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The brain is made up of billions of nerve cells, intricately connected with each other. It contains nerve centers (groups of neurons and their connections) which control many involuntary functions, such as circulation, temperature regulation, and respiration, and interpret sensory impressions received from the eyes, ears, and other sense organs. Consciousness, emotion, thought, and reasoning are functions of the brain. It also contains centers or areas for associative memory which allow for recording, recalling, and making use of past experiences.
In appearance the cortex is rather like a relief map, with one very deep valley (longitudinal fissure) dividing it lengthwise into symmetrical halves, and each of the halves again divided by two major valleys and many shallower folds. The longitudinal fissure runs from the brow to the back of the head, and deep within it is a bed of matted white fibers, the corpus callosum, which connects the left and right cerebral hemispheres.
The major folds of the cortex divide each hemisphere into four sections or lobes: the occipital lobe at the back of the skull, the parietal lobe at the side, the frontal lobe at the forehead, and the temporal lobe at the temple.
It is in the sensory areas of the brain that all perception takes place. Here sweet and sour, hot and cold, and the form of an object held in the hand are recognized. Here are sorted out the sizes, colors, depth, and space relationships of what the eye sees, and the timbre, pitch, intensity, and harmony of what the ear hears. The significance of these perceptions is interpreted in the cortex and other parts of the brain. A face is not merely seen; it is recognized as familiar or interesting or attractive. Remembering takes place at the same time as perception, so that other faces seen in the past, or experiences linked to that face are called up. Emotions may also be stirred. For this type of association the cortex draws on other parts of the brain by way of the communicating network of nerves.
The symptoms of brain tumor vary and depend on the location and size of the tumor. Headache together with nausea is sometimes the first sign. The headache can be generalized or localized in one part of the head, and the pain is usually intense. Vomiting can be significant if it is sudden and without nausea. Disturbances of vision, loss of coordination in movement, weakness, and stiffness on one side of the body are also possible symptoms. Loss of sight, hearing, taste, or smell may result from brain tumor. A tumor can also cause a distortion of any of these senses, such as seeing flashes at the sides of the field of vision, or smelling odors or hearing sounds that do not exist. It can affect the ability to speak clearly or to understand the speech of others. Varying degrees of weakness or paralysis in the arms or legs may appear. A tumor may cause convulsions. Changes in personality or mental ability are rare in cases of brain tumor. When such changes occur they may take the form of lapses of memory or absentmindedness, mental sluggishness, or loss of initiative.
See also: encephalon. Compare: cerebrum, cerebellum.
brain(brān) encephalon; that part of the central nervous system contained within the cranium, comprising the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain); it develops from the anterior part of the embryonic neural tube. See also cerebrum.
brainThe epicentre of the central nervous system, which is located within the cranial vault and divided into the right and left hemispheres. The brain functions as a primary receiver, organiser and distributor of information for the body; it is the centre of thought and emotion, co-ordinates and controls bodily activities and interprets sensory visual, auditory, olfactory, tactile and other information.
watershed infarctNeurology Infarction of a region peripheral to 2 arteries and susceptible to ischemia; WIs are often hemorrhagic, as restoration of the circulation allows blood to flow into damaged capillaries and 'leak' into the ischemic tissue
See also: encephalon
Compare: cerebrum, cerebellum
The brain is a soft, compact organ responsible for consciousness, planned neural programs, and cognition. The brain is continually active, and, although it is only 2% of the body’s mass, it receives 17% of the heart's output and consumes 20% of the body's oxygen supply. The brain receives its blood through four arteries: two large arteries, the right and left internal carotid arteries, run up from the chest in the front (anterior half) of the neck; and two smaller arteries, the right and left vertebral arteries, run in the back (posterior half) of the neck. The carotid arteries supply blood to about 80% of the brain, including most of the frontal, parietal, and temporal lobes of the cerebral hemispheres and the basal ganglia. The vertebral arteries supply blood to the remaining 20% of the brain, including the brainstem, cerebellum, and most of the posterior lobes of the cerebral hemispheres. See: illustration
The most basic divisions of the brain are (from rostral to caudal) the forebrain (prosenchephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon). Physically, the forebrain dominates: the rostral end of the forebrain comprises the two cerebral hemispheres, which grow over much of the remaining brain (the brainstem) and fill the skull with their wavy infolded cortices. Between the cerebral hemispheres lies the caudal portion of the forebrain, the diencephalon, which contains the thalami, collections of nuclei that are way-stations and gatekeepers for signals to and from the cerebral cortices, and the hypothalamus, a center of visceral signals and the site of the pituitary gland. Caudal to the diencephalon is the midbrain, marked by two pairs of bulges (the tectum or colliculi) on its dorsal surface. The final segment of the brainstem, the hindbrain, has a rostral division, the pontine region (metencephalon), from the dorsal side of which bulges the cerebellum. The most caudal portion of the hindbrain is the medulla oblongata (myelencephalon or, in older literature, the bulb), which smoothly grades into the spinal cord. See: fasciculus; tract; illustration
brainThe central organ of the body, to the maintenance, supply, transport and protection of which all the remainder of the body is dedicated. The brain contain more than 100 billion nerve cells with more than 1015 synapses. There are two main parts to the brain, the cerebrum and the cerebellum. The larger part, the cerebrum, initiates and coordinates all voluntary and most involuntary functions and is the seat of emotion, memory and intelligence. It is the medium by which all sensation, and the results of the mechanisms underlying all satisfaction, are conveyed to consciousness. It is essentially concerned with the collection, processing and storage of information, with the correlation of new data with stored data and with the organization and control of resulting responsive action. Response to stimulus is of the essence of brain function. Much is known, from the effects of disease and injury, of the localization of functions, in the brain, such as movement, sensation, vision, hearing, smell and speech. The location of areas responsible for registration and recall of memory is known, but the physical basis of memory storage remains obscure. Memory is not, like some other functions, located in a single definable area but is probably dispersed into all areas concerned with functions which may involve it. The cerebellum, the smaller part, is concerned mainly with the complex computations necessary to organize the muscle contractions needed to maintain the balance of the body and to allow walking and other movements. More than one tenth of the cardiac output is required to maintain brain function. See also BRAINSTEM.
brainthe enlarged part of the CENTRAL NERVOUS SYSTEM beginning at the anterior end of bilaterally symmetrical animals (see BILATERAL SYMMETRY). The enlargement is associated with the aggregation of sense organs at the point which first contacts the changing environment. The brain, together with the rest of the central nervous system, coordinates the body functions. See also HEAD, CEPHALIZATION.
brainthe part of the central nervous system (CNS) within the skull. Uppermost are the anatomically symmetrical left and right cerebral hemispheres with frontal, temporal and occipital lobes, the grey matter of the cerebral cortex forming the infolded outermost layer. Below the hemispheres the central brain stem (midbrain, pons and medulla oblongata), is in continuity with the spinal cord at the large hole (foramen magnum) in the base of the skull. The main sensory and motor nerve tracts to and from the cerebral hemispheres cross over in the brain stem, so brain damage on one side (e.g. stroke) disturbs function on the opposite side of the body. The cerebellum, also with a cortex of grey matter, lies behind and alongside the brain stem, with connections to it, and relays up and down to other parts of the CNS. grey matter refers to regions and clusters consisting mainly of neuron cell bodies (forming the cortical layers and more deeply the various control centres and 'nuclei'); white matter is composed mainly of myelinated nerve fibres in the tracts that link neurons in the different parts of the brain to each other and to the spinal cord. Interconnecting cerebral ventricles deep in the brain contain cerebrospinal fluid (CSF), in continuity with CSF on the surface of both brain and spinal cord, where it is enclosed within membranous coverings, the meninges. See Figure 1.
Patient discussion about brain
Q. What effect it will have in his brain………. hi all…………..whenever my bipolar son gets in to different episodes it makes me to think what effect it will have in his brain……….does it got anything to do with brain? But It didn’t strike me to discuss about this with my doctor….
Q. Does the brain recognize pain? How does the brain recognize pain.
Q. Is surfing the internet good for your brain? I am 72 and I just discovered computers and the internet at our library. I find myself fascinated by it and I spend hours in front of the computer. Is surfing the internet good for your brain?