Systole heart beats—is cued by messages from the brain, reflecting the brain's responses to conditions of the body, such as pain, emotional stress, level of activity, and to ambient conditions including external temperature, time of day, etc. Electrical systole opens voltage-gated sodium, potassium and calcium channels in cells of myocardium tissue. Subsequently, a rise in intracellular calcium triggers the interaction of actin and myosin in the presence of ATP which generates mechanical force in the cells in the form of muscular contraction, or mechanical systole. The contractions generate intra-ventricular pressure, which is increased until it exceeds the external, residual pressures in
Muscular branches of the radial nerve Muscular branches of the radial nerve The muscular branches of the radial nerve supply the Triceps brachii, Anconæus, Brachioradialis, and Extensor carpi radialis longus, and are grouped as medial, posterior, and lateral. The medial muscular branches supply the medial head of the Triceps brachii. That to the medial head is a long, slender filament, which lies close to the ulnar nerve as far as the lower third of the arm, and is therefore frequently spoken of as the "ulnar collateral nerve". The posterior muscular branch, of large size, arises from the nerve in the groove between the Triceps brachii and