Peripheral nervous system cell types

There is a second type of cholinesterase called butyrylcholinesterase, pseudocholinesterase, or cholinesterase. This enzyme is present in some nonneural cells in the central and peripheral nervous systems as well as in plasma and serum, the liver, and other organs. Its physiologic function is not known, but is hypothesized to be the hydrolysis of esters ingested from plants (Lefkowitz et al. 1996). Plasma cholinesterases are also inhibited by organophosphate compounds through irreversible binding this binding can act as a detoxification mechanism as it affords some protection to acetylcholinesterase in the nervous system (Parkinson 1996 Taylor 1996). 

Furthermore, any particular type of site belonging to any one of these categories may exist in a number of different cellular or tissue locations. For example, acetylcholinesterase is located in a number of different mammalian tissues (e.g., brain, peripheral nervous system, and red blood cells), and all of these may be inhibited by... 

Type XXVIII collagen belongs to the class of VWA domain-containing proteins. The primary structure is similar to type VI collagen. It is mainly a component of the basement membranes around Schwann cells in the peripheral nervous system. ... 

The nervous system consists of two main units the central nervous system (CNS), which includes the brain and the spinal cord and the peripheral nervous system (PNS), which includes the body s system of nerves that control the muscles (motor function), the senses (the sensory nerves), and which are involved in other critical control functions. The individual units of the nervous system are the nerve cells, called neurons. Nenrons are a nniqne type of cell becanse they have the capacity to transmit electrical messages aronnd the body. Messages pass from one nenron to the next in a strnctnre called a synapse. Electric impnlses moving along a branch of the nenron called the axon reach the synapse (a space between nenrons) and canse the release of certain chemicals called neurotransmitters, one of which, acetylcholine, we described earlier in the chapter. These chemicals migrate to a nnit of the next nenron called the dendrites, where their presence canses the bnild-np of an electrical impnlse in the second nenron. 

The fats also have a plastic function as they are included in cell membranes and other cell structures. The central and peripheral nervous systems are rich in lipids. PNFA are included in cell membranes, with their most significant function being the synthesis of cell hormones — prostaglandins. The properties of cell membranes as well as their interaction with external factors depend on the relation of PNFA concentration in cell components. In humans, prostaglandins are created not only in tissues but also in thrombocytes (thromboxanes) and in leucocytes (leukotrienes). The biological action of thrombocytes is extremely variant and depends on PNFA type which are the basis for fatty acid creation. 

The nervous system is divided into two parts the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord. The PNS consists of all afferent (sensory) neurons, which carry nerve impulses into the CNS from sensory end organs in peripheral tissues, and all efferent (motor) neurons, which carry nerve impulses from the CNS to effector cells in peripheral tissues. The peripheral efferent system is further divided into the somatic nervous system and the autonomic nervous system. The effector cells innervated by the somatic nervous system are skeletal muscle cells. The autonomic nervous system innervates three types of effector cells (1) smooth muscle, (2) cardiac muscle, and (3) exocrine glands. While the somatic nervous system can function on a reflex basis, voluntary control of skeletal muscle is of primary importance. In contrast, in the autonomic nervous system voluntary control can be exerted, but reflex control is paramount. 

Proteins or protein complexes of the cell surface involved in cell excitation and the resultant cell-cell communication are grouped here as excitability proteins. They include ion channels, neurotransmitter receptors which influence the excitability of cells, and ion pumps that transport ions across cell membranes to establish ionic concentration gradients that make excitation of cells possible. Such proteins are found in various combinations on membranes of neurons of the central and peripheral nervous system, and on muscle cells that contract in response to neuronal excitation. They are also found on other cell types which specialize in functions such as secretion. They play vital roles in the specialized functions of these cells. 

The central effects are dependent on a first type of cannabinoid receptor (CBl), which is present in the brain. Furthermore, Munro et al. [Nature (1993) 365, 61-65] have cloned a second cannabinoid receptor coupled to protein G, called CB2, which is present only in the peripheral nervous system and more particularly on the cells of immune origin. The presence of CB2 cannabinoid receptors on the lymphoid cells may... 

Serotonin is unsurpassed among monoamine neurotransmitters in the number of receptor subtypes reported to-date. Fourteen subtypes of seven major serotonin receptor classes have been identified in the central nervous system, the peripheral nervous system, myeloid/immune cell types, and smooth musculature of mammals [1]. While discreet, endogenous release of serotonin is able to manifest a variety of responses and behaviours, exogenous administration of serotonin (and nonselective mimetics) suffers from indiscriminate actions at all populations of accessible receptors. Hence, the discovery of subtype-specific agonists and/or antagonists to the various serotonin receptors have been sought as specific therapeutic agents. 

The concept of synaptic transmission postulates the release and subsequent recognition of specific chemical substances by adjacent cellular elements. In the central and peripheral nervous systems, neurons appear to form communication networks where the specificity of information transfer resides in the specific neurotransmitters and the appropriate receptors. Although large number of compounds have been suggested to be neurotransmitters, there seem to be no more than one or two expressed in any one cell type. Specificity appears to lie in the genetic expression of the enzymes necessary for the biosynthesis of each of the substances. 

Humphries, M.J., Akiyama, S.K., Komoriya, A., Olden, K. and Yamada, K.M. (1988) Neurite extension of chicken peripheral nervous system neurons on fibronectin relative importance of specific adhesion sites in the central cellbinding domain and the alternatively spliced type 111 connecting segment. J. Cell Biol. 106 1989-1297. 

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