Human brain

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Human brain
The human brain, obtained after an autopsy
Human brain and skull
Details
PrecursorNeural tube
SystemCentral nervous system
ArteryInternal carotid arteries, vertebral arteries
VeinInternal jugular vein, internal cerebral veins;
external veins: (superior, middle, and inferior cerebral veins), basal vein, and cerebellar veins
Identifiers
Latinencephalon
Greekἐγκέφαλος (enképhalos)[1]
TA98A14.1.03.001
TA25415
FMA50801
Anatomical terminology

The brain is the central

organ of the human nervous system, and with the spinal cord makes up the central nervous system. The brain consists of the cerebrum, the brainstem and the cerebellum. It controls most of the activities of the body, processing, integrating, and coordinating the information it receives from the sense organs, and making decisions as to the instructions sent to the rest of the body. The brain is contained in, and protected by, the skull bones of the head
.

The cerebrum, the largest part of the human brain, consists of two cerebral hemispheres. Each hemisphere has an inner core composed of white matter, and an outer surface – the cerebral cortex – composed of grey matter. The cortex has an outer layer, the neocortex, and an inner allocortex. The neocortex is made up of six neuronal layers, while the allocortex has three or four. Each hemisphere is conventionally divided into four lobes – the frontal, temporal, parietal, and occipital lobes. The frontal lobe is associated with executive functions including self-control, planning, reasoning, and abstract thought, while the occipital lobe is dedicated to vision. Within each lobe, cortical areas are associated with specific functions, such as the sensory, motor and association regions. Although the left and right hemispheres are broadly similar in shape and function, some functions are associated with one side, such as language in the left and visual-spatial ability in the right. The hemispheres are connected by commissural nerve tracts, the largest being the corpus callosum.

The cerebrum is connected by the brainstem to the spinal cord. The brainstem consists of the

network systems. The whole circuitry is driven by the process of neurotransmission
.

The brain is protected by the

.

The study of the anatomy of the brain is neuroanatomy, while the study of its function is neuroscience. Numerous techniques are used to study the brain. Specimens from other animals, which may be examined microscopically, have traditionally provided much information. Medical imaging technologies such as functional neuroimaging, and electroencephalography (EEG) recordings are important in studying the brain. The medical history of people with brain injury has provided insight into the function of each part of the brain. Neuroscience research has expanded considerably, and research is ongoing.

In culture, the philosophy of mind has for centuries attempted to address the question of the nature of consciousness and the mind–body problem. The pseudoscience of phrenology attempted to localise personality attributes to regions of the cortex in the 19th century. In science fiction, brain transplants are imagined in tales such as the 1942 Donovan's Brain.

Structure

Human brain (sagittal section)

Gross anatomy

The adult human brain weighs on average about 1.2–1.4 kg (2.6–3.1 lb) which is about 2% of the total body weight,[2][3] with a volume of around 1260 cm3 in men and 1130 cm3 in women.[4] There is substantial individual variation,[4] with the standard reference range for men being 1,180–1,620 g (2.60–3.57 lb)[5] and for women 1,030–1,400 g (2.27–3.09 lb).[6]

The cerebrum, consisting of the cerebral hemispheres, forms the largest part of the brain and overlies the other brain structures.[7] The outer region of the hemispheres, the cerebral cortex, is grey matter, consisting of cortical layers of neurons. Each hemisphere is divided into four main lobes – the frontal lobe, parietal lobe, temporal lobe, and occipital lobe.[8] Three other lobes are included by some sources which are a central lobe, a limbic lobe, and an insular lobe.[9] The central lobe comprises the precentral gyrus and the postcentral gyrus and is included since it forms a distinct functional role.[9][10]

The

Latin: little brain).[7]

The cerebrum, brainstem, cerebellum, and spinal cord are covered by four[11] membranes called meninges. The membranes are the tough dura mater; the middle arachnoid mater and the more delicate inner pia mater. Between the arachnoid mater and the pia mater is the subarachnoid space and subarachnoid cisterns, which contain the cerebrospinal fluid.[12] The outermost membrane of the cerebral cortex is the basement membrane of the pia mater called the glia limitans and is an important part of the blood–brain barrier.[13] The living brain is very soft, having a gel-like consistency similar to soft tofu.[14] The cortical layers of neurons constitute much of the cerebral grey matter, while the deeper subcortical regions of myelinated axons, make up the white matter.[7] The white matter of the brain makes up about half of the total brain volume.[15]

Structural and functional areas of the human brain
A diagram showing various structures within the human brain
Human brain bisected in the sagittal plane, showing the white matter of the corpus callosum
A diagram of the functional areas of the human brain
Functional areas of the human brain. Dashed areas shown are commonly left hemisphere dominant.

Cerebrum

Major gyri and sulci on the lateral surface of the cortex
Lobes of the brain

The cerebrum is the largest part of the brain and is divided into nearly symmetrical left and right hemispheres by a deep groove, the longitudinal fissure.[16] Asymmetry between the lobes is noted as a petalia.[17] The hemispheres are connected by five commissures that span the longitudinal fissure, the largest of these is the corpus callosum.[7] Each hemisphere is conventionally divided into four main

frontal gyrus of the frontal lobe or the central sulcus separating the central regions of the hemispheres. There are many small variations in the secondary and tertiary folds.[19]

The outer part of the cerebrum is the cerebral cortex, made up of grey matter arranged in layers. It is 2 to 4 millimetres (0.079 to 0.157 in) thick, and deeply folded to give a convoluted appearance.[20] Beneath the cortex is the cerebral white matter. The largest part of the cerebral cortex is the neocortex, which has six neuronal layers. The rest of the cortex is of allocortex, which has three or four layers.[7]

The cortex is

association areas. These areas receive input from the sensory areas and lower parts of the brain and are involved in the complex cognitive processes of perception, thought, and decision-making.[23] The main functions of the frontal lobe are to control attention, abstract thinking, behaviour, problem-solving tasks, and physical reactions and personality.[24][25] The occipital lobe is the smallest lobe; its main functions are visual reception, visual-spatial processing, movement, and colour recognition.[24][25] There is a smaller occipital lobule in the lobe known as the cuneus. The temporal lobe controls auditory and visual memories, language, and some hearing and speech.[24]

Cortical folds and white matter in horizontal bisection of head

The cerebrum contains the ventricles where the cerebrospinal fluid is produced and circulated. Below the corpus callosum is the septum pellucidum, a membrane that separates the lateral ventricles. Beneath the lateral ventricles is the thalamus and to the front and below is the hypothalamus. The hypothalamus leads on to the pituitary gland. At the back of the thalamus is the brainstem.[26]

The basal ganglia, also called basal nuclei, are a set of structures deep within the hemispheres involved in behaviour and movement regulation.[27] The largest component is the striatum, others are the globus pallidus, the substantia nigra and the subthalamic nucleus.[27] The striatum is divided into a ventral striatum, and dorsal striatum, subdivisions that are based upon function and connections. The ventral striatum consists of the nucleus accumbens and the olfactory tubercle whereas the dorsal striatum consists of the caudate nucleus and the putamen. The putamen and the globus pallidus lie separated from the lateral ventricles and thalamus by the internal capsule, whereas the caudate nucleus stretches around and abuts the lateral ventricles on their outer sides.[28] At the deepest part of the lateral sulcus between the insular cortex and the striatum is a thin neuronal sheet called the claustrum.[29]

Below and in front of the striatum are a number of basal forebrain structures. These include the nucleus basalis, diagonal band of Broca, substantia innominata, and the medial septal nucleus. These structures are important in producing the neurotransmitter, acetylcholine, which is then distributed widely throughout the brain. The basal forebrain, in particular the nucleus basalis, is considered to be the major cholinergic output of the central nervous system to the striatum and neocortex.[30]

Cerebellum

Human brain viewed from below, showing cerebellum and brainstem

The cerebellum is divided into an anterior lobe, a posterior lobe, and the flocculonodular lobe.[31] The anterior and posterior lobes are connected in the middle by the vermis.[32] Compared to the cerebral cortex, the cerebellum has a much thinner outer cortex that is narrowly furrowed into numerous curved transverse fissures.[32] Viewed from underneath between the two lobes is the third lobe the flocculonodular lobe.[33] The cerebellum rests at the back of the cranial cavity, lying beneath the occipital lobes, and is separated from these by the cerebellar tentorium, a sheet of fibre.[34]

It is connected to the brainstem by three pairs of

balance[35] although debate exists as to its cognitive, behavioural and motor functions.[36]

Brainstem

The brainstem lies beneath the cerebrum and consists of the

base known as the clivus, and ends at the foramen magnum, a large opening in the occipital bone. The brainstem continues below this as the spinal cord,[37] protected by the vertebral column
.

Ten of the twelve pairs of

cranial nerves[a] emerge directly from the brainstem.[37] The brainstem also contains many cranial nerve nuclei and nuclei of peripheral nerves, as well as nuclei involved in the regulation of many essential processes including breathing, control of eye movements and balance.[38][37] The reticular formation, a network of nuclei of ill-defined formation, is present within and along the length of the brainstem.[37] Many nerve tracts, which transmit information to and from the cerebral cortex to the rest of the body, pass through the brainstem.[37]

Microanatomy

The human brain is primarily composed of

glial cells, neural stem cells, and blood vessels. Types of neuron include interneurons, pyramidal cells including Betz cells, motor neurons (upper and lower motor neurons), and cerebellar Purkinje cells. Betz cells are the largest cells (by size of cell body) in the nervous system.[39] The adult human brain is estimated to contain 86±8 billion neurons, with a roughly equal number (85±10 billion) of non-neuronal cells.[40] Out of these neurons, 16 billion (19%) are located in the cerebral cortex, and 69 billion (80%) are in the cerebellum.[3][40]

Types of glial cell are

ependymal cells (including tanycytes), radial glial cells, microglia, and a subtype of oligodendrocyte progenitor cells. Astrocytes are the largest of the glial cells. They are stellate cells with many processes radiating from their cell bodies. Some of these processes end as perivascular end-feet on capillary walls.[41] The glia limitans of the cortex is made up of astrocyte foot processes that serve in part to contain the cells of the brain.[13]

Some 400

GABA – is expressed in interneurons. Proteins expressed in glial cells include astrocyte markers GFAP and S100B whereas myelin basic protein and the transcription factor OLIG2 are expressed in oligodendrocytes.[46]

Cerebrospinal fluid

Cerebrospinal fluid circulates in spaces around and within the brain

Cerebrospinal fluid is a clear, colourless

middle and two lateral apertures, drain the cerebrospinal fluid from the fourth ventricle to the cisterna magna, one of the major cisterns. From here, cerebrospinal fluid circulates around the brain and spinal cord in the subarachnoid space, between the arachnoid mater and pia mater.[47]
At any one time, there is about 150mL of cerebrospinal fluid – most within the subarachnoid space. It is constantly being regenerated and absorbed, and is replaced about once every 5–6 hours.[47]

A

interstitial fluid from the tissue of the brain.[54]

Blood supply

Two circulations joining at the circle of Willis (inferior view)
Diagram showing features of cerebral outer membranes and supply of blood vessels

The

vertebral arteries supply blood to the back of the brain.[55] These two circulations join in the circle of Willis, a ring of connected arteries that lies in the interpeduncular cistern between the midbrain and pons.[56]

The internal carotid arteries are branches of the

insula cortex, where final branches arise. The middle cerebral arteries send branches along their length.[57]

The vertebral arteries emerge as branches of the left and right

posterior cerebral arteries. These travel outwards, around the superior cerebellar peduncles, and along the top of the cerebellar tentorium, where it sends branches to supply the temporal and occipital lobes.[59] Each posterior cerebral artery sends a small posterior communicating artery
to join with the internal carotid arteries.

Blood drainage

Cerebral veins drain deoxygenated blood from the brain. The brain has two main networks of veins: an exterior or superficial network, on the surface of the cerebrum that has three branches, and an interior network. These two networks communicate via anastomosing (joining) veins.[60] The veins of the brain drain into larger cavities of the dural venous sinuses usually situated between the dura mater and the covering of the skull.[61] Blood from the cerebellum and midbrain drains into the great cerebral vein. Blood from the medulla and pons of the brainstem have a variable pattern of drainage, either into the spinal veins or into adjacent cerebral veins.[60]

The blood in the deep part of the brain drains, through a venous plexus into the cavernous sinus at the front, and the superior and inferior petrosal sinuses at the sides, and the inferior sagittal sinus at the back.[61] Blood drains from the outer brain into the large superior sagittal sinus, which rests in the midline on top of the brain. Blood from here joins with blood from the straight sinus at the confluence of sinuses.[61]

Blood from here drains into the left and right

transverse sinuses.[61] These then drain into the sigmoid sinuses, which receive blood from the cavernous sinus and superior and inferior petrosal sinuses. The sigmoid drains into the large internal jugular veins.[61][60]

The blood–brain barrier

The larger arteries throughout the brain supply blood to smaller

anaesthetics and alcohol).[43] The blood-brain barrier is not present in the circumventricular organs—which are structures in the brain that may need to respond to changes in body fluids—such as the pineal gland, area postrema, and some areas of the hypothalamus.[43] There is a similar blood–cerebrospinal fluid barrier, which serves the same purpose as the blood–brain barrier, but facilitates the transport of different substances into the brain due to the distinct structural characteristics between the two barrier systems.[43][63]

Development

Neurulation and neural crest cells
Simple drawing of the lateral view of the three primary vesicle stage of the three to four week old embryo shown in different colors, and the five secondary vesicle stage of the five week old embryo shown in different colors and a lateral view of this
Primary and secondary vesicle stages of development in the early embryo to the fifth week
Very simple drawing of the front end of a human embryo, showing each vesicle of the developing brain in a different color.
Brain of a human embryo in the sixth week of development

At the beginning of the third week of development, the embryonic ectoderm forms a thickened strip called the neural plate.[64] By the fourth week of development the neural plate has widened to give a broad cephalic end, a less broad middle part and a narrow caudal end. These swellings are known as the primary brain vesicles and represent the beginnings of the forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon).[65][66]

Neural crest cells (derived from the ectoderm) populate the lateral edges of the plate at the neural folds. In the fourth week—during the neurulation stage—the neural folds close to form the neural tube, bringing together the neural crest cells at the neural crest.[67] The neural crest runs the length of the tube with cranial neural crest cells at the cephalic end and caudal neural crest cells at the tail. Cells detach from the crest and migrate in a craniocaudal (head to tail) wave inside the tube.[67] Cells at the cephalic end give rise to the brain, and cells at the caudal end give rise to the spinal cord.[68]

The tube flexes as it grows, forming the crescent-shaped cerebral hemispheres at the head. The cerebral hemispheres first appear on day 32.[69] Early in the fourth week, the cephalic part bends sharply forward in a

telencephalon and a posterior diencephalon. The telencephalon gives rise to the cerebral cortex, basal ganglia, and related structures. The diencephalon gives rise to the thalamus and hypothalamus. The hindbrain also splits into two areas – the metencephalon and the myelencephalon. The metencephalon gives rise to the cerebellum and pons. The myelencephalon gives rise to the medulla oblongata.[71] Also during the fifth week, the brain divides into repeating segments called neuromeres.[65][72] In the hindbrain these are known as rhombomeres.[73]

A characteristic of the brain is the cortical folding known as gyrification. For just over five months of prenatal development the cortex is smooth. By the gestational age of 24 weeks, the wrinkled morphology showing the fissures that begin to mark out the lobes of the brain is evident.[74] Why the cortex wrinkles and folds is not well-understood, but gyrification has been linked to intelligence and neurological disorders, and a number of gyrification theories have been proposed.[74] These theories include those based on mechanical buckling,[75][18] axonal tension,[76] and differential tangential expansion.[75] What is clear is that gyrification is not a random process, but rather a complex developmentally predetermined process which generates patterns of folds that are consistent between individuals and most species.[75][77]

The first groove to appear in the fourth month is the lateral cerebral fossa.[69] The expanding caudal end of the hemisphere has to curve over in a forward direction to fit into the restricted space. This covers the fossa and turns it into a much deeper ridge known as the lateral sulcus and this marks out the temporal lobe.[69] By the sixth month other sulci have formed that demarcate the frontal, parietal, and occipital lobes.[69] A gene present in the human genome (ARHGAP11B) may play a major role in gyrification and encephalisation.[78]

Function

Motor and sensory regions of the brain

Motor control

The frontal lobe is involved in reasoning, motor control, emotion, and language. It contains the

Broca’s area, which is essential for language production.[79] The motor system of the brain is responsible for the generation and control of movement.[80] Generated movements pass from the brain through nerves to motor neurons in the body, which control the action of muscles. The corticospinal tract carries movements from the brain, through the spinal cord, to the torso and limbs.[81] The cranial nerves
carry movements related to the eyes, mouth and face.

Gross movement – such as

decussate) at the medullary pyramids. These then travel down the spinal cord, with most connecting to interneurons, in turn connecting to lower motor neurons within the grey matter that then transmit the impulse to move to muscles themselves.[81] The cerebellum and basal ganglia, play a role in fine, complex and coordinated muscle movements.[83] Connections between the cortex and the basal ganglia control muscle tone, posture and movement initiation, and are referred to as the extrapyramidal system.[84]

Sensory

Cortical areas
Routing of neural signals from the two eyes to the brain

The

smell, hearing, and taste. Mixed motor and sensory signals are also integrated.[85]

From the skin, the brain receives information about

sensory receptor on the skin is changed to a nerve signal, that is passed up a series of neurons through tracts in the spinal cord. The dorsal column–medial lemniscus pathway contains information about fine touch, vibration and position of joints. The pathway fibres travel up the back part of the spinal cord to the back part of the medulla, where they connect with second-order neurons that immediately send fibres across the midline. These fibres then travel upwards into the ventrobasal complex in the thalamus where they connect with third-order neurons which send fibres up to the sensory cortex.[86] The spinothalamic tract carries information about pain, temperature, and gross touch. The pathway fibres travel up the spinal cord and connect with second-order neurons in the reticular formation of the brainstem for pain and temperature, and also terminate at the ventrobasal complex of the thalamus for gross touch.[87]

optic nerves
. Optic nerve fibres from the retinas' nasal halves
optic tracts
. The arrangements of the eyes' optics and the visual pathways mean vision from the left
visual field is received by the right half of each retina, is processed by the right visual cortex, and vice versa. The optic tract fibres reach the brain at the lateral geniculate nucleus, and travel through the optic radiation to reach the visual cortex.[88]

auditory radiation to the auditory cortex.[89]

The sense of

a relatively permeable part. This nerve transmits to the neural circuitry of the olfactory bulb from where information is passed to the olfactory cortex.[90][91]
Taste is generated from receptors on the tongue and passed along the facial and glossopharyngeal nerves into the solitary nucleus in the brainstem. Some taste information is also passed from the pharynx into this area via the vagus nerve. Information is then passed from here through the thalamus into the gustatory cortex.[92]

Regulation

Autonomic functions of the brain include the regulation, or rhythmic control of the heart rate and rate of breathing, and maintaining homeostasis.

nerve joining with the glossopharyngeal nerve. This information travels up to the solitary nucleus in the medulla. Signals from here influence the vasomotor centre to adjust vein and artery constriction accordingly.[94]

The brain controls the

pulmonary stretch receptors in the lungs which, when activated, prevent the lungs from overinflating by transmitting information to the respiratory centres via the vagus nerve.[95]

The

neuroendocrine regulation, regulation of the circadian rhythm, control of the autonomic nervous system, and the regulation of fluid, and food intake. The circadian rhythm is controlled by two main cell groups in the hypothalamus. The anterior hypothalamus includes the suprachiasmatic nucleus and the ventrolateral preoptic nucleus which through gene expression cycles, generates a roughly 24 hour circadian clock. In the circadian day an ultradian rhythm takes control of the sleeping pattern. Sleep is an essential requirement for the body and brain and allows the closing down and resting of the body's systems. There are also findings that suggest that the daily build-up of toxins in the brain are removed during sleep.[96] Whilst awake the brain consumes a fifth of the body's total energy needs. Sleep necessarily reduces this use and gives time for the restoration of energy-giving ATP. The effects of sleep deprivation show the absolute need for sleep.[97]

The

ascending reticular activating system.[98][99] The hypothalamus controls the pituitary gland through the release of peptides such as oxytocin, and vasopressin, as well as dopamine into the median eminence. Through the autonomic projections, the hypothalamus is involved in regulating functions such as blood pressure, heart rate, breathing, sweating, and other homeostatic mechanisms.[100] The hypothalamus also plays a role in thermal regulation, and when stimulated by the immune system, is capable of generating a fever. The hypothalamus is influenced by the kidneys: when blood pressure falls, the renin released by the kidneys stimulates a need to drink. The hypothalamus also regulates food intake through autonomic signals, and hormone release by the digestive system.[101]

Language

Broca's area and Wernicke's area are linked by the arcuate fasciculus.

While language functions were traditionally thought to be localised to Wernicke's area and Broca's area,[102] it is now mostly accepted that a wider network of cortical regions contributes to language functions.[103][104][105]

The study on how language is represented, processed, and acquired by the brain is called neurolinguistics, which is a large multidisciplinary field drawing from cognitive neuroscience, cognitive linguistics, and psycholinguistics.[106]

Lateralisation

The cerebrum has a

axial twist.[107] Motor connections from the brain to the spinal cord, and sensory connections from the spinal cord to the brain, both cross sides in the brainstem. Visual input follows a more complex rule: the optic nerves from the two eyes come together at a point called the optic chiasm, and half of the fibres from each nerve split off to join the other.[108] The result is that connections from the left half of the retina, in both eyes, go to the left side of the brain, whereas connections from the right half of the retina go to the right side of the brain.[109] Because each half of the retina receives light coming from the opposite half of the visual field, the functional consequence is that visual input from the left side of the world goes to the right side of the brain, and vice versa.[110] Thus, the right side of the brain receives somatosensory input from the left side of the body, and visual input from the left side of the visual field.[111][112]

The left and right sides of the brain appear symmetrical, but they function asymmetrically.[113] For example, the counterpart of the left-hemisphere motor area controlling the right hand is the right-hemisphere area controlling the left hand. There are, however, several important exceptions, involving language and spatial cognition. The left frontal lobe is dominant for language. If a key language area in the left hemisphere is damaged, it can leave the victim unable to speak or understand,[113] whereas equivalent damage to the right hemisphere would cause only minor impairment to language skills.

A substantial part of current understanding of the interactions between the two hemispheres has come from the study of "split-brain patients"—people who underwent surgical transection of the corpus callosum in an attempt to reduce the severity of epileptic seizures.[114] These patients do not show unusual behaviour that is immediately obvious, but in some cases can behave almost like two different people in the same body, with the right hand taking an action and then the left hand undoing it.[114][115] These patients, when briefly shown a picture on the right side of the point of visual fixation, are able to describe it verbally, but when the picture is shown on the left, are unable to describe it, but may be able to give an indication with the left hand of the nature of the object shown.[115][116]

Emotion

incentive salience.[118] Others, however, have found evidence of activation of specific regions, such as the basal ganglia in happiness, the subcallosal cingulate cortex in sadness, and amygdala in fear.[119]

Cognition

The brain is responsible for

reasoning and problem solving).[123]

The

parietal cortex.[121][124] Inhibitory control involves multiple areas of the prefrontal cortex, as well as the caudate nucleus and subthalamic nucleus.[123][124][125]

Physiology

Neurotransmission

Brain activity is made possible by the interconnections of

network systems such as the salience network and the default mode network, and the activity between them is driven by the process of neurotransmission
.

Metabolism

A flat oval object is surrounded by blue. The object is largely green-yellow, but contains a dark red patch at one end and a number of blue patches.
PET image of the human brain showing energy consumption

The brain consumes up to 20% of the energy used by the human body, more than any other organ.

heptanoic acid, can cross the blood–brain barrier and be metabolised by brain cells.[135][136][137]

Although the human brain represents only 2% of the body weight, it receives 15% of the cardiac output, 20% of total body oxygen consumption, and 25% of total body

fMRI.[140] These techniques provide a three-dimensional image of metabolic activity.[141] A preliminary study showed that brain metabolic requirements in humans peak at about five years old.[142]

The function of

neurotoxic, from the brain and may also permit repair.[52][143][144] Evidence suggests that the increased clearance of metabolic waste during sleep occurs via increased functioning of the glymphatic system.[52] Sleep may also have an effect on cognitive function by weakening unnecessary connections.[145]

Research

The brain is not fully understood, and research is ongoing.[146] Neuroscientists, along with researchers from allied disciplines, study how the human brain works. The boundaries between the specialties of neuroscience, neurology and other disciplines such as psychiatry have faded as they are all influenced by basic research in neuroscience.

Neuroscience research has expanded considerably. The "Decade of the Brain", an initiative of the United States Government in the 1990s, is considered to have marked much of this increase in research,[147] and was followed in 2013 by the BRAIN Initiative.[148] The Human Connectome Project was a five-year study launched in 2009 to analyse the anatomical and functional connections of parts of the brain, and has provided much data.[146]

An emerging phase in research may be that of simulating brain activity.[149]

Methods

Information about the structure and function of the human brain comes from a variety of experimental methods, including animals and humans. Information about brain trauma and stroke has provided information about the function of parts of the brain and the effects of brain damage. Neuroimaging is used to visualise the brain and record brain activity. Electrophysiology is used to measure, record and monitor the electrical activity of the cortex. Measurements may be of local field potentials of cortical areas, or of the activity of a single neuron. An electroencephalogram can record the electrical activity of the cortex using electrodes placed non-invasively on the scalp.[150][151]

Invasive measures include electrocorticography, which uses electrodes placed directly on the exposed surface of the brain. This method is used in cortical stimulation mapping, used in the study of the relationship between cortical areas and their systemic function.[152] By using much smaller microelectrodes, single-unit recordings can be made from a single neuron that give a high spatial resolution and high temporal resolution. This has enabled the linking of brain activity to behaviour, and the creation of neuronal maps.[153]

The development of cerebral organoids has opened ways for studying the growth of the brain, and of the cortex, and for understanding disease development, offering further implications for therapeutic applications.[154][155]

Imaging

SPECT and PET of not needing the use of radioactive materials and of offering a higher resolution.[156] Another technique is functional near-infrared spectroscopy. These methods rely on the haemodynamic response that shows changes in brain activity in relation to changes in blood flow, useful in mapping functions to brain areas.[157] Resting state fMRI
looks at the interaction of brain regions whilst the brain is not performing a specific task.[158] This is also used to show the default mode network.

Any electrical current generates a magnetic field;

MRI and image analysis to create 3D images of the nerve tracts of the brain. Connectograms give a graphical representation of the neural connections of the brain.[160]

Differences in

obsessive-compulsive disorder. A key source of information about the function of brain regions is the effects of damage to them.[161]

Advances in neuroimaging have enabled objective insights into mental disorders, leading to faster diagnosis, more accurate prognosis, and better monitoring.[162]

Gene and protein expression

Bioinformatics is a field of study that includes the creation and advancement of databases, and computational and statistical techniques, that can be used in studies of the human brain, particularly in the areas of gene and protein expression. Bioinformatics and studies in genomics, and functional genomics, generated the need for DNA annotation, a transcriptome technology, identifying genes, their locations and functions.[163][164][165] GeneCards is a major database.

As of 2017, just under 20,000 protein-coding genes are seen to be expressed in the human,[163] and some 400 of these genes are brain-specific.[166][167] The data that has been provided on gene expression in the brain has fuelled further research into a number of disorders. The long term use of alcohol for example, has shown altered gene expression in the brain, and cell-type specific changes that may relate to alcohol use disorder.[168] These changes have been noted in the synaptic transcriptome in the prefrontal cortex, and are seen as a factor causing the drive to alcohol dependence, and also to other substance abuses.[169]

Other related studies have also shown evidence of synaptic alterations and their loss, in the

ageing brain. Changes in gene expression alter the levels of proteins in various neural pathways and this has been shown to be evident in synaptic contact dysfunction or loss. This dysfunction has been seen to affect many structures of the brain and has a marked effect on inhibitory neurons resulting in a decreased level of neurotransmission, and subsequent cognitive decline and disease.[170][171]

Clinical significance

Injury

Disease

HIV dementia, syphilis-related dementia and Wilson's disease. Neurodegenerative diseases can affect different parts of the brain, and can affect movement, memory, and cognition.[174]

Cerebral atherosclerosis is atherosclerosis that affects the brain. It results from the build-up of plaques formed of cholesterol, in the large arteries of the brain, and can be mild to significant. When significant, arteries can become narrowed enough to reduce blood flow. It contributes to the development of dementia, and has protein similarities to those found in Alzheimer’s disease.[175]

The brain, although protected by the blood–brain barrier, can be affected by infections including

prion diseases including Creutzfeldt–Jakob disease and its variant, and kuru may also affect the brain.[176]

Tumours

radiotherapy or chemotherapy may be considered more suitable.[177]

Mental disorders

cognitive behavioural therapy; the underlying issues and associated prognoses vary significantly between individuals.[179]

Epilepsy

medical examination findings.[180] In addition to treating an underlying cause and reducing exposure to risk factors, anticonvulsant medications can play a role in preventing further seizures.[180]

Congenital

Some brain disorders, such as

Most cerebral arteriovenous malformations are congenital, these tangled networks of blood vessels may remain without symptoms but at their worst may rupture and cause intracranial hemorrhaging.[189]

Stroke

intraparenchymal bleed (bottom arrow) with surrounding edema
(top arrow)

A

finding words or forming sentences).[190] Symptoms relate to the function of the affected area of the brain and can point to the likely site and cause of the stroke. Difficulties with movement, speech, or sight usually relate to the cerebrum, whereas imbalance, double vision, vertigo and symptoms affecting more than one side of the body usually relate to the brainstem or cerebellum.[191]

Most strokes result from loss of blood supply, typically because of an

Some treatments for stroke are time-critical. These include

MRI scans, not as widely available, may be able to demonstrate the affected area of the brain more accurately, particularly with ischaemic stroke.[194]

Having experienced a stroke, a person may be admitted to a

physiotherapists, occupational therapists, and psychologists plays a large role in supporting a person affected by a stroke and their rehabilitation.[198][194] A history of stroke increases the risk of developing dementia by around 70%, and recent stroke increases the risk by around 120%.[199]

Brain death

Brain death refers to an irreversible total loss of brain function.

apnoea,[200] however, the declaration of brain death varies geographically and is not always accepted.[201] In some countries there is also a defined syndrome of brainstem death.[202] Declaration of brain death can have profound implications as the declaration, under the principle of medical futility, will be associated with the withdrawal of life support,[203] and as those with brain death often have organs suitable for organ donation.[201][204] The process is often made more difficult by poor communication with patients' families.[205]

When brain death is suspected, reversible

neural imaging evidence, may all play a role in the decision to pronounce brain death.[200]

Society and culture

Neuroanthropology is the study of the relationship between culture and the brain. It explores how the brain gives rise to culture, and how culture influences brain development.[206] Cultural differences and their relation to brain development and structure are researched in different fields.[207]

The mind

The skull of Phineas Gage, with the path of the iron rod that passed through it without killing him, but altering his cognition. The case helped to convince people that mental functions were localised in the brain.[208]

The

Gottfried Leibniz
in the analogy known as Leibniz's Mill:

One is obliged to admit that perception and what depends upon it is inexplicable on mechanical principles, that is, by figures and motions. In imagining that there is a machine whose construction would enable it to think, to sense, and to have perception, one could conceive it enlarged while retaining the same proportions, so that one could enter into it, just like into a windmill. Supposing this, one should, when visiting within it, find only parts pushing one another, and never anything by which to explain a perception.

— Leibniz, Monadology[209]

Doubt about the possibility of a mechanistic explanation of thought drove

dualism: the belief that the mind is to some degree independent of the brain.[210] There has always, however, been a strong argument in the opposite direction. There is clear empirical evidence that physical manipulations of, or injuries to, the brain (for example by drugs or by lesions, respectively) can affect the mind in potent and intimate ways.[211][212] In the 19th century, the case of Phineas Gage, a railway worker who was injured by a stout iron rod passing through his brain, convinced both researchers and the public that cognitive functions were localised in the brain.[208] Following this line of thinking, a large body of empirical evidence for a close relationship between brain activity and mental activity has led most neuroscientists and contemporary philosophers to be materialists, believing that mental phenomena are ultimately the result of, or reducible to, physical phenomena.[213]

Brain size

The size of the brain and a person's intelligence are not strongly related.[214] Studies tend to indicate small to moderate correlations (averaging around 0.3 to 0.4) between brain volume and IQ.[215] The most consistent associations are observed within the frontal, temporal, and parietal lobes, the hippocampi, and the cerebellum, but these only account for a relatively small amount of variance in IQ, which itself has only a partial relationship to general intelligence and real-world performance.[216][217]

Other animals, including whales and elephants have larger brains than humans. However, when the

chimpanzee. However, a high ratio does not of itself demonstrate intelligence: very small animals have high ratios and the treeshrew has the largest quotient of any mammal.[218]

In popular culture

Phrenology summarised in an 1883 chart

Earlier ideas about the relative importance of the different organs of the human body sometimes emphasised the heart.[219] Modern Western popular conceptions, in contrast, have placed increasing focus on the

brain.[220]

Research has disproved some common misconceptions about the brain. These include both ancient and modern myths. It is not true (for example) that neurons are not replaced after the age of two; nor that normal humans use only ten per cent of the brain.[221] Popular culture has also oversimplified the lateralisation of the brain by suggesting that functions are completely specific to one side of the brain or the other. Akio Mori coined the term "game brain" for the unreliably supported theory that spending long periods playing video games harmed the brain's pre-frontal region, and impaired the expression of emotion and creativity.[222]

Historically, particularly in the early-19th century, the brain featured in popular culture through phrenology, a pseudoscience that assigned personality attributes to different regions of the cortex. The cortex remains important in popular culture as covered in books and satire.[223][224]

The human brain can feature in

cyborgs (beings with features like partly artificial brains).[225] The 1942 science-fiction book (adapted three times for the cinema) Donovan's Brain tells the tale of an isolated brain kept alive in vitro, gradually taking over the personality of the book's protagonist.[226]

History

Early history

Hieroglyph
for the word "brain" (c. 1700 BC)

The

hieroglyph for brain, occurring eight times in this papyrus, describes the symptoms, diagnosis, and prognosis of two traumatic injuries to the head. The papyrus mentions the external surface of the brain, the effects of injury (including seizures and aphasia), the meninges, and cerebrospinal fluid.[227][228]

In the fifth century BC,

Magna Grecia, first considered the brain to be the seat of the mind.[228] Also in the fifth century BC in Athens, the unknown author of On the Sacred Disease, a medical treatise which is part of the Hippocratic Corpus and traditionally attributed to Hippocrates, believed the brain to be the seat of intelligence. Aristotle, in his biology initially believed the heart to be the seat of intelligence, and saw the brain as a cooling mechanism for the blood. He reasoned that humans are more rational than the beasts because, among other reasons, they have a larger brain to cool their hot-bloodedness.[229] Aristotle did describe the meninges and distinguished between the cerebrum and cerebellum.[230]

Herophilus of Chalcedon in the fourth and third centuries BC distinguished the cerebrum and the cerebellum, and provided the first clear description of the ventricles; and with Erasistratus of Ceos experimented on living brains. Their works are now mostly lost, and we know about their achievements due mostly to secondary sources. Some of their discoveries had to be re-discovered a millennium after their deaths.[228] Anatomist physician Galen in the second century AD, during the time of the Roman Empire, dissected the brains of sheep, monkeys, dogs, and pigs. He concluded that, as the cerebellum was denser than the brain, it must control the muscles, while as the cerebrum was soft, it must be where the senses were processed. Galen further theorised that the brain functioned by movement of animal spirits through the ventricles.[228][229]

Renaissance

De humani corporis fabrica
One of Leonardo da Vinci's sketches of the human skull

In 1316, Mondino de Luzzi's Anathomia began the modern study of brain anatomy.[231]

De humani corporis fabrica.[233][234][235] The seventh book covered the brain and eye, with detailed images of the ventricles, cranial nerves, pituitary gland, meninges, structures of the eye, the vascular supply to the brain and spinal cord, and an image of the peripheral nerves.[236] Vesalius rejected the common belief that the ventricles were responsible for brain function, arguing that many animals have a similar ventricular system to humans, but no true intelligence.[233]

dualism to tackle the issue of the brain's relation to the mind. He suggested that the pineal gland was where the mind interacted with the body, serving as the seat of the soul and as the connection through which animal spirits passed from the blood into the brain.[232] This dualism likely provided impetus for later anatomists to further explore the relationship between the anatomical and functional aspects of brain anatomy.[237]

Latin: Anatomy of the brain)[c] in 1664, followed by Cerebral Pathology in 1667. In these he described the structure of the cerebellum, the ventricles, the cerebral hemispheres, the brainstem, and the cranial nerves, studied its blood supply; and proposed functions associated with different areas of the brain.[233] The circle of Willis was named after his investigations into the blood supply of the brain, and he was the first to use the word "neurology".[238] Willis removed the brain from the body when examining it, and rejected the commonly held view that the cortex only consisted of blood vessels, and the view of the last two millennia that the cortex was only incidentally important.[233]

In the middle of 19th century Emil du Bois-Reymond and Hermann von Helmholtz were able to use a galvanometer to show that electrical impulses passed at measurable speeds along nerves, refuting the view of their teacher Johannes Peter Müller that the nerve impulse was a vital function that could not be measured.[239][240][241] Richard Caton in 1875 demonstrated electrical impulses in the cerebral hemispheres of rabbits and monkeys.[242] In the 1820s, Jean Pierre Flourens pioneered the experimental method of damaging specific parts of animal brains describing the effects on movement and behavior.[243]

Modern period

Drawing by Camillo Golgi of vertical section of rabbit hippocampus, from his "Sulla fina anatomia degli organi centrali del sistema nervoso", 1885
Drawing of cells in chick cerebellum by Santiago Ramón y Cajal, from "Estructura de los centros nerviosos de las aves", Madrid, 1905

Studies of the brain became more sophisticated with the use of the

Nobel prize in 1906 for their studies and discoveries in this field.[244]

Charles Sherrington published his influential 1906 work The Integrative Action of the Nervous System examining the function of reflexes, evolutionary development of the nervous system, functional specialisation of the brain, and layout and cellular function of the central nervous system.[245] In 1942 he coined the term enchanted loom as a metaphor for the brain. John Farquhar Fulton, founded the Journal of Neurophysiology and published the first comprehensive textbook on the physiology of the nervous system during 1938.[246] Neuroscience during the twentieth century began to be recognised as a distinct unified academic discipline, with David Rioch, Francis O. Schmitt, and Stephen Kuffler playing critical roles in establishing the field.[247] Rioch originated the integration of basic anatomical and physiological research with clinical psychiatry at the Walter Reed Army Institute of Research, starting in the 1950s.[248] During the same period, Schmitt established the Neuroscience Research Program, an inter-university and international organisation, bringing together biology, medicine, psychological and behavioural sciences. The word neuroscience itself arises from this program.[249]

epileptic seizures through the body. Carl Wernicke described a region associated with language comprehension and production. Korbinian Brodmann divided regions of the brain based on the appearance of cells.[250] By 1950, Sherrington, Papez, and MacLean had identified many of the brainstem and limbic system functions.[251][252] The capacity of the brain to re-organise and change with age, and a recognised critical development period, were attributed to neuroplasticity, pioneered by Margaret Kennard, who experimented on monkeys during the 1930-40s.[253]

Harvey Cushing (1869–1939) is recognised as the first proficient brain surgeon in the world.[254] In 1937, Walter Dandy began the practice of vascular neurosurgery by performing the first surgical clipping of an intracranial aneurysm.[255]

Comparative anatomy

The human brain has many properties that are common to all vertebrate brains.[256] Many of its features are common to all mammalian brains,[257] most notably a six-layered cerebral cortex and a set of associated structures,[258] including the hippocampus and amygdala.[259] The cortex is proportionally larger in humans than in many other mammals.[260] Humans have more association cortex, sensory and motor parts than smaller mammals such as the rat and the cat.[261]

As a primate brain, the human brain has a much larger cerebral cortex, in proportion to body size, than most mammals,[259] and a highly developed visual system.[262][263]

As a

Homo neanderthalensis.[267] Differences in DNA, gene expression, and gene–environment interactions help explain the differences between the function of the human brain and other primates.[268]

See also

References

  1. ^ "Encephalo- Etymology". Online Etymology Dictionary. Archived from the original on October 2, 2017. Retrieved October 24, 2015.
  2. .
  3. ^ .
  4. ^ .
  5. .
  6. .
  7. ^ a b c d e Gray's Anatomy 2008, pp. 227–9.
  8. ^ a b Gray's Anatomy 2008, pp. 335–7.
  9. ^
    PMID 20121437
    .
  10. .
  11. .
  12. ^ Purves 2012, p. 724.
  13. ^ a b Cipolla, M.J. (January 1, 2009). "Anatomy and Ultrastructure". The Cerebral Circulation. Morgan & Claypool Life Sciences. Archived from the original on October 1, 2017 – via NCBI Bookshelf.
  14. ^ "A Surgeon's-Eye View of the Brain". NPR. Fresh Air. May 10, 2006. Archived from the original on November 7, 2017.
  15. PMID 29268094
    .
  16. .
  17. .
  18. ^ .
  19. ^ Larsen 2001, pp. 455–456.
  20. .
  21. ^ Guyton & Hall 2011, p. 574.
  22. ^ Guyton & Hall 2011, p. 667.
  23. ^ Principles of Anatomy and Physiology 12th Edition – Tortora, p. 519.
  24. ^ .
  25. ^ .
  26. ^ Pocock 2006, p. 64.
  27. ^ a b Purves 2012, p. 399.
  28. ^ Gray's Anatomy 2008, pp. 325–6.
  29. S2CID 38353825
    .
  30. .
  31. ^ Guyton & Hall 2011, p. 699.
  32. ^ a b c Gray's Anatomy 2008, p. 298.
  33. .
  34. ^ a b Gray's Anatomy 2008, p. 297.
  35. ^ Guyton & Hall 2011, pp. 698–9.
  36. ^ Squire 2013, pp. 761–763.
  37. ^ a b c d e f Gray's Anatomy 2008, p. 275.
  38. ^ Guyton & Hall 2011, p. 691.
  39. ^ Purves 2012, p. 377.
  40. ^
    S2CID 5200449
    . despite the widespread quotes that the human brain contains 100 billion neurons and ten times more glial cells, the absolute number of neurons and glial cells in the human brain remains unknown. Here we determine these numbers by using the isotropic fractionator and compare them with the expected values for a human-sized primate. We find that the adult male human brain contains on average 86.1 ± 8.1 billion NeuN-positive cells ("neurons") and 84.6 ± 9.8 billion NeuN-negative ("nonneuronal") cells.
  41. .
  42. ^ .
  43. ^ a b c d e Guyton & Hall 2011, pp. 748–749.
  44. PMID 24833851
    .
  45. .
  46. .
  47. ^ a b c d Gray's Anatomy 2008, pp. 242–244.
  48. ^ Purves 2012, p. 742.
  49. ^ Gray's Anatomy 2008, p. 243.
  50. PMID 23709744
    .
  51. ^ Gaillard, F. "Glymphatic pathway". radiopaedia.org. Archived from the original on October 30, 2017.
  52. ^
    PMID 29163074
    . The paravascular pathway, also known as the "glymphatic" pathway, is a recently described system for waste clearance in the brain. According to this model, cerebrospinal fluid (CSF) enters the paravascular spaces surrounding penetrating arteries of the brain, mixes with interstitial fluid (ISF) and solutes in the parenchyma, and exits along paravascular spaces of draining veins.  ... In addition to Aβ clearance, the glymphatic system may be involved in the removal of other interstitial solutes and metabolites. By measuring the lactate concentration in the brains and cervical lymph nodes of awake and sleeping mice, Lundgaard et al. (2017) demonstrated that lactate can exit the CNS via the paravascular pathway. Their analysis took advantage of the substantiated hypothesis that glymphatic function is promoted during sleep (Xie et al., 2013; Lee et al., 2015; Liu et al., 2017).
  53. .
  54. ^ .
  55. ^ Gray's Anatomy 2008, p. 247.
  56. ^ Gray's Anatomy 2008, pp. 251–2.
  57. ^ a b c Gray's Anatomy 2008, p. 250.
  58. ^ a b Gray's Anatomy 2008, p. 248.
  59. ^ a b Gray's Anatomy 2008, p. 251.
  60. ^ a b c Gray's Anatomy 2008, pp. 254–6.
  61. ^ a b c d e Elsevier's 2007, pp. 311–4.
  62. PMID 20944625
    .
  63. ^ Laterra, J.; Keep, R.; Betz, L.A.; et al. (1999). "Blood–cerebrospinal fluid barrier". Basic neurochemistry: molecular, cellular and medical aspects (6th ed.). Philadelphia: Lippincott-Raven.
  64. .
  65. ^ a b Larsen 2001, p. 419.
  66. S2CID 260286574
    .
  67. ^ a b c Larsen 2001, pp. 85–88.
  68. ^ Purves 2012, pp. 480–482.
  69. ^ a b c d Larsen 2001, pp. 445–446.
  70. ^ "OpenStax CNX". cnx.org. Archived from the original on May 5, 2015. Retrieved May 5, 2015.
  71. ^ Larsen 2001, pp. 85–87.
  72. ^ Purves 2012, pp. 481–484.
  73. .
  74. ^ .
  75. ^ .
  76. .
  77. .
  78. .
  79. ^ "Parts of the Brain | Introduction to Psychology". courses.lumenlearning.com. Retrieved September 20, 2019.
  80. ^ Guyton & Hall 2011, p. 685.
  81. ^ a b Guyton & Hall 2011, p. 687.
  82. ^ a b Guyton & Hall 2011, p. 686.
  83. ^ Guyton & Hall 2011, pp. 698, 708.
  84. ^ Davidson's 2010, p. 1139.
  85. ^ .
  86. ^ a b Guyton & Hall 2011, pp. 571–576.
  87. ^ Guyton & Hall 2011, pp. 573–574.
  88. ^ Guyton & Hall 2011, pp. 623–631.
  89. ^ Guyton & Hall 2011, pp. 739–740.
  90. ^ Pocock 2006, pp. 138–139.
  91. ^ Squire 2013, pp. 525–526.
  92. ^ Guyton & Hall 2011, pp. 647–648.
  93. ^ Guyton & Hall 2011, pp. 202–203.
  94. ^ Guyton & Hall 2011, pp. 205–208.
  95. ^ a b c d Guyton & Hall 2011, pp. 505–509.
  96. ^ "Brain Basics: Understanding Sleep | National Institute of Neurological Disorders and Stroke". www.ninds.nih.gov. Archived from the original on December 22, 2017.
  97. ^ Guyton & Hall 2011, p. 723.
  98. .
  99. ^ Squire 2013, p. 800.
  100. ^ Squire 2013, p. 803.
  101. ^ Squire 2013, p. 805.
  102. ^ Guyton & Hall 2011, pp. 720–2.
  103. PMID 23055482
    .
  104. .
  105. .
  106. .
  107. .
  108. .
  109. .
  110. .
  111. .
  112. .
  113. ^ .
  114. ^ .
  115. ^ .
  116. .
  117. .
  118. .
  119. .
  120. .
  121. ^ .
  122. ^ .
  123. ^
  124. ^ .
  125. ^ . In conditions in which prepotent responses tend to dominate behavior, such as in drug addiction, where drug cues can elicit drug seeking (Chapter 16), or in attention deficit hyperactivity disorder (ADHD; described below), significant negative consequences can result. ... ADHD can be conceptualized as a disorder of executive function; specifically, ADHD is characterized by reduced ability to exert and maintain cognitive control of behavior. Compared with healthy individuals, those with ADHD have diminished ability to suppress inappropriate prepotent responses to stimuli (impaired response inhibition) and diminished ability to inhibit responses to irrelevant stimuli (impaired interference suppression). ... Functional neuroimaging in humans demonstrates activation of the prefrontal cortex and caudate nucleus (part of the dorsal striatum) in tasks that demand inhibitory control of behavior. ... Early results with structural MRI show a thinner cerebral cortex, across much of the cerebrum, in ADHD subjects compared with age-matched controls, including areas of [the] prefrontal cortex involved in working memory and attention.
  126. ^ Pocock 2006, p. 68.
  127. PMID 20007821
    .
  128. ^ Pocock 2006, pp. 70–74.
  129. ^ a b "NIMH » Brain Basics". www.nimh.nih.gov. Archived from the original on March 26, 2017. Retrieved March 26, 2017.
  130. .
  131. ^ Swaminathan, N (April 29, 2008). "Why Does the Brain Need So Much Power?". Scientific American. Archived from the original on January 27, 2014. Retrieved November 19, 2010.
  132. ^
    PMID 18840763
    . Four grams of glucose circulates in the blood of a person weighing 70 kg. This glucose is critical for normal function in many cell types. In accordance with the importance of these 4 g of glucose, a sophisticated control system is in place to maintain blood glucose constant. Our focus has been on the mechanisms by which the flux of glucose from liver to blood and from blood to skeletal muscle is regulated. ... The brain consumes ~60% of the blood glucose used in the sedentary, fasted person. ... The amount of glucose in the blood is preserved at the expense of glycogen reservoirs (Fig. 2). In postabsorptive humans, there are ~100 g of glycogen in the liver and ~400 g of glycogen in muscle. Carbohydrate oxidation by the working muscle can go up by ~10-fold with exercise, and yet after 1 h, blood glucose is maintained at ~4 g. ... It is now well established that both insulin and exercise cause translocation of GLUT4 to the plasma membrane. Except for the fundamental process of GLUT4 translocation, [muscle glucose uptake (MGU)] is controlled differently with exercise and insulin. Contraction-stimulated intracellular signaling (52, 80) and MGU (34, 75, 77, 88, 91, 98) are insulin independent. Moreover, the fate of glucose extracted from the blood is different in response to exercise and insulin (91, 105). For these reasons, barriers to glucose flux from blood to muscle must be defined independently for these two controllers of MGU.
  133. .
  134. .
  135. .
  136. . Uptake of valproic acid was reduced in the presence of medium-chain fatty acids such as hexanoate, octanoate, and decanoate, but not propionate or butyrate, indicating that valproic acid is taken up into the brain via a transport system for medium-chain fatty acids, not short-chain fatty acids. ... Based on these reports, valproic acid is thought to be transported bidirectionally between blood and brain across the BBB via two distinct mechanisms, monocarboxylic acid-sensitive and medium-chain fatty acid-sensitive transporters, for efflux and uptake, respectively.
  137. . Monocarboxylate transporters (MCTs) are known to mediate the transport of short chain monocarboxylates such as lactate, pyruvate and butyrate. ... MCT1 and MCT4 have also been associated with the transport of short chain fatty acids such as acetate and formate which are then metabolized in the astrocytes [78].
  138. .
  139. .
  140. .
  141. .
  142. .
  143. ^ "Brain may flush out toxins during sleep". National Institutes of Health. Archived from the original on October 20, 2013. Retrieved October 25, 2013.
  144. PMID 24136970
    . Thus, the restorative function of sleep may be a consequence of the enhanced removal of potentially neurotoxic waste products that accumulate in the awake central nervous system.
  145. S2CID 54052089. Archived from the original
    (PDF) on December 26, 2018.
  146. ^ .
  147. .
  148. ^ "A $4.5 Billion Price Tag for the BRAIN Initiative?". Science | AAAS. June 5, 2014. Archived from the original on June 18, 2017.
  149. PMID 31133838
    .
  150. .
  151. ^ Purves 2012, pp. 632–633.
  152. from the original on November 17, 2012.
  153. .
  154. .
  155. .
  156. ^ "Magnetic Resonance, a critical peer-reviewed introduction; functional MRI". European Magnetic Resonance Forum. Archived from the original on June 2, 2017. Retrieved June 30, 2017.
  157. S2CID 8736954
    .
  158. .
  159. ^ Purves 2012, p. 20.
  160. . Irimia, Chambers, Torgerson, and Van Horn (2012) provide a first-step graphic on how best to display connectivity findings, as is presented in Figure 13.15. This is referred to as a connectogram.
  161. .
  162. ^ Lepage, M. (2010). "Research at the Brain Imaging Centre". Douglas Mental Health University Institute. Archived from the original on March 5, 2012.
  163. ^
    PMID 28558813
    .
  164. .
  165. .
  166. ^ "The human proteome in brain – The Human Protein Atlas". www.proteinatlas.org. Archived from the original on September 29, 2017. Retrieved September 29, 2017.
  167. S2CID 802377
    .
  168. .
  169. .
  170. .
  171. .
  172. ^ "Brain Injury, Traumatic". Medcyclopaedia. GE. Archived from the original on May 26, 2011.
  173. ^ Dawodu, S.T. (March 9, 2017). "Traumatic Brain Injury (TBI) – Definition and Pathophysiology: Overview, Epidemiology, Primary Injury". Medscape. Archived from the original on April 9, 2017.
  174. ^ Davidson's 2010, pp. 1196–7.
  175. PMID 32424284
    .
  176. ^ a b Davidson's 2010, pp. 1205–15.
  177. ^ a b c d e Davidson's 2010, pp. 1216–7.
  178. PMID 26816013
    .
  179. .
  180. ^ a b c d Davidson's 2010, pp. 1172–9.
  181. ^ "Status Epilepticus". Epilepsy Foundation.
  182. .
  183. .
  184. .
  185. ^ .
  186. .
  187. .
  188. .
  189. ^ "Arteriovenous Malformations (AVMs) | National Institute of Neurological Disorders and Stroke". www.ninds.nih.gov. Retrieved February 8, 2023.
  190. S2CID 36692451
    .
  191. ^ Davidson's 2010, p. 1183.
  192. ^ a b Davidson's 2010, pp. 1180–1.
  193. ^ Davidson's 2010, pp. 1181, 1183–1185.
  194. ^ a b c d e f Davidson's 2010, pp. 1183–1185.
  195. ^ a b Davidson's 2010, pp. 1185–1189.
  196. S2CID 34799180
    .
  197. .
  198. .
  199. .
  200. ^ .
  201. ^ .
  202. .
  203. ^ a b c d Davidson's 2010, p. 1158.
  204. ^ Davidson's 2010, p. 200.
  205. .
  206. PMID 19874961. {{cite book}}: |journal= ignored (help
    )
  207. ^ "Cultural Environment Influences Brain Function | Psych Central News". Psych Central News. August 4, 2010. Archived from the original on January 17, 2017.
  208. ^ .
  209. .
  210. ^ Hart, WD (1996). Guttenplan S (ed.). A Companion to the Philosophy of Mind. Blackwell. pp. 265–267.
  211. .
  212. .
  213. ^ Schwartz, J.H. Appendix D: Consciousness and the Neurobiology of the Twenty-First Century. In Kandel, E.R.; Schwartz, J.H.; Jessell, T.M. (2000). Principles of Neural Science, 4th Edition.
  214. .
  215. (PDF) from the original on September 6, 2014.
  216. .
  217. .
  218. ^ "Tupaia belangeri". The Genome Institute, Washington University. Archived from the original on June 1, 2010. Retrieved January 22, 2016.
  219. ^ Carrier, Martin; . Retrieved May 22, 2021. [...] the Aristotelian view that the soul resides primarily in the heart [...].
  220. ^ . Retrieved May 22, 2021. [...] the ways in which we think about [the brain] are much richer than in the past, not simply because of the amazing facts we have discovered, but above all because of how we interpret them.
  221. .
  222. ^ Phillips, Helen (July 11, 2002). "Video game "brain damage" claim criticised". New Scientist. Archived from the original on January 11, 2009. Retrieved February 6, 2008.
  223. ^ Popova, Maria (August 18, 2011). "'Brain Culture': How Neuroscience Became a Pop Culture Fixation". The Atlantic. Archived from the original on July 28, 2017.
  224. .
  225. ^ Cyborgs and Space Archived October 6, 2011, at the Wayback Machine, in Astronautics (September 1960), by Manfred E. Clynes and Nathan S. Kline.
  226. .
  227. .
  228. ^ (PDF) from the original on May 5, 2013.
  229. ^ .
  230. ^ von Staden, p.157
  231. .
  232. ^ a b Lokhorst, Gert-Jan (January 1, 2016). "Descartes and the Pineal Gland". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved March 11, 2017.
  233. ^ .
  234. .
  235. .
  236. .
  237. .
  238. .
  239. ^ Olesko, Kathryn M.; Holmes, Frederic L. (1994). Cahan, David (ed.). "Experiment, Quantification, and Discovery: Helmholtz's Early Physiological Researches, 1843-50". Hermann von Helmholtz and the Foundations of Nineteenth Century Science. Berkeley; Los Angeles; London: University of California Press: 50–108. {{cite journal}}: Cite journal requires |journal= (help)
  240. ^ Sabbatini, Renato M.E. "Sabbatini, R.M.E.: The Discovery of Bioelectricity. Nerve Conduction". www.cerebromente.org.br. Archived from the original on June 26, 2017. Retrieved June 10, 2017.
  241. OCLC 864592470.{{cite book}}: CS1 maint: location missing publisher (link
    )
  242. .
  243. .
  244. ^ .
  245. .
  246. .
  247. .
  248. .
  249. .
  250. ^ a b Principles of Neural Science, 4th ed. Eric R. Kandel, James H. Schwartz, Thomas M. Jessel, eds. McGraw-Hill:New York, NY. 2000.
  251. PMID 7711480
    .
  252. .
  253. .
  254. .
  255. .
  256. .
  257. .
  258. .
  259. ^ .
  260. .
  261. .
  262. .
  263. .
  264. .
  265. .
  266. . As human's position changed and the manner in which the skull balanced on the spinal column pivoted, the brain expanded, altering the shape of the cranium.
  267. .
  268. .

Bibliography

Notes

External links