In reflex action, reflex arch is formed by

Question

Accepted Answer

The correct answer is: **2. Receptor → Spinal cord → Muscle**

### Explanation:

In reflex action, the reflex arc is a neural pathway that controls a reflex. It typically involves the following components:

1. **Receptor**: This is the sensory organ or nerve ending that detects a stimulus (e.g., heat, pain).
2. **Sensory Neuron**: This neuron carries the impulse from the receptor to the spinal cord.
3. **Spinal Cord**: The spinal cord acts as a processing center where the sensory information is relayed to the motor neuron.
4. **Motor Neuron**: This neuron transmits the impulse from the spinal cord to the muscle.
5. **Effector (Muscle)**: The muscle responds to the impulse by contracting or performing an action.

### Why Option 2 is Correct:
- **Receptor → Spinal cord → Muscle** accurately describes the sequence of events in a reflex action. The receptor detects the stimulus, sends the signal to the spinal cord, which then sends a signal to the muscle to respond.

### Why Other Options are Incorrect:
1. **Brain → Muscle → Spinal cord**: This option suggests that the brain is involved in the reflex action, which is incorrect. Reflex actions are typically processed at the spinal cord level without direct involvement of the brain.
   
3. **Muscle → Brain → Spinal cord**: This option implies that the muscle sends signals to the brain, which is not how reflex actions work. Reflexes are automatic responses that do not require brain involvement for the immediate action.

4. **Muscle → Receptor → Spinal cord**: This option incorrectly suggests that the muscle sends a signal to the receptor, which does not happen in reflex actions. The receptor detects the stimulus first, not the muscle.

In summary, the correct sequence in a reflex action is from the receptor to the spinal cord and then to the muscle, making option 2 the accurate choice.