Describe the role of summation in postsynaptic cells.

What causes a nerve signal to move from one end of a neuron along the length of the neuron to the other end? What is a nerve signal, exactly? Why can't it go backward? How is a nerve signal transmitted from one neuron to the next across a synapse? Write a short paragraph that answers these questions.

Which of the following is the most direct result of depolarizing the presynaptic membrane of an axon terminal?a. Voltage-gated calcium channels in the membrane open.b. Synaptic vesicles fuse with the membrane.c. Ligand-gated channels open, allowing neurotransmitters to enter the synaptic cleft.d. An EPSP or IPSP is generated in the postsynaptic cell.

Explain the difference between a ligand-gated K+ channel and a voltage-gated K+ channel.

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

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 membranesb. a chemical that inhibits the enzymes that degrade neurotransmittersc. a chemical that blocks neurotransmitter receptors

SCIENTIFIC THINKING 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?

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.

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