Wakefulness is a daily recurring

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

state and state of

consciousness Consciousness, at its simplest, is awareness of a state or object, either internal to oneself or in one's external environment. However, its nature has led to millennia of analyses, explanations, and debate among philosophers, scientists, an ...

in which an individual is conscious and engages in coherent

cognitive Cognition is the "mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...

and behavioral responses to the external world. Being awake is the opposite of being

asleep Sleep is a state of reduced mental and physical activity in which consciousness is altered and certain sensory activity is inhibited. During sleep, there is a marked decrease in muscle activity and interactions with the surrounding environme ...

, in which most external inputs to the brain are excluded from neural processing.

Effects upon the brain

The longer the brain has been awake, the greater the synchronous firing rates of

cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. It is the largest site of Neuron, neural integration in the central nervous system, and plays ...

neurons. After sustained periods of sleep, both the speed and synchronicity of the neurons firing are shown to decrease. Another effect of wakefulness is the reduction of

glycogen Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria. It is the main storage form of glucose in the human body. Glycogen functions as one of three regularly used forms ...

held in the

astrocyte Astrocytes (from Ancient Greek , , "star" and , , "cavity", "cell"), also known collectively as astroglia, are characteristic star-shaped glial cells in the brain and spinal cord. They perform many functions, including biochemical control of en ...

s, which supply energy to the neurons. Studies have shown that one of sleep's underlying functions is to replenish this glycogen energy source.

Maintenance by the brain

Wakefulness is produced by a complex interaction between multiple neurotransmitter systems arising in the

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is conti ...

and ascending through the

midbrain The midbrain or mesencephalon is the uppermost portion of the brainstem connecting the diencephalon and cerebrum with the pons. It consists of the cerebral peduncles, tegmentum, and tectum. It is functionally associated with vision, hearing, mo ...

hypothalamus The hypothalamus (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...

thalamus The thalamus (: thalami; from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter on the lateral wall of the third ventricle forming the wikt:dorsal, dorsal part of the diencephalon (a division of ...

and

basal forebrain Part of the human brain, the basal forebrain structures are located in the forebrain to the front of and below the striatum. They include the ventral basal ganglia (including nucleus accumbens and ventral pallidum), nucleus basalis, diagonal ba ...

. The posterior hypothalamus plays a key role in the maintenance of the cortical activation that underlies wakefulness. Several systems originating in this part of the brain control the shift from wakefulness into sleep and sleep into wakefulness.

Histamine Histamine is an organic nitrogenous compound involved in local immune responses communication, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Discovered in 19 ...

neurons in the tuberomammillary nucleus and nearby adjacent posterior hypothalamus project to the entire brain and are the most wake-selective system so far identified in the brain. Another key system is that provided by the

orexins Orexin (), also known as hypocretin, is a neuropeptide that regulates arousal, wakefulness, and appetite. It exists in the forms of orexin-A and orexin-B. The most common form of narcolepsy, type 1, in which the individual experiences brief loss ...

(also known as hypocretins) projecting neurons. These exist in areas adjacent to histamine neurons and like them project widely to most brain areas and associate with

arousal Arousal is the physiology, physiological and psychology, psychological state of being awoken or of Five senses, sense organs stimulated to a point of perception. It involves activation of the ascending reticular activating system (ARAS) in the hu ...

. Orexin deficiency has been identified as responsible for

narcolepsy Narcolepsy is a chronic neurological disorder that impairs the ability to regulate sleep–wake cycles, and specifically impacts REM (rapid eye movement) sleep. The symptoms of narcolepsy include excessive daytime sleepiness (EDS), sleep-r ...

. Research suggests that orexin and histamine neurons play distinct, but complementary roles in controlling wakefulness with orexin being more involved with wakeful behavior and histamine with cognition and activation of cortical

EEG Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The bio signals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neoc ...

. It has been suggested the

fetus A fetus or foetus (; : fetuses, foetuses, rarely feti or foeti) is the unborn offspring of a viviparous animal that develops from an embryo. Following the embryonic development, embryonic stage, the fetal stage of development takes place. Pren ...

is not awake, with wakefulness occurring in the

newborn In common terminology, a baby is the very young offspring of adult human beings, while infant (from the Latin word ''infans'', meaning 'baby' or 'child') is a formal or specialised synonym. The terms may also be used to refer to Juvenile (orga ...

due to the stress of being

born Born may refer to: * Childbirth * Born (surname), a surname (see also for a list of people with the name) * ''Born'' (comics), a comic book limited series Places * Born, Belgium, a village in the German-speaking Community of Belgium * Born, Luxe ...

and the associated activation of the

locus coeruleus The locus coeruleus () (LC), also spelled locus caeruleus or locus ceruleus, is a nucleus in the pons of the brainstem involved with physiological responses to stress and panic. It is a part of the reticular activating system in the reticular ...

References

External links

{{Authority control Cognition Mental states

Effects upon the brain

Maintenance by the brain

See also

References

External links