Final answer:
Calcium is the electrolyte that maintains the ionic gradient crucial for impulse transmission and muscle contractility, playing significant roles in heart physiology and muscle function.
Step-by-step explanation:
The electrolyte responsible for maintaining the ionic gradient essential for impulse transmission and the contractility of both cardiac and skeletal muscle is calcium. Calcium ions play a vital role in the physiology of the heart muscle by contributing to the plateau phase and the absolute refractory period that regulate cardiac muscle function. Additionally, calcium binds with the regulatory protein troponin in the troponin-tropomyosin complex, facilitating cross-bridge formation between actin and myosin for muscle contraction. This process is critical for the contractility of cardiac and skeletal muscle. Electrolytes like sodium, potassium, and calcium are also crucial for nerve impulse conduction, water balance, and the rhythmic contractions of the heart, as depicted in electrocardiograms. The meticulous regulation of sodium, calcium, and potassium is essential for the proper function of these physiological processes, with the heart's natural pacemaker, the sinoatrial (SA) node, coordinating the depolarization wave across the heart.