Using microelectrodes, a researcher recorded nerve signals in four neurons in the brain of a snail, called A, B, C, and D in the table below. A, B, and C can all transmit signals to D. In three experiments, the animal was stimulated in different ways. The number of nerve signals transmitted per second by each of the cells is recorded in the table. Write a short paragraph explaining the different results of the three experiments.

Suppose a particular neurotransmitter causes an IPSP in postsynaptic cell X and an EPSP in postsynaptic cell Y. A likely explanation is that

a. The threshold value in the postsynaptic membrane is different for cell X and cell Y

b. The axon of cell X is myelinated, but that of cell Y is not

c. Only cell Y produces an enzyme that terminates the activity of the neurotransmitter

d. Cells X and Y express different receptor molecules for this particular neurotransmitter

Describe the role of summation in postsynaptic cells.

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

A proposal to test an SSRI in a large number of individuals with depression was submitted to the FDA. Through random assignments, half of the patients would be controls, receiving nothing at all, and half the patients would receive the drug in pill form. Patients in both groups would note changes in their own mood in a daily journal. What flaw(s) do you note in this experimental design?

Explain why drugs that prevent neurotransmitters from being taken back up by a presynaptic neuron have dramatic effects on the activity of postsynaptic neurons.

Certain species of frogs in the genus Phyllobates have a powerful defensive adaptation—their skin can secrete a milky fluid that contains an extremely toxic compound called batrachotoxin (BTX). These frogs, which are found in Colombia, are known as poison dart frogs because some indigenous Colombian hunters coat the tips of their blowgun darts with the frogs' skin secretions. An animal hit by one of these darts dies quickly.

What is the mechanism of action of BTX? The graph here shows the effect of BTX on the membrane potential of a squid giant axon.

Which of the following is the most likely explanation for the effect of BTX on the squid giant axon?

a. Inactivation of Na⁺/K⁺-ATPase

b. Closing of sodium channels

c. Opening of sodium channels

d. Opening of potassium channels

Certain species of frogs in the genus Phyllobates have a powerful defensive adaptation—their skin can secrete a milky fluid that contains an extremely toxic compound called batrachotoxin (BTX). These frogs, which are found in Colombia, are known as poison dart frogs because some indigenous Colombian hunters coat the tips of their blowgun darts with the frogs' skin secretions. An animal hit by one of these darts dies quickly.

What is the mechanism of action of BTX?

Identify a research technique that could be used to discover how BTX affects specific membrane proteins.

Based on the graph in Question 11, what would you expect this technique to show?

Certain species of frogs in the genus Phyllobates have a powerful defensive adaptation—their skin can secrete a milky fluid that contains an extremely toxic compound called batrachotoxin (BTX). These frogs, which are found in Colombia, are known as poison dart frogs because some indigenous Colombian hunters coat the tips of their blowgun darts with the frogs' skin secretions. An animal hit by one of these darts dies quickly.

What is the mechanism of action of BTX? As the graph in Question 11 shows, BTX depolarizes the membrane and prevents repolarization.

What effect would this have on electrical signaling by the nervous system?