Mammalian Cardiac Muscle Cells Are Stimulated to Contract by

Mammalian cardiac muscle cells are stimulated to contract by

A) hormonal signals that trigger Ca²⁺ release and myosin light-chain phosphorylation.
B) electrical signals transmitted through gap junctions from other autorhythmic cardiac muscle cells.
C) action potentials from excitatory autonomic neurons.
D) ion channels that open in response to stretch of the cardiac muscle cell membranes.