d) muscle fibers contract in an all-or-none- fashionNOT A- b/c even when a person is at rest, vital muscular contractions involving smooth muscle are still occurringNOT B- b/c muscle contraction is activated by ACTIN & MYOSIN (not myelin!!!!) ********- MYELIN is the insulation surrounding axons****NOT C- b/c sensory neurons carry signals from the muscle to the brain- motor neurons stimulate muscle tissue to contract