Before You Begin

Question #45260

Difficulty: 8/10 | 🟢 Free

The Question

A researcher isolates a mammalian motor neuron—permanently arrested in the $G_0$ phase—along with its innervated skeletal muscle fiber. An electrical stimulus is applied to the axon to generate an action potential, but the preparation is simultaneously treated with a highly specific neurotoxin that selectively blocks voltage-gated $Ca^{2+}$ channels at the synaptic knob. Which of the following represents the most accurate physiological consequence?

Options

A.
The action potential fails to propagate to the synaptic terminal, preventing sarcolemma depolarization and causing flaccid paralysis.
B.
Synaptic vesicles fail to fuse with the pre-synaptic membrane, preventing the generation of an end-plate potential while the neuron remains intact in the $G_0$ phase.
C.
Acetylcholine is released but fails to bind to the motor end plate, as extracellular $Ca^{2+}$ is required to activate post-synaptic ligand-gated channels.
D.
The muscle fiber undergoes sustained tetanic contraction because the lack of $Ca^{2+}$ influx prevents the activation of acetylcholinesterase in the synaptic cleft.

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Comparative_Analysis

Sharpen your ability to evaluate multiple scenarios and distinguish between competing potential answers.

Concepts Behind This Question

Interphase Duration Paradox|Synaptic Vesicle Exocytosis Trigger|Calcium Homeostasis

Why This Question Is Tricky

Common Mistakes

Conceptual Pivot: Students frequently confuse the presynaptic role of Calcium (triggering vesicle exocytosis) with its postsynaptic/intracellular role in the muscle fiber (binding to troponin for contraction).

Furthermore, this question tests the ability to decouple electrical propagation (which remains intact) from chemical transmission (which fails), while confirming that localized synaptic blockade does not alter the neuron's fundamental cell cycle status ( $G_0$ ).

Quick Facts About This Question

Question Information

Subject	Biology
Chapter	Cell Cycle and Cell Division - Class 11
Concept	Interphase Duration Paradox
Difficulty	8
Cognitive Load	5
Target Solve Time	120 sec
Access	Free