6.5.4 Define resting potential and action potential (depolarization and repolarization ).

1. 6.5.4 Define resting potential and action potential (depolarization and repolarization). • The resting potential is measured in mV (millivolts) across a cell membrane when it’s not involved in an impulse. It is the membrane potential energy of a neuron membrane. • The action potential is also measured in mV. It’s the state of the cell membrane while in an impulse. It is a measure of the rapid polarization and depolarization of the cell membrane.

2. 6.5.5 Explain how a nerve impulse passes along a non-myelinated neuron. • If the resting potential rises above the threshold level, voltage gated channels open and sodium can diffuse into the cell down its concentration gradient. • This reduces the membrane potential and results in more sodium channels opening. Sodium ions are positively charged and so the inside of the cell develops a net positive charge (depolarization).

3. Continued… • After this, voltage gated potassium channels open and potassium ions flow out of the cell down the concentration gradient. • Potassium ions are positively charged. The potential across the membrane is restored (repolarization). • The concentration gradients of both ions are now restored by the sodium-potassium pump. Sodium is pumped out of the cell while potassium is pumped in. The resting potential is restored and the neuron is ready to conduct another nerve impulse.