The Anatomy of Human Brain
The brain is the central nervous system in all vertebrates and invertebrates. Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges have no nervous system. In vertebrates, protected the brain in the head, through the skull and near the primary sensory apparatus of vision, hearing, balance, smell and taste.
Brains can be extremely complex. The cerebral cortex of the brain contains about 15 to 33 billion neurons, perhaps more, by sex and age, in relation to a maximum of 10,000 synaptic connections each. Each cubic millimeter of cortex contains about a billion synapses. These neurons are connected by long fibers called axons protoplasmic result, the pulse train signals called action potentials to other parts of the brain or body and target-specific receptor cells.
The brain controls the other systems of the body, either by activating muscles or causing the release of chemicals such as hormones and neurotransmitters. This central control allows a rapid and coordinated response to changes in the environment. Some basic types of reaction are possible without a brain, also can be single-celled organisms that are capable of information from the environment and act in response to , extract the sponges, which have no central nervous system are able to coordinate the contractions of the body. and locomotion. In vertebrates produce contains the spinal cord neural circuits can answer reflexes and simple motor patterns such as swimming or running. needs to integrate it but a sophisticated control of behavior on the basis of complex sensory information to obtain information from a central brain.
Despite rapid scientific advances, both about how the brain works remains a mystery. The activity of individual neurons and synapses are covered in detail, but the way they work together in groups of thousands or millions of was very difficult to decipher. Observation methods such as EEG and functional imaging of the brain tell us that brain operations are very well organized, while the recording unit can regulate the activity of individual nerve cells, but how the individual cells result in complex operations is unknown.
The brain is the most complex biological structure is known and the comparison of brains of different species on the basis of the phenomenon is often difficult. However, there are common principles of brain architecture that apply to a wide range of species. It is mainly demonstrated by three approaches. The evolutionary approach compares brain structures of different species, and the principle characteristics that have fallen in all sectors, the past somehow, probably in the common ancestors were. development approach as it examines how changes in the brain during the progression of embryonic stages to adults. The genetic approach to analysis of gene expression in different parts of the brain by a variety of species. Each approach complements and informs the other two.
Bilateria
A rod-shaped body contains a digestive system that extends from the mouth at one end of the anus at the other end. With the digestive system is a nerve cord with a brain at the end, near the mouth.
nervous system of bilaterian animals, in the form of a nerve cord with segmental extensions and a "brain" of the front
With the exception of some primitive forms such as sponges and jellyfish, all animals Bilateria, ie animals with bilaterally symmetrical body shape (ie left and right are mirror images of one).
All Bilateria think from a common ancestor, the descendants appeared in the early Cambrian, 550-600000000 years. This ancestor was in the form of a simple tube worm with a segmented body, and an abstract level, like a worm, which is reflected in the body plans and nervous system of all modern bilateral animals continues including humans. The basic form is a tube with a bilateral abdominal cavity of the mouth to the anus and spinal cord with an extension (a "node") for each body segment, with a large ganglion in front, This is called the "brains".
Invertebrates
A fly rests on a reflective surface. A large eyes, red faces at the camera. The body appears transparent, and more black pigment at the tip of their abdomen.
Drosophila
For invertebrates (insects, mollusks, worms, etc.) components of the brain are so different vertebrate model is difficult to make meaningful comparisons, except on the basis of genetics. Two groups of invertebrates are remarkably complex brains: the arthropods (insects, crabs, spiders, etc.) and cephalopods (octopus, squid and other molluscs) The brain of arthropods and cephalopods from two nerve cords, parallel extension . through the body of the animal. Arthropods have a central brain with three divisions and large optical lobes behind each eye for visual processing. Cephalopods have the largest brains of all invertebrates. The brain of the octopus is well developed, comparable to the complexity of the vertebrate brain.
There are invertebrate animals, whose brain has been studied intensively. The marine snail Aplysia was high, the neurophysiologist Eric Kandel won the Nobel Prize because of the simplicity and accessibility of its nervous system as a model for studying the cellular basis of learning and memory, and hundreds of experiments selected . Studies of the brains of invertebrates that are the fruit fly and the tiny nematode worm Caenorhabditis elegans (C. elegans).
Because of the variety of techniques available for studying the genetics of fruit flies have a natural subject for studying the role of genes in brain development. It should be noted that many aspects of Drosophila neurogenetics should be relevant to humans. The first clock genes were, for example, by examining mutants of Drosophila, cycles of daily activity showed changes identified. In search of vertebrate genomes have the same set of genes found to have similar functions in the biological clock of mice and were almost certainly present in the human biological clock as well.
As in Drosophila, the nematode C. elegans studied mainly because of its importance in genetics. In late 1970, Sydney Brenner to study, which was chosen as a model system, such that genes control the development. One advantage of working with this worm is that the body plan is very stereotypical: the nervous system metamorphosis hermaphrodites contains exactly 302 neurons, always in the same places, same synaptic connections to each worm in a heroic. Project Team burner to cut thousands of ultra-thin sections and each section was photographed with an electron microscope, then adjusted visually to pull fibers from one section to another for all neurons and synapses throughout the body . Nothing approach this level of detail is available to any other organization, and information for a variety of studies that would not be possible without them were used.
Vertebrates
A T-shaped object is formed by the cable at the bottom, which is introduced into a mass of less central. This is surmounted by a larger central mass with an arm that extends on both sides.
The brain of a shark
The vertebrate brain is made of very soft, with a texture that was compared with Jell-O. Living brain tissue is pink inside and outside the mostly white, with subtle color variations. the vertebrate brain are surrounded by a membrane of connective tissue called meninges, which separate the skull of the brain. The cover is made of three layers (from outside to inside) of the dura mater ("tough mother"), arachnoid ("spider mother) and Pia (" soft mother "). The arachnoid and pia are physically connected and thus often in a single layer, the pia-arachnoid considered. Below the arachnoid is the subarachnoid space with cerebrospinal fluid (CSF), circulating in the narrow space between cells and cavities called ventricles, and is used to care, provide support and protection of brain tissue. the blood vessels in the central nervous system through the perivascular space above the pia mater. The cells in the vessel walls are interlocked to form the blood-brain barrier protects the brain against toxins that may enter the bloodstream.
The first vertebrates appeared over 500 million years (Ma), during the Cambrian, and thus something like the modern form have hagfish. The shark appeared about 450 million years, about 400 million years ago amphibians, reptiles, mammals and about 350 million years to 200 million years. No modern species must be a "primitive" describes other because everyone has a story of the evolution of the same length, but the brain of modern lampreys show hagfish, sharks, amphibians, reptiles and mammals a gradient size and complexity, which roughly follows the evolution sequence. All these brains contain the same basic set of anatomical components, but many are rudimentary in hagfish, while in mammals the major developed and expanded.
All vertebrate brains have a common form of basic, most easily by examining how they can grow to estimate. The first appearance of the nervous system is like a thin band of tissue that covers the back of the embryo. This thick strips and then folded to form a hollow tube. The front end of the tube is the brain. In its original form, the brain appears as three bumps that become the forebrain, midbrain and hindbrain at last. In many classes of vertebrates, these three parties are similar in size adults, but in the forebrain in mammals is far greater than elsewhere, and the midbrain very low.
been the relationship between brain size, body size and other variables examined in a variety of vertebrate species. brain size increases in body size, but not proportionately. Average of all mammalian orders, follows a power law with an exponent of about 0.75. This formula applies to the average of the mammalian brain, but each turns away from his family, which reflects the sophistication of behavior. For example, primates have brains of 5 to 10 times higher than the formula predicts. Predators tend to have larger brains. When increases in brain size in mammals, not all parties to increase unabated. The biggest shows of the brain case, [the greater part of the bark.
