Which of the following is not involved in transmission of a nerve impulse across a chemical synapse?

Options

A. Synapsin
B. Acetylcholinesterase
C. Calmodulin
D. Calcium ions

Explanation

To determine which of the following is not involved in the transmission of a nerve impulse across a chemical synapse, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of a Chemical Synapse**:
A chemical synapse consists of the presynaptic neuron (axon terminal) and the postsynaptic neuron (receptor site). The presynaptic neuron contains synaptic vesicles filled with neurotransmitters.

**Hint**: Familiarize yourself with the basic structure of a synapse, including the roles of the presynaptic and postsynaptic neurons.

2. **Identify Key Components Involved in Transmission**:
- **Neurotransmitters**: These are chemicals that transmit signals across the synapse. For example, acetylcholine is a common neurotransmitter.
- **Calcium Ions (Ca²⁺)**: When an action potential reaches the axon terminal, voltage-gated calcium channels open, allowing calcium ions to enter the neuron, which triggers the release of neurotransmitters.
- **Synaptic Vesicles**: These vesicles store neurotransmitters and release them into the synaptic cleft when stimulated.

**Hint**: List the components that actively participate in the transmission process at the synapse.

3. **Consider the Role of Enzymes**:
- **Acetylcholinesterase**: This enzyme breaks down acetylcholine after it has transmitted the signal, preventing continuous stimulation of the postsynaptic neuron. However, it does not participate in the actual transmission of the nerve impulse itself.

**Hint**: Differentiate between enzymes that facilitate transmission and those that act after transmission to terminate the signal.

4. **Identify the Incorrect Option**:
Based on the roles identified, acetylcholinesterase is the only component that does not take part in the transmission of the nerve impulse across the synapse; it acts post-synaptically to break down acetylcholine.

**Hint**: Look for the option that describes a function that occurs after the signal has been transmitted rather than during the transmission itself.

### Conclusion:
The correct answer is **Acetylcholinesterase**, as it does not participate in the transmission of nerve impulses at the chemical synapse; it functions to degrade neurotransmitters after the signal has been sent.