. Biophysical science. Biophysics. 8 : 3/ Muscles 145 probably acetylcholine, which is probably also important in the trans- mission of impulses across synapses between nerves. (Acetylcholine and its action are described more completely in Chapter 4.) The released acetyl- choline diffuses across the myoneural junction (which is of the order of a few tenths of a micron) and stimulates the formation of a spike potential in the muscle fiber. The acetylcholine is rapidly destroyed by a protein catalyst, cholinesterase, present in the muscle end plate. Under certain conditions, the myoneural juncti
. Biophysical science. Biophysics. 8 : 3/ Muscles 145 probably acetylcholine, which is probably also important in the trans- mission of impulses across synapses between nerves. (Acetylcholine and its action are described more completely in Chapter 4.) The released acetyl- choline diffuses across the myoneural junction (which is of the order of a few tenths of a micron) and stimulates the formation of a spike potential in the muscle fiber. The acetylcholine is rapidly destroyed by a protein catalyst, cholinesterase, present in the muscle end plate. Under certain conditions, the myoneural junction acts as a "computer," putting out a number of muscle spike potentials different from the number of incoming nerve spike potentials. The muscle fiber membrane is polarized, just as is the axon membrane discussed in Chapter 4. An action spike potential, similar to that in. -90mv Figure 6. Spike potential of striated muscle. V is the poten- tial difference inside minus that outside the sarcolemma. The arrow indicates application of stimulus. In cardiac muscle, the peak of the crest of the action potential lasts much longer. nerves, is the first result of stimulation of a muscle fiber, whether the stimulus be the physiological one from the nervous system or an arti- ficial one, that is, electrical, mechanical, or heat. A typical muscle spike potential is shown in Figure 6. The action potential differs from that in nerves only in the duration of the peak, which lasts much longer in muscle than in nerve. Originally, the muscle potentials were recorded by means of so-called "bipolar" or "differentiating" electrodes which measured the potential difference between two neighboring spots on the muscle. These gave no possibility of measuring a resting or d-c potential, nor any certainty of the size of the cellular potentials. These electrodes have been replaced by microelectrodes made by drawing out a capillary glass tube to a diameter of less than 1 /x. Th
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