Muscle contraction representative

The above three discussed protein-based machines—Complex III of the electron transport chain, ATP synthase/Fj-ATPase, and the myosin II motor of muscle contraction—represent the three major classes of energy conversion that sustain Life. Therefore, the facility with which the consilient mechanisms explain their function indeed support the thesis that biology s vital force arises from the coupled hydrophobic and elastic consilient mechanisms. 

Certain proteins endow cells with unique capabilities for movement. Cell division, muscle contraction, and cell motility represent some of the ways in which cells execute motion. The contractile and motile proteins underlying these motions share a common property they are filamentous or polymerize to form filaments. Examples include actin and myosin, the filamentous proteins forming the contractile systems of cells, and tubulin, the major component of microtubules (the filaments involved in the mitotic spindle of cell division as well as in flagella and cilia). Another class of proteins involved in movement includes dynein and kinesin, so-called motor proteins that drive the movement of vesicles, granules, and organelles along microtubules serving as established cytoskeletal tracks. ... 

The major biochemical events occurring during one cycle of muscle contraction and relaxation can be represented in the five steps shown in Figure 49-6 ... 

Tension-type headache (TTH) is the most common primary headache disorder. It is often underrepresented in clinical practice, as many patients do not present for care.6 The term tension-type headache is used to describe all headache syndromes in which muscle contraction is the most significant factor in the pathogenesis of pain. The 1-year prevalence of TTH in the population ranges from 30% to 90%.6 It is more common in adult females. Environmental factors, as opposed to genetic predisposition, play a more central role in their development. Tension-type headaches can be further divided into episodic or chronic the mean frequency of attacks is 3 days per month in episodic disorders, and chronic TTH is defined as 15 or more attacks in a 1-month period.7 The estimated prevalence of chronic TTH is less than 5%.6 Some researchers believe that chronic TTHs represent a continuum of headache severity with migraine headache.8 When severe headaches are difficult to differentiate clinically, treatment should initially target TTH. 

Nicholls and Skidmore (65) demonstrated that dust collected from mills with a higher prevalence of byssinosis caused greater smooth muscle contractile activity than dust from mills with a lower prevalence. Recently, Russell e al. (66) used an isolated tissue bath to measure canine trachealis muscle contraction caused by cotton bract extracts (CBE). Morey et al. (67) showed that cotton bract represents 20-43% of the cotton dust total thus, the findings of Paton and Davenport using cotton dust agree in principle with Russell e al., who used cotton bract. Davenport and Paton (62) found a percentage of the activity of CDE represented by a 5HT-like component, but they also found at least one more active substance in the CDE than Russell et al. (66). 

Figure 22.13 a-Adrenergic receptor control of contraction of smooth muscle. IP3 represents inositol trisphosphate. Binding of a catecholamine to an a-receptor activates a membrane-bound phospholipase which hydrolyses phosphatidyUnositol bisphosphate within the membrane to produce IP, and diacylglycerol (DAG). IP3 binds a receptor on the sarcoplasmic reticulum in smooth muscle, which activates a Ca ion channel and the cytosolic Ca ion concentration increases, which results in contraction of smooth muscle in arterioles. This results in vasoconstriction and hence decreases blood flow which can leading to an increase in blood pressure. 

Figure 8. Original tracings showing the effects of (R)a-methylhistamine (MHA, pM), thioperamide (TH, pM), the selective a2 adrenoceptor agonist UK-14304 (UK, nM) and the a2-adrenoceptor antagonist idazoxan (ID, pM) on different in vitro assays from the guinea pig ileum A) Electrically-evoked longitudinal contractions of the whole ileum B) Peristaltic waves of the perfused ileum, C) Reflex-evoked circular muscle contractions Vertical calibrations represent (A and C) centimeters of isotonic contractions or (B) changes in perfusion pressure. Horizontal calibration is the chart speed, w = washing of the preparation...

Voltage-activated Ca " channels are activated by membrane depolarization and represent a large family of related channels with a wide tissue distribution. They are found ubiquitously in neurons, muscles, and endocrine cells as well as in many epithelial and endothelial cells. In addition to neurotransmitter release, they mediate a variety of essential functions in the body including muscle contraction, insulin secretion, gene expression, modulation of signal transduction events and in excess can cause cell death. 

The nitroxyls (a.k.a. nitroxides) are remarkably stable free radicals. Nitroxyls have two major resonance structures, one N-centered and one O-centered the lone electron may also be considered to be in the 7T orbital of an N=0 tt bond. Nitroxyls are thermodynamically stable because dimerization would give a very weak N-N, N-O, or 0-0 bond. TEMPO (2,2,6,6-tetramethylgiperidin-l-oxyl), a commercially available nitroxyl, is further stabilized by steric shielding. Other thermodynamically stable free radicals include the small molecules O2 (a 1,2-diradical, best represented as -0-0-) and nitric oxide ( N=0), a messenger molecule in mammals that mediates smooth muscle contraction. 

Figure 16.17 Regulation of glycolysis in muscle. At rest (left), glycolysis is not very active (thin arrows). The high concentration of ATP inhibits phosphofructokinase (PFK), pyruvate kinase, and hexokinase. Glucose 6-phosphate is converted into glycogen (Chapter 21). During exercise (right), the decrease in the ATP/AMP ratio resulting from muscle contraction activates phosphofructokinase and hence glycolysis. The flux down the pathway is increased, as represented by the thick arrows.

Cyclic AMP (cAMP) is an important intracellular mediator regulating the activation of inflammatory cells. Particularly important with respect to asthma, cAMP also plays a role in regulating airway and vascular smooth muscle contractibility, inflammatory cell proliferation, and pulmonary neuronal responsiveness. Cyclic phosphodiesterases (PDEs) comprise a protein superfamily, whose function is to inactivate cyclic AMP and cyclic GMP. The fact that certain PDE inhibitors suppress immune cell functions in vitro and pulmonary inflammation in vivo may represent an opportunity for the development of novel anti-inflammatory drugs. 

In humans, energy stored in adenosine triphosphate (ATP) is released when a phosphate group is removed to create adenosine diphosphate (ADP). The energy is used to cause muscle contractions. What type of energy transformation does this represent ... 

This reaction normally represents hepatic detoxification of cyanide ions produced from nitroprusside in erythrocytes. The SCN- is 99% less toxic than CN-. NaSCN was also still official in the NF X (1960) as an antihypertensive drug. A nitroprusside mechanism on vascular smooth muscle by interference with the role of Ca2+ in the muscle contraction process has also been suggested. 

The term iG represents the portion of an energy change (AH) that is available to do useful work. If AH is the total energy in a reaction, then AG = AH -T AS indicates that part of AH is alway dissipated as heat (the T AS term) and is therefore unavailable for other things, such as muscle contraction, ion transport, or tissue growth. The remaining amount (AG ) is available for useful work, but may not actually be fully utilized for useful work because the efficiency of a process (the ratio of work actually accomplished to AG, the maximum work available) is always less than 100%. 

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