Organizational Divisions, Levels, and Zones of the RF

• Midbrain (RF_midbrain)
  
  
  • The RF_midbrain is comprised of the following nuclei:
    • Cuniform Nucleus
    • Subcuniform Nucleus
  
  
  • The Cuneiform Nucleus and Subcuneiform Nucleus are involved in motor functions
  
  
  • Physical destruction of the reticular core at the Cuniform Nucleus or “wasp's waist” destroys the function of the entire reticular formation and leads to inevitable and unavoidable death.


• Pons (RF_pons)
  
  
  • The RF_pons is comprised of the following nuclei:
    • Pontis Caudalis
    • Pontis Oralis
  
  
  • The RF_pons projects to the:
    • Abducens Nucleus
    • Nucleus Prepositus Hypoglossi
    • Vestibular Nuclei
    • Medial Rectus Motorneurons in the Occulomotor Nucleus
  
  
  • The medial zone of the pontine RF (medialRF_pons) is associated with motor functions.
  
  
  • The paramedian zone of the pontine RF (paraRF_pons) are responsible for generating the horizontal saccades involved in smooth visual pursuit.


• Medulla (RF_medulla)
  
  
  • The RF_medulla is comprised of the following nuclei:
    • Paramedian Reticular Group
    • Nucleus Gigantocellularis
    • Lateral Reticular Nucleus
    • Nucleus Parvocellularis
    • Intermediate Reticular Nucleus

Three Midbrain-Pontine and Four Medullary Zones

The midbrain and pontine reticular can be divided into three organizational and functional zones.
In the medulla there are four organizational and functional zones:

• Paramedian (paraRF) - consisting of neuronal cell groups located adjacent to the Raphe_{(Greek, seam)} nuclei which are positioned along the midline of the brainstem.
  
  
  • The paraRF projects to the cerebellum and participate in motor function.


• Medial (medialRF) - consisting of neuronal cell groups positioned in the medial 2/3^rds of the tegmentum.
  
  
  • The medialRF is the major site of origin for RF outflow:
    
    
    • The medialRF_midbrain projects to the hypothalamus and thalamus via the central tegmental tract.
    • The medialRF_pons projects to the spinal cord via the Medial Reticulospinal Tract (mRST).
    • The medialRF_medulla projects to the spinal cord via the Lateral Reticulospinal Tract (lRST).


• Lateral (lateralRF) - consisting of diffuse cell groups positioned in the lateral 1/3^rd of the tegmentum.
  
  
  • The lateralRF receives multiple sensory inputs from the general and special columns as well as the cerebral cortex.
  
  
  • The lateralRF appears to function as an afferent association area.


• Intermediate (intermediateRF_medulla) - consisting of cell groups positioned between the medialRF_medulla and lateralRF_medulla and is restricted to the medulla.
  
  
  • The intermediateRF_medulla participates in the regulation of visceral functions such as respiration, heart rate and blood pressure via the autonomic systems.