which of the following helps in transmission of impulse across the synapse ?

Options

A. `Na^(+)`
B. `K^(+)`
C. `Ca^(2+)`
D. `Mg^(2+)`

Answer

To solve the question "Which of the following helps in the transmission of impulse across the synapse?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks which ion is involved in the transmission of nerve impulses across the synapse.

2. **Identify the Options**: The options given are:
- A. Sodium ion
- B. Potassium ion
- C. Calcium ion
- D. Magnesium ion

3. **Review the Role of Neurotransmitters**: Transmission of impulses across the synapse involves neurotransmitters. These are chemicals released by the neuron that transmit signals to other neurons.

4. **Recognize the Role of Calcium Ions**: Calcium ions play a crucial role in the release of neurotransmitters. When an action potential reaches the synaptic terminal, calcium ions enter the neuron, which causes vesicles containing neurotransmitters to fuse with the presynaptic membrane and release their contents into the synaptic cleft.

5. **Evaluate Other Ions**:
- **Sodium ions**: Primarily involved in depolarization and generating action potentials, not directly in the transmission across the synapse.
- **Potassium ions**: Involved in repolarization of the neuron after an action potential, not in the transmission across the synapse.
- **Magnesium ions**: Generally involved in various cellular functions but not specifically in neurotransmitter release.

6. **Conclusion**: Based on the role of calcium ions in facilitating the release of neurotransmitters, the correct answer is **C. Calcium ion**.

### Final Answer:
**C. Calcium ion**

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