Review of Medical Physiology - William F. Ganong 2002

Functions of the Nervous System
Anxiety, Sleep, and Electrical Activity of the Brain
Reticular Formation and Reticular Activating System

The reticular formation, a phylogenetically ancient core of the Brainstem, occupies the ventromedial region of the Medulla Oblongata and Midbrain. Primarily, it is an anatomical zone composed of diverse neuronal clusters and fibers with varied Functions. For example, it contains The Cell bodies and fibers of serotonergic, noradrenergic, and adrenergic systems, discussed in Chapter 15, as well as many areas involved in the Regulation of Heart rate, Blood pressure, and Respiration, as described in Chapters 33 and 36. Some of the descending fibers inhibit transmission in spinal sensory pathways (see Chapter 7). Various Regions of the reticular formation and their pathways are responsible for spasticity and regulate stretch Reflexes (see Chapter 12). The reticular activating system (RAS) and its related Brain components, which govern states of consciousness and Sleep, are examined in this chapter. The RAS is a complex polysynaptic network. Collaterals enter it not only from long ascending sensory pathways but also from the trigeminal, auditory, visual, and olfactory systems. The complexity of the neuronal network and the high degree of convergence negate sensory modality Specificity, allowing most reticular Neurons to be activated with equal ease by various sensory stimuli. Thus, the system is non-specific, whereas classical sensory pathways are specific because their fibers are activated by only one type of sensory stimulus. Part of the RAS bypasses the thalamus, projecting diffusely to the cortex. Another part terminates in the intralaminar and related thalamic nuclei, which give rise to diffuse and non-specific projections throughout the neocortex (Fig. 11-3).

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Fig. 11-1. Structure OF THE Cerebral Cortex. Cortical layers are indicated by numbers. A: Golgi stain showing neuronal cell bodies and dendrites. B: Nissl stain showing cell bodies. C: Weigert stain showing Cytology/practical/65.html">Myelinated nerve fibers. D: Depiction of neural connections (A, B, and C reproduced with permission from Ranson SW, Clark SL: The Anatomy of The Nervous system. 10th ed. Saunders, 1959).



Last update: 10/08/2026

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