Neurology: Athetosis and Dystonia

Athetosis

• Slow, writhing, worm-like involuntary movement of the extremities, trunk, and neck
• Associated with brain damage/cerebral palsy
• Involves mostly the distant limbs
• Involves cerebral cortex and basal ganglia
• Caused by the degeneration of the globus pallidus
• Also known as “Tics”, “Tourette’s” and “Choreoathetosis”

Dystonia

• Fixed posture or sustained postural contractions of the limb, neck, and facial muscles
• Most commonly secondary to cerebral palsy (CP)
• Component of the Extrapyramidal System (EPS)

Cerebellum

• Ovoid-shaped organ with 2 hemispheres joined by a vermis
• Situated in the posterior cranial fossa
• Lies posterior to the fourth ventricle, pons, and medulla oblongata
• Consists of two cerebellar hemispheres
• Each cerebellar hemisphere controls muscular movements on the same side (ipsilateral) of the body

Cerebellar Function

• Involved in the following:
  • Fine control and coordination of simple and complex movements
  • Layers of the Cerebellar Cortex:
    • Molecular layer (outermost)
      • Contains two types of neurons: stellate (outer) cells and basket (inner) cells
      • Few neuroglia present in this layer
      • Contain dendrites of Purkinje and parallel fibers (axons from granule cells which synapse with Purkinje cells)
    • Purkinje layer
      • Single layer consisting of Purkinje cell bodies
      • Purkinje cells are large Golgi Type I neurons
      • Purkinje cell axons are the ONLY OUTPUT FIBERS of the cerebellar cortex
      • Axons arise and pass through the granular layer to enter the white matter where it acquires myelin sheaths
    • Granular layer
      • Composed of 3Gs: Granule cells, Golgi cells Type II, and Glomeruli
      • Packed with small cells with densely staining nuclei and scanty cytoplasm
      • Granule Cells
        • Axons of each granule cell pass into the molecular layer, running parallel to the long axis of the cerebellar folium
      • Golgi Cell Type II
        • Scattered throughout the granular layer
        • Dendrites also go through the molecular layer
        • Axons terminate and synapse with the dendrites of granule cells

Cerebellar Afferent Fibers

• CORTICOPONTOCEREBELLAR PATHWAY
  • Information from: primary motor and sensory areas, and associate areas, primary visual cortex
  • Path: information will descend to corona radiata then to the internal capsule, terminate in the pontine nuclei, pontine nuclei give rise to the transverse fibers of the pons, cross the midline and enter the opposite cerebellar hemisphere at the middle cerebellar peduncle
• CEREBRORETICULOCEREBELLAR PATHWAY
  • Information from: motor areas, sensory motor areas
  • Path: fibers terminate on the reticular formation on the same side (ipsilateral), the cells in the reticular formation give rise to the reticulocerebellar fibers that enter the cerebral hemisphere on the same side through the inferior and middle cerebellar peduncle, some fibers will also terminate on the opposite side (contralateral) in the pons and medulla
• CEREBELLAR AFFERENT FIBERS FROM SPINAL CORD
  • From the spinal cord to cerebellum: information is sent from the somatosensory receptors
  • Anterior spinocerebellar pathway, posterior spinocerebellar pathway, cuneocerebellar pathway

Cerebellar Efferent Pathways

• Summary of the Efferent Cerebellar Pathways:
  • Pathway: Globose-emboliform rubral
  • Function: influences ipsilateral motor activity
  • Destination: to contralateral red nucleus, then via crossed rubrospinal tract to ipsilateral motor neurons in the spinal cord
  • Pathway: Dentatothalamic
  • Function: influences ipsilateral motor activity
  • Destination: to contralateral ventrolateral nucleus of the thalamus, then to contralateral motor cerebral cortex; corticospinal tract crosses midline and controls ipsilateral motor neurons in the spinal cord
  • Pathway: Fastigial vestibular
  • Function: influences ipsilateral extensor muscle tone
  • Destination: to contralateral ventrolateral nucleus of the thalamus, then to contralateral motor cerebral cortex; corticospinal tract crosses midline and controls ipsilateral motor neurons in the spinal cord
  • Pathway: Fastigial reticular
  • Function: influences ipsilateral muscle tone
  • Destination: to neurons of reticular formation; reticulospinal tract to ipsilateral motor neurons to the spinal cord