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.
brain
brain [brān]
split brain one in which the connections between the hemispheres have been disrupted or severed; used to provide access to the third ventricle or to control epilepsy.
brain (br n)n. The portion of the central nervous system that is enclosed within the cranium, continuous with the spinal cord, and composed of gray matter and white matter. It is the primary center for the regulation and control of bodily activities, receiving and interpreting sensory impulses, and transmitting information to the muscles and body organs. It is also the seat of consciousness, thought, memory, and emotion. Also called encephalon. |   cross section |
brain
Etymology: AS, bragen
the portion of the central nervous system contained within the cranium. It consists principally of the cerebrum, thalamus, hypothalamus, cerebellum, midbrain, pons, and medulla. Specialized cells in its mass of convoluted, soft gray or white tissue coordinate and regulate the functions of the central nervous system, integrating the functions of the body as a whole.
brain [brān]
that part of the central nervous system contained within the cranium, comprising the forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon); it develops from the embryonic neural tube. The brain is a mass of soft, spongy, pinkish gray nerve tissue that weighs about 1.2 kg in a human being. It is connected at its base with the spinal cord, which is also part of the central nervous system. Called also encephalon. (See also color plates.)
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.
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.
Cerebrum. The largest and main portion of the brain, the cerebrum is made up of an outer coating, or cerebral cortex, consisting of gray matter, several cell layers deep, covering the cerebral hemispheres. The cortex is the thinking and reasoning brain, the intellect, as well as the part of the brain that receives information from the senses and directs the conscious movements of the body.
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.
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.
The Senses. The major senses of vision and hearing have been well mapped in the cortex; the center for vision is at the back, in the occipital lobe, and the center for hearing is at the side, in the temporal lobe. Two other areas have been carefully explored, the sensory and motor areas for the body, which parallel each other along the fissure of Rolando. In the sensory strip are the brain cells that register all sensations, and in the motor strip are the nerves that control the voluntary muscles. In both, the parts of the body are represented in an orderly way.
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.
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.
Memory. In the temporal lobe, near the auditory area, is a center for memory. This center appears to be a storehouse where memories are filed. When this area alone is stimulated, a particular event, a piece of music, or an experience long forgotten or deeply buried is brought to the individual's mind, complete in every detail. This is a very mechanical type of memory; when the stimulation is removed the memory ends. When it is applied again, the memory begins again, not where it left off, but from the beginning.
Brainstem. This is the stemlike portion of the brain connecting the cerebral hemispheres with the spinal cord, and comprising midbrain, pons, and medulla oblongata. Some consider it to include the diencephalon.
Thalamus. This organ lies beneath the cortex, deep within the cerebral hemispheres. It is a relay station for body sensations, and integrates these sensations on their way to the cortex. The thalamus is an organ of crude consciousness and of sensations of rough contact and extreme temperatures, either hot or cold. It is principally here that pain is felt. In the thalamus, responses are of the all-or-nothing sort; even mild stimuli would be felt as acutely painful if they were not graded and modified by the cortex.
Hypothalamus. This organ lies below the thalamus, at the base of the cerebrum. It is small (no larger than a lump of sugar), but takes part in such vital activities as the ebb and flow of the body's fluids and the regulation of metabolism, blood sugar levels, and body temperature. It directs the body's many rhythms, including those of activity and rest, appetite and digestion, sexual desire, and menstrual and reproductive cycles. The hypothalamus is also the body's emotional brain. It is the integrating center of the autonomic nervous system, with its sympathetic and parasympathetic branches, and is located close to the pituitary gland.
Midbrain. Just below the thalamus is the short narrow pillar of the midbrain. This contains a center for visual reflexes, such as moving the head and eyes, as well as a sound-activated center, obsolete in humans, for pricking up the ears.
Medulla Oblongata. Below the midbrain is the medulla oblongata, the continuation upward of the spinal cord. In the medulla, the great trunk nerves, both motor and sensory, cross over, left to right and right to left, producing the puzzling phenomenon by which the left cerebral hemisphere controls the right half of the body, while the right hemisphere controls the left half of the body. This portion of the brain also contains the centers that activate the heart, blood vessels, and respiratory system.
Cerebellum. The cerebellum (Latin for “little brain”) is attached to the back of the brainstem, under the curve of the cerebrum. It is connected, by way of the midbrain, with the motor area of the cortex and with the spinal cord, as well as with the semicircular canals, the organs of balance. The function of the cerebellum is apparently to blend and coordinate motion of the various muscles involved in voluntary movements. It does not direct these movements; that is the function of the cortex. The cortex, however, operates in terms of movements, not of muscles. As a conscious function the cortex may, for example, direct the arm to pick up a glass of water; the cerebellum, which operates entirely below the level of consciousness, then translates this instruction into detailed actions by the 32 different muscles in the hand, plus several more in the arm and shoulder. When the cerebellum is injured, the patient's movements are jerky and uncoordinated.
Cranial Nerves. These are twelve nerves that arise within the skull. All but the olfactory nerve emerge from the brainstem. Most, with the important exception of the vagus nerve, serve the head and neck. See also cranial nerves.
Protection of the Brain. The brain is protected by the bony skull and by three layers of membranes, the meninges. Between the middle and inner layer is a space filled with cerebrospinal fluid, which serves as a shock absorber. The same system of membranes and fluid protects the spinal cord. The brain is protected from harmful substances in the bloodstream by a barrier called the blood-brain barrier, which keeps some of the substances out of the brain entirely and delays the entry of others for hours or even days after they have penetrated the rest of the body.
Projection areas of the brain.
brain abscess a localized suppurative lesion within the intracranial cavity; most cases are secondary to middle ear infections. Other causes include compound fracture of the skull with contamination of brain tissue, sinusitis, and infections of the face, lung or heart. Symptoms include fever, malaise, irritability, severe headache, convulsions, vomiting, and other signs of intracranial hypertension. Treatment consists of surgical removal of the infected area and administration of antibiotics.
brain death the irreversible cessation of all brain activity for an appropriate observation period, at least 24 hours, so that cardiopulmonary functions must be artificially maintained. A presidential commission in the USA accepted criteria for such a diagnosis, including cessation of all brain functions, including cerebral functions and brainstem (reflex) functions; irreversibility of the cessation; establishment of the cause of coma, sufficient to explain the loss of brain function; exclusion of possibility of recovery of brain function; and persistence of the cessation for an appropriate period of observation or trial of therapy. Complicating conditions must also be excluded. Called also irreversible coma.
brain scanning a nuclear medicine procedure for the detection of brain tumors, areas of stroke syndrome, abscesses, hematomas, and other intracranial lesions. A radiopharmaceutical, such as 99mTc-pertechnetate, is injected intravenously and is carried to the brain, where it localizes around any lesion that alters the blood-brain barrier. A scintillation camera makes an image of the distribution of radioactivity in which a lesion appears as a region of increased activity. Computed tomography brain scanning is an alternative procedure, which is more effective than radionuclide scans for the detection of some lesions.
brain tumor a neoplasm of the intracranial portion of the central nervous system. Any abnormal growth within the skull creates a special problem because it is in a confined space and will press on normal brain tissue and interfere with the functions of the body controlled by the affected parts. This is true whether the tumor itself is benign or malignant. Fortunately, the functions of certain areas of the brain are well known, and a disturbance of some specific function guides the clinician to the affected area. If diagnosed early, a benign tumor often can be removed surgically with a good chance of recovery. Malignant tumors are more difficult to remove. The causes of brain tumors are not known. They are not common, but they can occur at any age and in any part of the brain. Some originate in the brain itself, while others metastasize from a tumor in another part of the body.
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.
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.
wet brain brain edema.
brain
encephalon; that part of the central nervous system contained within the cranium, comprising the forebrain, midbrain and hindbrain, and developed from the embryonic neural tube. It is connected at its base with the spinal cord. The brain is a mass of soft, pinkish gray nerve tissue. For specific brain diseases see under headings relating to etiology and lesion.
brain abscess
common signs caused by an abscess in the brain are circling, rotation of the head, abnormal reflexes in one eye. The CSF may show evidence of infection.
brain aneurysm
see berry aneurysm.
brain anoxia
acute or chronic insufficiency of the blood supply to the brain causes anoxia which causes clinical signs that vary with the severity of the deprivation. Acute anoxia causes muscle tremor, recumbency, convulsions and death or recovery if the anoxia is relieved soon enough. Chronic anoxia causes lethargy, weakness, blindness and sometimes convulsions. In either case there may be permanent damage.
brain case
the cranium.
brain cestodal cyst
see coenurosis.
brain coup lesion
a derivation from contrecoup.
brain dead
irreversible coma with apnea, loss of all brainstem reflexes and absence of activity on an electroencephalogram.
brain decompression
relieving the pressure within the cranial vault. This may be done surgically by opening the cranium, or medically by administering hypertonic solutions of slowly metabolized materials, such as mannitol, intravenously.
brain edema
an important part of a number of acute diseases, e.g. lead poisoning, encephalitis, salt poisoning in swine, polioencephalomalacia of ruminants and hypoxia due to any cause. Clinically manifested by blindness, opisthotonos, nystagmus, recumbency and tonic convulsions. Inherited in polled and horned Herefords; calves are recumbent at birth and are never able to stand but consciousness is normal. See also neuraxial edema.
brain ependymal lining
see ependyma.
brain hematoma
may occur with trauma, in extradural, subdural or intraparenchymal locations. They can cause progressive increase in intracranial pressure and eventually death.
brain hemorrhage
intracranial hemorrhage affecting the brain usually follows traumatic injury but spontaneous hemorrhage may result from an intrinsic vascular lesion. Loss of consciousness is a common sign followed by residual signs depending on the locality and size of the hemorrhage. Ataxia and convulsions are common sequelae.
brain herniation
displacement of brain from the cranial vault through the foramina (tentorial notch or foramen magnum) or ventral to dural septae. The usual causes are brain edema or hemorrhage with resulting increase in intracranial pressure.
brain hypoxia
see brain anoxia (above).
brain infarction
see feline ischemic encephalopathy.
brain inflammation
brain ischemia
see brain anoxia (above).
brain laceration
occurs in cranial trauma that fractures the skull, causes severe acceleration or deceleration, or penetrates the skull and brain tissue.
brain necrosis
see encephalomalacia.
brain pigmentation
occurs in phalaris spp. poisoning; a characteristic greenish brown color grossly of the gray matter in brainstem nuclei and spinal cord, caused by a suspected lysosomal storage of granules of pigment material; usually associated with some degree of Wallerian degeneration within spinal cord tracts.
brain sand
see acervuli.
brain scanning
a radiographic, magnetic or nuclear medical procedure for the detection of brain tumors, abscesses, hematomas and other intracranial lesions. Not widely used in veterinary medicine because of the expensive equipment required.
brain spongy degeneration
brain staggers
see dummy.
brain trauma
injury to the brain, including that caused by migrating worm larvae, will have diffuse effects including the development of edema, and local effects due to pressure by displaced bone or to hemorrhage. Initial shock, manifested as unconsciousness, is likely to be followed by residual localizing signs, e.g. facial paralysis, head rotation.
brain tumors
cause signs suggestive of local space-occupying lesion in the cranial cavity, including the increased intracranial pressure syndrome, blindness with disturbance of ocular reflexes, head rotation, circling and jacksonian epileptic episodes.
brain ventricles
see third, fourth, fifth ventricle.
Patient discussion about brain.
Q. Could I be going through a Brain aneurysm? i woke up in the night with a bad headache in the back of my head and above my eye. never had a headache like that. but all day today have not had the headache. could this be an aneurysm?
A. An Aneurysm is when a blood vessel just pops out in you’re brain. Very ironically, there are no sensory nerves inside the brain and the headache that comes with aneurysm is when the brain starts pressuring the material that surrounds it. That means this will be a later symptoms and you’ll probably have a paralyses before, or have problem speaking and things like that. If you are not convinced – you can go to the hospital and ask for a scan.
Q. can anyone tell me why i am having brain pain that i have never had before. i have been having severe pain far worse than a migraine headache in my forehead and eyes and the worse of the pain is on top of my head in my brain and the back of my head in the brain area.i have had this pain and other symptoms now for about 2 weeks and seem to get worse as each day passes. getting real had to sleep with the pain getting to intense. also with it i have been having stomach pains in my right side and ringing in both of my ears off and on.chest pain even though my chest is completely clear. anyone have any suggestions on what it could be would be really appreciated. thank you
A. GO SEE A DOCTOR...SOON...THE SYMTOMS YOU SAY YOU HAVE COULD BE SERIOUS IN NATURE...mrfoot56
Q. What damage does depression do to the brain and how can you treat it? How does it affect your chemical balance, your brain? Is it critical or will be critical later in life? I just read on Yahoo News that Clinical stress could increase risk of Alzheimer's later in life. Does age matter like during teen years? I had depression and begun running. I noticed that I have a hard time focusing and absorbing information. I forgot a lot of things. All my brain seems to focus on is emotions. Can I change that? The running has made me feel a lot better afterwards
A. What you describe is considered as an attention disorder. But it’s very understandable while being on a depression episode. If it’s not on a depression episode- then it was strange… I suffer from depression for the last 12 years and I’m not sure I saw a real change in my cognitive abilities. But I’m not so sure…good idea about the running! it releases Endorphins which elevate mood.
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