
• Describe the striatum and the lentiform nucleus
• Map out the direct and indirect pathways
• Describe the basal ganglia motor circuit
• Identify the cerebellar lobes, zones, and nuclei
• Describe the connections and fibers of the cerebellar peduncles
• Trace out the cerebrocerebellar and spinocerebellar circuits

Basal Ganglia

• Consists of five interconnected nuclei within the subcortical white matter:
  • Caudate Nucleus
  • Putamen
  • Globus Pallidus (divided into internal and external segments)
  • Subthalamic Nucleus (STN)
  • Substantia Nigra (located in the midbrain, includes SNc: pars compacta and SNr: pars reticulata)

Striatum

• Comprised of:
  • Caudate: divided into head, body, and tail segments
  • Putamen: fuses with the head of the caudate nucleus
  • Majority of the ventral striatum consists of the Nucleus Accumbens

Lenticular Nucleus

• Formed by the Putamen and the Globus Pallidus:
  • Globus Pallidus External Segment
  • Globus Pallidus Internal Segment
• Important anatomical relationships:
  • Related structures include the anterior limb of the internal capsule, claustrum, insular cortex, temporal cortex, and amygdala.

Internal Capsule

• Divided into anterior and posterior limbs:
  • Anterior Limb: Contains projections from the thalamus to the striatum.
  • Posterior Limb: Contains projection fibers to the cortex.

Basal Ganglia Pathways

• Two primary pathways that relay in the thalamus to alter motor function:
  • Direct Pathway
  • Stimulates thalamic output to the cortex
  • Increases motor function
  • Indirect Pathway
  • Inhibits thalamic output to the cortex
  • Decreases motor function
• Each pathway involves various connection fibers (e.g., corticostriatal, thalamocortical, etc.).

Basal Ganglia Motor Circuit

1. Cortex to Striatum
2. Choose Direct or Indirect pathway
3. Relay through Thalamus (VA/VL)
4. Send output to Motor Cortex
5. Outputs to Lateral Corticospinal Tract (LCST)

Cerebellum

• Known as the "little brain"
• Contains approximately 50% of all brain neurons
• Involved in modulating both motor and sensory outputs

Cerebellar Structure

• Comprised of three lobes:
  • Anterior Lobe
  • Posterior Lobe
  • Flocculonodular Lobe (Flocculus and Nodule)
• Three Zones with distinct functions:
  • Vermal Zone
  • Paravermal Zone
  • Lateral Zone

Cerebellar Peduncles

• Three pairs of cerebellar peduncles connect the cerebellum to the brainstem:
  • Superior Peduncle: Connects to the midbrain and primarily transmits outputs.
  • Middle Peduncle: Links to the pons, allowing for both inputs and outputs.
  • Inferior Peduncle: Connects to the medulla, receiving inputs from the spinal cord.

Deep Cerebellar Nuclei

• Comprised of four nuclei:
  • Fastigial Nucleus
  • Globose Nucleus
  • Emboliform Nucleus
  • Dentate Nucleus
• Each nucleus has specific functional roles:
  • Fastigial: Involved in postural stability control.
  • Interposed (Globose and Emboliform): Involved in error correction.
  • Dentate: Involved in motor planning and programming.

Functional Division of Cerebellum

• Functionally divided into:
  • Vestibulocerebellum: Balance and eye movements
  • Cerebrocerebellum: Motor planning and programming
  • Spinocerebellum: Error detection and correction, engages with motor cortical areas and spinal cord input

Interplay Between Basal Ganglia and Cerebellum

• Both systems work together to modulate motor movements effectively.