NS TO 7

Definition of Polarized: In the context of a plasma membrane, a cell is considered polarized when there is a distinct separation of electrical charges across the membrane. Specifically, this state is characterized by having a more positive ( $+$ ) environment on the outside of the cell and a more negative ( $-$ ) environment on the inside.
Stored Energy: When a cell is in a polarized state, it possesses stored energy. This electrical gradient represents potential energy that can be utilized for cellular work or signaling.

Numerical Value of Resting Potential: The resting membrane potential ( $RMP$ ) of a standard neuron is measured at approximately $-70\,\text{mV}$ .
Interpretation of the Negative Sign: The negative sign attached to the voltage value ( $-70\,\text{mV}$ ) is a critical indicator of the charge distribution. It explicitly states that there is a higher concentration of negative charges residing on the inside of the plasma membrane relative to the outside.

Definition of Depolarization: Depolarization refers to the process where the membrane potential becomes less negative (moves toward zero). This occurs when the charge difference across the membrane is reduced.
Ionic Mechanism: Depolarization is triggered by the influx of positively charged ions into the cell.
Role of Sodium ( $Na^+$ ): A specific example of this process occurs when sodium ions ( $Na^+$ ) flow into the cell. Because sodium carries a positive charge, its entry neutralizing the internal negative environment causes the cell to become depolarized.

Definition of Repolarization: Repolarization is the specific physiological process of restoring the normal resting membrane potential following a period of depolarization.
Movement of Potassium ( $K^+$ ): The mechanism for repolarization involves the efflux or movement of potassium ions ( $K^+$ ) out of the cell. As these positive ions leave the intracellular space, the internal environment returns to its negative state.
Hyperpolarization: This state, also known as the refractory period, occurs when there is excess repolarization. During this phase, the movement of ions causes the internal charge of the cell to become even more negative than the standard resting potential (falling below $-70\,\text{mV}$ ).

Question: Define the term polarized in terms of the plasma membrane.
Answer: Polarized refers to a state where there is more positive charge on the outside of the membrane and more negative charge on the inside.
Question: State the resting potential of a neuron in millivolts ( $\text{mV}$ ) and what the negative sign of this measurement tells us.
Answer: The resting potential is $-70\,\text{mV}$ . The negative sign indicates that there are more negative charges on the inside of the membrane than on the outside.
Question: State what causes a change in the membrane potential when sodium ions flow into the cell and why.
Answer: The influx of sodium ions ( $Na^+$ ) causes the membrane potential to become more positive (depolarized) because positively charged ions are entering a previously negative environment.
Question: Describe what depolarization means.
Answer: Depolarization is the process of the cell interior becoming less negative due to the entry of positive ions.
Question: Define repolarization and state what causes it.
Answer: Repolarization is the restoration of the resting potential after depolarization, caused by the movement of potassium ( $K^+$ ) out of the cell.
Question: Define hyperpolarization and what causes it.
Answer: Hyperpolarization is a state where the membrane potential becomes more negative than the resting potential, caused by excess repolarization during the refractory period.