File Name: parts of brain and its function .zip
The Frontal Lobes are located in the front of the brain.
The Central Nervous System
NCBI Bookshelf. Outside the specialized world of neuroanatomy and for most of the uses of daily life, the brain is more or less an abstract entity.
We do not experience our brain as an assembly of physical structures nor would we wish to, perhaps ; if we envision it at all, we are likely to see it as a large, rounded walnut, grayish in color. This schematic image refers mainly to the cerebral cortex, the outermost layer that overlies most of the other brain structures like a fantastically wrinkled tissue wrapped around an orange.
The preponderance of the cerebral cortex which, with its supporting structures, makes up approximately 80 percent of the brain's total volume is actually a recent development in the course of evolution. The cortex contains the physical structures responsible for most of what we call ''brainwork": cognition, mental imagery, the highly sophisticated processing of visual information, and the ability to produce and understand language. But underneath this layer reside many other specialized structures that are essential for movement, consciousness, sexuality, the action of our five senses, and more—all equally valuable to human existence.
Indeed, in strictly biological terms, these structures can claim priority over the cerebral cortex. In the growth of the individual embryo, as well as in evolutionary history, the brain develops roughly from the base of the skull up and outward. The human brain actually has its beginnings, in the four-week-old embryo, as a simple series of bulges at one end of the neural tube.
The brain owes its outer appearance of a walnut to the wrinkled and deeply folded cerebral cortex, which handles the innumerable signals responsible for perception and movement and also for mental processes. Below the surface of the cortex are packed more The bulges in the neural tube of the embryo develop into the hindbrain, midbrain, and forebrain—divisions common to all vertebrates, from sharks to squirrels to humans.
The original hollow structure is commemorated in the form of the ventricles, which are cavities containing cerebrospinal fluid. During the course of development, the three bulges become four ventricles. In the hindbrain is the fourth ventricle, continuous with the central canal of the spinal cord. A cavity in the forebrain becomes the third ventricle, which leads further forward into the two lateral ventricles, one in each cerebral hemisphere.
The hindbrain contains several structures that regulate autonomic functions, which are essential to survival and not under our conscious control. The brainstem, at the top of the spinal cord, controls breathing, the beating of the heart, and the diameter of blood vessels. This region is also an important junction for the control of deliberate movement.
Through the medulla, at the lower end of the brainstem, pass all the nerves running between the spinal cord and the brain; in the pyramids of the medulla, many of these nerve tracts for motor signals cross over from one side of the body to the other. Thus, the left brain controls movement of the right side of the body, and the right brain controls movement of the left side. In addition to being the major site of crossover for nerve tracts running to and from the brain, the medulla is the seat of several pairs of nerves for organs of the chest and abdomen, for movements of the shoulder and head, for swallowing, salivation, and taste, and for hearing and equilibrium.
At the top of the brainstem is the pons—literally, a bridge—between the lower brainstem and the midbrain. Nerve impulses traversing the pons pass on to the cerebellum or "little brain" , which is concerned primarily with the coordination of complex muscular movement.
In addition, nerve fibers running through the pons relay sensations of touch from the spinal cord to the upper brain centers. Many nerves for the face and head have their origin in the pons, and these nerves regulate some movements of the eyeball, facial expression, salivation, and taste.
Together with nerves of the medulla, nerves from the pons also control breathing and the body's sense of equilibrium. What had been the middle bulge in the neural tube develops into the midbrain, which functions mainly as a relay center for sensory and motor nerve impulses between the pons and spinal cord and the thalamus and cerebral cortex.
Nerves in the midbrain also control some movements of the eyeball, pupil, and lens and reflexes of the eyes, head, and trunk. Deep in the core area of the brain, just above the top of the brainstem, are structures that have a great deal to do with perception, movement, and the body's vital functions.
The thalamus consists of two oval masses, each embedded in a cerebral hemisphere, that are joined by a bridge. The masses contain nerve cell bodies that sort information from four of the senses—sight, hearing, taste, and touch—and relay it to the cerebral cortex.
Only the sense of smell sends signals directly to the cortex, bypassing the thalamus. Sensations of pain, temperature, and pressure are also relayed through the thalamus, as are the nerve impulses from the cerebral hemispheres that initiate voluntary movement. The hypothalamus, despite its relatively small size roughly that of a thumbnail , controls a number of drives essential for the functioning of a wide-ranging omnivorous social mammal.
At the autonomic level, the hypothalamus stimulates smooth muscle which lines the blood vessels, stomach, and intestines and receives sensory impulses from these areas.
Thus it controls the rate of the heart, the passage of food through the alimentary canal, and contraction of the bladder. The hypothalamus is the main point of interaction for the body's two physical control systems: the nervous system, which transmits information in the form of minute electrical impulses, and the endocrine system, which brings about changes of state through the release of chemical factors.
It is the hypothalamus that first detects crucial changes in the body and responds by stimulating various glands and organs to release hormones. The hypothalamus is also the brain's intermediary for translating emotion into physical response. When strong feelings rage, fear, pleasure, excitement are generated in the mind, whether by external stimuli or by the action of thoughts, the cerebral cortex transmits impulses to the hypothalamus; the hypothalamus may then send signals for physiological changes through the autonomic nervous system and through the release of hormones from the pituitary.
Physical signs of fear or excitement, such as a racing heartbeat, shallow breathing, and perhaps a clenched "gut feeling," all originate here. Also in the hypothalamus are neurons that monitor body temperature at the surface through nerve endings in the skin, and other neurons that monitor the blood flowing through this part of the brain itself, as an indicator of core body temperature. The front part of the hypothalamus contains neurons that act to lower body temperature by relaxing smooth muscle in the blood vessels, which causes them to dilate and increases the rate of heat loss from the skin.
Through its neurons associated with the sweat glands of the skin, the hypothalamus can also promote heat loss by increasing the rate of perspiration. In opposite conditions, when the body's temperature falls below the rather narrow ideal range, a portion of the hypothalamus directs the contraction of blood vessels, slows the rate of heat loss, and causes the onset of shivering which produces a small amount of heat.
The hypothalamus is the control center for the stimuli that underlie eating and drinking. The sensations that we interpret as hunger arise partly from a degree of emptiness in the stomach and partly from a drop in the level of two substances: glucose circulating in the blood and a hormone that the intestine produces shortly after the intake of food.
Receptors for this hormone gauge how far digestion has proceeded since the last meal. This system is not a simple "on" switch for hunger, however: another portion of the hypothalamus, when stimulated, actively inhibits eating by promoting a feeling of satiety. In experimental animals, damage to this portion of the brain is associated with continued excessive eating, eventually leading to obesity.
In addition to these numerous functions, there is evidence that the hypothalamus plays a role in the induction of sleep. For one thing, it forms part of the reticular activating system, the physical basis for that hard-to-define state known as consciousness about which more later ; for another, electrical stimulation of a portion of the hypothalamus has been shown to induce sleep in experimental animals, although the mechanism by which this works is not yet known.
In all, the hypothalamus is a richly complex cubic centimeter of vital connections, which will continue to reward close study for some time to come. Because of its unique position as a midpost between thought and feeling and between conscious act and autonomic function, a thorough understanding of its workings should tell us much about the earliest history and development of the human animal.
The pituitary and the pineal glands function in close association with the hypothalamus. The pituitary responds to signals from the hypothalamus by producing an array of hormones, many of which regulate the activities of other glands: thyroid-stimulating hormone, adrenocorticotropic hormone which stimulates an outpouring of epinephrine in response to stress , prolactin involved in the production of milk , and the sex hormones follicle-stimulating hormone and luteinizing hormone, which promote the development of eggs and sperm and regulate the timing of ovulation.
The pituitary gland also produces several hormones with more general effects: human growth hormone, melanocyte-stimulating hormone which plays a role in the pigmentation of skin , and dopamine, which inhibits the release of prolactin but is better known as a neurotransmitter see Chapter 5. The pineal gland produces melatonin, the hormone associated with skin pigmentation.
The secretion of melatonin varies significantly over a hour cycle, from low levels during the day to a peak at night, and the pineal gland has been called a "third eye" because it is controlled by neurons sensitive to light, which originate in the retina of each eye and end in the hypothalamus. In animals with a clear-cut breeding season, the pineal gland is a link between the shifting hours of daylight and the hormonal responses of the hypothalamus, which in turn guide reproductive functions.
In humans, who can conceive and give birth throughout the year, the pineal gland plays no known role in reproduction, although there is evidence that melatonin has a share in regulating ovulation. While autonomic and endocrine functions are being maintained by structures deep inside the brain, another specialized area is sorting and processing the signals required to maintain balance and posture and to carry out coordinated movement.
The cerebellum the term in Latin means "little brain" is actually a derived form of the hindbrain—as suggested by its position at the back of the head, partly tucked under the cerebral hemispheres.
In humans, with our almost unlimited repertoire of movement, the cerebellum is accordingly large; in fact, it is the second-largest portion of the brain, exceeded only by the cerebral cortex. Its great surface area is accommodated within the skull by elaborate folding, which gives it an irregular, pleated look.
In relative terms, the cerebellum is actually largest in the brain of birds, where it is responsible for the constant streams of information between brain and body that are required for flight. In humans, the cerebellum relays impulses for movement from the motor area of the cerebral cortex to the spinal cord; from there, they pass to their designated muscle groups.
At the same time, the cerebellum receives impulses from the muscles and joints that are being activated and in some sense compares them with the instructions issued from the motor cortex, so that adjustments can be made this time by way of the thalamus.
The cerebellum thus is neither the sole initiator of movement nor a simple link in the chain of nerve impulses, but a site for the rerouting and in some cases refining of instructions for movement. There is evidence, too, that the cerebellum can store a sequence of instructions for frequently performed movements and for skilled repetitive movements—those that we think of as learned "by rote.
The right and left hemispheres of the cerebellum each connect with the nerve tracts from the spinal cord on the same side of the body, and with the opposite cerebral hemisphere. For example, nerve impulses concerned with movement of the left arm originate in the right cerebral hemisphere, and information about the orientation, speed, and force of the movement is fed back to the right cerebral hemisphere, through the left half of the cerebellum.
The nerves responsible for movement at the ends of the arms and legs tend to have their origin near the outer edges of the cerebellum. By contrast, nerves that have their origin near the center of the cerebellum serve to monitor the body's overall orientation in space and to maintain upright posture, in response to information about balance that is transmitted by nerve impulses from the inner ear, among other sources.
Some nerve fibers from the cerebellum also contribute to the reticular formation, a widespread network of neurons "reticular" is derived from the Latin word for "net". This formation and some neurons in the thalamus, together with others from various sensory systems of the brain, make up the reticular activating system—the means by which we maintain consciousness. The reticular activating system also comes into play when we deliberately focus our attention, "tuning out" distractions to some degree.
At the midline of the brainstem are the raphe nuclei, whose axons extend down into the spinal cord and up to the cerebral cortex—a reach that makes it possible for many areas of the nervous system to be contacted simultaneously. The reticular formation plays a role in movement, particularly those forms of movement that do not call for conscious attention: it is also involved in transmitting or inhibiting sensations of pain, temperature, and touch.
Less tangibly, the reticular activating system appears to work as a filter for the countless stimuli that can act on the nervous system both from within and from outside the body. It is this filtering of signals that allows a passenger on an airplane, for example, to doze off undisturbed by sounds of nearby conversation and steady jet engines, but to awake and become alert when the pitch of the engines changes and the plane tilts into its descent.
The limbic system from the Latin limbus , for "hem" or "border" is another assembly of linked structures that form a loose circuit throughout the brain. This system is a fairly old part of the brain and one that humans share with many other vertebrates; in reptiles, it is known as the rhinencephalon, or "smell-brain," because it reacts primarily to signals of odor.
In humans, of course, the stimuli that can affect the emotional brain are just about limitless in their variety. The limbic system is responsible for most of the basic drives and emotions and the associated involuntary behavior that are important for an animal's survival: pain and pleasure, fear, anger, sexual feelings, and even docility and affection. As with the rhinencephalon, the sense of smell is a powerful factor. Nerves from the olfactory bulb, by which all odor is perceived, track directly into the limbic system at several points and are then connected through it to other parts of the brain; hence the ability of pheromones, and perhaps of other odors as well, to influence behavior in quite complex ways without necessarily reaching our conscious awareness.
Also feeding into the limbic system are the thalamus and hypothalamus, as well as the amygdala, a small, almond-shaped complex of nerve cells that receive input from both the olfactory system and the cerebral cortex.
These connections are illustrated in an unusual way in the context of epilepsy. Perhaps because the amygdala is located near a common site of origin of epileptic seizures—that is, in the temporal lobe of the cerebral hemispheres—epileptics sometimes experience unidentifiable or unpleasant odors or changes of mood as part of the aura preceding a seizure. The limbic system is not thought to be involved in the causes of epilepsy, but it is indirectly stimulated by the electric discharge in the brain that sets off a seizure and gives evidence of the stimulation in its own characteristic ways.
The hippocampus is another major structure of the limbic system. Named for its fanciful resemblance to the shape of a sea horse, the hippocampus is located at the base of the temporal lobe near several sets of association fibers. These are bundles of nerve fibers that connect one region of the cerebral cortex with another, so that the hippocampus, as well as other parts of the limbic system, exchanges signals with the entire cerebral cortex.
The hippocampus has been shown to be important for the consolidation of recently acquired information. In contrast, long-term memory is thought to be stored throughout the cerebral cortex. The means by which short-term memory is converted into long-term memory has posed a particularly challenging riddle that only now is beginning to yield to investigation; see Chapter 8.
The Central Nervous System
Although we now know that most brain functions rely on many different regions across the entire brain working in conjunction, it is still true that each lobe carries out the bulk of certain functions. In humans, the lobes of the brain are divided by a number of bumps and grooves. These are known as gyri bumps and sulci groves or fissures. The folding of the brain, and the resulting gyri and sulci, increases its surface area and enables more cerebral cortex matter to fit inside the skull. This is why in frontotemporal dementia , personality changes are often the first signs of the disease.
We include products we think are useful for our readers. If you buy through links on this page, we may earn a small commission. It plays a role in just about every major body system. The cerebrum is the largest part of the brain. The two hemispheres are separated by a groove called the interhemispheric fissure.
The Lobes of the Brain and Their Functions
The human brain is the command center for the human nervous system. It receives signals from the body's sensory organs and outputs information to the muscles. The human brain has the same basic structure as other mammal brains but is larger in relation to body size than any other brains.
It also integrates sensory impulses and information to form perceptions, thoughts, and memories. The brain gives us self-awareness and the ability to speak and move in the world. Its four major regions make this possible: The cerebrum , with its cerebral cortex, gives us conscious control of our actions.
Мир опять замер. Три… три… три… 238 минус 235. Разница равна трем. Он медленно потянул к себе микрофон. В то же самое мгновение Сьюзан опять бросила взгляд на руку Танкадо, на этот раз посмотрев не на кольцо… не на гравировку на золоте, а на… его пальцы. Три пальца. Дело было вовсе не и кольце, a в человеческой плоти.
34-62-10, - ответили на другом конце провода. Ролдан нахмурился. Голос показался ему отдаленно знакомым. Он попытался определить акцент - может быть, Бургос.
Три строки по пять, семь и снова пять слогов. Во всех храмах Киото… - Довольно! - сказал Джабба. - Если ключ - простое число, то что с. Варианты бесконечны.
Я скорее предпочту умереть, чем жить в тени позора.