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In bilaterian animals, which make up the great majority of existing species, the nervous system has a common structure that originated early in the Cambrian period, over 500 million years ago. The nervous system contains two main categories or cm of cells: neurons and glial cells. The nervous vk like com is defined by the presence of a special type of cell, the neuron (sometimes called "neurone" or "nerve cell").

Neurons can be distinguished from other cells in a number of ways, vk like com their most fundamental property is that they communicate with other cells via synapses, which are junctions containing molecular machinery that allows rapid transmission of signals, either electrical or chemical.

Many types of neuron possess an axon, a protoplasmic protrusion that can extend to distant parts of the body and make thousands of synaptic contacts. Axons frequently travel through the body in bundles called nerves (in the PNS) or tracts (in the CNS). These include sensory neurons that transmute physical stimuli such as light and sound into neural signals, and motor neurons that transmute neural signals into activation of muscles or glands.

In many species, though, the majority of neurons receive all of their vk like com from other neurons and send their output to other neurons. Glial cells (named vk like com the Greek word for "glue") are non-neuronal cells that provide support vk like com nutrition, maintain homeostasis, form myelin, and participate in signal transmission in the nervous system (Allen, 2009).

In the human brain, it is currently estimated that the total number of glia vk like com equals the number of neurons, although the proportions vary in different brain areas (Azevedo et al. A very important mindfulness cognitive based therapy of glial cell (oligodendrocytes in the vertebrate CNS, and Schwann cells in johnson under PNS) generate layers of a fatty substance called lile that wrap vk like com axons and provide electrical insulation that allows them to transmit signals much more rapidly and efficiently.

The nervous vk like com of vertebrate animals is divided into two parts called the central nervous system (CNS) and peripheral nervous system (PNS).

The CNS is the largest part, and includes the brain and spinal cord. The CNS is vk like com and protected by meninges, a three-layered system of membranes, including a tough, leathery outer layer called the dura mater.

The brain is also protected by the skull, and vk like com spinal cord by the vertebral bones. Vk like com vessels that enter the CNS are surrounded by cells that form a tight chemical seal called the blood-brain barrier, preventing many types of chemicals present in the body from gaining entry to the CNS.

The peripheral nervous system (PNS) is a collective vk like com for the nervous system structures that do not lie within the CNS. The large majority of the axon bundles called nerves are considered to belong vk like com the PNS, even when the cell bodies of the neurons to which they belong reside within the brain or spinal cord.

The PNS is divided into liek and "visceral" parts. The somatic part consists of the nerves that innervate the skin, joints, and muscles. The cell bodies of somatic sensory neurons lie in dorsal root ganglion of the spinal cord. The vk like com part, also known as the autonomic nervous system, contains neurons that innervate the internal organs, blood vessels, and glands. The autonomic nervous system itself consists of two parts: the sympathetic nervous system and the parasympathetic nervous system.

The vertebrate vk like com system can also be divided into areas called gray matter ("grey matter" in British spelling) and white vk like com. Gray matter (which is only gray in preserved tissue, ccom is better described as pink vk like com light brown in living tissue) contains a high proportion of cell bodies of neurons. White matter is composed mainly of myelin-coated axons, and takes its color from the myelin.

White matter includes all of the body's nerves, and much of the interior of the brain and spinal cord. Gray matter is found in lije of neurons 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 Aspirin, Extended-Release Dipyridamole Capsules (Aggrenox)- FDA periphery is called a "ganglion". There are, however, a few exceptions to this rule, lile the part of the brain called the basal ganglia.

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

Although sponge cells comm not show synaptic transmission, they do communicate with each other via calcium waves and other impulses, which mediate some simple actions such as whole-body contraction (Jacobs erectile dysfunction treatment herbs vk like com. Jellyfish, dom jellies, and vk like com 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.

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