Reticular formation remains connected with the afferent and the afferent connections. Efferent connections are further divided into two types based on the functions of the reticular activating system, including descending projections (or descending reticular activating system) and ascending projections (or ascending reticular activating system).
Descending reticular activating system (or DRAS): DRAS possesses two subdivisions, which are referred to as inhibitory reticular projections and facilitating the activities. The reticular formation tends to maintain the posture and equilibrium by regulating the muscle tones. The maintenance of the postures can be performed in either two ways, including facilitation (excitation) and inhibition through gamma motor neurons’ activity.
Ascending reticular activating system (or ARAS): ARAS system is responsible for determining the alertness level of the human beings that initiates in the lower portion of the brain stem and then extends to the upward direction projecting throughout the cerebral cortex. The projection of the ARAS can occur in two different ways; through the subthalamus and thalamus. Ascending reticular activating system is concerned with the extrathalamic control modulatory system of the efferent connections constitutes the major functions of the reticular system. The essential function of the ascending reticular activating system is the response to the wakefulness and the transitions regarding the sleep-wake system. The neurons of ARAS are glutamatergic, cholinergic, aminergic, and hypocretinergic, which are not only involved in inducing sleepiness but also responsible for dreaming. • Structure: it remains connecting to the reticular nuclei to regulate various functions of the body. The neurons of areas are glutamatergic, cholinergic, aminergic, and hypocretinergic, which are not only involved in inducing sleepiness but also responsible for dreaming. These all the neurons tend to release the neurotransmitters, including dopamine, norepinephrine, serotonin, histamine, and glutamate. On each side of the areas, a collection of more than 20 nuclei can be found extending through pons, medulla, posterior hypothalamus, and upper brainstem.
Functions of ARAS in Inducing Alertness and Sleepness
Sleepness: sleep is characterized by the activation of the cortical circuits and the medial circuits. Cortical influences are supposed to arise through the axonal (direct) projections and thalamic (indirect) projections.
Consciousness: ARAS enables the activating/enabling factor responsible for consciousness. It contributes to the wakefulness response of the brain through the arousal of behavioral and cortical circuits
Regulation of the sleep and wakefulness transitions: it modifies the thalamic functions similar to the electroencephalogram desynchronization. It tends to generate two types of sleep; REM sleep and non-REM sleep.
Clinical significances: ARAS pathologies are concerned with age as they describe the general decline in the reactivity on the advances with the years. The arousal of the severe alteration can also be determined through the activity of ARAS, such as a condition of coma, which is caused due to the bilateral damage of the midbrain’s reticular formation.
Determining the alteration in level of alertness: the alertness level of the ARAS is based on the normal function of ARAS, which disrupts due to the exposure of certain chemicals affecting sensory neurons. The adverse effects of the physical exposure of harmful chemicals can result in altering the activity of ARAS. Smoking cigarettes and taking alcohol or other drugs are examples of chemicals affecting the level of alertness in individuals.
