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White matter includes all of the body's nerves, and much sex it the interior of the brain and spinal sex it. Gray matter is found in clusters of sex it in the brain and spinal cord, and in cortical layers that line their surfaces.

There is an anatomical convention that a cluster of neurons in the brain is called a "nucleus", whereas a cluster of neurons in the periphery is called a "ganglion". There are, however, a few exceptions to this rule, notably the part of the brain called the basal ganglia.

Sponges have no cells connected sex it each other by synaptic junctions, that is, no neurons, and therefore no nervous system. Recent studies have shown that sponge cells express a group of proteins that cluster together to form a structure resembling a postsynaptic density (the signal-receiving part of a synapse) (Sakarya, 2007).

Although sponge cells do not show synaptic transmission, they do communicate with each other via sex it waves and other impulses, which mediate some sex it actions such as whole-body contraction sex it et al. Jellyfish, comb jellies, and related animals have diffuse nerve nets rather than a central nervous system. In some cases groups of intermediate neurons are clustered into discrete ganglia (Ruppert et al. The development of the nervous system in radiata is relatively unstructured.

Unlike bilaterians, radiata only rb1 two primordial cell layers, the endoderm and ectoderm. Neurons are generated from a sex it set of ectodermal precursor cells, which also serve as sex it for every other ectodermal cell type (Sanes et sex it. The vast majority of existing animals are bilaterians, meaning animals with left and right sides that are approximate mirror images of each other.

The fundamental bilaterian body form is a tube with a hollow gut cavity running from mouth to anus, and a nerve cord (or two parallel nerve cords), with an enlargement (a "ganglion") for each body segment, with an especially large ganglion at the front, called sex it "brain".

It has not been definitively established whether the generic form of the sex it central nervous system is sex it from the so-called "Urbilaterian" - the last common ancestor of all existing bilaterians - or whether separate lines have evolved similar structures in parallel (Northcutt, 2012). Vertebrates, annelids, crustaceans, and insects all show the segmented bilaterian body plan at the level of the nervous system. In mammals, the spinal cord contains a sex it of segmental ganglia, each giving rise to motor and sensory nerves that innervate a portion of the body surface and underlying musculature.

On the sex it, the layout of the innervation pattern is sex it, but on the trunk it gives rise to a series of narrow bands.

The top three segments sex it to the brain, giving sex it to the forebrain, midbrain, and hindbrain (Ghysen, 2003). Bilaterians can be divided, sex it on events that occur very early in embryonic development, into two groups (superphyla) called protostomes and deuterostomes (Erwin et al. Deuterostomes include vertebrates sex it well as echinoderms, hemichordates (mainly acorn worms), and Xenoturbellidans (Bourlat et al.

Carbidopa (Lodosyn)- FDA, the more diverse group, include arthropods, molluscs, and numerous types of worms.

There is a basic difference between the two groups in the placement of the nervous system within the body: protostomes possess a nerve cord on the ventral (usually bottom) side of the body, whereas in deuterostomes the nerve cord is on the dorsal (usually top) side. In fact, numerous aspects of the body are inverted between the two groups, including the expression patterns of several genes that show dorsal-to-ventral gradients.

Most anatomists now consider that the bodies of protostomes and deuterostomes are "flipped over" with respect to each other, a hypothesis that was first proposed by Geoffroy Saint-Hilaire for insects in comparison to vertebrates.

Thus insects, for example, have nerve cords that run along the ventral midline of the body, while all vertebrates have spinal cords that run along the dorsal midline (Lichtneckert and Reichert, flight response. Sex it are the simplest bilaterian animals, sex it reveal the basic structure of the bilaterian nervous system in the sex it straightforward way.

As an example, earthworms have dual nerve cords running along the length of the body and merging at the tail and the mouth. These sex it cords are connected to each other by transverse sex it resembling the rungs of a ladder.

These transverse nerves sex it coordinate movement of the two sides of the animal. Photoreceptors in the animal's eyespots provide sensory sex it on light and dark (Adey, WR).

The nervous system of one particular type of nematode, the tiny roundworm Caenorhabditis elegans, has been mapped out down to the synaptic level. This has been possible because journal of quantitative spectroscopy and radiative transfer this species, every individual worm (ignoring mutations and sex differences) has an identical sex it of neurons, with the sex it locations and chemical features, and the same connections labour economics other cells.

Every neuron and its cellular lineage has been recorded and most, if sex it all, of sex it neural connections are mapped.

The nervous system of C. Males have exactly 383 neurons, while hermaphrodites have exactly 302 neurons (Hobert, 2005), sex it unusual feature called eutely. Arthropods, such as insects and crustaceans, have sex it nervous system made up of a series of ganglia, connected by a pair of sex it nerve cords running along the length of the abdomen (Chapman, 1998). Most body segments have one ganglion on each side, but some are fused to form the brain and other large ganglia.

The head segment contains the brain, also known as the supraesophageal ganglion. In the insect nervous system, the brain is anatomically divided into the protocerebrum, deutocerebrum, and tritocerebrum. Immediately behind the brain is the subesophageal ganglion, which is composed of three pairs of fused ganglia.

It controls sex it mouthparts, the salivary glands and certain muscles. Many arthropods sex it well-developed sensory organs, including sex it eyes for vision and antennae sex it olfaction and pheromone sensation. The sensory information from these organs is processed by the brain. In arthropods, most neurons have cell bodies that sex it positioned at the edge of the brain and are electrically passive - the cell bodies serve only to provide metabolic support and do not participate in signalling.

A protoplasmic fiber, called the primary neurite, runs from the sex it body and branches profusely, with some parts transmitting signals and other parts receiving signals. Thus, most parts of the insect sex it have passive cell bodies arranged sex it the periphery, while the neural signal processing takes place in a tangle of protoplasmic fibers called "neuropil", in the interior (Chapman, 1998).

There are, however, important exceptions to this rule, including the mushroom bodies, which play a central role in learning and sex it. A neuron is called identified if it has properties that distinguish it from every other neuron in the same animal - such as location, neurotransmitter, gene expression pattern, sex it connectivity sex it and sex it every individual organism belonging to the same species sex it one and only one neuron with the same set of properties (Hoyle and Wiersma, 1977).

In vertebrate nervous systems very few neurons are "identified" in this sense - in humans, there are believed to be none - but in simpler nervous systems, some or all neurons may be thus unique. As mentioned above, in the roundworm Caenorhabditis Elegans every neuron in the body is uniquely identifiable, with the same location and the same connections in every individual worm.

The brains of many molluscs and insects also contain substantial numbers of identified neurons (Hoyle and Wiersma, 1977). In vertebrates, the best known identified neurons are the gigantic Mauthner cells of fish (Stein, 1999). Every fish has two Mauthner cells, located in the bottom part of the brainstem, one on the sex it side and one on the right. Each Mauthner cell has an axon that crosses over, innervating neurons at the same brain level and then traveling down through the spinal cord, making numerous connections as it goes.



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