chapter 2

During the overshoot phase of an action potential, membrane potential briefly reaches a value near _______ mV.

+50

Hodgkin and Katz discovered that the resting membrane potential changes by _______ mV per tenfold change in K+ concentration.

+58

The resting membrane potential typically ranges from _______ to _______.

-40 mV; -90 mV

In a two-compartment model of a cell with a K+-permeable membrane and a 10-fold excess of K+ in the inside compartment, how would K+ ions flow across the membrane?

. They would flow from the inside compartment to the outside compartment.

Which statement best describes the action potential?

An action potential occurs when the cell's membrane potential reaches threshold.

Explain the difference between hyperpolarization and depolarization. quizlet

Depolarization is a shift in membrane potential toward a more positive value; repolarization is the return of the membrane potential to resting; and hyperpolarization is a shift in membrane potential toward a more negative value.

Which statement regarding membrane potential and equilibrium potential is true?

Equilibrium potential is affected by the concentration and electrical gradients of one ion; membrane potential is affected by gradients of all ions.

The amplitude of the action potential of a given neuron is

always the same

The resting potential of a cell is negative because

at rest there is an excess of K+ inside the cell, and the membrane is permeable chiefly to K+.

Studies of the ionic basis of the action potential in squid giant axon found that

decreasing sodium outside the cell decreases the size of the action potential.

An action potential occurs if current injected into a neuron _______ the neuron to reach _______ potential.

depolarizes; threshold

In a two-compartment model of a cell with a K+- and Ca2+-permeable membrane and a 10-fold excess of K+ in the inside compartment, how would the membrane potential change if all K+ ions were replaced by Ca2+ ions?

it would be reduced by half.

The synaptic potential

makes communication between nerve cells possible.

Which statement best describes the electrical properties of nerve cells?

In comparison to copper wires, they are relatively poor conductors of electricity.

Subthreshold current injected into an axon flows _______ along the axon and _______ with distance from the site of injection.

passively; decays

Concentrations of which ion, inside and outside of a neuron, have the greatest effect on the resting membrane potential?

potassim (K+)

In the phase labeled D, _______ ions are moving _______ the cell.

potassium; out of

Which statement about the ionic permeability of cell membranes is true?

In resting nerve cells, the membrane is quite permeable to potassium.

How is stimulus strength encoded by graded potentials? How is stimulus strength encoded by action potentials

Intensity of a stimulus is encoded in the FREQUENCY of action potentials, rather than their amplitude. Graded potentials are in proportion to the magnitude of the stimulus

How would you explain the statement, "Ion channels and ion pumps have complementary functions"?

Ion channels open and allow ion movement in an energetically favorable direction (for instance, Na+ moves in). The pump then redistributes these ions in the opposite direction back across the membrane

Which statement about electrochemical equilibrium is true?

It occurs when the potential across the membrane exactly offsets the concentration gradient.

Which statement best describes the Nernst equation?

It relates the equilibrium potential of an ion to it's intra- and extracellular components

In the phase labeled B, _______ ions are moving _______ the cell.

sodium; into

How will a neuron respond to an injection of negative current?

It will become hyperpolarized.

In a two-compartment model of a cell with a K+- and Cl--permeable membrane and a 10-fold excess of K+ in the inside compartment, how would the membrane potential change if all K+ ions were replaced by Cl- ions?

It would become positive

The squid giant axon is useful in neuronal studies because

the cytoplasm in the axon can be extruded, thus allowing studies of its composition.

In a two-compartment model of a cell with a K+- and Na+-permeable membrane and a 10-fold excess of K+ in the inside compartment, how would the membrane potential change if all K+ ions were replaced by Na+ ions?

It would not change.

Hodgkin and Katz proposed that sodium was the predominant ion associated with the firing of an action potential because

the membrane potential approaches the Na+ Nernst potential during the rising phase.

Which stimulus is most likely to evoke an action potential?

Large depolarizing current pulse

Which experimental model did Hodgkin and Katz use in their studies of the resting membrane potential?

Living squid neuron

Explain the difference between action potentials (all-or-none) and synaptic potentials (graded).

ynaptic potential refers to the difference in voltage between the inside and outside of a postsynaptic neuron. In other words, it is the "incoming" signal of a neuron (graded). And an action potential is all or none, reaches the threshold and fires.

Which type(s) of electrical signals occur(s) within the neural circuit for a spinal reflex?

Receptor potential, synaptic potential, and action potential

Which state of the plasma membrane does not occur during an action potential?

Resting phase

During which phase of an action potential does membrane permeability to Na+ exceed membrane permeability to K+?

Rising and overshoot phases

Which of the following is not necessary for neurons to communicate electrically?

Separation of large amounts of electrical charge, with excess positive charges stored inside the cell

A dull probe stimulates a Pacinian corpuscle. An electrode is placed midway down the axon, and action potentials are recorded. After one second, the probe is pushed with greater force. What change will occur in the recording?

The frequency of action potentials will increase.

How does the resting membrane potential of a typical neuron compare to the equilibrium potential (calculated by the Nernst equation) for potassium?

The resting membrane potential is not exactly equal to the equilibrium potential for potassium because the membrane has some resting permeability to species other than potassium.

In a two-compartment model of a cell with a K+-permeable membrane and a 10-fold excess K+ in the inside compartment, the membrane potential is experimentally made more negative than the K+ equilibrium potential. How would K+ ions flow across the membrane?

They would flow from the outside compartment to the inside compartment.

Under which circumstances is the Goldman equation equivalent to the Nernst equation?

When a membrane is permeable to only one ion

In what situation would you use the Goldman equation instead of the Nernst equation

_If there is more than one permeant ion in the environment you would use the Goldman equation.

Which factor is important in determining the membrane potential when there are multiple permeant ions?

a nd b (a. The concentration gradient of the individual ionic speciesb. The permeability of the membrane to the individual ionic species)

How does membrane permeability to K+ (PK) and Na+ (PNa) change during an action potential?

PK exceeds PNa at rest; PNa temporarily increases during the action potential.

What is the mechanism of action of most local anesthetics?

Block Na+ channels involved in the generation of action potentials

There is an excess of _______ in the extracellular compartment, relative to the intracellular compartment.

Na+, Cl-, and Ca2+

A friend has taken a job in a neuroscience research lab, and is studying neurons in a freshwater snail. He has been told to calculate the equilibrium potential of K+. Which equation will he use and what other information will he need?

Nernst equation; concentration of K+ inside and outside of the cell

In a two-compartment model of a cell with a K+-permeable membrane and a 10-fold excess of K+ in the inside compartment, how would the membrane potential change if all K+ ions were replaced by Na+ ions?

No potential would be generated.

What is the major determinant of the permeability of a membrane to a specific ion?

Number of open ion channels specific for that ion

Suppose a water-filled aquarium is divided into two compartments by a membrane that is impermeable to all ions. If KCl is added to one compartment, what will happen to the distribution of K+ and Cl-? Will there be a potential difference between the two compartments? What will happen to the membrane potential if the membrane suddenly becomes selectively permeable to K+ (but not to Cl-)?

Since the membrane is impermeable, there is no difference in the distribution of ions in the two compartments. There will be no potential difference between the two compartments. When it becomes selectively permeable to K+, then K+ ions will move into the other compartment until the concentration of K+ ions in both the compartments are equal. since there are Cl- ion in the first compartment, there is an increased negative charge in there and presence of K+ in the other compartment makes it positive, which develops a potential difference across the membrane. If NaCl is added to one compartment which is impermeable, no difference in ionic distribution or potential is observed across the membrane.

Which statement about ionic distributions in nerve cells is true?

Sodium is higher outside cells than inside cells.

What would happen if the membrane became permeable to the Y+ ions?

The Y+ ions would move into the top chamber, down their concentration gradient.

A student new to neuroscience research is practicing recording resting membrane potentials from giant squid axons. During one of the trials, the resting membrane potential, which is normally around -60 mV, measured -15 mV. Which statement best describes what might have occurred during the experiment?

The student added too much potassium to the extracellular solution.

Which statement about active ion transporters is true?

They move certain ions against the concentration gradient.