Nervous system sensory neuron

Complex feedback regulation of hormone secretion. Hormones of level III endocrine ti,s,sues are regulated by a complex system having both a neuroendocrine reflex component and a simple negative feedback component. Invariably, the former involves the extrahypothalamic central nervous system (sensory neurons), the hypothalamus (endocrine cell 1), and the anterior pituitary (endocrine cell 2), while the latter involves the anterior pituitary (endocrine cell 2) and a level III endocrine tissue (endocrine cell 3). Hormone 3 exerts negative feedback on endocrine cell 2 and hence on its own secretion. Hormone 3 may also feed back to endocrine cell I and to higher centers, although such ca.ses of feedback may be positive ones. 

Chitosan Mouse 4 d Plasmid 4.8 gg Peripheral nervous system, sensory neurons 65... 

The nervous system is conventionally divided into the central nervous system (CNS the brain and spinal cord) and the peripheral nervous system (PNS neuronal tissues outside the CNS). The motor (efferent) portion of the nervous system can be divided into two major subdivisions autonomic and somatic. The autonomic nervous system (ANS) is largely independent (autonomous) in that its activities are not under direct conscious control. It is concerned primarily with visceral functions such as cardiac output, blood flow to various organs, and digestion, which are necessary for life. The somatic subdivision is largely concerned with consciously controlled functions such as movement, respiration, and posture. Both systems have important afferent (sensory) inputs that provide information regarding the internal and external environments and modify motor output through reflex arcs of varying size and complexity. 

In the primitive nervous system, sensory cells evolved from general epithelial cells. Primitive nervous systems of modern echinoderms and lower deuterostomes are still composed of three cell types that include the primary sensory cells, the neurons that connect the sensory cells to distal targets, and a supporting cell that serves the special physiological needs of such a system (Lacalli, 2001). The basic structural plan of the retina is comparable to such a primitive nervous system. In the course of evolution, the photoreceptive system developed specialized photoreceptor cells (rods and cones), intra-retinal second-order neurons (bipolar cells), and tertiary output neurons (ganglion cells). This evolution perhaps took place in photopic conditions therefore early photoreceptor cells were more like cones. 

Only in the last few centuries has the link between the brain and behaviour become clear, and only at the end of the nineteenth century was it demonstrated that the nervous system was made up of billions of separate nerve cells or neurons. We now know that during evolution complex networks of such neurons have developed in order to effect certain behaviours. Whilst the neurons of the central, peripheral and autonomic nervous systems vary enormously in form and function, they can be classed into three broad groups sensory neurons which convey information into the central nervous system effector neurons which carry information out of the central nervous system to muscles and other effector organs and interneurons within the central nervous system which link the sensory and effector neurons and also have links with one another. 

CGRP has a wide distribution in the nervous system (19) and was the first peptide to be localized to motoneurons (124). It is also found in primary sensory neurons where it is colocalized with substance P (125). CGRP is derived from a precursor stmcturaHy related to the calcitonin precursor. The latter precursor produces two products, calcitonin itself and katacalcin, while the CGRP precursor produces one copy of CGRP (123). Like other peptides, CGRP is cleaved from its precursor by tryptic breakdown between double basic amino acid residues. 

CGRP is widely distributed throughout the peripheral and central nervous systems and is found ia sensory neurons and ia the autonomic and enteric nervous systems. In many iastances CGRP is co-localized with other neuroregulators, eg, ACh ia motor neurons, substance P, somatostatin, vasoactive intestinal polypeptide (VIP), and galanin ia sensory neurons. It is also present ia the CNS, with ACh ia the parabigeminal nucleus and with cholecystokinin (CCK) ia the dorsal parabrachial area. CGRP functions as a neuromodulator or co-transmitter. 

Many different types of sensory receptors are located throughout the body. These receptors monitor the status of the internal environment or that of the surroundings. Sensory receptors are sensitive to specific types of stimuli and measure the value of a physiological variable. For example, arterial baroreceptors measure blood pressure and chemoreceptors measure the oxygen and carbon dioxide content of the blood. The information detected by these sensors then travels by way of afferent neuronal pathways to the central nervous system (CNS). The CNS is the integrative portion of the nervous system and consists of the (1) brain and the (2) spinal cord. 

The afferent division carries sensory information toward the CNS and the efferent division carries motor information away from the CNS toward the effector tissues (muscles and glands). The efferent division is further divided into two components (1) the somatic nervous system, which consists of motor neurons that innervate skeletal muscle and (2) the autonomic nervous system that innervates cardiac muscle, smooth muscle, and glands. 

Figure 6.1 Types of neurons. Afferent neurons, which transmit impulses toward the CNS and efferent neurons, which transmit impulses away from the CNS, lie predominantly in the peripheral nervous system. Intemeurons, which process sensory input and coordinate motor responses, lie entirely within the central nervous system.

Histamine in the nervous system may participate in a variety of brain functions. Several of the suspected physiological roles for histamine are related to its ability to increase the neuronal excitability [1, 2,15]. For example, mutant mice lacking the H, receptor show defective locomotor and exploratory behaviors [57], Neuronal histamine may increase attention and/or arousal by many mechanisms, including by enhancing sensory input [58], All available evidence from several species shows that histaminergic neurons, when activated, increase wakefulness... 

Although histamine is not stored in neurons outside of the central nervous system, mast-cell-derived histamine can modify peripheral sensory nerve function. Both acute and chronic pain states can result from inflammation or peripheral nerve cell injury, and there is substantial evidence that mast cell histamine participates in these disorders. 

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