Answer
A potential is a voltage difference between two sites/locations. The resting membrane potential (RMP) is the voltage difference between the outside and inside of of the cell membrane/plasmalemma of an unstimulated cell. The cell membrane of a muscle cell is called the sarcolemma.
In an unstimulated cell there is a negative voltage difference across the ell membrane . In other words, the cell is polarized. However, because of the proteins, and nucleic acids, and phosphates inside the cell the inside of the cell is usually negative with respect to the outside. This voltage difference is about -70 mV in nerve cells and -90 mV in muscle cells
Other chemicals that are important in generating and maintaining cell polarity are sodium ions(Na+), potassium ions(K+) calcium ions (Ca++) , chlorine ions (Cl-) and bicarbonate ions (HCO3-).
Work Step by Step
All these ions play roles in generating and maintaining the cells polarity. But the major actors are Na+ and K+cations. The concentration of Na+ is higher in the ISF and the concentration of K+ ions is higher in the cytosol or sarcoplasm. Also. the Na+/K+ ATPase pump tends to kick out three sodium ions ( that leak into the cytosol) for every two K+ ions it kicks out). Consequently, in spite of the attempts Na+ to leak into the cell down their electrochemical gradient ( the inside of the cell is negative), and the propensity of K+ to leak out down their chemical gradient, the resting cell membrane potential is maintained by the selective permeability of the plasma membrane, the negative charges of the large protein molecules inside the cell, and the action of the Na+/K+ ATPase pump.
The RMP is disrupted and the cell depolarized when voltage-gated or a ligand-gated ion channels are opened by action potentials or neurotransmitters, and Na+ and K+ ions are allowed to pour in and out of the cell for brief periods.
