Describe the condition in muscles that produces the effect called summation. What happens to the muscle fibers to make summation possible?
When a muscle is subjected to a series of stimuli that occur too frequently for the muscle to relax in between each stimulation, the muscle can be made to deliver an even stronger response than the maximal response possible under a single stimulus. This scenario, called summation, results due to the fact that the contractions caused by subsequent stimuli are effectively added together. The increase in the muscle's response beyond its expected maximal response level is the result of chemical changes that occur when a muscle is subjected to frequent stimulations. The chemical changes cause an increase in muscle fiber irritability and are the result of the condition of increased temperature that is produced by frequent contractions.
