A-beta fibers

Another important factor in peripheral sen tization is through A-beta afferent fibers. Normally, nonpainful sensations are detected by specialized corpuscle structures and free nerve endings that transduce mechanical stimuli via large myelinated A-beta afferent fibers. However, injured A-beta fibers in damaged tissue paradoxically begin to express SP and CGRP. These abnormal receptors have a low threshold and they release SP in the dorsal horn and cause hyperexcitabihty. 

Certain aspects of neural anatomy and ultrastructure favor LA blockade of noxious impulses [2-5]. To reduce conduction safely in sensory and motor fibers, at least three myelin inter-nodes must be blocked. This rule of three favors blockade of thin unmyelinated fibers and also A-delta fibers which have small inter-nodal distances. Larger A-alpha and A-beta fibers are more resistant to blockade because of their size and large distance between nodes of Ranvier (Figure 64.3). Unmyelinated C fibers are easiest to block since LAs can impede Na+ conductance and action potential propagation at any single site along the course of the nerve fiber. 

Figure 64 J. The rule of three suggests that a minimum of three internodes must be blocked by local anesthetic to reduce salutatory conduction safety to the point that an action potential will no longer be propagated along the nerve fibers. Because of the large internodal distance of thick myelinated A-alpha and A-beta fibers, a relatively large amount of surface must be bathed in local anesthetic solution in order to ensure conduction blockade.

St. Louis Sample Collection. Ambient aerosols were collected in St. Louis in 6-h Intervals with a TWOMASS automated sequential tape sampler. This sampler fractionated the aerosol into two size classes, fine particles having aerodynamic diameters less than 3pm, and coarse particles with diameters greater than 3pm. It was equipped with a beta-attenuation mass monitor to determine fine-particle mass (11). Only the fine particle filter was examined in this study. Pallflex E70 glass-fiber filter tape with a detachable cellulose backing (Pallflex Inc. Putnam, CT) was used with this sampler. An aerosol sampler operating from the same inlet manifold as the... 

Vitamins C and A, beta carotene, riboflavin, folate, various minerals, and fiber these are needed to prevent deficiency disorders and may protect against cancer... 

Figure 1-36. Portions of two polypeptide chains in the beta configuration. The cylinder represents a hair fiber, and the axis identifies the orientation of the proteins in the fiber. See corresponding molecular models in Figure 1-37.

D-Glucose can, at least theoretically, form a total of 8 homopolymers, ie. the alpha- and beta-1,2-, 1,3-, 1,4- and 1,6-glucans. Only one of these, the beta 1,4-glucan (cellulose), is of primary importance as a textile fiber. It is of interest to compare the structural properties of cellulose with those of other glucans in order to obtain greater insight to its unique qualities, as well as to better understand the overall relationship of polysier structure to polymer properties. 

Koo H.M., Song S.H., Pyun Y.R., and Btim Y.S. 1998. Evidence that a beta-l,4-endoglucanase secreted by Acetobacter xylinum plays an essential role for the formation of cellulose fiber. Biosci Biotechnol Biochem 62 2257-2259. 

In the peripheral and central nervous system, there are several inhibitory mechanisms such as A-beta neiu-ons and enkephalins. Repetitive stimulation of nerve fibers called A-beta mechanoreceptives, for example, initially excites and then inhibits dorsal horn spinothalamic tract (STT) neurons via interposed interneurons releasing y-aminobutyric acid (GABA) or enkephalin, which decreases the stimulation of C fibers. 

Lidocaine s differential blockade has been examined with peripheral and neuraxial administration [ 10-11 ]. Peripheral nerve libers seem to respond differently to lidocaine than dorsal nerve roots. Epidural lidocaine seems to block small unmyelinated C fibers (supplying temperature sensation) more effectively than 281 larger myelinated A fibers (A-beta supplying touch. 

Wojcik S, Engel WK, Yan R et al. (2007) NOGO is increased and binds to BACEl in sporadic inclusion-body myositis and in A beta PP-overexpressing cultured human musde fibers. Acta Neuropathol 114, 517-526. 

Alzheimer s Disease. Figure 1 A(3 monomers can self-associate to form dimers, trimers and higher oligomers. Globular structures of synthetic A(342 are known as A(3-derived diffusible ligands (ADDLs) (3-12-mers of A(3). These structures are similar to the smallest protofibrils and represent the earliest macromolecular assembly of synthetic A(3. The characteristic amyloid fiber exhibits a high beta-sheet content and is derived in vitro by a nucleation-dependent self-association and an associated conformational transition from random to beta-sheet conformation of the A(3 molecule. Intermediate protofibrils in turn self-associate to form mature fibers. 

Baldo B. A., Daniel R. A., Berridge C. W., Kelley A. E. (2003). Overlapping distributions of orexin/hypocretin- and dopamine-beta-hydroxylase immunoreactive fibers in rat brain regions mediating arousal, motivation, and stress. J. Comp. Neurol. 464, 220-37. 

Figure 17.5. The precursor molecule APP and the three different proteases a, (i, y secretase that are involved in the processing of APPto fS-amyloid peptide. The aberrant processing of the amyloid precursor protein (APP) leads to accumulation of beta-amyloid fragments, first as protofibrils and then as fibers that aggregate in the senile plaque structures. (See color insert.)...

Kirschner, D. A., Abraham, C., and Selkoe, D. J. (1986). X-ray diffraction from intraneuronal paired helical filaments and extraneuronal amyloid fibers in Alzheimer disease indicates cross-beta conformation. Proc. Natl. Acad. Sci. USA 83, 503-507. 

Kishimoto, A., Hasegawa, K., Suzuki, H., Taguchi, H., Namba, K., and Yoshida, M. (2004). Beta-helix is a likely core structure of yeast prion Sup35 amyloid fibers. Biochem. Biophys. Res. Commun. 315, 739-745. 

Papanikolopoulou, K., Schoehn, G., Forge, V., Forsyth, V. T., Riekel, C., Hernandez, J.-F., Ruigrok, R. W. H., and Mitraki, A. (2005). Amyloid fibril formation from sequences of a natural beta-structured fibrous protein, the adenovirus fiber. / Biol. Chem. 280, 2481-2490. 

Dual-layer polyethersulfone (PES)/BTDA-TD1/MD1 co-polyimide (P84) hollow fiber membranes with a submicron PES-zeolite beta mixed matrix dense-selective layer for... 

Figure 6b shows a side view (observed from the Z>-axis). The conformations are different from one another. The alpha form consists of G and —G, while the beta form has an all-trans structure. The fiber identity lengths are 10.9 A and 11.9 A for alpha and beta forms, respectively. 

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