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 these statements about myelination in neurons is/are correct? Select True or False for each statement.T/FIt speeds propagation by increasing the density of voltage-gated channels all along the axon.T/FMultiple sclerosis is characterized by disrupted myelination of certain neurons in the central nervous system.T/FIt speeds propagation by preventing cations from leaking out across the membrane as they spread down the axon.T/FIt is more commonly observed in vertebrates than in invertebrates.

Where are neurotransmitter receptors located?a. the nuclear membraneb. the nodes of Ranvierc. the postsynaptic membraned. synaptic vesicle membranes

In a neuron, what creates the electrochemical gradient favoring the outflow of K+ when the cell is at rest?a. Na+/K+-ATPaseb. voltage-gated K+ channelsc. voltage-gated Na+ channelsd. ligand-gated Na+/K+ channels

Why are action potentials usually conducted in one direction?a. Ions can flow along the axon in only one direction.b. The brief refractory period prevents reopening of voltage-gated Na+ channels.c. The axon hillock has a higher membrane potential than the terminals of the axon.d. Voltage-gated channels for both Na+ and K+ open in only one direction.

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.

Describe the role of summation in postsynaptic cells.