Which of the following statements is not true regarding contraction?

Options

A. Z discs are drawn toward each other
B. Acetylcholinesterase is released from the synaptic end bulbs of a neuron
C. Movement is caused by the power stroke of myosin cross bridges
D. `Ca^(++)` ions and ATP are required for the muscle to contract

Explanation

To determine which statement is not true regarding muscle contraction, we will analyze each of the provided options step by step.

### Step 1: Analyze the Statements
1. **Z-discs are drawn towards each other.**
- This statement is true. During muscle contraction, the sarcomeres shorten as the Z-discs are pulled closer together.

2. **Acetylcholine esterase is released from the synaptic end bulbs of a neuron.**
- This statement is not true in the context of muscle contraction. Acetylcholine is released from the synaptic end bulbs, but acetylcholine esterase is an enzyme that breaks down acetylcholine after it has activated the muscle fiber, not something that is released to initiate contraction.

3. **Movement is caused by the power stroke of myosin cross bridges.**
- This statement is true. The power stroke of myosin cross bridges is responsible for the sliding of actin filaments over myosin, leading to muscle contraction.

4. **Calcium ions and ATP are required for the muscle to contract.**
- This statement is true. Calcium ions bind to troponin, allowing myosin to interact with actin, and ATP is necessary for the myosin heads to detach and re-cock for another contraction cycle.

### Step 2: Conclusion
After analyzing each statement, we find that the second statement, "Acetylcholine esterase is released from the synaptic end bulbs of a neuron," is not true regarding muscle contraction. Therefore, the answer is:

**The second statement is not true regarding muscle contraction.**

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