Brain - Wikipedia. This article is about the brains of all types of animals, including humans. For information specific to the human brain, see Human brain. For other uses, see Brain (disambiguation). The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. The brain is located in the head, usually close to the sensory organs for senses such as vision. The brain is the most complex organ in a vertebrate's body. In a human, the cerebral cortex contains approximately 1. These neurons communicate with one another by means of long protoplasmic fibers called axons, which carry trains of signal pulses called action potentials to distant parts of the brain or body targeting specific recipient cells. Physiologically, the function of the brain is to exert centralized control over the other organs of the body. The brain acts on the rest of the body both by generating patterns of muscle activity and by driving the secretion of chemicals called hormones. This centralized control allows rapid and coordinated responses to changes in the environment. Some basic types of responsiveness such as reflexes can be mediated by the spinal cord or peripheral ganglia, but sophisticated purposeful control of behavior based on complex sensory input requires the information integrating capabilities of a centralized brain. The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. The brain is located in the head, usually close to the sensory organs for senses such as vision. Sleep Innovations Taylor 12-inch Gel Swirl Memory Foam Mattress, Queen. There’s no easier way to improve your photography than devouring all the free photography books available on the Internet. Along with watching free YouTube tutorials, you can improve your photography and learn how to run a. Now that the dust has settled and we have returned from the Dix Mille Tours, it is time to round up the highlights from this week's Paris Motor Show. Hyundai grabbed the limelight with this very wild RN30 Concept. What’s a Vortec engine? In 1996, GM introduced the 5.0L and 5.7L Vortec engines were that included several key enhancements: hydraulic roller camshaft, new higher flow Vortec cylinder heads, central port fuel injection (CPFI. Print, Copy, Fax, Scan; Tray 1: Letter; Legal; Executive; Oficio (8.5 x 13 in); A4; A5; A6; B5 (JIS); Oficio (216 x 340 mm); 16K (195 x 270 mm); 16K (184 x 260 mm); 16K (197 x 273 mm); Japanese Postcard; Double Japan Postcard. ![]() The operations of individual brain cells are now understood in considerable detail but the way they cooperate in ensembles of millions is yet to be solved. It deals with the human brain insofar as it shares the properties of other brains. The ways in which the human brain differs from other brains are covered in the human brain article. Several topics that might be covered here are instead covered there because much more can be said about them in a human context. ![]() The most important is brain disease and the effects of brain damage, that are covered in the human brain article. Anatomy. Cross section of the olfactory bulb of a rat, stained in two different ways at the same time: one stain shows neuron cell bodies, the other shows receptors for the neurotransmitter. GABA. The shape and size of the brain varies greatly between species, and identifying common features is often difficult. Brain tissue in its natural state is too soft to work with, but it can be hardened by immersion in alcohol or other fixatives, and then sliced apart for examination of the interior. Visually, the interior of the brain consists of areas of so- called grey matter, with a dark color, separated by areas of white matter, with a lighter color. Further information can be gained by staining slices of brain tissue with a variety of chemicals that bring out areas where specific types of molecules are present in high concentrations. It is also possible to examine the microstructure of brain tissue using a microscope, and to trace the pattern of connections from one brain area to another. When a pulse of electricity reaches a junction called a synapse, it causes a neurotransmitter chemical to be released, which binds to receptors on other cells and thereby alters their electrical activity. The brains of all species are composed primarily of two broad classes of cells: neurons and glial cells. Glial cells (also known as glia or neuroglia) come in several types, and perform a number of critical functions, including structural support, metabolic support, insulation, and guidance of development. Neurons, however, are usually considered the most important cells in the brain. The length of an axon can be extraordinary: for example, if a pyramidal cell, (an excitatory neuron) of the cerebral cortex were magnified so that its cell body became the size of a human body, its axon, equally magnified, would become a cable a few centimeters in diameter, extending more than a kilometer. Some neurons emit action potentials constantly, at rates of 1. A single axon may make as many as several thousand synaptic connections with other cells. The neurotransmitter binds to receptor molecules in the membrane of the target cell. The human brain has been estimated to contain approximately 1. It is widely believed that activity- dependent modification of synapses is the brain's primary mechanism for learning and memory. A myelinated axon is wrapped in a fatty insulating sheath of myelin, which serves to greatly increase the speed of signal propagation. Myelin is white, making parts of the brain filled exclusively with nerve fibers appear as light- colored white matter, in contrast to the darker- colored grey matter that marks areas with high densities of neuron cell bodies. The brain is small and simple in some species, such as nematode worms; in other species, including vertebrates, it is the most complex organ in the body. It has not been definitively established whether the existence of these brainless species indicates that the earliest bilaterians lacked a brain, or whether their ancestors evolved in a way that led to the disappearance of a previously existing brain structure. The diversity of invertebrate body plans is matched by an equal diversity in brain structures. Arthropods have a central brain, the supraesophageal ganglion, with three divisions and large optical lobes behind each eye for visual processing. The first biological clock genes, for example, were identified by examining Drosophila mutants that showed disrupted daily activity cycles. One of the advantages of working with this worm is that the body plan is very stereotyped: the nervous system of the hermaphrodite contains exactly 3. Each species has an equally long evolutionary history, but the brains of modern hagfishes, lampreys, sharks, amphibians, reptiles, and mammals show a gradient of size and complexity that roughly follows the evolutionary sequence. All of these brains contain the same set of basic anatomical components, but many are rudimentary in the hagfish, whereas in mammals the foremost part (the telencephalon) is greatly elaborated and expanded. The relationship between brain size, body size and other variables has been studied across a wide range of vertebrate species. As a rule, brain size increases with body size, but not in a simple linear proportion. In general, smaller animals tend to have larger brains, measured as a fraction of body size. For mammals, the relationship between brain volume and body mass essentially follows a power law with an exponent of about 0. For example, primates have brains 5 to 1. Predators tend to have larger brains than their prey, relative to body size. In its earliest form, the brain appears as three swellings at the front end of the neural tube; these swellings eventually become the forebrain, midbrain, and hindbrain (the prosencephalon, mesencephalon, and rhombencephalon, respectively). At the earliest stages of brain development, the three areas are roughly equal in size. In many classes of vertebrates, such as fish and amphibians, the three parts remain similar in size in the adult, but in mammals the forebrain becomes much larger than the other parts, and the midbrain becomes very small. Vertebrate brains are surrounded by a system of connective tissuemembranes called meninges that separate the skull from the brain. Blood vessels enter the central nervous system through holes in the meningeal layers. The cells in the blood vessel walls are joined tightly to one another, forming the blood. Each of these areas has a complex internal structure. Some parts, such as the cerebral cortex and the cerebellar cortex, consist of layers that are folded or convoluted to fit within the available space. Other parts, such as the thalamus and hypothalamus, consist of clusters of many small nuclei. Thousands of distinguishable areas can be identified within the vertebrate brain based on fine distinctions of neural structure, chemistry, and connectivity. The brain of a shark shows the basic components in a straightforward way, but in teleost fishes (the great majority of existing fish species), the forebrain has become . In birds, there are also major changes in forebrain structure. The same parts are present, but they differ greatly in size and shape. Here is a list of some of the most important vertebrate brain components, along with a brief description of their functions as currently understood: The medulla, along with the spinal cord, contains many small nuclei involved in a wide variety of sensory and involuntary motor functions such as vomiting, heart rate and digestive processes. Among other things, it contains nuclei that control often voluntary but simple acts such as sleep, respiration, swallowing, bladder function, equilibrium, eye movement, facial expressions, and posture. It is composed of numerous small nuclei, each with distinct connections and neurochemistry. The hypothalamus is engaged in additional involuntary or partially voluntary acts such as sleep and wake cycles, eating and drinking, and the release of some hormones. The subthalamic area (zona incerta) seems to contain action- generating systems for several types of . Removal of the cerebellum does not prevent an animal from doing anything in particular, but it makes actions hesitant and clumsy. This precision is not built- in, but learned by trial and error. The muscle coordination learned while riding a bicycle is an example of a type of neural plasticity that may take place largely within the cerebellum. In mammals it is usually referred to as the superior colliculus, and its best- studied function is to direct eye movements. It also directs reaching movements and other object- directed actions. It receives strong visual inputs, but also inputs from other senses that are useful in directing actions, such as auditory input in owls and input from the thermosensitive pit organs in snakes. In some primitive fishes, such as lampreys, this region is the largest part of the brain. Multiple functions involve the pallium, including smell and spatial memory.
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