Introduction

Nerve impulse transmission is an essential physiological process allowing neurons to communicate rapidly and efficiently. Certain fundamental properties characterize this process, including threshold requirements, ion channel dynamics, and the nature of the action potential signal. Understanding these helps in correctly interpreting neural signal behavior.

Analysis of the Statements

1. Minimum threshold neurotransmitter concentration is required
   For an action potential to be generated at the postsynaptic membrane, a minimum concentration of neurotransmitter must bind to receptors to depolarize the membrane to threshold. This is true.

2. Threshold number of Na+ channels must be open
   Action potential initiation requires opening a threshold number of voltage-gated sodium channels to allow enough Na⁺ influx for depolarization. This is also true.

3. Amplitude is directly proportional to signal intensity
   This is false. Nerve impulses have a fixed amplitude for a given neuron and exhibit the all-or-none law—the amplitude does not increase with the strength of the stimulus once threshold is reached.

4. It shows all-or-none effect
   True. The action potential either occurs fully or not at all once the threshold is reached; no partial impulses occur.

Summary Table

Conclusion

The incorrect statement about nerve impulse transmission is:

(3) Amplitude is directly proportional to signal intensity

Nerve impulses maintain a constant amplitude regardless of the stimulus strength beyond the threshold, adhering to the all-or-none principle.