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The human brain is the central
organ Organ may refer to: Biology * Organ (biology), a part of an organism Musical instruments * Organ (music), a family of keyboard musical instruments characterized by sustained tone ** Electronic organ, an electronic keyboard instrument ** Hammond ...
of the human
nervous system In Biology, biology, the nervous system is the Complex system, highly complex part of an animal that coordinates its Behavior, actions and Sense, sensory information by transmitting action potential, signals to and from different parts of its ...

nervous system
, and with the
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spinal ...

spinal cord
makes up the
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...

central nervous system
. The
brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...

brain
consists of the
cerebrum The cerebrum, telencephalon or endbrain is the largest part of the brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually ...
, 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 ...

brainstem
and the
cerebellum The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebel ...

cerebellum
. It controls most of the activities of the
body
body
, processing, integrating, and coordinating the information it receives from the
sense organs A sense is a biological system used by an organism for sensation, the process of gathering information about the world through the detection of Stimulus (physiology), stimuli. (For example, in the human body, the brain which is part of the cen ...
, 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 A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as visual perception, sight, hearing, olfaction, smell, and taste. Some ...

head
. The cerebrum, the largest part of the human brain, consists of two
cerebral hemisphere The vertebrate cerebrum (brain) is formed by two cerebral hemispheres that are separated by a groove, the longitudinal fissure. The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres ...
s. Each hemisphere has an inner core composed of
white matter White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called Nerve tract, tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the ...
, and an outer surface – the
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. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting o ...
– composed of
grey matter Grey matter is a major component of the central nervous system, consisting of neuronal Soma (biology), cell bodies, neuropil (dendrites and unmyelinated axons), Glia, glial cells (astrocytes and oligodendrocytes), synapses, and Capillary, capil ...
. The cortex has an outer layer, the
neocortex The neocortex, also called the neopallium, isocortex, or the six-layered cortex, is a set of layers of the mammalian cerebral cortex involved in higher-order brain functions such as sense, sensory perception, cognition, generation of motor cortex ...

neocortex
, and an inner
allocortex The allocortex or heterogenetic cortex, and neocortex are the two types of cerebral cortex in the brain. The allocortex is the much smaller area of cortex taking up just 10 %, the neocortex takes up the remaining 90 %. It is characterized by havi ...
. The neocortex is made up of six neuronal layers, while the allocortex has three or four. Each hemisphere is conventionally divided into four
lobes
lobes
– the
frontal Front may refer to: Arts, entertainment, and media Films * The Front (1943 film), ''The Front'' (1943 film), a 1943 Soviet drama film * ''The Front'', 1976 film Music *The Front (band), an American rock band signed to Columbia Records and acti ...

frontal
,
temporal
temporal
,
parietal
parietal
, and
occipital lobe The occipital lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin ''ob'', "behind", and ''caput'', "head". The occipi ...

occipital lobe
s. The frontal lobe is associated with
executive functions In cognitive science and neuropsychology, executive functions (collectively referred to as executive function and cognitive control) are a set of cognitive processes that are necessary for the cognitive control of behavior: selecting and su ...
including
self-control Self-control, an aspect of inhibitory control, is the ability to regulate one's emotions, thoughts, and behavior in the face of temptations and impulses. As an executive function, it is a Control (psychology), cognitive process that is necessary ...

self-control
,
planning Planning is the process of thinking regarding the activities required to achieve a desired goal. Planning is based on foresight, the fundamental capacity for mental time travel. The evolution of forethought, the capacity to think ahead, is consi ...

planning
,
reason Reason is the capacity of Consciousness, consciously applying logic by Logical consequence, drawing conclusions from new or existing information, with the aim of seeking the truth. It is closely associated with such characteristically human activ ...
ing, and
abstract thought
abstract thought
, while the
occipital lobe The occipital lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin ''ob'', "behind", and ''caput'', "head". The occipi ...

occipital lobe
is dedicated to vision. Within each lobe, cortical areas are associated with specific functions, such as the sensory,
motor An engine or motor is a machine A machine is a physical system using Power (physics), power to apply Force, forces and control Motion, movement to perform an action. The term is commonly applied to artificial devices, such as those employ ...

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 Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by which humans communicate, and may be conveyed through a variety of met ...

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 corpus callosum (Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) aroun ...

corpus callosum
. The cerebrum is connected by the brainstem to the spinal cord. The brainstem consists of the
midbrain The midbrain or mesencephalon is the forward-most portion of 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 co ...

midbrain
, the
pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of Var ...

pons
, and the
medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic nervous s ...

medulla oblongata
. The
cerebellum The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebel ...

cerebellum
is connected to the brainstem by three pairs of
nerve tract A nerve tract is a bundle of nerve fibers (axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences), is a long, slender project ...
s called cerebellar peduncles. Within the cerebrum is the
ventricular system The ventricular system is a set of four interconnected cavities known as cerebral ventricles in the brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. I ...
, consisting of four interconnected
ventricles
ventricles
in which
cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless Extracellular fluid#Transcellular fluid, body fluid found within the meninges, tissue that surrounds the brain and spinal cord of all vertebrates. CSF is produced by specialised Ependyma, ependym ...
is produced and circulated. Underneath the cerebral cortex are several important structures, including the
thalamus The thalamus (from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter located in the wikt:dorsal, dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the th ...

thalamus
, the
epithalamus The epithalamus is a posterior Dorsum (biology), (dorsal) segment of the diencephalon. The epithalamus includes the habenular nuclei and their interconnecting fibers, the habenular commissure, the stria medullaris of thalamus, stria medullaris an ...

epithalamus
, the
pineal gland The pineal gland, conarium, or epiphysis cerebri, is a small endocrine gland in the brain of most vertebrates. The pineal gland produces melatonin, a serotonin-derived hormone which modulates sleep, sleep patterns in both circadian rhythm, circ ...

pineal gland
, the
hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalam ...

hypothalamus
, the
pituitary gland In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The hypoph ...

pituitary gland
, and the
subthalamus The subthalamus or prethalamus is a part of the diencephalon. Its most prominent structure is the subthalamic nucleus. The subthalamus connects to the globus pallidus, a basal ganglia, basal nucleus of the telencephalon. Structure The subthalam ...
; the limbic structures, including the
amygdala The amygdala (; plural: amygdalae or amygdalas; also '; Latin from Greek language, Greek, , ', 'almond', 'tonsil') is one of two almond-shaped clusters of nucleus (neuroanatomy), nuclei located deep and lateral and medial, medially within the ...

amygdala
and the
hippocampus The hippocampus (via Latin from Ancient Greek, Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each cerebral hemisphere, side of the brain. The hippocamp ...

hippocampus
; the
claustrum The claustrum (Latin, meaning "to close" or "to shut") is a thin, bilateral collection of neurons and supporting glial cells, that connects to cerebral cortex, cortical (e.g., the pre-frontal cortex) and subcortical regions (e.g., the thalamus) o ...
, the various nuclei of the
basal ganglia The basal ganglia (BG), or basal nuclei, are a group of subcortical Nucleus (neuroanatomy), nuclei, of varied origin, in the brains of vertebrates. In humans, and some primates, there are some differences, mainly in the division of the globus p ...

basal ganglia
; the
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 band ...

basal forebrain
structures, and the three circumventricular organs. The cells of the brain include
neuron A neuron, neurone, or nerve cell is an membrane potential#Cell excitability, electrically excitable cell (biology), cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous ...

neuron
s and supportive
glial cells Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cell (biology), cells in the central nervous system (brain and spinal cord) and the peripheral nervous system that do not produce electrical impulses. They maintain homeos ...

glial cells
. There are more than 86 billion neurons in the brain, and a more or less equal number of other cells. Brain activity is made possible by the interconnections of neurons and their release of
neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a Chemical synapse, synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or mus ...
s in response to
nerve impulses An action potential occurs when the membrane potential of a specific Cell (biology), cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of ...

nerve impulses
. Neurons connect to form
neural pathway In neuroanatomy Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry ...
s,
neural circuit A neural circuit is a population of neurons interconnected by synapses to carry out a specific function when activated. Neural circuits interconnect to one another to form large scale brain networks. Biological neural networks have inspired the ...
s, and elaborate network systems. The whole circuitry is driven by the process of
neurotransmission Neurotransmission (Latin: ''transmissio'' "passage, crossing" from ''transmittere'' "send, let through") is the process by which signaling molecules called neurotransmitters are released by the axon terminal of a neuron (the presynaptic neuron), ...
. The brain is protected by the
skull The skull is a bone protective Cranial cavity, cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible ...
, suspended in
cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless Extracellular fluid#Transcellular fluid, body fluid found within the meninges, tissue that surrounds the brain and spinal cord of all vertebrates. CSF is produced by specialised Ependyma, ependym ...
, and isolated from the
bloodstream The blood circulatory system is a organ system, system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascula ...
by the
blood–brain barrier The blood–brain barrier (BBB) is a highly selective semipermeable membrane, semipermeable border of endothelium, endothelial cells that prevents solutes in the circulating blood from ''non-selectively'' crossing into the extracellular fluid of ...
. However, the brain is still susceptible to damage,
disease A disease is a particular abnormal condition that negatively affects the structure or function (biology), function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medica ...
, and
infection An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmiss ...
. Damage can be caused by trauma, or a loss of blood supply known as a
stroke A stroke is a disease, medical condition in which poor cerebral circulation, blood flow to the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemorr ...
. The brain is susceptible to degenerative disorders, such as
Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a chronic condition, long-term neurodegeneration, degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disea ...
,
dementia Dementia is a disorder which manifests as a Syndrome, set of related symptoms, which usually surfaces when the brain is damaged by injury or disease. The symptoms involve progressive impairments in memory, thinking, and behavior, which negativ ...
s including
Alzheimer's disease Alzheimer's disease (AD) is a neurodegeneration, neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in short-term me ...
, and
multiple sclerosis Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the Myelin, insulating covers of nerve cells in the Human brain, brain and spinal cord ...
.
Psychiatric condition A mental disorder, also referred to as a mental illness or psychiatric disorder, is a behavioral or mental pattern that causes significant distress or impairment of personal functioning. Such features may be persistent, relapsing and remitti ...
s, including
schizophrenia Schizophrenia is a mental disorder characterized by continuous or relapsing episodes of psychosis. Major symptoms include hallucinations (typically hearing voices), delusions, and disorganized thinking. Other symptoms include social w ...
and
clinical depression Major depressive disorder (MDD), also known as clinical depression, is a mental disorder characterized by at least two weeks of pervasive depression (mood), low mood, low self-esteem, and anhedonia, loss of interest or pleasure in normally e ...
, are thought to be associated with brain dysfunctions. The brain can also be the site of
tumours A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
, both
benign Malignancy () is the tendency of a medical condition to become progressively worse. Malignancy is most familiar as a characterization of cancer. A ''malignant'' tumor contrasts with a non-cancerous benign tumor, ''benign'' tumor in that a malign ...
and
malignant Malignancy () is the tendency of a medical condition to become progressively worse. Malignancy is most familiar as a characterization of cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the p ...
; these mostly originate from other sites in the body. The study of the anatomy of the brain is
neuroanatomy Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defin ...
, while the study of its function is
neuroscience Neuroscience is the science, scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions and disorders. It is a Multidisciplinary approach, multidisciplinary science that combines physiology, an ...
. Numerous techniques are used to study the brain. Specimens from other animals, which may be examined microscopically, have traditionally provided much information.
Medical imaging Medical imaging is the technique and process of imaging the interior of a body for clinical analysis and medical intervention, as well as visual representation of the function of some organs or tissues (physiology). Medical imaging seeks to rev ...
technologies such as
functional neuroimaging Functional neuroimaging is the use of neuroimaging technology to measure an aspect of brain function, often with a view to understanding the relationship between activity in certain brain areas and specific mental functions. It is primarily used a ...
, and
electroencephalography Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex ...
(EEG) recordings are important in studying the brain. The
medical history The medical history, case history, or anamnesis (from Greek: ἀνά, ''aná'', "open", and μνήσις, ''mnesis'', "memory") of a patient A patient is any recipient of health care services that are performed by Health professional, health ...
of people with
brain injury An injury is any physiological damage to living tissue caused by immediate physical stress. An injury can occur intentionally or unintentionally and may be caused by blunt trauma, penetrating trauma, burning, toxic exposure, asphyxiation, ...
has provided insight into the function of each part of the brain. Brain research has evolved over time, with philosophical, experimental, and theoretical phases. An emerging phase may be to
simulate A simulation is the imitation of the operation of a real-world process or system over time. Simulations require the use of Conceptual model, models; the model represents the key characteristics or behaviors of the selected system or proc ...
brain activity. In culture, the
philosophy of mind Philosophy of mind is a branch of philosophy Philosophy (from , ) is the systematized study of general and fundamental questions, such as those about existence, reason, knowledge, values, mind, and language. Such questions are often ...
has for centuries attempted to address the question of the nature of
consciousness Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scient ...
and the
mind–body problem The mind–body problem is a philosophical debate concerning the relationship between thought and consciousness in the human mind, and the brain as part of the physical body. The debate goes beyond addressing the mere question of how mind and bo ...
. The
pseudoscience Pseudoscience consists of statements, beliefs, or practices that claim to be both scientific and factual but are incompatible with the scientific method. Pseudoscience is often characterized by contradictory, exaggerated or falsifiability, unfa ...
of
phrenology Phrenology () is a pseudoscience Pseudoscience consists of statements, beliefs, or practices that claim to be both scientific and factual but are incompatible with the scientific method. Pseudoscience is often characterized by contradictory ...
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


Gross anatomy

The adult human brain weighs on average about which is about 2% of the total body weight, with a volume of around 1260  cm3 in men and 1130 cm3 in women. There is substantial individual variation, with the standard
reference range In medicine Medicine is the science and Praxis (process), practice of caring for a patient, managing the diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment, Palliative care, palliation of their injury or disease, and He ...
for men being and for women . The
cerebrum The cerebrum, telencephalon or endbrain is the largest part of the brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually ...
, consisting of the
cerebral hemisphere The vertebrate cerebrum (brain) is formed by two cerebral hemispheres that are separated by a groove, the longitudinal fissure. The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres ...
s, forms the largest part of the brain and overlies the other brain structures. The outer region of the hemispheres, the
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. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting o ...
, is
grey matter Grey matter is a major component of the central nervous system, consisting of neuronal Soma (biology), cell bodies, neuropil (dendrites and unmyelinated axons), Glia, glial cells (astrocytes and oligodendrocytes), synapses, and Capillary, capil ...
, consisting of
cortical layers 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. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting of a ...
of
neuron A neuron, neurone, or nerve cell is an membrane potential#Cell excitability, electrically excitable cell (biology), cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous ...

neuron
s. Each hemisphere is divided into four main – the
frontal lobe The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a Sulcus (neur ...
,
parietal lobe The parietal lobe is one of the four major lobes of the 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. The cerebral corte ...
,
temporal lobe The temporal lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The temporal lobe ...
, and
occipital lobe The occipital lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin ''ob'', "behind", and ''caput'', "head". The occipi ...

occipital lobe
. Three other lobes are included by some sources which are a ''central lobe'', a limbic lobe, and an insular lobe. The central lobe comprises the
precentral gyrus The precentral gyrus is a prominent gyrus on the surface of the posterior frontal lobe of the brain. It is the site of the primary motor cortex that in humans is cytoarchitecture, cytoarchitecturally defined as Brodmann area 4. Structure The pr ...
and the
postcentral gyrus In neuroanatomy, the postcentral gyrus is a prominent gyrus in the lateral parietal lobe of the human brain. It is the location of the primary somatosensory cortex, the main sensory receptive area for the somatosensory system, sense of touch. Lik ...
and is included since it forms a distinct functional role. 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 ...

brainstem
, resembling a stalk, attaches to and leaves the cerebrum at the start of the
midbrain The midbrain or mesencephalon is the forward-most portion of 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 co ...

midbrain
area. The brainstem includes the midbrain, the
pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of Var ...

pons
, and the
medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic nervous s ...

medulla oblongata
. Behind the brainstem is the
cerebellum The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebel ...

cerebellum
( la , little brain). The cerebrum, brainstem, cerebellum, and spinal cord are covered by three membranes called
meninges In anatomy Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old sci ...
. The membranes are the tough
dura mater In neuroanatomy, dura mater is a thick membrane made of dense irregular connective tissue that surrounds the brain and spinal cord. It is the outermost of the three layers of membrane called the meninges that protect the central nervous system. T ...
; the middle
arachnoid mater The arachnoid mater (or simply arachnoid) is one of the three meninges, the protective membranes that cover the brain and spinal cord. It is so named because of its resemblance to a spider web. The arachnoid mater is a derivative of the neural cr ...
and the more delicate inner
pia mater Pia mater ( or ),Entry "pia mater"
in
subarachnoid space In anatomy, the meninges (, ''singular:'' meninx ( or ), ) are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located in th ...
and subarachnoid cisterns, which contain the
cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless Extracellular fluid#Transcellular fluid, body fluid found within the meninges, tissue that surrounds the brain and spinal cord of all vertebrates. CSF is produced by specialised Ependyma, ependym ...
. 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 The blood–brain barrier (BBB) is a highly selective semipermeable membrane, semipermeable border of endothelium, endothelial cells that prevents solutes in the circulating blood from ''non-selectively'' crossing into the extracellular fluid of ...
. The living brain is very soft, having a gel-like consistency similar to soft tofu. The cortical layers of neurons constitute much of the cerebral
grey matter Grey matter is a major component of the central nervous system, consisting of neuronal Soma (biology), cell bodies, neuropil (dendrites and unmyelinated axons), Glia, glial cells (astrocytes and oligodendrocytes), synapses, and Capillary, capil ...
, while the deeper subcortical regions of
myelin Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can ...
ated
axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, th ...
s, make up the
white matter White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called Nerve tract, tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the ...
. The white matter of the brain makes up about half of the total brain volume.


Cerebrum

The cerebrum is the largest part of the brain, and is divided into nearly
symmetrical Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics Mathematics is an area of knowle ...
left and right hemispheres by a deep groove, the
longitudinal fissure The longitudinal fissure (or cerebral fissure, great longitudinal fissure, median longitudinal fissure, interhemispheric fissure) is the deep groove that separates the two cerebral hemispheres of the vertebrate brain. Lying within it is a continu ...
. Asymmetry between the lobes is noted as a petalia. The hemispheres are connected by five
commissures A commissure () is the location at which two objects wikt:abut#Verb, abut or are joined. The term is used especially in the fields of anatomy and biology. * The most common usage of the term refers to the brain's commissures, of which there are fi ...
that span the longitudinal fissure, the largest of these is the
corpus callosum The corpus callosum (Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) aroun ...

corpus callosum
. Each hemisphere is conventionally divided into four main ; the
frontal lobe The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a Sulcus (neur ...
,
parietal lobe The parietal lobe is one of the four major lobes of the 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. The cerebral corte ...
,
temporal lobe The temporal lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The temporal lobe ...
, and
occipital lobe The occipital lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin ''ob'', "behind", and ''caput'', "head". The occipi ...

occipital lobe
, named according to the skull bones that overlie them. Each lobe is associated with one or two specialised functions though there is some functional overlap between them. The surface of the brain is folded into ridges (
gyri In neuroanatomy, a gyrus (pl. gyri) is a ridge on the cerebral cortex. It is generally surrounded by one or more sulcus (neuroanatomy), sulci (depressions or furrows; sg. ''sulcus''). Gyri and sulci create the folded appearance of the brain ...
) and grooves (
sulci Sulci or Sulki (in Greek , Steph. B., Ptol.; , Strabo Strabo''Strabo'' (meaning "squinty", as in strabismus) was a term employed by the Romans for anyone whose eyes were distorted or deformed. The father of Pompey was called "Pompeius Stra ...
), many of which are named, usually according to their position, such as the frontal gyrus of the frontal lobe or the
central sulcus In neuroanatomy, the central sulcus (also central fissure, fissure of Rolando, or Rolandic fissure, after Luigi Rolando) is a Sulcus (neuroanatomy), sulcus, or groove, in the cerebral cortex in the brains of vertebrates. It is sometimes confused ...
separating the central regions of the hemispheres. There are many small variations in the secondary and tertiary folds. The outer part of the cerebrum is the
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. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting o ...
, made up of
grey matter Grey matter is a major component of the central nervous system, consisting of neuronal Soma (biology), cell bodies, neuropil (dendrites and unmyelinated axons), Glia, glial cells (astrocytes and oligodendrocytes), synapses, and Capillary, capil ...
arranged in layers. It is thick, and deeply folded to give a convoluted appearance. Beneath the cortex is the cerebral
white matter White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called Nerve tract, tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the ...
. The largest part of the cerebral cortex is the
neocortex The neocortex, also called the neopallium, isocortex, or the six-layered cortex, is a set of layers of the mammalian cerebral cortex involved in higher-order brain functions such as sense, sensory perception, cognition, generation of motor cortex ...

neocortex
, which has six neuronal layers. The rest of the cortex is of
allocortex The allocortex or heterogenetic cortex, and neocortex are the two types of cerebral cortex in the brain. The allocortex is the much smaller area of cortex taking up just 10 %, the neocortex takes up the remaining 90 %. It is characterized by havi ...
, which has three or four layers. The cortex is mapped by divisions into about fifty different functional areas known as Brodmann's areas. These areas are distinctly different when seen under a microscope. The cortex is divided into two main functional areas – a
motor cortex The motor cortex is the region of the cerebral cortex believed to be involved in the planning, motor control, control, and execution of voluntary movements. The motor cortex is an area of the frontal lobe located in the posterior precentral gyru ...
and a
sensory cortex The sensory cortex can refer informally to the primary somatosensory cortex, or it can be used as a term for the primary and secondary Cerebral cortex, cortices of the different senses (two cortices each, on left and right cerebral hemispheres, hemi ...
. The
primary motor cortex The primary motor cortex (Brodmann area 4) is a Human brain, brain region that in humans is located in the dorsal portion of the frontal lobe. It is the primary cortex, primary region of the motor system and works in association with other motor ...
, which sends axons down to
motor neuron A motor neuron (or motoneuron or efferent neuron) is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectly ...
s in the brainstem and spinal cord, occupies the rear portion of the frontal lobe, directly in front of the somatosensory area. The primary sensory areas receive signals from the
sensory nerve A sensory nerve, or afferent nerve, is a general anatomic term for a nerve which contains predominantly Somatic nervous system, somatic afferent nerve fibers. Afferent nerve fibers in a sensory nerve carry sensory system, sensory information towar ...
s and tracts by way of relay nuclei in the
thalamus The thalamus (from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter located in the wikt:dorsal, dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the th ...

thalamus
. Primary sensory areas include the
visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus ...
of the
occipital lobe The occipital lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin ''ob'', "behind", and ''caput'', "head". The occipi ...

occipital lobe
, the
auditory cortex The auditory cortex is the part of the temporal lobe The temporal lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebr ...
in parts of the
temporal lobe The temporal lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The temporal lobe ...
and
insular cortex The insular cortex (also insula and insular lobe) is a portion of the cerebral cortex folded deep within the lateral sulcus (the fissure separating the temporal lobe from the parietal lobe, parietal and frontal lobes) within each brain hemisphere, ...
, and the
somatosensory cortex In physiology, the somatosensory system is the network of Nervous system, neural structures in the brain and body that produce the perception of touch (haptic perception), as well as temperature (thermoception), body position (proprioception), ...
in the
parietal lobe The parietal lobe is one of the four major lobes of the 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. The cerebral corte ...
. The remaining parts of the cortex are called the 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 Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous syste ...
,
thought In their most common sense, the terms thought and thinking refer to conscious cognitive Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasse ...
, and
decision-making In psychology Psychology is the science, scientific study of mind and behavior. Psychology includes the study of consciousness, conscious and Unconscious mind, unconscious phenomena, including feelings and thoughts. It is an academic dis ...
. The main functions of the frontal lobe are to control attention, abstract thinking, behaviour, problem-solving tasks, and physical reactions and personality. The occipital lobe is the smallest lobe; its main functions are visual reception, visual-spatial processing, movement, and colour recognition. There is a smaller occipital lobule in the lobe known as the
cuneus The cuneus (; plural cunei) is a smaller lobe in the occipital lobe of the brain. The cuneus is bounded anteriorly by the parieto-occipital sulcus and Inferior (anatomy), inferiorly by the calcarine sulcus. Function The cuneus (Brodmann area ...
. The temporal lobe controls auditory and visual memories,
language Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by which humans communicate, and may be conveyed through a variety of met ...
, and some hearing and speech. The cerebrum contains the ventricles where the cerebrospinal fluid is produced and circulated. Below the corpus callosum is the
septum pellucidum The septum pellucidum (Latin for "translucent wall") is a thin, triangular, vertical double membrane separating the anterior horn of lateral ventricle, anterior horns of the left and right lateral ventricles of the brain. It runs as a sheet from ...
, a membrane that separates the
lateral ventricles The lateral ventricles are the two largest ventricular system, ventricles of the brain and contain cerebrospinal fluid (CSF). Each cerebral hemisphere contains a lateral ventricle, known as the left or right ventricle, respectively. Each lateral ...
. Beneath the lateral ventricles is the
thalamus The thalamus (from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter located in the wikt:dorsal, dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the th ...

thalamus
and to the front and below this is the
hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalam ...

hypothalamus
. The hypothalamus leads on to the
pituitary gland In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The hypoph ...

pituitary gland
. At the back of the thalamus is the brainstem. The
basal ganglia The basal ganglia (BG), or basal nuclei, are a group of subcortical Nucleus (neuroanatomy), nuclei, of varied origin, in the brains of vertebrates. In humans, and some primates, there are some differences, mainly in the division of the globus p ...

basal ganglia
, also called basal nuclei, are a set of structures deep within the hemispheres involved in behaviour and movement regulation. The largest component is the
striatum The striatum, or corpus striatum (also called the striate nucleus), is a nucleus (neuroanatomy), nucleus (a cluster of neurons) in the cerebral cortex, subcortical basal ganglia of the forebrain. The striatum is a critical component of the moto ...
, others are the
globus pallidus The globus pallidus (GP), also known as paleostriatum or dorsal pallidum, is a Cerebral cortex, subcortical structure of the brain. It consists of two adjacent segments, one external, known in rodents simply as the globus pallidus, and one intern ...
, the
substantia nigra The substantia nigra (SN) is a basal ganglia structure located in the midbrain that plays an important role in reward system, reward and Motor system, movement. ''Substantia nigra'' is Latin for "black substance", reflecting the fact that parts ...
and the
subthalamic nucleus The subthalamic nucleus (STN) is a small lens-shaped Nucleus (neuroanatomy), nucleus in the brain where it is, from a functional point of view, part of the basal ganglia system. In terms of anatomy, it is the major part of the subthalamus. As sugg ...
. The striatum is divided into a ventral striatum, and a dorsal striatum, subdivisions that are based upon function and connections. The ventral striatum consists of the
nucleus accumbens The nucleus accumbens (NAc or NAcc; also known as the accumbens nucleus, or formerly as the ''nucleus accumbens septi'', Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European ...
and the
olfactory tubercle The olfactory tubercle (OT), also known as the tuberculum olfactorium, is a Multisensory integration, multi-sensory processing center that is contained within the olfactory cortex and ventral striatum and plays a role in reward system, reward cog ...
whereas the dorsal striatum consists of the
caudate nucleus The caudate nucleus is one of the structures that make up the corpus striatum, which is a component of the basal ganglia in the human brain. While the caudate nucleus has long been associated with motor processes due to its role in Parkinson's di ...
and the
putamen The putamen (; from Latin, meaning "nutshell") is a round structure located at the base of the forebrain (telencephalon). The putamen and caudate nucleus together form the dorsal striatum. It is also one of the structures that compose the basal n ...
. The putamen and the globus pallidus lie separated from the lateral ventricles and thalamus by the
internal capsule The internal capsule is a white matter White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called Nerve tract, tracts. Long thought to be passive tissue, white matter affects lear ...
, whereas the caudate nucleus stretches around and abuts the lateral ventricles on their outer sides. At the deepest part of the
lateral sulcus In neuroanatomy, the lateral sulcus (also called Sylvian fissure, after Franciscus Sylvius, or lateral fissure) is one of the most prominent features of the human brain. The lateral sulcus (neuroanatomy), sulcus is a deep fissure (anatomy), fissu ...
between the
insular cortex The insular cortex (also insula and insular lobe) is a portion of the cerebral cortex folded deep within the lateral sulcus (the fissure separating the temporal lobe from the parietal lobe, parietal and frontal lobes) within each brain hemisphere, ...
and the striatum is a thin neuronal sheet called the
claustrum The claustrum (Latin, meaning "to close" or "to shut") is a thin, bilateral collection of neurons and supporting glial cells, that connects to cerebral cortex, cortical (e.g., the pre-frontal cortex) and subcortical regions (e.g., the thalamus) o ...
. Below and in front of the striatum are a number of
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 band ...

basal forebrain
structures. These include the nucleus basalis, diagonal band of Broca,
substantia innominata The substantia innominata also innominate substance, or substantia innominata of Meynert (Latin for unnamed substance) is a series of layers in the human brain consisting partly of grey matter, gray and partly of white matter, which lies below the ...
, and the medial septal nucleus. These structures are important in producing the
neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a Chemical synapse, synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or mus ...
,
acetylcholine Acetylcholine (ACh) is an organic chemical that functions in the brain and body of many types of animals (including humans) as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Parts ...
, which is then distributed widely throughout the brain. The basal forebrain, in particular the nucleus basalis, is considered to be the major
cholinergic Cholinergic agents are compounds which mimic the action of acetylcholine and/or butyrylcholine. In general, the word "choline" describes the various quaternary ammonium salts containing the choline, ''N'',''N'',''N''-trimethylethanolammonium c ...
output of the central nervous system to the striatum and neocortex.


Cerebellum

The cerebellum is divided into an
anterior lobe The anterior lobe of cerebellum is the portion of the cerebellum The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid f ...
, a
posterior lobe The cerebellum (Latin for "little brain") is a major feature of the hindbrain The hindbrain or rhombencephalon or lower brain is a Morphogenesis, developmental categorization of portions of the central nervous system in vertebrates. It include ...
, and the
flocculonodular lobe The flocculonodular lobe ( vestibulocerebellum) is a lobe of the cerebellum The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as th ...
. The anterior and posterior lobes are connected in the middle by the
vermis The cerebellar vermis (from Latin ''vermis,'' "worm") is located in the medial, cortico-nuclear zone of the cerebellum, which is in the posterior cranial fossa, posterior fossa of the cranium. The primary fissure in the vermis curves ventrolatera ...
. Compared to the cerebral cortex, the cerebellum has a much thinner outer cortex that is narrowly furrowed into numerous curved transverse fissures. Viewed from underneath between the two lobes is the third lobe the flocculonodular lobe. The cerebellum rests at the back of the
cranial cavity The cranial cavity, also known as intracranial space, is the space within the skull that accommodates the brain. The skull minus the mandible is called the ''cranium''. The cavity is formed by eight cranial bones known as the neurocranium that in ...
, lying beneath the occipital lobes, and is separated from these by the cerebellar tentorium, a sheet of fibre. It is connected to the brainstem by three pairs of
nerve tract A nerve tract is a bundle of nerve fibers (axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences), is a long, slender project ...
s called cerebellar peduncles. The superior pair connects to the midbrain; the middle pair connects to the medulla, and the inferior pair connects to the pons. The cerebellum consists of an inner medulla of white matter and an outer cortex of richly folded grey matter. The cerebellum's anterior and posterior lobes appear to play a role in the coordination and smoothing of complex motor movements, and the flocculonodular lobe in the maintenance of
balance Balance or balancing may refer to: Common meanings * Balance (ability) in biomechanics * Balance (accounting) * Balance or weighing scale * Equality (mathematics), Balance as in equality or equilibrium Arts and entertainment Film * Balance (1983 ...
although debate exists as to its cognitive, behavioural and motor functions.


Brainstem

The brainstem lies beneath the cerebrum and consists of the
midbrain The midbrain or mesencephalon is the forward-most portion of 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 co ...

midbrain
,
pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of Var ...

pons
and medulla. It lies in the back part of the skull, resting on the part of the base known as the clivus, and ends at the
foramen magnum The foramen magnum ( la, great hole) is a large, oval-shaped opening in the occipital bone The occipital bone () is a neurocranium, cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in ...
, a large opening in the
occipital bone The occipital bone () is a neurocranium, cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobe ...
. The brainstem continues below this as the
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spinal ...

spinal cord
, protected by the
vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordata, ...
. Ten of the twelve pairs of
cranial nerve Cranial nerves are the nerves that emerge directly from the brain (including 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 ...
s emerge directly from the brainstem. The brainstem also contains many
cranial nerve nuclei A cranial nerve nucleus is a collection of neurons (gray matter) in the brain stem that is associated with one or more of the cranial nerves. Axons carrying information to and from the cranial nerves form a synapse first at these nucleus (neuroana ...
and nuclei of peripheral nerves, as well as nuclei involved in the regulation of many essential processes including
breathing Breathing (or ventilation) is the process of moving air into and from the lungs to facilitate gas exchange with the Milieu intérieur, internal environment, mostly to flush out carbon dioxide and bring in oxygen. All Aerobic respiration, aer ...
, control of eye movements and balance. The
reticular formation The reticular formation is a set of interconnected nuclei that are located throughout 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 ...
, a network of nuclei of ill-defined formation, is present within and along the length of the brainstem. Many
nerve tract A nerve tract is a bundle of nerve fibers (axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences), is a long, slender project ...
s, which transmit information to and from the cerebral cortex to the rest of the body, pass through the brainstem.


Microanatomy

The human brain is primarily composed of
neuron A neuron, neurone, or nerve cell is an membrane potential#Cell excitability, electrically excitable cell (biology), cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous ...

neuron
s,
glial cell Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cell (biology), cells in the central nervous system (brain and spinal cord) and the peripheral nervous system that do not produce electrical impulses. They maintain homeos ...
s,
neural stem cell Neural stem cells (NSCs) are self-renewing, multipotency, multipotent cells that firstly generate the radial glial cell, radial glial progenitor cells that generate the neurons and glia of the nervous system of all animals during embryonic develop ...
s, and
blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide aw ...
s. Types of neuron include
interneuron Interneurons (also called internuncial neurons, relay neurons, association neurons, connector neurons, intermediate neurons or local circuit neurons) are neurons that connect two brain regions, i.e. not direct motor neurons or sensory neurons. In ...
s,
pyramidal cell Pyramidal cells, or pyramidal neurons, are a type of multipolar neuron found in areas of the brain including the cerebral cortex, the hippocampus, and the amygdala. Pyramidal neurons are the primary excitation units of the mammalian prefrontal cor ...
s including
Betz cell Betz cells (also known as pyramidal cells of Betz) are giant pyramidal cells (neurons A neuron, neurone, or nerve cell is an membrane potential#Cell excitability, electrically excitable cell (biology), cell that communicates with other cells ...
s,
motor neuron A motor neuron (or motoneuron or efferent neuron) is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectly ...
s ( upper and
lower motor neuron Lower motor neurons (LMNs) are motor neurons located in either the anterior grey column, anterior root of spinal nerve, anterior nerve roots (spinal lower motor neurons) or the cranial nerve nucleus, cranial nerve nuclei of the brainstem and crani ...
s), and cerebellar
Purkinje cell Purkinje cells, or Purkinje neurons, are a class of GABAergic inhibitory neurons located in the cerebellum. They are named after their discoverer, Czech people, Czech anatomist Jan Evangelista Purkyně, who characterized the cells in 1839. Stru ...
s. Betz cells are the largest cells (by size of cell body) in the nervous system. The adult human brain is estimated to contain 86±8 billion neurons, with a roughly equal number (85±10 billion) of non-neuronal cells. Out of these neurons, 16 billion (19%) are located in the cerebral cortex, and 69 billion (80%) are in the cerebellum. Types of glial cell are
astrocyte Astrocytes (from Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following perio ...
s (including
Bergmann glia Radial glial cells, or radial glial progenitor cells (RGPs), are bipolar-shaped progenitor cells that are responsible for producing all of the neuron A neuron, neurone, or nerve cell is an membrane potential#Cell excitability, electrically e ...
),
oligodendrocyte Oligodendrocytes (), or oligodendroglia, are a type of neuroglia Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cell (biology), cells in the central nervous system (brain and spinal cord) and the peripheral nervous s ...
s, ependymal cells (including tanycytes),
radial glial cell Radial glial cells, or radial glial progenitor cells (RGPs), are Bipolar neuron, bipolar-shaped progenitor cells that are responsible for producing all of the neurons in the cerebral cortex. RGPs also produce certain lineages of glia, including as ...
s,
microglia Microglia are a type of neuroglia (glial cell) located throughout the brain and spinal cord. Microglia account for about 7% of cells found within the brain. As the resident macrophage cells, they act as the first and main form of active immune de ...
, and a subtype of oligodendrocyte progenitor cells. Astrocytes are the largest of the glial cells. They are
stellate cell Stellate cells are neurons in the central nervous system, named for their star-like shape formed by Dendrite, dendritic processes radiating from the cell body. Many stellate cells are GABAergic and are located in the Cerebellum#Molecular layer, mo ...
s with many processes radiating from their cell bodies. Some of these processes end as perivascular end-feet on
capillary A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter. Capillaries are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells. They are the smallest blood vessels in the body: ...
walls. The glia limitans of the cortex is made up of astrocyte foot processes that serve in part to contain the cells of the brain.
Mast cell A mast cell (also known as a mastocyte or a labrocyte) is a resident cell of connective tissue that contains many granule (cell biology), granules rich in histamine and heparin. Specifically, it is a type of granulocyte derived from the CFU-GEMM, ...
s are
white blood cell White blood cells, also called leukocytes or leucocytes, are the cell (biology), cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and de ...
s that interact in the
neuroimmune system The neuroimmune system is a system of structures and processes involving the biochemical Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and b ...
in the brain. Mast cells in the central nervous system are present in a number of structures including the meninges; they mediate neuroimmune responses in inflammatory conditions and help to maintain the blood–brain barrier, particularly in brain regions where the barrier is absent. Mast cells serve the same general functions in the body and central nervous system, such as effecting or regulating allergic responses,
innate {{Short pages monitorHarvey Cushing (1869–1939) is recognised as the first proficient neurosurgery, brain surgeon in the world. In 1937, Walter Dandy began the practice of vascular neurosurgery by performing the first surgical clipping of an intracranial aneurysm.


Comparative anatomy

The human brain has many properties that are common to all vertebrate brains. Many of its features are common to all mammalian brains, most notably a six-layered cerebral cortex and a set of associated structures, including the hippocampus and
amygdala The amygdala (; plural: amygdalae or amygdalas; also '; Latin from Greek language, Greek, , ', 'almond', 'tonsil') is one of two almond-shaped clusters of nucleus (neuroanatomy), nuclei located deep and lateral and medial, medially within the ...

amygdala
. The cortex is proportionally larger in humans than in many other mammals. Humans have more association cortex, sensory and motor parts than smaller mammals such as the rat and the cat. As a primate brain, the human brain has a much larger cerebral cortex, in proportion to body size, than most mammals, and a highly developed visual system. As a hominidae, hominid brain, the human brain is substantially enlarged even in comparison to the brain of a typical monkey. The sequence of human evolution from ''Australopithecus'' (four million years ago) to human, ''Homo sapiens'' (modern humans) was marked by a steady increase in brain size. As brain size increased, this altered the size and shape of the skull, from about 600 Cubic centimetre, cm3 in ''Homo habilis'' to an average of about 1520 cm3 in ''Homo neanderthalensis''. Differences in DNA,
gene expression Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, protein or non-coding RNA, and ultimately affect a phenotype, as the final effect. T ...
, and gene–environment interactions help explain the differences between the function of the human brain and other primates.


See also

*Cerebral atrophy *Cortical spreading depression *Evolution of human intelligence *Large-scale brain networks *Outline of neuroscience *Superficial veins of the brain


References


Bibliography

* * * * * * * *


Notes


External links


Brain facts and figures
{{DEFAULTSORT:Human Brain Brain Human anatomy by organ, Brain Brain anatomy