Which of the following are the major positive ions located outside the neuron when it is in a polarized (resting) state?

• A. Sodium ions (Na\(^+\))
• B. Potassium ions (K\(^+\))
• C. Chloride ions (Cl\(^-\))
• D. Calcium ions (Ca\(^{2+}\))

Answer: (A)

Verified step by step guidance

1. Understand the concept of a polarized (resting) neuron: In a resting state, a neuron maintains a resting membrane potential, which is typically around -70 mV. This is achieved by the distribution of ions across the neuron's membrane, with specific ions concentrated either inside or outside the cell.
2. Recall the major ions involved in maintaining the resting membrane potential: Sodium ions (Na\(^+\)), Potassium ions (K\(^+\)), Chloride ions (Cl\(^-\)), and Calcium ions (Ca\(^{2+}\)) are the key players in this process.
3. Identify the ions predominantly located outside the neuron during the resting state: Sodium ions (Na\(^+\)) and Calcium ions (Ca\(^{2+}\)) are found in higher concentrations outside the neuron, while Potassium ions (K\(^+\)) are more concentrated inside the neuron.
4. Understand the role of the sodium-potassium pump: This pump actively transports 3 Na\(^+\) ions out of the neuron and 2 K\(^+\) ions into the neuron, maintaining the concentration gradient and contributing to the polarized state.
5. Conclude that the major positive ions located outside the neuron in a polarized state are Sodium ions (Na\(^+\)) and Calcium ions (Ca\(^{2+}\)), as they are in higher concentrations outside the cell compared to inside.