ENTRIES A–Z
Philip Winn in Dictionary of Biological Psychology, 2003
The reticular formation refers to the net-like structure in the central core of the BRAINSTEM. It is composed of nerve cell bodies lying among fascicles of myelinated nerve fibres which course longitudinally, as well as transversely, through the MEDULLA, PONS and MID-BRAIN. The reticular neurons have long smooth dendrites (see DENDRITE) that radiate out from the cell body and through the passing fibres. They can thus receive input from multiple sources. Neurons in the lateral portion of the reticular formation are medium sized (15-25 m in diameter) and project predominantly to other brainstem sites. They are important for sensorimotor reflexes involving the cranial sensory and motor nerves. Neurons in the medial portion of the reticular formation are large (>25 m) or giant (>50 m) in size and give rise to bifurcating axons of which one major branch extends to the SPINAL CORD or to the FOREBRAIN. The large and giant reticular neurons concentrated in the caudal pons and medulla give rise to the major reticulo-spinal projections that are important in the control of POSTURE and movement (see LOCOMOTION). Medium and large reticular neurons concentrated in the ORAL PONS and midbrain give rise to the ascending projections which pass to the THALAMUS (and innervate the midline, medial and intralaminar nuclei) along a dorsal pathway, and to the HYPOTHALAMUS and BASAL FOREBRAIN, along a ventral pathway. These neurons comprise the ASCENDING RETICULAR ACTIVATING SYSTEM which via the dorsal relay to the non-specific thalamo-cortical projection system and the ventral relay to the hypothalamo- and basalo- cortical projection systems, stimulate and maintain cortical activation. Through both its descending and ascending components, the reticular formation thus plays a critical role in the generation and maintenance of behavioural and cortical responsiveness and arousal that characterize wakefulness. Particular reticular neurons are also important for the central activation that occurs during the state of REM SLEEP. Extensive lesions of the pontine and mesencephalic reticular formation in animals and humans can result in COMA, in which a loss of responsiveness and cortical activation occurs. The reticular formation is made up of neurons containing different chemical neurotransmitters. The major population of cells contains the excitatory amino acid GLUTAMATE. Although pharmacological studies have not yet specifically proven the importance of these glutamatergic neurons in mechanisms of activation, they must be presumed to be the most important component of the ascending reticular activating system. In addition, however, there are collections of cells containing other neurotransmitters. A large group of cells in the PONTOMESENCEPHALIC TEGMENTUM (see PEDUNCULOPONTINE TEGMENTAL NUCLEUS and LATERODORSAL TEGMENTAL NUCLEUS) contain ACETYLCHOLINE and project in parallel with other reticular neurons in this region to the thalamus and less so to the hypothalamus and basal forebrain. These cholinergic cells play an important role in mechanisms of both waking and REM sleep. Clustered in a small nucleus (LOCUS COERULEUS) dorsal to the reticular core in the pons, NORADRENERGIC neurons also serve to enhance wakefulness and cortical activation, although these cells prevent the occurrence of REM sleep. Ventral to the reticular core in the midbrain, DOPAMINERGIC cells (of the VENTRAL TEGMENTAL AREA and SUBSTANTIA NIGRA) play an important role in behavioural arousal and responsiveness of wakefulness.
Pain pathways
Alison Twycross, Anthony Moriarty, Tracy Betts in Paediatric Pain Management a multi-disciplinary approach, 2018
Nerves from the spinoreticular tract synapse here, and tertiary nerves both ascend to the cortex and descend to the spinal cord (Figure 3.2). The reticular formation is important for other non-painful stimuli and is thought to be important in the sleep/awake state. It may be that this region produces a higher awareness when painful stimuli are present.
The Central Nervous System Organization of Behavior
Rolland S. Parker in Concussive Brain Trauma, 2016
One function of the reticular formation is activation of the brain for behavioral arousal and different levels of awareness. The ARAS consists of the axons of a network extending from the medulla, the upper brainstem (including the midbrain), the hypothalamus, and basal forebrain. It includes the following systems: pedunculopontine, parabrachial, medial raphe, locus ceruleus, tuberomammillary, melanin-concentrating hormones and orexin, and the basal forebrain. Its function is increasing wakefulness and the responsiveness of cortical and thalamic neurons to sensory stimuli (arousal). In contrast to direct sensory pathways through the thalamus, their function is to diffusely innervate the thalamus and cerebral cortex and maintain them in a state in which they can transmit and respond appropriately to incoming sensory information. These pathways innervate the reticular nucleus and intralaminar nuclei of the thalamus. The ARAS divides into two branches at the junction of the midbrain and diencephalon. One branch (direct) enters the thalamus, where it activates and modulates thalamic relay nuclei and intralaminar nuclei with diffuse cortical projections. The other branch (indirect and diffuse) travels through the lateral hypothalamic area to be joined by ascending output from the hypothalamus and basal forebrains. These diffusely innervate the cerebral cortex (Saper, 2000). The locus ceruleus (LC) of the pons is a noradrenergic (NE) nucleus in the floor of the cerebral aqueduct and the fourth ventricle.
Experts, but not novices, exhibit StartReact indicating experts use the reticulospinal system more than novices
Published in Journal of Motor Behavior, 2021
Brandon M. Bartels, Maria Jose Quezada, Vengateswaran J. Ravichandran, Claire F. Honeycutt
Motor skill acquisition utilizes a wide array of neural structures; however, few articles evaluate how the relative contributions of these structures shift over the course of learning. Recent evidence from rodents and songbirds suggests there is a transfer from cortical to subcortical structures following intense, repetitive training. Evidence from humans indicate that the reticulospinal system is modulated over the course of skill acquisition and may be a subcortical facilitator of learning. The objective of this study was to evaluate how reticulospinal contributions are modulated by task expertise. Reticulospinal contributions were assessed using StartReact (SR). We hypothesized that expert typists would show SR during an individuated, keystroke task but SR would be absent in novices. Expert (75.2 ± 9.8 WPM) and novice typists (41.6 ± 8.2 WPM) were evaluated during an individuated, keystroke movements. In experts, SR was present but was absent in novices. Together, these results suggest that experts use reticulospinal contributions more for movement than novices indicating that the reticular formation becomes increasingly important for movement execution in highly trained, skilled tasks even those that require individuated movement of the fingers.
Distributed Gamma Band Responses in the Brain Studied in Cortex, Reticular Formation, Hippocampus and Cerebellum
Published in International Journal of Neuroscience, 1996
Tamer Demiralp, Canan Başar-eroglu, Erol Başar
The transient evoked responses of auditory cortex, reticular formation, hippocampus and cerebellar cortex to auditory stimulation have been analysed in the gamma frequency band on cats with chronically implanted electrodes. We found gamma band transient responses consisting of wave packets with 3-4 oscillations in all of the studied brain structures in the first 100 ms of the poststimulus period. The responses were strongly time-locked to the stimulation time point. The observation that the gamma band responses exist simultaneously in various brain structures supports the tentative proposal of our group on the “diffuse gamma response system” of the brain, which seems to be an important, universal operator in brain function. Furthermore, it shows that in search for generalized approaches to brain phenomena it is important to analyse the simultaneous behavior of different brain structures.
Dose effects of Halothane on Sensory Evoked Responses Obtained from the Cortex, Reticular Formation and Central Gray
Published in International Journal of Neuroscience, 1985
C. M. Prasad, L. Pardo, B. M. Rigor, N. Dafny
Sensory evoked field potentials were recorded from the mesencephalic reticular formation (MRF), central gray (CG) and somatosensory cortex (SCX), following incremental doses of halothane in freely-moving rats. Halothane concentrations of 0.25%, 0.5% 1.0% and 2.0% were used. In general, the responses from each structure were affected in dose response manner. The averaged acoustic evoked responses (AAER.) exhibit more sensitivity to halothane than the averaged visual evoked responses (AVER). The evoked response and its components obtained from each structure were affected differently by halothane mainly following the initial two halothane doses, (0.25 % and 0.5%); mainly increase in amplitude was observed in the recording obtained from the MRF, decrease in the CG, and mixed (increase and/or decrease) in SCX. The degree of the depression of the sensory evoked responses was directly correlated to the level of anesthesia as assessed by sural nerve stimulation.