Chapter 48

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 \(\mathrm{K}^{+}\left(E_{\mathrm{k}}\right)\) becomes more positive. (C) The neuron's membrane voltage becomes more positive. (D) The cell's inside becomes more negative than the outside.

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.

Where are neurotransmitter receptors located? (A) the nuclear membrane (B) the nodes of Ranvier (C) the postsynaptic membrane (D) synaptic vesicle membranes

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 voltagegated Na \(^{+}\) channels. (C) The axon hillock has a higher membrane potential than the terminals of the axon. (D) Voltage-gated channels for both \(\mathrm{Na}^{+}\) and \(\mathrm{K}^{+}\) 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.

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 for cell \(\mathrm{X}\) is different from that for cell \(\mathrm{Y}\). (B) the axon of cell \(\mathrm{X}\) is myelinated, but that of cell \(\mathrm{Y}\) 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.

Ouabain, a plant substance used in some cultures to poison hunting arrows, disables the sodium-potassium pump. What change in the resting potential would you expect to see if you treated a neuron with ouabain? Explain.

If a drug mimicked the activity of GABA in the CNS, what general effect on behavior might you expect? Explain.

An action potential is an all-ornone event. This on/off signaling is an evolutionary adaptation of animals that must sense and act in a complex environment. Imagine a nervous system in which the action potentials are graded, with the amplitude depending on the size of the stimulus. Describe what evolutionary advantage on/off signaling might have over this continuously variable kind of signaling.

From what you know about action potentials and synapses, propose two hypotheses for how various anesthetics might block pain.

In a short essay (100-150 words), describe how the structure and electrical properties of vertebrate neurons reflect similarities and differences with other animal cells.

This diamond-back rattlesnake (Crotalus atrox) alerts enemies to its presence with a rattle-a set of modified scales at the tip of its tail. Describe the roles of gated ion channels in initiating and moving a signal along the nerve from the snake's head to its tail and then to the muscle that shakes the rattle.