**Core Concept**

The resting membrane potential of myocytes is a crucial concept in understanding the function and excitability of cardiac and skeletal muscle cells. Myocytes, or muscle cells, have a specific electrical property called the resting membrane potential, which is essential for their contraction and communication. The resting membrane potential represents the electrochemical gradient maintained by various membrane proteins, ion channels, and transporters.

**Why the Correct Answer is Right**

The correct answer is **D**: -70 millivolts (mV). The resting membrane potential of myocytes is determined by the balance of ions, mainly sodium (Na+) and potassium (K+) ions, across the cell membrane. Sodium channels are predominantly inactivated, while potassium channels are open, leading to a net outward movement of potassium ions and a negative resting membrane potential. Additionally, the presence of voltage-gated calcium channels and their role in excitation-contraction coupling contribute to maintaining the resting membrane potential.

**Why Each Wrong Option is Incorrect**

Option A (0 mV) is incorrect because it represents a neutral membrane potential, meaning there is no net movement of ions across the membrane, resulting in no electrical gradient. Option B (10 mV) is incorrect as it represents an extremely positive membrane potential, which is not physiologically relevant for myocytes. Option C (30 mV) is incorrect because a positive membrane potential would hinder the cell's ability to generate action potentials and respond to signals.

**Clinical Pearl / High-Yield Fact**

Understanding the resting membrane potential is essential for understanding the electrical activity of myocytes and their function in cardiac and skeletal muscle contraction. Any significant deviation from the normal resting membrane potential can lead to abnormal muscle contraction or arrhythmias, making this concept crucial to clinical practice in cardiology and neurology.

**Explanation of the Correct Answer (D)**

The resting membrane potential of myocytes is determined by the balance of ions, mainly sodium and potassium ions, across the cell membrane. Sodium channels are predominantly inactivated, preventing the influx of sodium ions (Na+) into the cell. Potassium ions (K+) are actively transported out of the cell by the Na+/K+ ATPase pump and passively by the leak channels. This results in a net outward movement of potassium ions and a negative resting membrane potential of approximately -70 millivolts (mV).

**Why Each Wrong Option is Incorrect**

Option A (0 mV) is incorrect because it represents a neutral membrane potential, with no net movement of ions across the membrane. Option B (10 mV) is incorrect as it represents a positive membrane potential, which would impede the cell's ability to generate action potentials and respond to signals. Option C (30 mV) is incorrect because a positive membrane potential would hinder the generation of action potentials and the cell's ability to respond to signals, which is crucial for normal muscle contraction and nerve impulse propagation.