The Human Brain : From Neurone to Nervous System

THE RETICULAR FORMATION


  1. The reticular formation is the substance of the brainstem, between the main nuclei and tracts, and consists of aggregations of neurones without distinct anatomic boundaries, but often grouped because of their similar chemical composition and function.

  2. The functions of the reticular formation have been examined using electrical stimuli, and this led to the vague concept of physiological 'centres', concerned with particular functions, such as cardiovascular or respiratory control. Modern studies have provided considerable detail as to the complex cellular circuitry underlying these functions.

  3. The substance of the brainstem surrounding the main nuclei and tracts within the brainstem consists of a hotchpotch of nerve cells called the reticular formation; their axons appear to pass in many directions, intersecting with each other, rather than travelling together in large discrete bundles over long distances. Unlike the specific sensory pathways that transmit specific modalities - touch, pain, proprioception, vision or hearing - reticular formation neurones often have multimodal, non-specific, inputs.

  4. Some reticular neurones are pacemakers, capable of generating intrinsic rhythms, such as those necessary for rhythmic breathing; these neurones contain ion channels that allow them to be rhythmically active. Others contain characteristic groups of putative neurotransmitters or receptors. Some cell groups send axons into the spinal cord (the descending reticular formation) while others send ther axons into the brain (the Ascending Reticular Activating System) or cerebellum; these control the activites of the spinal cord, and the sleep-waking cycle respectively.

  5. Key Words: Reticular Formation, non-specific inputs, respiratory 'centre', cholinergic, noradrenergic, dopaminergic, peptidergic nuclei and projections.





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