QS Study

Reticular Formation

Diffused ill-defined mass of nerve cells and fibers forming a meshwork or reticulum in the control portion of brain stern is collectively known as a reticular formation. It is found in the brainstem, at the center of an area of the brainstem known as the tegmentum. It regulates consciousness, sleep, and wakefulness.


Downward into the spinal cord and upward into the thalamus and subthalamus. It is divided into three columns: raphe nuclei (median), gigantocellular reticular nuclei (medial zone), and parvocellular reticular nuclei (lateral zone).

Fig: Reticular Formation

Comprises two systems

(1) Ascending reticular activating system: Play roles in wakefulness and control over all activities of the brain.

(2) Descending reticular system: Comprises two projection.

Descending inhibitory reticular projection:

  • Inhibition of γ-motor neuron
  • Inhibition of muscle spindle discharge
  • Inhibition of knee-jerk.

Descending facilitatory reticular projection:

  • Produces exaggerated movements and muscle tone.


  • Control smooth and purposeful movements,
  • Maintain muscle tone and posture,
  • Maintain alert wakefulness,
  • Regulation of vegetative and endocrine function,
  • Concerned with emotional and sexual behaviors.
  • Comprises most of the brain stem and is a critical region for functioning.