. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Muscle and Electric Organs 589 summate. Eserine, which inactivates choHnesterase, enhances the , but has no effect on the muscle impulse. The , then, is graded, is local, can summate, decreases rapidly with distance from the end-plate, and when of sufficient size sets up a muscle impulse which is propagated along the muscle fiber, is all-or-none in height, and is conducted at a measurable velocity. Propagation in frog muscle at room temperature is 1-2 ^-^^ (Table 71). In most striated muscle f
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Muscle and Electric Organs 589 summate. Eserine, which inactivates choHnesterase, enhances the , but has no effect on the muscle impulse. The , then, is graded, is local, can summate, decreases rapidly with distance from the end-plate, and when of sufficient size sets up a muscle impulse which is propagated along the muscle fiber, is all-or-none in height, and is conducted at a measurable velocity. Propagation in frog muscle at room temperature is 1-2 ^-^^ (Table 71). In most striated muscle fibers there is a marked negative after-poten- jJ3|204, 241 (Fig. 220). Veratrine enhances the negative after-potential; it also may delay relaxation by causing repetitive discharge.^^"^ "'^ Negative after-potentials can summate and fuse in multifiber preparations, owing to asynchrony.^" The contractile response to a propagated all-or-none muscle impulse is a twitch. The muscle membrane recovers quickly, more quickly than the muscle can relax, hence the membrane can conduct impulses at high fre- quencies, keeping the muscle in a contracted state (fused tetanus). An. Fig. 220. Action potential (solid line) and myogram (broken line) for sartorius of cat. Rapid propagated spike followed by slow negative after-potential. From Rosenblueth and Hoagland.^ isolated entire muscle fiber can be stimulated to give all-or-none twitches;^^'^ a piece of fiber or intact fibers in poor condition, however, give local con- tractions which are not propagated.^^^' ^^ In all-or-none twitches the muscle impulse activates the contractile elements over which it passes; in graded local responses the contractile elements are stimulated directly without a muscle impulse. The local contractions are graded, summate, and show no refractory period; hence the all-or-none nature of a muscle contraction re- sides in the mechanism of conduction rather than in that of ^^ Under conditions
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