45. Nervous System

What happens when a resting neuron's membrane depolarizes? a. There is a net diffusion of Na+ out of the cell. b. The equilibrium potential for K+(EK) becomes more positive. c. The neuron's membrane voltage becomes more positive. d. The cell's inside is more negative than the outside.

Which ion most readily leaks across a neuron's membrane, helping to establish the resting potential?

A common feature of action potentials is that they a. cause the membrane to hyperpolarize and then depolarize. b. can undergo temporal and spatial summation. c. are triggered by a depolarization that reaches threshold. d. move at the same speed along all axons.

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

Where are neurotransmitter receptors located? a. the nuclear membrane b. the nodes of Ranvier c. the postsynaptic membrane d. 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+-ATPase b. voltage-gated K+ channels c. voltage-gated Na+ channels d. 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 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.

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?

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? Like neurons, cells in skeletal and cardiac muscle also produce action potentials. Create a concept map showing how BTX could kill a mammal through its effects on nervous and muscle tissues.

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? Predict the effects of each of the following on the membrane potential of a neuron simultaneously poisoned with BTX: (a) removing extracellular sodium ions; (b) increasing the intracellular potassium ion concentration; and (c) adding tetrodotoxin from puffer fish.

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?Although BTX is a powerful antipredator poison, one snake species in Colombia eats poison dart frogs. Suggest a hypothesis that might explain how the snake is resistant to the toxin.