Membrane and Action Potential Quiz

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Questions and Answers

What characterizes the resting membrane potential in a neuron?

The inner side is positive relative to the outside.

There is an equal distribution of ions on both sides of the membrane.

The inner side is negative relative to the outside. (correct)

Potassium ions are more concentrated in the extracellular fluid.

What causes the polarization of the plasma membrane?

Unequal distribution of ions across the membrane. (correct)

High temperature affecting ion movement.

Presence of water molecules on the membrane.

Absence of negatively charged proteins.

What is the threshold stimulus?

The average resting potential of the membrane.

A stimulus that cannot activate a neuron.

The weakest stimulus that can activate a neuron. (correct)

The maximum stimulus that activates a neuron.

What occurs during depolarization?

Sodium ions diffuse rapidly into the cell. Signup and view all the answers

How is action potential propagated along the membrane?

By sequential depolarization of adjacent membrane areas. Signup and view all the answers

What happens immediately after depolarization during an action potential?

Potassium channels open and sodium channels close. Signup and view all the answers

What is the typical resting membrane potential (RMP) in neurons?

-70 mV Signup and view all the answers

Which ions contribute to restoring the negative charge during repolarization?

Potassium ions Signup and view all the answers

What is the role of the sodium-potassium pump?

To restore the ionic conditions of resting potential. Signup and view all the answers

How do local anesthetics, such as procaine and lidocaine, function?

They block the opening of voltage-gated Na+ channels. Signup and view all the answers

What happens when an action potential reaches the axon terminal of a presynaptic neuron?

Calcium channels open, allowing calcium ions to enter. Signup and view all the answers

What is a characteristic of multiple sclerosis?

It attacks the myelin sheaths surrounding CNS fibers. Signup and view all the answers

What is the effect of tetrodotoxin (TTX) from puffer fish?

It inhibits the propagation of action potentials. Signup and view all the answers

Which of the following statements about the synapse is true?

Calcium ions trigger neurotransmitter release at the synapse. Signup and view all the answers

What primarily happens during the repolarization phase of an action potential?

Potassium ions exit the cell. Signup and view all the answers

Study Notes

Membrane Potential and Action Potential

Membrane Potential (Polarization): The resting membrane is polarized, meaning the inside is negative relative to the outside, which is positive. The reason for this polarization is an unequal distribution of ions on both sides of the membrane.
Resting Neuron Ions: In a resting neuron, sodium (Na+) concentration is high outside the cell (extracellular fluid, ECF), while potassium (K+) concentration is high inside the cell (intracellular fluid, ICF). There are also large, negatively charged proteins and ions like phosphates (PO43-) within the cytosol that cannot easily cross the plasma membranes.
Resting Membrane Potential (RMP): The difference in charge across the membrane (polarization) is called resting membrane potential (RMP). In neurons, the RMP averages around -70mV.
Action Potential: An "All-or-None" Response. The action potential shows an "all-or-none" response, where the weakest stimulus needed to activate a neuron to generate a nerve impulse is called the threshold stimulus. Nerve impulses are identical in their electrical change, meaning all impulses are similar.

Depolarization

Strong Stimulus: If a stimulus is strong enough, it changes the membrane's permeability, allowing sodium (Na+) ions to rapidly enter the cell.
Polarity Reversal: This rapid influx of Na+ causes the polarity to reverse, making the inside of the membrane positively charged relative to the outside (+30mV). This reversal is called depolarization. The plasma membrane now becomes depolarized.
Initiation of Action Potential: This sudden depolarization initiates the nerve impulse or action potential.

Propagation of the Action Potential

Adjacent Area: Depolarization of the first membrane area triggers permeability changes in the adjacent area, leading to further depolarization. The events of depolarization are repeated.
Rapid Propagation: This initiates the rapid propagation of the action potential along the entire length of the membrane.

Repolarization

K+ Channels Open: Immediately after depolarization, potassium (K+) channels open, and sodium (Na+) channels close.
K+ Diffusion: K+ ions diffuse out of the cell into the extracellular fluid. This restores the negative charge on the inside of the membrane and the positive charge on the outside.
Voltage Change: As a result, the membrane voltage changes from +30mV back to -70mV. The membrane repolarizes and the resting membrane potential (RMP) is re-established.

Hyperpolarization

More Negative: Hyperpolarization is a change in the membrane potential that makes it even more negative than the resting potential. This is the opposite of depolarization.
Inhibition of Action Potentials: Hyperpolarization inhibits further action potentials by increasing the stimulus needed to reach the action potential threshold.

Restoring Ionic Conditions

Sodium-Potassium Pump: The ionic conditions of the resting state are restored later through the activity of the sodium-potassium pump.
Ion Exchange: The pump ejects three sodium (Na+) ions for every two potassium (K+) ions it brings back into the cell.

Transmission at Synapses

Synapse Definition: A synapse is a junction between a neuron and another neuron or an effector cell (muscle or gland).
Calcium Channels: When the action potential reaches the axon terminal of the presynaptic neuron, calcium (Ca2+) channels open.
Neurotransmitter Release: Calcium ions cause synaptic vesicles containing neurotransmitters (like acetylcholine) to fuse with the membrane and release their contents into the synaptic cleft.
Postsynaptic Neuron Response: Neurotransmitters bind to receptors on the postsynaptic membrane, triggering a response in the postsynaptic neuron. The nerve impulse is then carried along the axon of the postsynaptic neuron to the next synapse.

Clinical Notes

Multiple Sclerosis (MS): An autoimmune disease where the immune system attacks the myelin sheath, the protective covering around nerve fibers in the CNS. MS leads to hardened sheaths and disrupted nerve signals. Consequences can include visual/speech problems and loss of muscle control.
Local Anesthetics: Drugs that block pain signals by preventing voltage-gated sodium (Na+) channels from opening, which stops propagation of action potentials to the central nervous system (CNS). Examples include procaine and lidocaine.
Puffer Fish Neurotoxin (Tetrodotoxin, TTX): A potent neurotoxin found in pufferfish viscera. TTX blocks the opening of voltage-gated sodium (Na+) channels, inhibiting action potentials and causing paralysis, often leading to suffocation.
Localized Cooling: Localized cooling of a nerve can produce an anesthetic effect, as lower temperatures reduce the speed of action potential propagation, which can help alleviate pain.

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Description

Test your knowledge on membrane potential and action potential. This quiz covers key concepts such as resting membrane potential, ion distribution in neurons, and the characteristics of action potentials. Perfect for students studying cellular biology or physiology.