About Sleep

Sleep is a function of the Brain. Like other Brain functions, sleep is organized to produce predictable electrophysiologic patterns that form the basis of behavioral sleep. Neural centers that intervene in the production and regulation of sleep are located in the Brain- stem, diencephalon and thalamus, with ample secondary expression in the cortex of the cerebral hemispheres. Hormones, neurotransmitters and active peptides exert a strong modulating influence over the neuroanatomic substrates that generate sleep and in turn, modify the physiology of most body organs.

Wakefulness and sleep alternate in the domain of Brain activity, sleep is subdivided into two distinct states, non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. Each state has anatomic electrophysiologic and behavioral characteristics distinct enough to allow their separation.

The person who is awake is aware of himself and the environment, whereas the person who is asleep is not aware and hence incapable of consciously processing stimuli coming from external or internal sources.

NREM SLEEP

Sleep appears as the wakefulness – maintaining mechanism waves, allowing sleep-promoting neurons to become active Light transitional sleep leading to synchronized sleep normally follows wakefulness. Light and synchronized sleep form the NREM state of sleep.

Synchronized sleep expresses the unified activity of many neuronal networks and is characterized by an EEG that shows high-voltage K-complexes, sleep spindles and, in deep sleep, high-voltage slow waves (slow-wave sleep).

There is overlap between sleep-generating centers and parasympathetic activity. Stimulation on the anterior hypothalamus and preoptic region elicit a decrease in blood pressure and heart rate with pupillary miosis and behavioral and unraveling the enigma of sleep function is important for all of neuroscience. Several new testable ideas concerning the sleep function exist. Many of these theories demand a new look at sleep mech, brain organization, and reinterpretation of the past sleep literature. We are in for exciting times.

EEG Signs of Sleep

Substances found in brain cells such as adenosine, gamma aminobutyric acid (GABA), opiates somatostatic, and d-melanocyte-stimulating hormone to facilitate sleep.

Several blood-borne factors, such as insulin and cholecystokinin, which is released in the gut after food ingestion promote sleep. No single chemical substance with a neurotransmitter, neuromodulator, or neurohormonal role has been identified that is critical or sufficient for the initiation and maintenance of sleep. Rather, it appears that multiple factors and systems are involved.

REM Sleep

REM sleep, also known as desynchronized paradoxical, active and dream sleep, is characterized by an apparently unrelated constellation of phenomena that are generated in different areas at the pons and caudal midbrain. Although no center has been shown to function as the unique neural orchestrator, the lateral portion of the incleus reticularis pontis oralis, ventral to the nucleus locus corruleus, is the brain region most critical for the production of REM sleep.

The purpose of REM Sleep remains unknown, although a correlation has been observed between active brain growth, brain development and complexity of REM sleep. Fetal sleep is mostly REM or active sleep, and the proportion of REM sleep observed in infancy (50%) is much higher than in the adult years (25%). Some authors have postulated that REM sleep generation is associated with the consolidation of memories.

Physiologic Characteristics of REM sleep:

Cardiorespiratory fluctuations, such as respiratory rhythm increases acceleration of theart rate and blood pressure variations are common in REM sleep. They appear as a result of phasic activation of centers in the medial and lateral para brachial nuclei of the pons, which exert a modulatory influence over bulbar neurons. Respiratory fluctuations of REM sleep are independent of peripheral metabolic changes (oxygen saturation, CO2 content, pH of blood) and are instead controlled directly by neural mechanisms originating in pneumotaxic centers of the brainstem.

Overview of Sleep and Wakefulness

The integrated anatomical overview of sleep reveals a multisegmental core of nuclei important to all states and an aggregate of centers in the pons critical to the development of REM sleep. From brainstem areas, ascending and descending fibers carry the nervous impulses that execute all functions of sleep and maintain wakefulness. Transection at the mesencephalic level causes permanent synchronization of the EEG and a state that resembles behavioral sleep.

In general, the executive functions are mediated by nerve cells in the medial two-thirds of the reticular formation, whereas the lateral third works as an association area. There are also differences between levels, some acting preponderantly or the spinal cord and other levels or more rostral parts of the brain.

The function of organs and the homeostasis of body systems shift in sleep to a different physiologic equilibrium with activation of new mechanisms in some instances and modification of the level of activity in others. Each stage of sleep has individual peculiarities but for practical purposes, it is sufficient to individualize the sleep physiology of body systems in NREM and REM states.