Guyton: Chapter 5

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Questions and Answers

What is the potassium ion concentration outside the cell?

35.0 mEq/L

94 mEq/L

4 mEq/L (correct)

140 mEq/L

What is the ratio of potassium ions inside to outside the cell?

0.1

35.0 (correct)

1.54

4.0

What is the Nernst potential corresponding to the potassium ion concentration ratio of 35:1?

0 millivolts

+35 millivolts

-94 millivolts (correct)

-61 millivolts

How does the permeability of the membrane to potassium compare to sodium?

Far more permeable to potassium Signup and view all the answers

What primarily contributes to the normal resting membrane potential?

Chemical gradients of potassium ions Signup and view all the answers

Which channel allows for the leakage of potassium ions in the resting cell membrane?

Potassium leak channel Signup and view all the answers

What is the implication of a resting membrane potential of -94 millivolts?

The inside of the cell is more negative than outside Signup and view all the answers

What does a sodium ion concentration ratio of inside to outside equal to 0.1 indicate?

Low sodium concentration inside the cell Signup and view all the answers

What is the Nernst potential for potassium diffusion as indicated in the content?

-94 millivolts Signup and view all the answers

What equation is suggested to determine the summated potential?

Goldman equation Signup and view all the answers

Which value represents a typical resting membrane potential in neurons based on the context?

-70 millivolts Signup and view all the answers

How is the potential described in the context specifically denoted?

Nernst potential Signup and view all the answers

Which of the following is unlikely to interact with the Nernst potential for potassium?

Potasium ion concentration Signup and view all the answers

What is the significance of the value -94 millivolts in the context?

It represents the Nernst potential for potassium. Signup and view all the answers

Which statement best describes the function of the Goldman equation?

Estimates the overall membrane potential based on ionic permeability. Signup and view all the answers

Given the Nernst potential, what does a value of -94 millivolts suggest about the state of the neuron?

It is hyperpolarized and less likely to fire. Signup and view all the answers

What occurs immediately after the activation of sodium channels during an action potential?

Closure of sodium channels Signup and view all the answers

What is the approximate increase in sodium conductance during the action potential?

5000-fold Signup and view all the answers

Which of the following ions is NOT primarily involved in generating the action potential as described?

Magnesium ions Signup and view all the answers

What type of ions are found inside the nerve axon that cannot pass through the membrane channels?

Impermeant negatively charged ions (anions) Signup and view all the answers

During the action potential, what role do negative anions play inside the axon?

They stabilize the membrane potential Signup and view all the answers

Which of the following correctly describes the state of sodium channels during the peak of an action potential?

Sodium channels are in the process of inactivating Signup and view all the answers

What happens to the membrane potential after the action potential peaks?

It returns to baseline Signup and view all the answers

How do organic phosphate compounds within the axon influence the action potential?

They act as impermeant anions Signup and view all the answers

What is the all-or-nothing principle in relation to action potentials?

Once initiated, action potentials either occur fully or not at all. Signup and view all the answers

What role does the Na+-K+ pump play in the action potential process?

It helps restore the original sodium and potassium concentration gradients. Signup and view all the answers

What requirement must be met for sustained propagation of an impulse in nerve fibers?

The action potential must exceed a greater than 1 ratio for continued propagation. Signup and view all the answers

What happens to the production of heat during the recharging process of a nerve fiber?

Heat production increases as the nerve fiber recharges. Signup and view all the answers

How does the Na+-K+ pump respond to excess sodium accumulation inside the cell?

It is stimulated to remove excess sodium from the cell. Signup and view all the answers

What is indicated by the term 'safety factor for propagation'?

The requirement for action potential levels to be high enough for successful propagation. Signup and view all the answers

What occurs to the spread of depolarization when the action potential does not generate sufficient voltage?

Propagation of depolarization is temporarily halted. Signup and view all the answers

What characterizes the depolarization process of a normal fiber membrane during an action potential?

It can be interrupted if sodium and potassium levels are not properly maintained. Signup and view all the answers

What happens to the activity of the sodium-potassium pump as intracellular sodium concentration increases from 10 to 20 mEq/L?

It increases about eightfold. Signup and view all the answers

What is the primary effect of action potentials on sodium and potassium ion concentration differences across the membrane?

They slightly reduce concentration differences. Signup and view all the answers

During depolarization of a nerve fiber, which ion primarily diffuses to the inside of the membrane?

Sodium ions. Signup and view all the answers

What characterizes the plateau phase in some action potentials?

Membrane potential remains stable near the peak for several milliseconds. Signup and view all the answers

How do changes in sodium concentrations affect the recharging process of the nerve fiber?

Higher sodium concentrations rapidly initiate the recharging process. Signup and view all the answers

Which ions primarily diffuse out of the cell during the repolarization phase of an action potential?

Potassium ions. Signup and view all the answers

What is the consequence of a neuron experiencing repeated action potentials in terms of sodium and potassium concentrations?

The concentration differences of sodium and potassium are reduced. Signup and view all the answers

What is the relationship between sodium concentration increase and pump activity regarding the sodium-potassium pump?

Pump activity increases approximately in proportion to the third power of sodium concentration. Signup and view all the answers

Study Notes

Ion Concentrations and Resting Membrane Potential

Potassium (K+) concentration inside cells: 140 mEq/L; outside: 4 mEq/L.
Sodium (Na+) concentration inside cells relative to outside: 0.1; critical for membrane dynamics.
K+ concentration ratio (inside to outside): 35, resulting in a Nernst potential of -94 mV; indicates driving force for potassium to exit the cell during resting state.

Action Potential Dynamics

Sodium channels activate rapidly at the onset of action potential, leading to increased Na+ conductance (up to 5000-fold).
Action potential follows all-or-nothing principle: once initiated, depolarization propagates along the nerve membrane if threshold conditions are met.

Role of Anions and Calcium Ions

Negatively charged impermanent ions (anions) and calcium ions play a role during the action potential.
Anions include protein anions and organic phosphate molecules, which cannot cross the membrane but influence membrane potential.

Re-establishing Ionic Gradients

After action potentials, sodium and potassium gradients need re-establishment via Na+-K+ pump, which requires ATP.
Pump activity is substantially stimulated by elevated intracellular sodium levels, increasing by approximately eightfold as Na+ concentration rises from 10 to 20 mEq/L.

Energy Metabolism and Propagation Safety Factor

Recharging of nerve fibers is an active process and measurable by increased heat production.
For continued impulse propagation, action potential to threshold ratio must remain greater than 1, termed the "safety factor for propagation."

Plateau Phenomenon

In certain cases, excited membranes exhibit a plateau phase where membrane potential remains near peak for several milliseconds before repolarizing, delaying the return to a resting state.

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Description

This quiz covers the essential concepts of ion concentrations, resting membrane potential, and action potential dynamics. Key topics include the role of sodium and potassium ions as well as the influence of anions and calcium ions during action potentials. Test your understanding of these fundamental neuroscience principles.