Problem 7 - Campbell Biology Concepts & Connections

Question

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 \(\mathrm{Na}^{+}\) channels in membranes b. a chemical that inhibits the enzymes that degrade neurotransmitters c. a chemical that blocks neurotransmitter receptors

Step-by-Step Solution

Answer

A and C can act as anesthetics by blocking the transmission of nerve signals.

Step 1: Understanding Nerve Signal Transmission

Nerve signal transmission involves the generation and propagation of action potentials, which depend on the opening and closing of voltage-gated ion channels and the release and binding of neurotransmitters.

Step 2: Analyze Chemical A

Chemical A prevents the opening of voltage-gated \(\text{Na}^{+}\) channels. These channels are crucial for the initiation and propagation of action potentials along neurons. If these channels are blocked, nerve signals cannot be transmitted, thus blocking pain signals.

Step 3: Analyze Chemical B

Chemical B inhibits the enzymes that degrade neurotransmitters. This would result in prolonged presence of neurotransmitters in the synaptic cleft, potentially desensitizing the receptors or causing continuous stimulation, which may not effectively block pain transmission.

Step 4: Analyze Chemical C

Chemical C blocks neurotransmitter receptors. By blocking these receptors, neurotransmitters cannot bind to propagate the nerve signal to the next neuron, thereby blocking the transmission of pain signals.

Step 5: Conclusion

Based on the analyses, chemicals A and C can act as anesthetics because they block the transmission of nerve signals, which is necessary for blocking pain.

Key Concepts

Voltage-Gated Ion Channels

Voltage-gated ion channels are proteins found in the membrane of nerve cells.
These channels open and close in response to changes in membrane potential.
When a nerve cell is stimulated, voltage-gated \(\text{Na}^{+}\) channels open, allowing sodium ions to rush into the cell.
This influx of sodium ions generates an electrical signal, known as an action potential.
Action potentials are crucial for transmitting nerve signals along neurons.
Blocking voltage-gated \(\text{Na}^{+}\) channels, as Chemical A does, prevents the initiation and propagation of these action potentials.
Consequently, if these channels are blocked, nerve signals, including pain signals, cannot be transmitted.
This mechanism is how some anesthetics work to block pain.

Neurotransmitter Receptors

Neurotransmitter receptors are specialized proteins located on the surface of nerve cells.
They bind to neurotransmitters, which are chemical messengers released by neurons.
When a neurotransmitter binds to its receptor, it induces a response in the receiving neuron, propagating the nerve signal.
Chemical C works by blocking these neurotransmitter receptors.
By doing so, it prevents neurotransmitters from binding and initiating a response in the next neuron.
This interruption in communication between neurons can effectively block the transmission of pain signals.
Thus, blocking neurotransmitter receptors can be a potent method for anesthetics to provide pain relief.

Action Potentials

Action potentials are the electrical impulses that neurons use to transmit signals.
They are initiated when a neuron receives a sufficient stimulus, leading to the opening of voltage-gated \(\text{Na}^{+}\) channels.
Once these channels open, sodium ions flow into the neuron, causing a rapid change in membrane potential.
This change propagates along the neuron, transmitting the signal.
After the action potential passes, voltage-gated \(\text{K}^{+}\) channels open, allowing potassium ions to exit the cell, returning the membrane potential to its resting state.
Anesthetic agents that block the initial steps of action potential generation, like those that inhibit voltage-gated \(\text{Na}^{+}\) channels, can effectively prevent nerve signal transmission and thus block pain perception.