This is thought to be a major component of descending pain control systems that allow us to suppress pain in certain situations e. Other descending projections from the reticular formation are involved in the control of posture and movement.
These fibers are mainly found in the reticulospinal tract , which extends from the reticular formation to help maintain posture, facilitate stereotyped movements like stepping, and modulate muscle tone to either aid or inhibit movement.
The reticular formation may be best known for its role in promoting arousal and consciousness. This function is mediated by the reticular activating system RAS , also known as the ascending arousal system. The reticular activating system contains circuits that originate in several areas of the brainstem, including the midbrain reticular formation, and ascend to the cerebral cortex and thalamus. These pathways are predominantly associated with the neurotransmitters acetylcholine and norepinephrine , both of which are thought to play important roles in regulating arousal and wakefulness.
The cholinergic neurons originate in the pedunculopontine nucleus and laterodorsal tegmental nucleus, while the noradrenergic neurons originate in the locus coeruleus. The fibers that arise from these locations combine with other pathways that ascend to the cerebral cortex and thalamus to promote wakefulness, vigilance, and overall arousal. These pathways from the reticular formation must be functional for normal attentional abilities and sleep-wake cycles to be preserved. Lesions to major pathways of the reticular activating system can thus impair consciousness, and severe damage can cause coma or a persistent vegetative state.
Nolte J. Philadelphia, PA. Elsevier; We experience these things every day, but how do our brains create them? For example, when you smile or laugh in response to a joke, the motor control to your facial muscles is provided by the reticular formation on both sides of the brain.
Because of its strategic central location in the cerebrospinal axis, the reticular formation can influence all ascending pathways that pass to higher levels. This influence can be facilitative or inhibitory. In particular, the. It is considered that the higher control of the autonomic nervous system , from the cerebral cortex, hypothalamus, and other subcortical nuclei, can be exerted by the reticulobulbar and reticulospinal tracts, which descend to the sympathetic.
The reticular formation is considered to influence the synthesis or release of releasing or release-inhibiting factors. In this way, it controls the activity of the hypophysis cerebri. The reticular formation can do this either directly or indirectly through the hypothalamic nuclei. The reticular formation also influences the biologic rhythms of the body by means of its afferent and efferent pathways to the hypothalamus. The level of consciousness and arousal are controlled by the reticular formation.
The ascending pathways carrying the sensory information to the higher centers are channeled through the reticular formation. The reticular formation, in turn, projects this information to different parts of the cerebral cortex. This causes a sleeping person to awaken.
It is considered that the state of consciousness is dependent on the continuous projection of sensory information to the cortex. Different degrees of wakefulness also depend on the degree of activity of the reticular formation. The activity of the reticular formation is strongly increased by the incoming pain sensations. This greatly excites the cerebral cortex.
As the main function of reticular formation is to control the level of wakefulness and consciousness, any abnormality of the reticular system results in the following manifestations. It is a sleep disorde r which causes excess sleep, day-time sleep, sleep paralysis, and hallucinations.
It can also cause partial or complete loss of muscle tone associated with some emotions. This condition is called cataplexy. Injury or damage to the reticular formation is considered to be a major cause of narcolepsy and cataplexy. It has been demonstrated in the experimental animals that damage to the reticular formation causes persistent unconsciousness.
Pathologic lesions of the reticular formation in humans can also result in loss of consciousness and even coma. It has been considered that the loss of consciousness in epilepsy may be due to the inhibition of the activity of the reticular formation in the upper part of the diencephalon.
The reticular formation is a network of neurons and nerve fibers extending throughout the length of the brainstem. These extraneuronal effects might explain the role of microglial phagocytosis in sleep disorders Nadjar et al. Glial cells are also critical for releasing cytokines and chemokines messengers with both proinflammatory and neuroprotective actions. This may lead to an endogenous neuroprotective effect mediated by P27R receptors, as demonstrated by Lim et al.
Within this framework, Giorgi et al. This may add on novel cell-to-cell-based pathogenic effects in which misfolded proteins may spread monosynaptically from reticular axons to cortical neurons, according to a prion-like pattern Giorgi et al. For instance, specific patterns of neuronal loss affecting catecholamine-containing reticular nuclei may produce a constellation of phenotypes in Parkinson Disease PD. In fact, depending on which reticular nucleus is affected, a variety of both motor and non-motor autonomic, sleep and mood-related, behavioral, and cognitive symptoms, may occur.
This mostly applies to non-motor symptoms, which appear to underlie different PD subtypes, each one owing a specific pattern of brainstem involvement Gambardella et al. Frequently, the onset of PD, instead of consisting of motor disturbances, coincides with autonomic alterations and pain. In this regard, the role of the RF in driving painful stimuli, and controlling pain-related circuitries, was reviewed by Martins and Tavares.
These authors centered brainstem pain control in a reticular loop, which includes the periaqueductal gray, the rostro-ventro-medial medulla and the ventro-lateral medulla Martins and Tavares. The key role of the brainstem RF in mediating those activities relevant to species survival, such as pain and reward, sets the ground for these brain regions as preferential targets for drugs of abuse as reported by Ferrucci et al.
In particular, while most of the literature on the effects of amphetamines has focused on their effects on dopaminergic neurons, there are several reports indicating a key role of the effects of amphetamines on LC in mediating many of their behavioral effects, including reward.
Furthermore, interesting data indicate that the interaction of RF pontine cholinergic neurons Ch5 and Ch6 with midbrain DA neurons might be crucial for the hyperlocomotion induced by amphetamines Ferrucci et al. So far, the RF has been viewed mainly as an archaic collection of ascending and descending systems, and interconnected nuclei, which play only a rough and ancestral role in interlacing various CNS areas.
Nevertheless, specific nuclei of the RF act as premotor centers, involved in the fine-tuning of the gaze, both along the vertical and horizontal plane.
This latter function was investigated by Wang et al. All these features are covered by specific contributions of the research topic, which offers an updated view to define the anatomical correlates of the multiple and interconnected roles played by the brainstem reticular formation in health and disease. All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Agnati, L. Volume versus wiring transmission in the brain: a new theoretical frame for neuropsychopharmacology. PubMed Abstract Google Scholar. Volume transmission as a key feature of information handling in the central nervous system possible new interpretative value of the Turing's B-type machine.
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