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Study Guide for Membrane Potentials, Graded Potentials, and Action Potentials (Anatomy & Physiology)

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Q1. What is the resting membrane potential (RMP)? What number does this represent? What ions are involved and where are they located?

Background

Topic: Membrane Potentials

This question tests your understanding of the electrical charge difference across the plasma membrane of a neuron at rest, the ions responsible for this potential, and their distribution inside and outside the cell.

Key Terms:

  • Resting Membrane Potential (RMP): The voltage difference across the cell membrane when the cell is not actively sending a signal.

  • Key ions: Sodium (Na+), Potassium (K+), Chloride (Cl-), and negatively charged proteins.

Step-by-Step Guidance

  1. Recall that the RMP is typically measured in millivolts (mV) and is negative inside the cell relative to the outside.

  2. Identify the main ions involved: Na+ and K+ are most important, with Na+ higher outside and K+ higher inside the cell.

  3. Consider the role of the sodium-potassium pump (Na+/K+ ATPase) in maintaining these gradients.

  4. Think about how the permeability of the membrane to different ions contributes to the RMP.

Try solving on your own before revealing the answer!

Final Answer:

The resting membrane potential (RMP) is typically about -70 mV in neurons. This value means the inside of the cell is 70 mV more negative than the outside.

Key ions involved are Na+ (high outside), K+ (high inside), and Cl- (high outside). The sodium-potassium pump maintains these gradients by pumping 3 Na+ out and 2 K+ in, keeping the inside negative.

Q2. What events during the action potential help to promote the re-establishment of the RMP? What maintains the RMP and how does it function?

Background

Topic: Action Potentials and Membrane Potential Restoration

This question tests your knowledge of how neurons return to their resting state after an action potential and the mechanisms that keep the RMP stable.

Key Terms:

  • Action Potential: A rapid change in membrane potential that propagates along the neuron.

  • Sodium-potassium pump (Na+/K+ ATPase)

  • Ion channel activity (especially K+ channels)

Step-by-Step Guidance

  1. Recall that during an action potential, Na+ rushes in (depolarization) and K+ rushes out (repolarization).

  2. After the action potential, the membrane potential may briefly become more negative than the RMP (hyperpolarization).

  3. Consider how the sodium-potassium pump restores the original ion gradients.

  4. Think about the continuous activity of the pump and selective permeability of the membrane to K+ in maintaining the RMP.

Try solving on your own before revealing the answer!

Final Answer:

After an action potential, the sodium-potassium pump (Na+/K+ ATPase) restores the original ion gradients by moving Na+ out and K+ in. This pump, along with selective permeability to K+, maintains the RMP by keeping the inside of the cell negative.

Q3. What is the equation for Ohm’s law?

Background

Topic: Electrical Properties of Membranes

This question tests your understanding of the relationship between voltage, current, and resistance in biological membranes.

Key Terms and Formula:

  • Voltage (V): Electrical potential difference

  • Current (I): Flow of charged particles

  • Resistance (R): Opposition to current flow

Key formula:

Step-by-Step Guidance

  1. Identify the variables: V (voltage), I (current), R (resistance).

  2. Recall that in neurons, voltage is the membrane potential, current is ion flow, and resistance is determined by membrane properties.

  3. Write the formula relating these variables.

Try solving on your own before revealing the answer!

Final Answer:

Ohm’s law is , where V is voltage, I is current, and R is resistance.

Q4. What are the characteristics of the different ion channels and what activates them?

Background

Topic: Ion Channels in Neurons

This question tests your knowledge of the types of ion channels found in neuronal membranes and what causes them to open or close.

Key Terms:

  • Voltage-gated channels

  • Ligand-gated channels

  • Mechanically-gated channels

Step-by-Step Guidance

  1. List the main types of ion channels: voltage-gated, ligand-gated, and mechanically-gated.

  2. Describe what activates each type: voltage changes, chemical signals, or physical deformation.

  3. Consider the ions each channel allows to pass (e.g., Na+, K+, Ca2+).

  4. Think about the role of these channels in generating and propagating electrical signals.

Try solving on your own before revealing the answer!

Final Answer:

Voltage-gated channels open in response to changes in membrane potential; ligand-gated channels open when a chemical binds; mechanically-gated channels open due to physical deformation. Each channel is selective for specific ions, contributing to neuronal signaling.

Q5. What are plasma membrane ion permeability differences?

Background

Topic: Membrane Permeability

This question tests your understanding of how the plasma membrane’s permeability to different ions affects the membrane potential.

Key Terms:

  • Permeability: How easily ions can cross the membrane

  • Selective permeability: Membrane allows some ions to pass more easily than others

Step-by-Step Guidance

  1. Recall that the membrane is more permeable to K+ than to Na+ at rest.

  2. Consider how this affects the RMP, making it closer to the equilibrium potential for K+.

  3. Think about how changes in permeability during an action potential affect the membrane potential.

Try solving on your own before revealing the answer!

Final Answer:

The plasma membrane is much more permeable to K+ than to Na+ at rest, which makes the RMP close to the equilibrium potential for K+. Changes in permeability during signaling events alter the membrane potential.

Q6. What are graded potentials? Where do they occur? What type of ion channel is involved? What are the characteristics of the channel? What ions are involved and know their movements?

Background

Topic: Graded Potentials

This question tests your understanding of local changes in membrane potential, where they happen, and the channels and ions involved.

Key Terms:

  • Graded potential: A local change in membrane potential that varies in size

  • Ligand-gated channels

  • Na+, K+, Cl- ions

Step-by-Step Guidance

  1. Recall that graded potentials occur in the dendrites and cell body of neurons.

  2. Identify the main ion channels involved: usually ligand-gated channels.

  3. Describe the characteristics: open in response to neurotransmitter binding, allow specific ions to flow.

  4. Consider the direction of ion movement: Na+ in (depolarization), K+ out or Cl- in (hyperpolarization).

Try solving on your own before revealing the answer!

Final Answer:

Graded potentials occur in the dendrites and cell body, involve ligand-gated channels, and can be depolarizing (Na+ in) or hyperpolarizing (K+ out, Cl- in). The channels open in response to neurotransmitters and allow specific ions to move.

Q7. What is an action potential? What is threshold? Where do they occur?

Background

Topic: Action Potentials

This question tests your understanding of the rapid electrical signal in neurons, the concept of threshold, and where action potentials are generated.

Key Terms:

  • Action potential: A rapid, all-or-none change in membrane potential

  • Threshold: The minimum membrane potential needed to trigger an action potential

  • Axon hillock: Typical site of action potential initiation

Step-by-Step Guidance

  1. Recall that an action potential is a rapid reversal of membrane potential.

  2. Identify the threshold value (usually around -55 mV in neurons).

  3. Action potentials are initiated at the axon hillock and propagate along the axon.

Try solving on your own before revealing the answer!

Final Answer:

An action potential is a rapid, all-or-none electrical signal. Threshold is typically around -55 mV, and action potentials occur at the axon hillock and travel down the axon.

Q8. What is depolarization? What type of ion channel is involved and what direction do the ions flow? What are the different states of this ion channel? What number represents when the depolarization has reached a maximum?

Background

Topic: Depolarization in Action Potentials

This question tests your understanding of the process of depolarization, the channels involved, their states, and the peak value reached.

Key Terms:

  • Depolarization: The membrane potential becomes less negative (more positive)

  • Voltage-gated Na+ channels

  • Channel states: closed, open, inactivated

Step-by-Step Guidance

  1. Recall that depolarization is caused by Na+ entering the cell through voltage-gated channels.

  2. Describe the channel states: initially closed, then open during depolarization, then inactivated.

  3. Identify the direction of ion flow: Na+ moves into the cell.

  4. Think about the peak value of depolarization (usually around +30 mV).

Try solving on your own before revealing the answer!

Final Answer:

Depolarization occurs when voltage-gated Na+ channels open and Na+ flows into the cell. The channels transition from closed to open to inactivated. Maximum depolarization is typically around +30 mV.

Q9. What are the characteristics of repolarization? What type of ion channel is activated? What are its different states? When does ion movement reach a maximum?

Background

Topic: Repolarization in Action Potentials

This question tests your understanding of how the membrane returns to a negative value after depolarization, the channels involved, and the timing of ion movement.

Key Terms:

  • Repolarization: Return of membrane potential to a negative value

  • Voltage-gated K+ channels

  • Channel states: closed, open

Step-by-Step Guidance

  1. Recall that repolarization is caused by K+ leaving the cell through voltage-gated channels.

  2. Describe the channel states: closed at rest, open during repolarization.

  3. Identify when K+ movement is at its maximum (shortly after channels open).

Try solving on your own before revealing the answer!

Final Answer:

Repolarization occurs when voltage-gated K+ channels open and K+ leaves the cell. The channels are closed at rest and open during repolarization. Maximum K+ movement occurs soon after the channels open.

Q10. What are the characteristics of hyperpolarization? What number represents the peak of hyperpolarization?

Background

Topic: Hyperpolarization in Action Potentials

This question tests your understanding of the phase where the membrane potential becomes more negative than the RMP.

Key Terms:

  • Hyperpolarization: Membrane potential becomes more negative than RMP

  • Voltage-gated K+ channels

Step-by-Step Guidance

  1. Recall that hyperpolarization occurs when K+ channels remain open longer than needed.

  2. Identify the typical value for peak hyperpolarization (often around -80 mV).

Try solving on your own before revealing the answer!

Final Answer:

Hyperpolarization happens when the membrane potential drops below the RMP, often reaching about -80 mV due to prolonged opening of K+ channels.

Q11. What is the all-or-none phenomenon?

Background

Topic: Action Potential Properties

This question tests your understanding of how action potentials are generated and whether their size depends on stimulus strength.

Key Terms:

  • All-or-none: Action potentials either occur fully or not at all

Step-by-Step Guidance

  1. Recall that if threshold is reached, an action potential is triggered.

  2. Consider whether the size of the action potential changes with stronger stimuli.

Try solving on your own before revealing the answer!

Final Answer:

The all-or-none phenomenon means that once threshold is reached, the action potential occurs with the same size and shape, regardless of stimulus strength.

Q12. How does the nervous system interpret the strength of a stimulus due to action potentials?

Background

Topic: Neural Coding

This question tests your understanding of how the frequency of action potentials encodes stimulus intensity.

Key Terms:

  • Frequency coding: Stronger stimuli cause more frequent action potentials

Step-by-Step Guidance

  1. Recall that action potential size does not change, but frequency can.

  2. Consider how the nervous system uses action potential frequency to represent stimulus strength.

Try solving on your own before revealing the answer!

Final Answer:

The nervous system interprets stimulus strength by the frequency of action potentials: stronger stimuli produce more frequent action potentials.

Q13. What are the characteristics of the absolute and relative refractory periods?

Background

Topic: Refractory Periods in Action Potentials

This question tests your understanding of the time intervals after an action potential when a neuron cannot or can only partially respond to another stimulus.

Key Terms:

  • Absolute refractory period: No new action potential can be generated

  • Relative refractory period: A stronger-than-normal stimulus is needed

Step-by-Step Guidance

  1. Recall that the absolute refractory period occurs when Na+ channels are inactivated.

  2. Relative refractory period occurs when K+ channels are still open and the membrane is hyperpolarized.

  3. Think about how these periods affect the timing and frequency of action potentials.

Try solving on your own before revealing the answer!

Final Answer:

The absolute refractory period is when no action potential can be generated due to inactivated Na+ channels. The relative refractory period is when a stronger stimulus is needed because the membrane is hyperpolarized and K+ channels are still open.

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