The ionic gradients across the resting membrane are maintained by the

Options

A. lon channels
B. Sodium - potassium pumps
C. Electrical synapses
D. Chemical synapses

Answer

To answer the question, "The ionic gradients across the resting membrane are maintained by the," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Resting Membrane Potential**:
- The resting membrane potential refers to the voltage difference across the neuronal membrane when the neuron is not actively firing an action potential. This state is characterized by a polarized membrane.

2. **Identifying Ionic Distribution**:
- In a resting neuron, there is a higher concentration of sodium ions (Na⁺) outside the cell and a higher concentration of potassium ions (K⁺) inside the cell. Additionally, there are negatively charged proteins inside the cell contributing to the negative charge.

3. **Role of Sodium-Potassium Pump**:
- The sodium-potassium pump (Na⁺/K⁺ ATPase) is a membrane protein that actively transports sodium ions out of the cell and potassium ions into the cell. Specifically, it moves 3 Na⁺ ions out for every 2 K⁺ ions it brings in.

4. **Energy Requirement**:
- This pump requires energy in the form of ATP because it is moving ions against their concentration gradients (from low to high concentration).

5. **Maintaining Ionic Gradients**:
- By continuously pumping sodium out and potassium in, the sodium-potassium pump maintains the necessary ionic gradients that are crucial for the resting membrane potential.

6. **Conclusion**:
- Therefore, the ionic gradients across the resting membrane are maintained by the sodium-potassium pump.

### Final Answer:
The ionic gradients across the resting membrane are maintained by the sodium-potassium pump.

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