Which component is responsible for initially stimulating a muscle contraction?
proteins
electrochemical signals
plasma membranes
striations

Option B, electrochemical signals

Explanation:

The first process that initiates the muscle contraction is the binding of calcium ion with troponin protein. After this chemical interaction, the active binding sites of actin gets exposed. After this myosin binds to the actin sites thereby forming a high-energy  head bridge and releasing the pi. Mysosin now goes to a lower energy state by undergoing conformational change. This causes power stroke and actin filament is pulled towards the M-line. Later on the muscle contracts by shortening  sarcomere.

This entire process is an electrochemical process. hence option B is correct.

what subject is this

answer; hydrologic cycle;