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40-469: It is functionally associated with vision, hearing, motor control, sleep and wakefulness, arousal ( alertness ), and temperature regulation. The name mesencephalon comes from the Greek mesos , "middle", and enkephalos , "brain". The midbrain is the shortest segment of the brainstem, measuring less than 2cm in length. It is situated mostly in the posterior cranial fossa , with its superior part extending above

80-522: A constant level of alertness is rare if not impossible." If people employed in safety-related or transportation jobs have lapses in alertness, this "may lead to severe consequences in occupations ranging from air traffic control to monitoring of nuclear power plants." Neurotransmitters that can initiate, promote, or enhance wakefulness or alertness include serotonin, (nor)epinephrine, dopamine (e.g. blockade of dopamine reuptake), glutamate, histamine, and acetylcholine. Neuromodulators that can do so include

120-403: A different role from one another within the basal ganglia system. The substantia nigra has extremely high production of melanin (hence the colour), dopamine, and noradrenalin ; the loss of dopamine-producing neurons in this region contributes to the progression of Parkinson's disease . The midbrain is supplied by the following arteries : Venous blood from the midbrain is mostly drained into

160-399: A relatively constant axial position; at the level of the inferior colliculus it is near the lateral edge, on the ventral side, and retains a similar position rostrally (due to widening of the tegmentum towards the rostral end, the position can appears more medial). The spinothalamic tract – another ribbon-like region of fibres – are located at the lateral edge of the tegmentum; at the level of

200-462: A symptom of a number of conditions, including narcolepsy , attention deficit disorder , chronic fatigue syndrome , depression , Addison's disease , and sleep deprivation . Pronounced lack of alertness is an altered level of consciousness . States with low levels of alertness include drowsiness . The word is formed from "alert", which comes from the Italian all'erta (on the watch, literally: on

240-554: Is also used to increase alertness, and is present in coca tea . The eugeroic modafinil has recently gained popularity with the US Military and other militaries . Beyond good sleep, physical activity, and healthy diet , a review suggests odours, music , and extrinsic motivation may increase alertness or decrease mental fatigue. Short rest periods and adjustments to lighting (level and type of) may also be useful. Various types of neurostimulation are being researched, as

280-428: Is not an isolated neurotransmitter that alone is responsible for the sensation of wakefulness. However, it is known that many transmitters are used together to cause this effect. Research to map the wakefulness circuitry is ongoing. Beta power has been used as an indicator of cortical arousal or alertness by several studies. A study also measured alertness with EEG data. Additional information can be found on

320-515: Is shared with the most ancient of vertebrates . Dopamine produced in the substantia nigra and ventral tegmental area plays a role in movement, movement planning, excitation, motivation and habituation of species from humans to the most elementary animals such as insects. Laboratory mice from lines that have been selectively bred for high voluntary wheel running have enlarged midbrains. The midbrain helps to relay information for vision and hearing. The term "tectal plate" or "quadrigeminal plate"

360-411: Is surrounded by the periaqueductal grey , which has a role in analgesia, quiescence, and bonding. The dorsal raphe nucleus (which releases serotonin in response to certain neural activity) is located at the ventral side of the periaqueductal grey, at the level of the inferior colliculus. The nuclei of two pairs of cranial nerves are similarly located at the ventral side of the periaqueductal grey –

400-479: Is the microbiome and related interventions. A study suggests non-genetic determinants of alertness upon waking up from sleep are: The baseline of daily alertness is related to the quality of their sleep (currently measured only by self-reported quality), positive emotional state (specifically self-report happiness), and age. There are genes that enable people to be apparently healthy and alert with little sleep . However, twin-pair analyses indicate that

440-415: Is the only part of the basal ganglia system outside the forebrain. It is ventrally wider at the rostral end. By means of the basal ganglia, the substantia nigra is involved in motor-planning, learning , addiction , and other functions. There are two regions within the substantia nigra – one where neurons are densely packed (the pars compacta ) and one where they are not (the pars reticulata ), which serve

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480-420: Is typically sectioned axially at either the superior or inferior colliculi levels. Visualizing these cross-sections as an upside-down bear face helps remember its structures, with the peduncles forming ears, aqueducts mouth, and tectum chin. The tectum (Latin for roof ) is the part of the midbrain dorsal to the cerebral aqueduct . The position of the tectum is contrasted with the tegmentum , which refers to

520-401: Is used to describe the junction of the gray and white matter in the embryo. ( ancil-453 at NeuroNames ) Alertness Alertness is a state of active attention characterized by high sensory awareness . Someone who is alert is vigilant and promptly meets danger or emergency, or is quick to perceive and act. Alertness is a psychological and physiological state. Lack of alertness is

560-404: The basal vein as it passes around the peduncle. Some venous blood from the colliculi drains to the great cerebral vein . During embryonic development , the midbrain (also known as the mesencephalon) arises from the second vesicle of the neural tube , while the interior of this portion of the tube becomes the cerebral aqueduct. Unlike the other two vesicles – the forebrain and hindbrain –

600-460: The mammillary bodies (from the Diencephalon ) and hypothalamus (of the diencephalon ). The cerebral peduncles each form a lobe ventrally of the tegmentum, on either side of the midline. Beyond the midbrain, between the lobes, is the interpeduncular fossa , which is a cistern filled with cerebrospinal fluid . The majority of each lobe constitutes the cerebral crus . The cerebral crus are

640-580: The neurobiology , neuroscience , brain , behavioral neuroscience , and neurotransmitter pages. The stimulant and adenosine receptor antagonist caffeine is widely used to increase alertness or wakefulness and improve mood or performance . People typically self-administer it in the form of drinks like green tea (where it is present alongside the l-theanine ), energy drinks (often containing sugar / sugar-substitutes ), or coffee (which contains various polyphenols ). The chemicals that accompany caffeine in these preparations can potentially alter

680-533: The neuropeptide orexin . Similarly inhibition or reduction of mechanisms causing sleepiness, or drowsiness such as certain cytokines and adenosine (as with caffeine) may also increase perceived wakefulness and thus alertness. Wakefulness depends on the coordinated effort of multiple brain areas. These are affected by neurotransmitters and other factors. Many Neurotransmitters are in effect to experience wakefulness to include GABA, Acetylcholine, Adenosine, Serotonin, Norepinephrine, Histamine, and Dopamine. There

720-416: The scaly-breasted munia . Oculomotor nucleus The fibers of the oculomotor nerve arise from a nucleus in the midbrain , which lies in the gray substance of the floor of the cerebral aqueduct and extends in front of the aqueduct for a short distance into the floor of the third ventricle . From this nucleus the fibers pass forward through the tegmentum , the red nucleus , and the medial part of

760-438: The substantia nigra , forming a series of curves with a lateral convexity, and emerge from the oculomotor sulcus on the medial side of the cerebral peduncle . The nucleus of the oculomotor nerve does not consist of a continuous column of cells, but is broken up into a number of smaller nuclei, which are arranged in two groups, anterior and posterior. Those of the posterior group are six in number, five of which are symmetrical on

800-401: The tentorial notch . The principal regions of the midbrain are the tectum , the cerebral aqueduct , tegmentum , and the cerebral peduncles . Rostrally the midbrain adjoins the diencephalon ( thalamus , hypothalamus , etc.), while caudally it adjoins the hindbrain ( pons , medulla and cerebellum ). In the rostral direction, the midbrain noticeably splays laterally. The midbrain

840-790: The Battle of Britain" according to one report. American bomber pilots used amphetamines ("go pills") to stay awake during long missions. The Tarnak Farm incident , in which an American F-16 pilot killed several friendly Canadian soldiers on the ground, was blamed by the pilot on his use of amphetamine. A nonjudicial hearing rejected the pilot's claim. Amphetamine is a common study aid among college and high-school students. Amphetamine increases energy levels, concentration, and motivation, allowing students to study for an extended period of time. These drugs are often acquired through diverted prescriptions of medication used to treat ADHD , acquired from fellow students, rather than illicitly produced drugs. Cocaine

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880-563: The Second World War, U.S. soldiers and aviators were given benzedrine , an amphetamine drug, to increase their alertness during long periods on duty. While air force pilots are able to use the drug to remain awake during combat flights, the use of amphetamines by commercial airline pilots is forbidden. British troops used 72 million amphetamine tablets in the second world war and the Royal Air Force used so many that " Methedrine won

920-515: The alertness-promoting effects of caffeine. Caffeine is the world's most consumed stimulant drug. Various natural biochemicals and herbs may have similar anti-fatigue effects, such as rhodiola rosea . Various psychostimulants like bromantane have also been investigated as potential treatments for conditions where fatigue is a primary symptom. The alkaloids theacrine and methylliberine are structurally similar to caffeine and preliminary research supports their pro-alertness effects. During

960-423: The cerebrum (usually via the diencephalon), and therefore would include much of the tegmentum as well. The remainder of the crus pedunculi – small regions around the main cortical tracts – contain tracts from the internal capsule . The portion of the lobes in connection with the tegmentum, except the most lateral portion, is dominated by a blackened band – the substantia nigra (literally black substance ) – which

1000-499: The corresponding lateral geniculate nucleus , with which it is directly connected. The homologous structure to the superior colliculus in non mammalian vertebrates including fish and amphibians , is called the optic tectum ; in those animals, the optic tectum integrates sensory information from the eyes and certain auditory reflexes. The inferior colliculi – located just above the trochlear nerve – process certain auditory information. Each inferior colliculus sends information to

1040-410: The corresponding medial geniculate nucleus , with which it is directly connected. The cerebral aqueduct is the part of the ventricular system which links the third ventricle (rostrally) with the fourth ventricle (caudally); as such it is responsible for continuing the circulation of cerebrospinal fluid . The cerebral aqueduct is a narrow channel located between the tectum and the tegmentum, and

1080-403: The genetic contribution to daytime alertness is small. Other factors such as natural light exposure and synchronicity with the circadian rhythm may matter as well. Vigilance is important for animals so that they may watch out for predators. Typically a reduction in alertness is observed in animals that live in larger groups. Studies on vigilance have been conducted on various animals including

1120-470: The height; 1618). Wakefulness refers mainly to differences between the sleep and waking states; vigilance refers to sustained alertness and concentration . Both terms are sometimes used synonymously with alertness. People who have to be alert during their jobs, such as air traffic controllers or pilots , often face challenges maintaining their alertness. Research shows that for people "...engaged in attention-intensive and monotonous tasks, retaining

1160-456: The inferior colliculus it is immediately dorsal to the medial lemiscus, but due to the rostral widening of the tegmentum, is lateral of the medial lemiscus at the level of the superior colliculus. A prominent pair of round, reddish, regions – the red nuclei (which have a role in motor co-ordination) – are located in the rostral portion of the midbrain, somewhat medially, at the level of the superior colliculus. The rubrospinal tract emerges from

1200-422: The main tracts descending from the thalamus to caudal parts of the central nervous system; the central and medial ventral portions contain the corticobulbar and corticospinal tracts , while the remainder of each crus primarily contains tracts connecting the cortex to the pons . Older texts refer to the crus cerebri as the cerebral peduncle ; however, the latter term actually covers all fibres communicating with

1240-415: The midbrain does not develop further subdivision for the remainder of neural development. It does not split into other brain areas. While the forebrain, for example, divides into the telencephalon and the diencephalon . Throughout embryonic development, the cells within the midbrain continually multiply; this happens to a much greater extent ventrally than it does dorsally. The outward expansion compresses

Midbrain - Misplaced Pages Continue

1280-399: The midbrain ventral to the cerebral aqueduct, and is much larger in size than the tectum. It communicates with the cerebellum by the superior cerebellar peduncles , which enter at the caudal end, medially, on the ventral side; the cerebellar peduncles are distinctive at the level of the inferior colliculus, where they decussate , but they dissipate more rostrally. Between these peduncles, on

1320-402: The pair of oculomotor nuclei (which control the eyelid, and most eye movements) is located at the level of the superior colliculus, while the pair of trochlear nuclei (which helps focus vision on more proximal objects) is located caudally to that, at the level of the inferior colliculus, immediately lateral to the dorsal raphe nucleus. The oculomotor nerve emerges from the nucleus by traversing

1360-411: The red nucleus and descends caudally, primarily heading to the cervical portion of the spine, to implement the red nuclei's decisions. The area between the red nuclei, on the ventral side – known as the ventral tegmental area – is the largest dopamine -producing area in the brain, and is heavily involved in the neural reward system . The ventral tegmental area is in contact with parts of the forebrain –

1400-419: The region in front of the ventricular system , or floor of the midbrain. It is involved in certain reflexes in response to visual or auditory stimuli. The reticulospinal tract , which exerts some control over alertness, takes input from the tectum, and travels both rostrally and caudally from it. The corpora quadrigemina are four mounds, called colliculi, in two pairs – a superior and an inferior pair, on

1440-455: The still-forming cerebral aqueduct, which can result in partial or total obstruction, leading to congenital hydrocephalus . The tectum is derived in embryonic development from the alar plate of the neural tube. The midbrain is the uppermost part of the brainstem . Its substantia nigra is closely associated with motor system pathways of the basal ganglia . The human midbrain is archipallian in origin, meaning that its general architecture

1480-415: The surface of the tectum. The superior colliculi process some visual information, aid the decussation of several fibres of the optic nerve (some fibres remain ipsilateral), and are involved with saccadic eye movements . The tectospinal tract connects the superior colliculi to the cervical nerves of the neck , and co-ordinates head and eye movements. Each superior colliculus also sends information to

1520-502: The two sides of the middle line, while the sixth is centrally placed and is common to the nerves of both sides. The anterior group consists of two nuclei, an antero-medial and an antero-lateral. The nucleus of the oculomotor nerve, considered from a physiological standpoint, can be subdivided into several smaller groups of cells, each group controlling a particular muscle. A nearby nucleus, the Edinger-Westphal nucleus lies dorsal to

1560-434: The ventral side, is the median raphe nucleus , which is involved in memory consolidation. The main bulk of the tegmentum contains a complex synaptic network of neurons, primarily involved in homeostasis and reflex actions. It includes portions of the reticular formation . A number of distinct nerve tracts between other parts of the brain pass through it. The medial lemniscus – a narrow ribbon of fibres – passes through in

1600-406: The ventral width of the tegmentum, while the trochlear nerve emerges via the tectum, just below the inferior colliculus itself; the trochlear is the only cranial nerve to exit the brainstem dorsally. The Edinger-Westphal nucleus (which controls the shape of the lens and size of the pupil) is located between the oculomotor nucleus and the cerebral aqueduct. The midbrain tegmentum is the portion of

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