Biological Systems MCAT Practice Exam

What term describes the buildup of signals leading to muscle contraction?

1. Spatial summation

2. Temporal summation

3. Action potential

4. Signal inhibition

The correct answer is: Temporal summation

The term that describes the buildup of signals leading to muscle contraction is temporal summation. This process occurs when multiple action potentials arrive at a muscle fiber in quick succession. Each individual action potential results in a small amount of calcium release from the sarcoplasmic reticulum, which is crucial for muscle contraction. If these action potentials occur closely together in time, the calcium levels do not have the chance to return to baseline before the next signal arrives, leading to an additive effect. This sustained increase in calcium concentration facilitates a stronger and more effective contraction of the muscle. In contrast, spatial summation refers to the integration of signals from multiple presynaptic neurons at the same time, contributing to the overall excitatory or inhibitory effects on a postsynaptic neuron, which is different from how temporal summation works. An action potential is the all-or-nothing electrical signal that travels along a neuron, but it does not describe the buildup of signals directly. Signal inhibition relates to processes that prevent muscle contraction, rather than enhance it, highlighting that temporal summation is indeed the most accurate term here.