Scientists and academics strive to comprehend the neuronal mechanisms and functionality of sleep, which is a complicated biological state defined by physiological, behavioural, and electrophysiological perimeters. The transition between sleep and wakefulness entails profound dynamics in cognition, brain activity, motor control, and consciousness. The pervasive fascination about the phenomenon of sleep is a basis for sleep architecture, which dwells on the basic physiological occurrence of normal sleep.
Stages of Sleep
There are five stages of sleep, four of which belong to the non-rapid eye movement category (NREM) and one in the rapid-eye-movement sleep category (REM). The NREM category occurs in four distinct stages, presenting a continuum of comparative depth (Patel & Araujo, 2018) . Each stage has defining characteristics owing to disparities in eye movements, muscle tone, and brain wavelengths (Patel & Araujo, 2018) . The four stages of NREM sleep are defined by distinct physiology and brain activity. NREM stage 1 marks the transitional phase between sleep and consciousness and is easily disrupted (Patel & Araujo, 2018) . The stage is marked by presence of both alpha and beta brain waves. In NREM stage 2, the body assumes a state of relaxation. Theta brain waves dominate brain activity. NREM stages three and four are collectively referred to as slow-wave sleep. In the third stage, delta waves dominate brain activity. During this phase, the pulse rate, blood pressure, and arousal decline tremendously. The fourth stage is similar to the third as delta waves dominate. Most dreams occur in this stage. REM sleep is marked by rapid eye movement and low muscle tone and is associated with the potential of the sleeper to have vivid dreams (Patel & Araujo, 2018) . The brain activity of this sleep category is similar to that of a conscious individual. A typical session of sleep entails a repetition of NREM-REM cycle.
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Brain Wavelengths
Our brain activity presents a wide range of brain wavelengths. Gamma waves are involved in cognitive functions and processing tasks. They are important for learning, information, and memory processing and play a key role in perception and meditation. Beta waves are low amplitude high-frequency brain waves observed when awake and are involved in logical thinking and conscious thought (Chauhan & Singh, 2016) . Alpha waves are the frequency wavelengths between theta and beta as they bridge the gap between sub consciousness and consciousness and promote deep relaxation. Theta waves are connected to emotions and are involved in daydreaming and sleep (Chauhan & Singh, 2016) . These waves are linked to low muscle tone and deep relaxation. The slowest brain waves are delta waves that are often observed in young ones and are associated with great levels of relaxation and REM sleep.
Neural Mechanisms
The function and interaction of several brain structures are attributable to wake/sleep inducement. The brain stem, located at the base of the brain, communicates with the hypothalamus to regulate the transitions between sleep and wake. The hypothalamus, a small brain structure contains a set of nerve cells that serve as controls for arousal and sleep. Within the hypothalamus is a cluster of cells that receive transmission that allows light detection. The thalamus relays information from sensory organs to the cortex which interprets and processes information. The basal forebrain also contributes to wakefulness and sleep, while part of the midbrain serves as an arousal system. The pineal gland receives transmission from the cluster of cells in the hypothalamus which influences sleep once the lights go out. Sleep and wake induction is a complex physiological process involving the function and interface of several brain features. Wake/sleep inducement is attributable to the interaction of different structures through ventral and dorsal pathways. The dorsal pathway innervates the thalamus which subsequently enhances transmission of sensory signals to the cortex (Rothschild et al., 2018) . Also, the ventral pathway innervates the basal forebrain, the hypothalamus, and other forebrain parts which harmoniously trigger the cortex. In this regard, wakefulness is achieved when the ventral and dorsal pathways are activated. It is understood that complicated interactions of brain functions influence physiological, behavioral and electrocortical wake/sleep states.
In conclusion, this topic is of importance as it attempts to bring insight regarding long researched and yet to be fully understood phenomena of sleep since time immemorial. Ideally, it reveals that sleep is a complicated process intertwined with multiple neural mechanisms and physiological functions in the body. Multiple brain functions couped with their interface trigger the wake/sleep state. Different wavelengths are observed in brain activity during the sleep-wake transition. Understanding different brain wavelengths and relative brain activity and their interface with the sleep/ wake transition are indispensable to comprehending the nature of sleep.
References
Chauhan, P., & Singh, M. (2016). Brain Waves and Sleep Science. Retrieved 27 November 2019, from https://pdfs.semanticscholar.org/0072/cf2985cef02e3cf247f7f322580f0e9ff887.pdfEban-
Rothschild, A., Appelbaum, L., & de Lecea, L. (2018). Neuronal mechanisms for sleep/wake regulation and modulatory drive. Neuropsychopharmacology , 43 (5), 937.
Patel, A. K., & Araujo, J. F. (2018). Physiology, sleep stages. In StatPearls [Internet] . StatPearls Publishing.
