SKELETAL MUSCLES

SKELETAL MUSCLES

Skeletal muscles are composed of individual muscle fibers that contract when stimulated by a somatic motor neu- ron. Each motor neuron branches to innervate a number of muscle fibers. Activation of varying numbers of motor neurons results in gradations in the strength of contraction of the whole muscle

the agonist muscle; in flexion, for example, the flexor is the agonist muscle. Flexors and extensors that act on the same joint to produce opposite actions are antagonistic muscles

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Malaria

Malaria Malaria Malaria affects 100 million people and kills 1.5million every year. The etiologic agent is a protozoa called plasmodium and the anopheles mosquito acts as a vector. The massive antimalaria campaign from 1950 to 1980 failed and produced resistant mosquito for DDT and resistant plasmodium to chloroquine. Life cycle and pathogenesis The sporozoites transmitted by the mosquito bites pass into the blood stream and invade the hepatocytes by binding hepatocyte receptors for serum proteins thrombospondin and properdin. this occurs because the sporozoites have similar domains to these proteins. Within the liver cell they multiply rapidly and as many as 30,000 merozoites (asexual haploid blood form) are released into the blood when hepatocyte ruptures. · The HLA-B53 associated resistance to PF. Infection showed by many Africans appears caused by the ability of HLA-B53 to present liver stage malaria Ag to cytotoxic T...

Regulation of Stroke Volume

Regulation of Stroke Volume The stroke volume is regulated by three variables: the end-diastolic volume (EDV), which is the volume of blood in the ventricles at the end of diastole; the total peripheral resistance, which is the frictional resistance, or impedance to blood flow, in the arteries; and the contractility, or strength, of ventricular contraction. The end-diastolic volume is the amount of blood in the ven- tricles immediately before they begin to contract. This is a work- load imposed on the ventricles prior to contraction, and thus is sometimes called a preload. The stroke volume is directly proportional to the preload; an increase in EDV results in an increase in stroke volume. (This relationship is known as the Frank-Starling law of the heart, discussed shortly.) The stroke volume is also directly proportional to contractility; when the ventricles contract more forcefully,...

Effect of pH and Temperature

Effect of pH and Temperature on Oxygen Transport In addition to changes in P O 2 , the loading and unloading reac- tions are influenced by changes in the affinity (bond strength) of hemoglobin for oxygen. Such changes ensure that active skeletal muscles will receive more oxygen from the blood than they do at rest. This occurs as a result of the lowered pH and increased temperature in exercising muscles. The affinity is decreased when the pH is lowered and increased when the pH is raised; this is called the Bohr effect. When the affinity of hemoglobin for oxygen is reduced, there is slightly less loading of the blood with oxygen in the lungs but greater unloading of oxygen in the tissues. The net effect is that the tissues receive more oxygen when the blood pH is lowered (table 16.8). Since the pH can be decreased by carbon dioxide (through the formation of carbonic acid), the Bohr effect helps to provide more oxygen to the tissue...

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