Initiation of Muscle Contraction. Step 1) Neuromuscular Control. The axons of the nerve cells of the spinal cord branch and attach to each muscle fiber forming a neuromuscular junction. i). An action potential passes down the nerve. ii). The nerve releases Ca++ that results in the release of Acetylcholine (ACh) Step 2). ACh binds with the sarcolemma. Step 3). Muscle Fiber Action Potential. i).