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116-497: In the human brain , the cerebral cortex consists of the larger neocortex and the smaller allocortex , respectively taking up 90% and 10%. The neocortex is made up of six layers , labelled from the outermost inwards, I to VI. The term is from cortex , Latin , " bark " or "rind", combined with neo- , Greek , "new". Neopallium is a similar hybrid, from Latin pallium , "cloak". Isocortex and allocortex are hybrids with Greek isos , "same", and allos , "other". The neocortex

232-408: A central lobe , a limbic lobe , and an insular lobe . The central lobe comprises the precentral gyrus and the postcentral gyrus and is included since it forms a distinct functional role. The brainstem , resembling a stalk, attaches to and leaves the cerebrum at the start of the midbrain area. The brainstem includes the midbrain, the pons , and the medulla oblongata . Behind the brainstem

348-455: A cephalic flexure . This flexed part becomes the forebrain (prosencephalon); the adjoining curving part becomes the midbrain (mesencephalon) and the part caudal to the flexure becomes the hindbrain (rhombencephalon). These areas are formed as swellings known as the three primary brain vesicles . In the fifth week of development five secondary brain vesicles have formed. The forebrain separates into two vesicles – an anterior telencephalon and

464-409: A complex developmentally predetermined process which generates patterns of folds that are consistent between individuals and most species. The first groove to appear in the fourth month is the lateral cerebral fossa. 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

580-466: A large white matter tract, the arcuate fasciculus . Damage to the Broca's area results in expressive aphasia (non-fluent aphasia) while damage to Wernicke's area results in receptive aphasia (also called fluent aphasia). Explicit or declarative (factual) memory formation is attributed to the hippocampus and associated regions of the medial temporal lobe . This association was originally described after

696-419: A microscope . The cortex is divided into two main functional areas – a motor cortex and a sensory cortex . The primary motor cortex , which sends axons down to motor neurons 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 nerves and tracts by way of relay nuclei in

812-438: A patient known as HM had both his left and right hippocampus surgically removed to treat chronic [temporal lobe epilepsy]. After surgery, HM had anterograde amnesia , or the inability to form new memories. Implicit or procedural memory , such as complex motor behaviors, involves the basal ganglia. Short-term or working memory involves association areas of the cortex, especially the dorsolateral prefrontal cortex , as well as

928-412: 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. Also during the fifth week,

1044-415: A set of structures deep within the hemispheres involved in behaviour and movement regulation. The largest component is the striatum , others are the globus pallidus , the substantia nigra and the subthalamic nucleus . 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

1160-474: A slow oscillation , called the down state. When the neurons of the neocortex are in the excitatory depolarizing phase and are firing briefly at a high rate, a period of excitation occurs during a slow oscillation, called the up state. Lesions that develop in neurodegenerative disorders , such as Alzheimer's disease , interrupt the transfer of information from the sensory neocortex to the prefrontal neocortex. This disruption of sensory information contributes to

1276-443: 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 endfeet on capillary walls. The glia limitans of the cortex is made up of astrocyte endfeet processes that serve in part to contain the cells of the brain. Mast cells are white blood cells that interact in

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1392-416: A thickened strip called the neural plate . 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). Neural crest cells (derived from

1508-488: Is 2 to 4 millimetres (0.079 to 0.157 in) thick, and deeply folded to give a convoluted appearance. 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. 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

1624-466: Is a transitional area between the true isocortex and the periallocortex (part of the allocortex ). It is found in the cingulate cortex (part of the limbic system ), in Brodmann's areas 24 , 25 , 30 and 32 , the insula and the parahippocampal gyrus . Of all the mammals studied to date (including humans), a species of oceanic dolphin known as the long-finned pilot whale has been found to have

1740-463: Is also the only sense that is represented by the ipsilateral side of the brain. Damage to the olfactory bulb results in a loss of olfaction (the sense of smell). Speech and language are mainly attributed to parts of the cerebral cortex. Motor portions of language are attributed to Broca's area within the frontal lobe. Speech comprehension is attributed to Wernicke's area , at the temporal-parietal lobe junction. These two regions are interconnected by

1856-428: Is an accepted version of this page The brain is the central organ of the human nervous system , and with the spinal cord , comprises the central nervous system . It consists of the cerebrum , the brainstem and the cerebellum . The brain controls most of the activities of the body , processing, integrating, and coordinating the information it receives from the sensory nervous system . The brain integrates

1972-416: Is divided into regions demarcated by the cranial sutures in the skull above, into frontal , parietal , occipital , and temporal lobes, which perform different functions. For example, the occipital lobe contains the primary visual cortex , and the temporal lobe contains the primary auditory cortex . Further subdivisions or areas of neocortex are responsible for more specific cognitive processes. In humans,

2088-664: Is driven by the process of neurotransmission . The brain is protected by the skull , suspended in cerebrospinal fluid , and isolated from the bloodstream by the blood–brain barrier . However, the brain is still susceptible to damage , disease , and infection . Damage can be caused by trauma , or a loss of blood supply known as a stroke . The brain is susceptible to degenerative disorders , such as Parkinson's disease , dementias including Alzheimer's disease , and multiple sclerosis . Psychiatric conditions , including schizophrenia and clinical depression , are thought to be associated with brain dysfunctions. The brain can also be

2204-405: Is evident. 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. These theories include those based on mechanical buckling , axonal tension , and differential tangential expansion . What is clear is that gyrification is not a random process, but rather

2320-400: 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. Cerebrospinal fluid is a clear, colourless transcellular fluid that circulates around the brain in the subarachnoid space , in the ventricular system , and in the central canal of

2436-401: Is generated by baroreceptors in aortic bodies in the aortic arch , and passed to the brain along the afferent fibres of the vagus nerve. Information about the pressure changes in the carotid sinus comes from carotid bodies located near the carotid artery and this is passed via a nerve joining with the glossopharyngeal nerve . This information travels up to the solitary nucleus in

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2552-450: Is made up of six neuronal layers , while the allocortex has three or four. Each hemisphere is 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

2668-423: Is much larger than in amphibians and its growth has pushed the basal nuclei into the central regions of the cerebrum. As in the lower vertebrates, the grey matter is generally located beneath the white matter , but in some reptiles, it spreads out to the surface to form a primitive cortex, especially in the anterior part of the brain. In mammals , this development proceeds further, so that the cortex covers almost

2784-455: 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 , 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 tracts called cerebellar peduncles . The superior pair connects to

2900-404: Is passed to the olfactory cortex . 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 . Autonomic functions of

3016-416: 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

3132-424: Is sustained to this area, patients do not develop anterograde amnesia and are able to recall episodic information . The neocortex is the newest part of the cerebral cortex to evolve (hence the prefix neo meaning new); the other part of the cerebral cortex is the allocortex . The cellular organization of the allocortex is different from the six-layered neocortex. In humans, 90% of the cerebral cortex and 76% of

3248-437: Is the cerebellum ( Latin : little brain ). The cerebrum, brainstem, cerebellum, and spinal cord are covered by three 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 . The outermost membrane of

3364-416: Is the main recipient of incoming sensory information and distributes it to the other layers for further processing. The neocortex is often described as being arranged in vertical structures called cortical columns , patches of neocortex with a diameter of roughly 0.5 mm (and a depth of 2 mm, i.e., spanning all six layers). These columns are often thought of as the basic repeating functional units of

3480-432: Is the most developed in its organisation and number of layers, of the cerebral tissues. The neocortex consists of the grey matter , or neuronal cell bodies and unmyelinated fibers, surrounding the deeper white matter ( myelinated axons ) in the cerebrum . This is a very thin layer though, about 2–4 mm thick. There are two types of cortex in the neocortex, the proisocortex and the true isocortex. The pro-isocortex

3596-475: Is thought to correlate with a number of social variables such as group size and the complexity of social mating behaviors. Humans have a large neocortex as a percentage of total brain matter when compared with other mammals. For example, there is only a 30:1 ratio of neocortical gray matter to the size of the medulla oblongata in the brainstem of chimpanzees, while the ratio is 60:1 in humans. Human brain This

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3712-446: The blood–brain barrier . Pericytes play a major role in the formation of the tight junctions. The barrier is less permeable to larger molecules, but is still permeable to water, carbon dioxide, oxygen, and most fat-soluble substances (including anaesthetics and alcohol). 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

3828-415: The cerebral hemispheres , forms the largest part of the brain and overlies the other brain structures. 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 . Three other lobes are included by some sources which are

3944-451: The common carotid arteries . They enter the cranium through the carotid canal , travel through the cavernous sinus and enter the subarachnoid space . They then enter the circle of Willis , with two branches, the anterior cerebral arteries emerging. These branches travel forward and then upward along the longitudinal fissure , and supply the front and midline parts of the brain. One or more small anterior communicating arteries join

4060-470: The extrapyramidal system . The sensory nervous system is involved with the reception and processing of sensory information . This information is received through the cranial nerves, through tracts in the spinal cord, and directly at centres of the brain exposed to the blood. The brain also receives and interprets information from the special senses of vision , smell , hearing , and taste . Mixed motor and sensory signals are also integrated. From

4176-460: The frontal lobe contains areas devoted to abilities that are enhanced in or unique to our species, such as complex language processing localized to the ventrolateral prefrontal cortex ( Broca's area ). In humans and other primates, social and emotional processing is localized to the orbitofrontal cortex . The neocortex has also been shown to play an influential role in sleep, memory and learning processes. Semantic memories appear to be stored in

4292-434: The human brain , the cerebrum is the uppermost region of the central nervous system . The cerebrum develops prenatally from the forebrain (prosencephalon). In mammals, the dorsal telencephalon, or pallium , develops into the cerebral cortex, and the ventral telencephalon, or subpallium , becomes the basal ganglia . The cerebrum is also divided into approximately symmetric left and right cerebral hemispheres. With

4408-443: The lateral sulcus and this marks out the temporal lobe. By the sixth month other sulci have formed that demarcate the frontal, parietal, and occipital lobes. A gene present in the human genome ( ARHGAP11B ) may play a major role in gyrification and encephalisation. The frontal lobe is involved in reasoning, motor control, emotion, and language. It contains the motor cortex , which is involved in planning and coordinating movement;

4524-409: The lateral sulcus that separates the temporal lobe from the parietal and frontal lobes, is located within each hemisphere of the mammalian brain. The cerebrum is divided by the medial longitudinal fissure into two cerebral hemispheres , the right and the left. The cerebrum is contralaterally organized , i.e., the right hemisphere controls and processes signals (predominantly) from the left side of

4640-428: The medial geniculate nucleus , and finally the auditory radiation to the auditory cortex . The sense of smell is generated by receptor cells in the epithelium of the olfactory mucosa in the nasal cavity . This information passes via the olfactory nerve which goes into the skull through a relatively permeable part . This nerve transmits to the neural circuitry of the olfactory bulb from where information

4756-541: The neuroimmune system 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 and adaptive immunity , autoimmunity , and inflammation . Mast cells serve as

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4872-401: 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. At the deepest part of the lateral sulcus between the insular cortex and

4988-428: The pineal gland , area postrema , and some areas of the hypothalamus . 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. At the beginning of the third week of development , the embryonic ectoderm forms

5104-419: The prefrontal cortex , which is responsible for higher-level cognitive functioning; and Broca’s area , which is essential for language production. The motor system of the brain is responsible for the generation and control of movement. 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

5220-404: 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

5336-420: 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. The cerebellum and basal ganglia , play a role in fine, complex and coordinated muscle movements. Connections between the cortex and the basal ganglia control muscle tone, posture and movement initiation, and are referred to as

5452-399: The telencephalon and the diencephalon . The dorsal telencephalon gives rise to the pallium (cerebral cortex in mammals and reptiles) and the ventral telencephalon generates the basal ganglia . The diencephalon develops into the thalamus and hypothalamus , including the optic vesicles (future retina ). The dorsal telencephalon then forms two lateral telencephalic vesicles, separated by

5568-463: The thalamus , the epithalamus , the pineal gland , the hypothalamus , the pituitary gland , and the subthalamus ; the limbic structures , including the amygdalae and the hippocampi , the claustrum , the various nuclei of the basal ganglia , the basal forebrain structures, and three circumventricular organs . Brain structures that are not on the midplane exist in pairs; for example, there are two hippocampi and two amygdalae. The cells of

5684-497: The thalamus . Primary sensory areas include the visual cortex of the occipital lobe , the auditory cortex in parts of the temporal lobe and insular cortex , and the somatosensory cortex in the parietal lobe . 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 , thought , and decision-making . The main functions of

5800-431: 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. The basal ganglia , also called basal nuclei, are

5916-424: The ventrobasal complex in the thalamus where they connect with third-order neurons which send fibres up to the sensory cortex. 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

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6032-475: The assistance of the cerebellum , the cerebrum controls all voluntary actions in the human body. The cerebrum is the largest part of the brain . Depending upon the position of the animal, it lies either in front or on top of the brainstem . In humans, the cerebrum is the largest and best-developed of the five major divisions of the brain. The cerebrum is made up of the two cerebral hemispheres and their cerebral cortices (the outer layers of grey matter ), and

6148-411: The body, while the left hemisphere controls and processes signals (predominantly) from the right side of the body. According to current knowledge, this is due to an axial twist that occurs in the early embryo . There is a strong but not complete bilateral symmetry between the hemispheres, while lateralization tends to increase with increasing brain size. The lateralization of brain function looks at

6264-415: The brain include neurons and supportive 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 neurotransmitters in response to nerve impulses . Neurons connect to form neural pathways , neural circuits , and elaborate network systems . The whole circuitry

6380-402: The brain divides into repeating segments called neuromeres . In the hindbrain these are known as rhombomeres . 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

6496-433: The brain include the regulation, or rhythmic control of the heart rate and rate of breathing , and maintaining homeostasis . Blood pressure and heart rate are influenced by the vasomotor centre of the medulla, which causes arteries and veins to be somewhat constricted at rest. It does this by influencing the sympathetic and parasympathetic nervous systems via the vagus nerve . Information about blood pressure

6612-427: The brain is folded into ridges ( gyri ) and grooves ( sulci ), many of which are named, usually according to their position, such as the 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. The outer part of the cerebrum is the cerebral cortex , made up of grey matter arranged in layers. It

6728-486: The brain, through the spinal cord , to the torso and limbs. The cranial nerves carry movements related to the eyes, mouth and face. Gross movement – such as locomotion and the movement of arms and legs – is generated in the motor cortex , divided into three parts: the primary motor cortex , found in the precentral gyrus and has sections dedicated to the movement of different body parts. These movements are supported and regulated by two other areas, lying anterior to

6844-450: 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

6960-435: The brainstem. 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. The reticular formation , a network of nuclei of ill-defined formation, is present within and along the length of the brainstem. Many nerve tracts , which transmit information to and from

7076-410: The cavernous sinus and superior and inferior petrosal sinuses. The sigmoid drains into the large internal jugular veins . The larger arteries throughout the brain supply blood to smaller capillaries . These smallest of blood vessels in the brain, are lined with cells joined by tight junctions and so fluids do not seep in or leak out to the same degree as they do in other capillaries; this creates

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7192-464: The cerebral blood vessels. The pathway drains interstitial fluid from the tissue of the brain. The internal carotid arteries supply oxygenated blood to the front of the brain and the vertebral arteries supply blood to the back of the brain. 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. The internal carotid arteries are branches of

7308-421: 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 . In 2023 a fourth meningeal membrane has been proposed known as the subarachnoid lymphatic-like membrane . 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 , while

7424-411: The cerebral cortex to the rest of the body, pass through the brainstem. The human brain is primarily composed of neurons , 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

7540-430: The cerebral surface (see gyrus , gyrification ) are also found only in higher mammals. Although some large mammals (such as elephants) have particularly large cerebra, dolphins are the only species (other than humans) to have cerebra accounting for as much as 2 percent of their body weight. The cerebra of birds are similarly enlarged to those of mammals, by comparison with reptiles. The increased size of bird brains

7656-434: The cerebrum as a whole serves. (See main articles on cerebral cortex and basal ganglia for more information.) The cerebrum is a major part of the brain, controlling emotions, hearing, vision, personality and much more. It controls all precision of voluntary actions. Upper motor neurons in the primary motor cortex send their axons to the brainstem and spinal cord to synapse on the lower motor neurons , which innervate

7772-404: The cerebrum and consists of the midbrain , 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 , a large opening in the occipital bone . The brainstem continues below this as the spinal cord , protected by the vertebral column . Ten of the twelve pairs of cranial nerves emerge directly from

7888-556: The cortex in the 19th century. In science fiction, brain transplants are imagined in tales such as the 1942 Donovan's Brain . 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, with a volume of around 1260  cm in men and 1130 cm in women. There is substantial individual variation, with the standard reference range for men being 1,180–1,620 g (2.60–3.57 lb) and for women 1,030–1,400 g (2.27–3.09 lb). The cerebrum , consisting of

8004-402: The crest and migrate in a craniocaudal (head to tail) wave inside the tube. Cells at the cephalic end give rise to the brain, and cells at the caudal end give rise to the spinal cord. The tube flexes as it grows, forming the crescent-shaped cerebral hemispheres at the head. The cerebral hemispheres first appear on day 32. Early in the fourth week, the cephalic part bends sharply forward in

8120-443: The deeper subcortical regions of myelinated axons , make up the white matter . The white matter of the brain makes up about half of the total brain volume. 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 . Asymmetry between the lobes is noted as a petalia . The hemispheres are connected by five commissures that span

8236-448: The dura mater and the covering of the skull. 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. 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

8352-401: 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 . 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

8468-424: The entire brain is neocortex. For a species to develop a larger neocortex, the brain must evolve in size so that it is large enough to support the region. Body size, basal metabolic rate and life history are factors affecting brain evolution and the coevolution of neocortex size and group size. The neocortex increased in size in response to pressures for greater cooperation and competition in early ancestors. With

8584-419: The fibres from the temporal halves of the opposite retinas to form the 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

8700-484: 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 temporal lobe controls auditory and visual memories , language , and some hearing and speech. The cerebrum contains

8816-459: The gyri form during embryogenesis is not entirely clear, and there are several competing hypotheses that explain gyrification, such as axonal tension, cortical buckling or differences in cellular proliferation rates in different areas of the cortex. The neocortex contains both excitatory (~80%) and inhibitory (~20%) neurons , named for their effect on other neurons. The human neocortex consists of hundreds of different types of cells. The structure of

8932-444: The hippocampus. In the most primitive vertebrates, the hagfishes and lampreys , the cerebrum is a relatively simple structure receiving nerve impulses from the olfactory bulb . In cartilaginous and lobe-finned fishes and also in amphibians , a more complex structure is present, with the cerebrum being divided into three distinct regions. The lowermost (or ventral) region forms the basal nuclei , and contains fibres connecting

9048-436: The instructions sent to the rest of the body. The brain is contained in, and protected by, the skull 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

9164-430: The internal carotid arteries. 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. The veins of the brain drain into larger cavities of the dural venous sinuses usually situated between

9280-417: The known and possible differences between the two. In the developing vertebrate embryo , the neural tube is subdivided into four unseparated sections which then develop further into distinct regions of the central nervous system ; these are the prosencephalon ( forebrain ), the mesencephalon ( midbrain ) the rhombencephalon ( hindbrain ) and the spinal cord . The prosencephalon develops further into

9396-417: The lack of the distinctive six-layer neocortical structure. Evidence suggest the avian pallium to be broadly equivalent to the mammalian neocortex. In a similar manner, reptiles , such as turtles , have primary sensory cortices. A consistent, alternative name has yet to be agreed upon. The neocortex ratio of a species is the ratio of the size of the neocortex to the rest of the brain. A high neocortex ratio

9512-409: The lateral and ventral regions of the cerebrum bulge up into the ventricles ; these include both the basal nuclei and the various parts of the pallium and may be complex in structure, especially in teleosts . The dorsal surface of the cerebrum is membranous, and does not contain any nervous tissue . In the amniotes, the cerebrum becomes increasingly large and complex. In reptiles , the paleopallium

9628-447: The left and right subclavian arteries . They travel upward through transverse foramina which are spaces in the cervical vertebrae . Each side enters the cranial cavity through the foramen magnum along the corresponding side of the medulla. They give off one of the three cerebellar branches . The vertebral arteries join in front of the middle part of the medulla to form the larger basilar artery , which sends multiple branches to supply

9744-404: The longitudinal fissure, the largest of these is the corpus callosum . Each hemisphere is conventionally divided into four main lobes ; the frontal lobe , parietal lobe , temporal lobe , and 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

9860-399: The main effector cell through which pathogens can affect the biochemical signaling that takes place between the gastrointestinal tract and the central nervous system . Some 400 genes are shown to be brain-specific. In all neurons, ELAVL3 is expressed, and in pyramidal cells, NRGN and REEP2 are also expressed. GAD1 – essential for the biosynthesis of the neurotransmitter GABA –

9976-435: The medulla and pons, and the two other anterior and superior cerebellar branches . Finally, the basilar artery divides into two 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. Each posterior cerebral artery sends a small posterior communicating artery to join with

10092-426: The medulla. Signals from here influence the vasomotor centre to adjust vein and artery constriction accordingly. Telencephalon The cerebrum ( pl. : cerebra ), telencephalon or endbrain is the largest part of the brain , containing the cerebral cortex (of the two cerebral hemispheres ) as well as several subcortical structures, including the hippocampus , basal ganglia , and olfactory bulb . In

10208-513: 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 although debate exists as to its cognitive, behavioural and motor functions. The brainstem lies beneath

10324-431: The midline, which develop into the left and right cerebral hemispheres. Birds and fish have a dorsal telencephalon, like all vertebrates, but it is generally unlayered and therefore not considered a cerebral cortex. Only a layered cytoarchitecture can be considered a cortex. Note : As the cerebrum is a gross division with many subdivisions and sub-regions, it is important to state that this section lists only functions that

10440-449: The most neocortical neurons. The neocortex is smooth in rodents and other small mammals, whereas in elephants , dolphins and primates and other larger mammals it has deep grooves ( sulci ) and ridges ( gyri ). These folds allow the surface area of the neocortex to be greatly increased. All human brains have the same overall pattern of main gyri and sulci, although they differ in detail from one person to another. The mechanism by which

10556-626: The muscles. Damage to motor areas of the cortex can lead to certain types of motor neuron disease . This kind of damage results in loss of muscular power and precision rather than total paralysis . It functions as the center of sensory perception, memory, thoughts and judgement; the cerebrum also functions as the center of voluntary motor activities. The primary sensory areas of the cerebral cortex receive and process visual , auditory , somatosensory , gustatory , and olfactory information. Together with association cortical areas, these brain regions synthesize sensory information into our perceptions of

10672-415: The neocortex is relatively uniform (hence the alternative names "iso-" and "homotypic" cortex), consisting of six horizontal layers segregated principally by cell type and neuronal connections. However, there are many exceptions to this uniformity; for example, layer IV is small or missing in the primary motor cortex . There is some canonical circuitry within the cortex; for example, pyramidal neurons in

10788-420: The neocortex, but their many definitions, in terms of anatomy, size, or function, are generally not consistent with each other, leading to a lack of consensus regarding their structure or function or even whether it makes sense to try to understand the neocortex in terms of columns. The neocortex is derived embryonically from the dorsal telencephalon , which is the rostral part of the forebrain . The neocortex

10904-423: The neocortex, specifically the anterolateral temporal lobe of the neocortex. It is also involved in instrumental conditioning ; responsible for transmitting sensory information and information about plans for movement to the basal ganglia . The firing rate of neurons in the neocortex also has an effect on slow-wave sleep . When the neurons are at rest and are hyperpolarizing , a period of inhibition occurs during

11020-447: 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 astrocytes (including Bergmann glia ), oligodendrocytes , ependymal cells (including tanycytes ), radial glial cells , microglia , and

11136-403: The nucleus basalis, is considered to be the major cholinergic output of the central nervous system to the striatum and neocortex. The cerebellum is divided into an anterior lobe , a posterior lobe , and the flocculonodular lobe . The anterior and posterior lobes are connected in the middle by the vermis . Compared to the cerebral cortex, the cerebellum has a much thinner outer cortex that

11252-435: The primary motor cortex: the premotor area and the supplementary motor area . The hands and mouth have a much larger area dedicated to them than other body parts, allowing finer movement; this has been visualised in a motor homunculus . Impulses generated from the motor cortex travel along the corticospinal tract along the front of the medulla and cross over ( decussate ) at the medullary pyramids . These then travel down

11368-406: The progressive symptoms seen in neurodegenerative disorders such as changes in personality, decline in cognitive abilities, and dementia . Damage to the neocortex of the anterolateral temporal lobe results in semantic dementia , which is the loss of memory of factual information ( semantic memories ). These symptoms can also be replicated by transcranial magnetic stimulation of this area. If damage

11484-425: The rest of the cerebrum to the thalamus. Above this, and forming the lateral part of the cerebrum, is the paleopallium , while the uppermost (or dorsal) part is referred to as the archipallium . The cerebrum remains largely devoted to olfactory sensation in these animals, in contrast to its much wider range of functions in amniotes . In ray-finned fishes , the structure is somewhat different. The inner surfaces of

11600-416: The sides, and the inferior sagittal sinus at the back. 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 . Blood from here drains into the left and right transverse sinuses . These then drain into the sigmoid sinuses , which receive blood from

11716-524: The site of tumours , both benign and malignant ; these mostly originate from other sites in the body . 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

11832-492: The size increase, there was greater voluntary inhibitory control of social behaviors resulting in increased social harmony. The six-layer cortex appears to be a distinguishing feature of mammals; it has been found in the brains of all mammals, but not in any other animals. There is some debate, however, as to the cross- species nomenclature for neocortex . In avians , for instance, there are clear examples of cognitive processes that are thought to be neocortical in nature, despite

11948-419: The skin, the brain receives information about fine touch , pressure , pain , vibration and temperature . From the joints, the brain receives information about joint position . The sensory cortex is found just near the motor cortex, and, like the motor cortex, has areas related to sensation from different body parts. Sensation collected by a sensory receptor on the skin is changed to a nerve signal, that

12064-416: The spinal cord. It also fills some gaps in the subarachnoid space, known as subarachnoid cisterns . The four ventricles, two lateral , a third , and a fourth ventricle , all contain a choroid plexus that produces cerebrospinal fluid. The third ventricle lies in the midline and is connected to the lateral ventricles. A single duct , the cerebral aqueduct between the pons and the cerebellum, connects

12180-431: The spinal cord. The brainstem consists of the midbrain , the pons , and the medulla oblongata . The cerebellum is connected to the brainstem by three pairs of nerve tracts called cerebellar peduncles . Within the cerebrum is the ventricular system , consisting of four interconnected ventricles in which cerebrospinal fluid is produced and circulated. Underneath the cerebral cortex are several structures, including

12296-441: The striatum is a thin neuronal sheet called the claustrum . 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

12412-405: The subarachnoid space. It is constantly being regenerated and absorbed, and is replaced about once every 5–6 hours. A glymphatic system has been described as the lymphatic drainage system of the brain. The brain-wide glymphatic pathway includes drainage routes from the cerebrospinal fluid, and from the meningeal lymphatic vessels that are associated with the dural sinuses , and run alongside

12528-410: The surface of the cerebral cortex folds to create gyri (ridges) and sulci (furrows) which increase the surface area . The cerebral cortex is generally classified into four lobes : the frontal , parietal , occipital and temporal lobes. The lobes are classified based on their overlying neurocranial bones . A smaller lobe is the insular lobe , a part of the cerebral cortex folded deep within

12644-415: The thalamus for gross touch. Vision is generated by light that hits the retina of the eye. Photoreceptors in the retina transduce the sensory stimulus of light into an electrical nerve signal that is sent to the visual cortex in the occipital lobe. Visual signals leave the retinas through the optic nerves . Optic nerve fibres from the retinas' nasal halves cross to the opposite sides joining

12760-441: The third ventricle to the fourth ventricle. Three separate openings, the 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. At any one time, there is about 150mL of cerebrospinal fluid – most within

12876-405: The two anterior cerebral arteries shortly after they emerge as branches. The internal carotid arteries continue forward as the middle cerebral arteries . They travel sideways along the sphenoid bone of the eye socket , then upwards through the insula cortex , where final branches arise. The middle cerebral arteries send branches along their length. The vertebral arteries emerge as branches of

12992-403: The underlying regions of white matter . Its subcortical structures include the hippocampus, basal ganglia and olfactory bulb. The cerebrum consists of two C-shaped cerebral hemispheres, separated from each other by a deep fissure called the longitudinal fissure . The cerebral cortex , the outer layer of grey matter of the cerebrum, is found only in mammals. In larger mammals, including humans,

13108-420: The upper layers II and III project their axons to other areas of neocortex, while those in the deeper layers V and VI often project out of the cortex, e.g. to the thalamus , brainstem , and spinal cord . Neurons in layer IV receive the majority of the synaptic connections from outside the cortex (mostly from thalamus), and themselves make short-range, local connections to other cortical layers. Thus, layer IV

13224-420: The visual cortex. Hearing and balance are both generated in the inner ear . Sound results in vibrations of the ossicles which continue finally to the hearing organ , and change in balance results in movement of liquids within the inner ear . This creates a nerve signal that passes through the vestibulocochlear nerve . From here, it passes through to the cochlear nuclei , the superior olivary nucleus ,

13340-425: The whole of the cerebral hemispheres, especially in more developed species, such as the primates . The paleopallium is pushed to the ventral surface of the brain, where it becomes the olfactory lobes, while the archipallium becomes rolled over at the medial dorsal edge to form the hippocampus . In placental mammals , a corpus callosum also develops, further connecting the two hemispheres. The complex convolutions of

13456-405: The world. The olfactory bulb , responsible for the sense of smell, takes up a large area of the cerebrum in most vertebrates. However, in humans, this part of the brain is much smaller and lies underneath the frontal lobe. The olfactory sensory system is unique since the neurons in the olfactory bulb send their axons directly to the olfactory cortex , rather than to the thalamus first. Olfaction

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