Anesthetics block pain by blocking the transmission of nerve signals. Which of these three chemicals might work as anesthetics? (Choose all that apply and explain your selections.)
a. A chemical that prevents the opening of voltage-gated Na⁺ channels in membranes
b. A chemical that inhibits the enzymes that degrade neurotransmitters
c. A chemical that blocks neurotransmitter receptors

Verified step by step guidance

1. Step 1: Understand the role of voltage-gated Na⁺ channels in nerve signal transmission. These channels are essential for the initiation and propagation of action potentials in neurons. If a chemical prevents the opening of these channels, it would stop the nerve signal from being transmitted, effectively blocking pain perception. This could make such a chemical a potential anesthetic.
2. Step 2: Analyze the role of enzymes that degrade neurotransmitters. These enzymes are responsible for breaking down neurotransmitters in the synaptic cleft, ensuring that the signal does not persist longer than necessary. If a chemical inhibits these enzymes, it would prolong the presence of neurotransmitters in the synapse, potentially leading to overstimulation of the postsynaptic neuron rather than blocking pain. This mechanism is unlikely to work as an anesthetic.
3. Step 3: Examine the function of neurotransmitter receptors. These receptors are located on the postsynaptic membrane and are responsible for receiving signals from neurotransmitters. If a chemical blocks these receptors, it would prevent the postsynaptic neuron from receiving the signal, effectively interrupting the transmission of nerve signals and potentially acting as an anesthetic.
4. Step 4: Compare the mechanisms of the three chemicals. Based on the analysis, chemicals that prevent the opening of voltage-gated Na⁺ channels (option a) and those that block neurotransmitter receptors (option c) are likely to work as anesthetics because they directly interfere with the transmission of nerve signals.
5. Step 5: Conclude that option b, which inhibits enzymes that degrade neurotransmitters, is unlikely to work as an anesthetic because it does not block nerve signal transmission but rather prolongs it, which could lead to increased neural activity instead of pain relief.

Key Concepts

Voltage-Gated Sodium Channels

Voltage-gated sodium channels are integral membrane proteins that open in response to changes in membrane potential, allowing Na+ ions to flow into the neuron. This influx is crucial for the generation and propagation of action potentials, which are essential for nerve signal transmission. Anesthetics that prevent the opening of these channels can effectively block pain signals by inhibiting action potential generation.

Neurotransmitter Degradation

Neurotransmitter degradation involves the breakdown of neurotransmitters in the synaptic cleft, which is essential for terminating the signal between neurons. Enzymes such as acetylcholinesterase degrade neurotransmitters like acetylcholine. A chemical that inhibits these enzymes would prolong the action of neurotransmitters, potentially leading to increased signaling rather than blocking pain, making it less effective as an anesthetic.

Neurotransmitter Receptors

Neurotransmitter receptors are proteins located on the postsynaptic membrane that bind neurotransmitters and mediate their effects on the neuron. Blocking these receptors prevents neurotransmitters from exerting their effects, which can inhibit pain transmission. Therefore, a chemical that blocks neurotransmitter receptors can serve as an effective anesthetic by preventing the propagation of pain signals.