Contraction, of muscle fibers

Sustained contraction of muscle fibers produces repetitive electrical potentials in them that increase in rapidity with strength of contraction and in number as more motor units take part. These potentials may be conducted from a coaxial needle electrode in the muscle, amplified, and their amplitude and frequency analyzed and recorded on a cathode-ray oscilloscope as the very typical full interference pattern of normal voluntary contraction. Characteristic departures from this normal electro-myogram are of very great importance in the diagnosis of muscle disease (B21a). 

In recent years, much attention has been paid to the role of calcium in receptor phenomena, besides its better known involvement in enzyme activation and contraction of muscle fibers. Earlier observations by Csillik and Savay (30) and Nakamura et al. (31) led Tazieff-Depierre and co-workers (32) to study calcium release at the motor end plates of mouse diaphragm in relation to receptor activation and inhibition. Of considerable interest was the observation that whereas membrane de-... 

EibriUation Spontaneous and individual contraction of muscle fibers. 

How to account for cases such as the heart pumps blood by the organized contraction of muscle fibers within a reductive framework Is there no option for the reductionist to accommodate such cases, without buying into a theory of nonderivative plural identity There is. Recall the brief discussion of reduction and... 

The high active tension and/or high active strain that occurs in muscle during lengthening contractions is believed to cause mechanical disruption of muscle fibers and connective tissue (Armstrong, 1984 Lieber and Friden, 1993). Activa-... 

False negative muscle contraction tests are very rare. To date, a negative muscle contraction test rules out MH. A false negative test can be explained by the presence of two types of muscle fibers in a MH susceptible patient the response being dependent on the proportion of the two types of muscle fibers. The K-type designation is used to describe a patient who has a positive joint halothane-caffeine contracture, but a negative separate halothane or caffeine contracture. Whether K-type individuals are MH-susceptible or not is a controversial issue. 

A muscle twitch is a brief, weak contraction produced in a muscle fiber in response to a single action potential. While the action potential lasts 1 to 2 msec, the resulting muscle twitch lasts approximately 100 msec. However, a muscle twitch in a single muscle fiber is too brief and too weak to be useful or to perform any meaningful work. In fact, hundreds or thousands of muscle fibers are organized into whole muscles. In this way, the fibers may work... 

Number of muscle fibers contracting. As the number of contracting muscle fibers increases, the strength of skeletal muscle contraction increases. Two major factors determine the number of muscle fibers activated at any given... 

Systems that develop contractile forces are very intriguing as analogues of physiological muscles. The idea for gel muscles was based upon the work of Katchalsky and Kuhn. They have prepared polyelectrolyte films or fibers which become elongated or contracted in response to a change in pH of the surrounding solution, and have estimated the induced force and response time. The contraction of gel fibers is also achieved by electric fields. Use of electric fields has the merit that the signals are easily controlled. 

Microscopists in the nineteenth century had begun to describe changes in the appearance of muscle fibers during contraction. Their experiments were concurrent with those of physiologists examining the relation between the work done by striated muscle and its heat... 

Muscle contraction is triggered by motor neurons that release the neurotransmitter acetylcholine (see p. 352). The transmitter diffuses through the narrow synaptic cleft and binds to nicotinic acetylcholine receptors on the plasma membrane of the muscle cell (the sarcolemma), thereby opening the ion channels integrated into the receptors (see p. 222). This leads to an inflow of Na which triggers an action potential (see p. 350) in the sarcolemma. The action potential propagates from the end plate in all directions and constantly stimulates the muscle fiber. With a delay of a few milliseconds, the contractile mechanism responds to this by contracting the muscle fiber. 

Actin and myosin fibers or filaments make possible the contraction of muscles. Actin and myosin fibers in muscle lie side by side and react chemically, sliding together and apart to shorten and lengthen in response to energy from adenosine triphosphate. 

Skeletal muscles are organized into extrafusal and intrafusal fibers. Extrafusal fibers are the strong, outer layers of muscle. This type of muscle fiber is the most common. Intrafusal fibers, which make up the central region of the muscle, are weaker than extrafusal fibers. Skeletal muscles fibers are additionally characterized as fast or slow based on their activity patterns. Fast, also called white, muscle fibers contract rapidly, have poor blood supply, operate anaerobically, and fatigue rapidly. Slow, also called red, muscle fibers contract more slowly, have better blood supplies, operate aerobically, and do not fatigue as easily. Slow muscle fibers are used in movements that are sustained, such as maintaining posture. 

In 1909 he began to study the nature of muscular contraction and the dependence of heat production on the length of muscle fiber. During the years 1911-14 until the start of World War I, he continued his work on the physiology of muscular contraction at Cambridge as well as on other studies of nerve impulse, hemoglobin, and calorimetry. 

The best known clinical application of cholinesterase assay concerns the abnormally prolonged effect of the muscle relaxant succinylcholine that is found in a small proportion of patients. This compound, which was introduced into clinical medicine in the early 1950s (B29, B41, T47), owes its relaxant action to competition with acetylcholine for the receptors at the neuromuscular junction both cause depolarization of the muscle fibers, which contract. Acetylcholine is rapidly destroyed by acetylcholinesterase, so that repeated stimuli are applied to the muscle, causing a controlled contraction which persists as long as the nerve is stimulated. When, however, succinylcholine is administered, it is not destroyed by acetylcholinesterase, and its action persists until a large proportion of the dose has been hydrolyzed in the plasma. After initial contraction, the muscle fibers passively elongate to give the relaxation required by the anesthetist. 

Fasciculations - A small local contraction of muscles, visible through the skin, representing a spontaneous discharge of a number of fibers innervated by a single motor nerve filament. 

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