Final answer:
Summation can occur in neurons and muscles, involving either spatial summation—multiple signals at various locations on a neuron—or temporal summation—signals at the same location but at different times. Wave summation in muscles leads to stronger contractions, and very frequent signals can result in tetanus.
Step-by-step explanation:
The concept of summation as it relates to nerve cells and muscles, involves the process of adding together multiple electrical signals to create a larger change in membrane potential, and hence, a more significant physiological response. This can occur through either spatial summation or temporal summation.
Spatial summation involves multiple signals at different parts of the neuron's membrane combined to create a larger effect. These separate signals do not need to arrive simultaneously; they can arrive at slightly different times and still contribute to the summation.
Temporal summation refers to multiple signals from the same part of the neuron but occurring at different times. These repeated signals can cumulatively lead to a significant change in the membrane's voltage.
In the context of muscle physiology, wave summation describes when successive signals to a muscle lead to a stronger contraction overall, due to an increased release of Ca++ ions which activate more sarcomeres. If the frequency of signals is high enough, it results in tetanus, where the relaxation phase between contractions disappears, resulting in continuous muscle tension.