Neurons, Synapses, and Signaling

Compare and contrast the structure and function of axons and dendrites.

The data above are expressed in scientific notation: a numerical factor times a power of 10. Remember that a negative power of 10 means a number less than 1. For example, 10^-1 M (molar) can also be written as 0.1 M. Write the concentrations in the table above for morphine and atropine in this alternative format.

How is it possible for a particular neurotransmitter to produce opposite effects in different tissues?

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⁺ (E_K) becomes more positive.

(C) The neuron’s membrane voltage becomes more positive.

(D) The cell’s inside is more negative than the outside.

Compare the concentrations listed in the table for methadone and phenobarbital. Which concentration is higher? By how much?

Some pesticides inhibit acetylcholinesterase, the enzyme that breaks down acetylcholine. Explain how these toxins would affect EPSPs produced by acetylcholine.

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.

Describe the basic pathway of information flow through neurons that causes you to turn your head when someone calls your name.

Would phenobarbital, atropine, or serotonin have blocked naloxone binding at a concentration of 10^-5 M? Explain why or why not.

Name one or more membrane activities that occur both in fertilization of an egg and in neurotransmission across a synapse (see Figure 47.3).

Where are neurotransmitter receptors located?

(A) the nuclear membrane

(B) the nodes of Ranvier

(C) the postsynaptic membrane

(D) synaptic vesicle membranes

How might increased branching of an axon help coordinate responses to signals communicated by the nervous system?

WHAT IF? Suppose a mutation caused gated sodiumchannels to remain inactivated longer after an actionpotential. How would this affect the frequency at whichaction potentials could be generated? Explain.

Which drugs blocked naloxone binding in this experiment? What do these results indicate about the brain receptors for naloxone?

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.

When the researchers instead used tissue from intestinal muscles rather than brains, they found no naloxone binding. What does that suggest about opiate receptors in mammalian muscle?

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 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.

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

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

Suppose a researcher inserts a pair of electrodes attwo different positions along the middle of an axon dissectedout of a squid. By applying a depolarizing stimulus, theresearcher brings the plasma membrane at both positionstothreshold. Using the drawing below as a model, create oneor more drawings that illustrate where each action potentialwould terminate.

An action potential is an all-or none event. This on/off signaling is an evolutionary adaptation of animals that must sense and act in a complex environment. It is possible to 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 a graded (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.

The rattlesnake alerts enemies to its presence with a rattle—a

set of modified scales at the tip of its tail. Describe the distinct roles of gated ion channels in initiating and moving a signal along the nerve from the snake’s head to its tail and then from that nerve to the muscle that shakes the rattle.

Under what circumstances could ions flow through anion channel from a region of lower ion concentration to a region of higher ion concentration?

WHAT IF? Suppose a cell’s membrane potential shiftsfrom -70 mV to -50 mV. What changes in the cell’spermeability to K+ or Na+ could cause such a shift?

MAKE CONNECTIONS Review Figure 7.10, which illustrates the diffusion of dye molecules across a membrane. Could diffusion eliminate the concentration gradient of a dye that has a net charge? Explain.

How do action potentials and graded potentials differ?

In multiple sclerosis (from the Greek skleros, hard), a person’s myelin sheaths harden and deteriorate. How would this affect nervous system function?

How do both negative and positive feedback contribute to the changes in membrane potential during an action potential?

Compare and contrast the structure and function of axons and dendrites.

Describe the basic pathway of information flow through neurons that causes you to turn your head when someone calls your name.

How might increased branching of an axon help coordinate responses to signals communicated by the nervous system?

Under what circumstances could ions flow through anion channel from a region of lower ion concentration to a region of higher ion concentration?

WHAT IF? Suppose a cell’s membrane potential shiftsfrom -70 mV to -50 mV. What changes in the cell’spermeability to K+ or Na+ could cause such a shift?

MAKE CONNECTIONS Review Figure 7.10, which illustrates the diffusion of dye molecules across a membrane.Could diffusion eliminate the concentration gradient of a dye that has a net charge? Explain.

How do action potentials and graded potentials differ?