Sensory pathway.
1) Reception. A stimulus such as bending of a crayfish body activates stretch receptors in the muscle. 2) Transduction. Ion channels open, resulting in depolarization of the membrane and creating a graded receptor potential. 3) Transmission. If the receptor potential exceeds the threshhold, an action potential is transmitted to the CNS via one or more axons. 4) Perception. Summation of the action potentials received by the brain results in interpretation of the stimulus as either a slight or large bend.