24 Reticular formation
Organization
The ground plan is shown in Figure 24.1A. In the midline, the median reticular formation comprises a series of raphe nuclei (pron. ‘raffay’ and derived from the Greek word for seam). The raphe nuclei are the major source of serotonergic projections throughout the neuraxis (see next section).
Aminergic neurons of the brainstem
Embedded in the reticular formation are sets of aminergic neurons (Figure 24.1B). They include one set producing serotonin (5-hydroxytryptamine) and three sets producing catecholamines, as listed in Table 24.1.
Transmitter | Location |
---|---|
Serotonin | Raphe nuclei of midbrain, pons, medulla |
Dopamine | Tegmentum of midbrain |
Norepinephrine | Midbrain, pons, medulla |
Epinephrine | Medulla |
Functional Anatomy
The range of functions served by different parts of the reticular formation is indicated in Table 24.2.
Element | Function |
---|---|
Premotor cranial nerve nuclei | Patterned cranial nerve activities |
Pontine locomotor center | Pattern generation |
Magnocellular nuclei | Posture, locomotion |
Salivatory nuclei | Salivary secretion, lacrimation |
Pontine micturition center | Bladder control |
Medial parabrachial nucleus | Respiratory rhythm |
Central reticular nucleus of medulla oblongata | Vital centers (circulation, respiration) |
Lateral medullary nucleus | Conveys somatic and visceral information to the cerebellum |
Ascending reticular activating system (ARAS) | Arousal |
Aminergic neurons | Sleeping and waking, attention and mood, sensory modulation, blood pressure control |
Pattern generators
Patterned activities involving cranial nerves include:
Locomotor pattern generators are described in Box 24.1. An overview of gait controls is provided in Box 24.2. Higher-level bladder controls are described in Box 24.3.
Box 24.1 Locomotor pattern generators
The MLR contains the pedunculopontine nucleus, close to the superior cerebellar peduncle where this passes along the upper corner of the fourth ventricle to enter the midbrain (Figure 17.16). These nuclei send fibers down the central tegmental tract to the oral and caudal pontine nuclei serving extensor motor neurons and to medullary magnocellular neurons serving flexor motor neurons.