Action Potentials

Transient membrane potentials, also called graded potentials, can occur at which of the following locations? I. Dendrite II. Soma III. Axon (A) I and II only (B) II and III only (C) I only (D) I, II, and III

(A) I and II only Graded potentials can occur in dendrites and somas. Action potentials occur in the axon.

Which of the following can trigger the Inactivation mechanism of Sodium Voltage-Gated Channels? I. Membrane Depolarization II. Increased Na/K/ATPase action III. Increased Potassium current (A) I only (B) I and II only (C) II and III only (D) I, II and III

(A) I only Membrane depolarization will both open the Sodium Voltage-Gated Channel and activate the Inactivation mechanism.

Transient changes in the membrane potential are known as: (A) Action Potentials (B) Graded Potentials (C) Dendritic Potentials (D) Threshold Potentials

(B) Graded Potentials Transient changes in the membrane potential are known as Graded Potentials.

Some channels also have an Inactivation mechanism that can prevent the flow of ions, even if the channel itself has not closed yet. Which of the following can be inactivated? (A) Sodium Leak channel (B) Potassium Leak channel (C) Sodium Voltage-Gated channel (D) Potassium Voltage-Gated channel

(C) Sodium Voltage-Gated channel

In addition, Tetraethylammonium (TEA) is commonly used to block which type of channel? (A) Leak Potassium Channel (B) Leak Sodium Channel (C) Voltage-Gated Potassium Channel (D) Voltage-Gated Sodium Channel

(C) Voltage-Gated Potassium Channel Tetraethylammonium (TEA) is commonly used in experiments to block Voltage-Gated Potassium Channels.

The Na+/K+ ATPase transports ____ ions into the cell while transporting ____ ions out of the cell. (A) 3 Na+, 2 K+ (B) 2 Na+, 3 K+ (C) 3 K+, 2 Na+ (D) 2 K+, 3 Na+

(D) 2 K+, 3 Na+ The Na+/K+ ATPase transports 2 K+ ions into the cell while transporting 3 Na+ ions out of the cell. This results in an increasing positive charge outside the cell and decreasing positive charge inside the cell, helping to maintain the negative resting membrane potential.

Neurotransmitters that are causing channels to open and threshold to be reached obviously should not stay bound to these channels forever. Which of the following are methods that can be used to clear neurotransmitters from the Synaptic Cleft? I. Breaking down the Neurotransmitters in Enzymatic Reactions II. Using Reuptake Carriers to return the Neurotransmitter to the Synaptic Bouton. III. Neurotransmitters themselves may diffuse out of the Synaptic Cleft. (A) I only (B) III only (C) I and III only (D) I, II and III

(D) I, II and III Each of the following are methods that can be used to clear neurotransmitters from the Synaptic Cleft: I. Breaking down the Neurotransmitters in Enzymatic Reactions II. Using Reuptake

Which of the following channels aid in maintaining the resting membrane potential? I. Na+/K+ ATP Pump II. Cl-/K+ Pump III. Ca2+/Na+ Pump (A) I and II only (B) I and III only (C) I only (D) I, II, and III

(D) I, II, and III All three pumps help maintain the resting membrane potential of about -60mV

In many ion channel experiments, researchers want to block all channels except the one they are interested in studying. Tetrodotoxin (TTX) is commonly used to block which type of channel? (A) Leak Potassium Channel (B) Leak Sodium Channel (C) Voltage-Gated Potassium Channel (D) Voltage-Gated Sodium Channel

(D) Voltage-Gated Sodium Channel Tetrodotoxin (TTX) is commonly used in experiments to block Voltage-Gated Sodium Channels.

Put the following steps in order,describing the mechanism of an action potential. 1) Threshold potential is reached 2) Repolarization 3) Depolarization 4) Refractory Period 5) Voltage-gated Na+ channels open 6) Voltage-gated K+ channels open

1 --> 5 --> 3 --> 6 --> 2 --> 4 Threshold potential is reached Voltage-gated Na+ channels open Depolarization Voltage-gated K+ channels open Repolarization Refractory Period

Describe the major ion causing the change in potential during the following steps and if the ions are moving into or out of the cell. 1) -50mV to +40mV 2) +40mV to -70mV 3) -70mV to -60mV

1) Na+ moves into the cell 2) K+ moves out of the cell 3) K+ voltage channels close and membrane comes back to resting membrane potential

In a resting membrane neuron, please indicate whether the following ions are in majority on the inside of the membrane or the outside and if they are anions or cations. 1) Organic Anions 2) Chlorine 3) Potassium 4) Sodium 5) Calcium

1) Organic Anions -- Inside (Anions) 2) Chlorine -- Outside (Anions) 3) Potassium -- Inside (Cations) 4) Sodium -- Outside (Cations) 5) Calcium -- Outside (Cations)

Why are the Nodes of Ranvier essential to the propagation of an Action Potential?

Action Potentials decrease in size during the myelinated segment of the axon. The Node of Ranvier has many more ions and ion channels, which can get the action potential back to its full size.

What equation relates capacitance and area?

C = ε (A/d) C = Capacitance ε = dielectric constant A = Area d = distance between 2 plates This means that for a myelinated axon, the capacitance decreases because there is more distance (d) between one side of the axon to the other.

Compare Absolute and Relative refractory period

During the Absolute Refractory Period, no matter the stimulus, the voltage-gated Na+ channels will not re-open; thus, another Action Potential cannot fire no matter what. During the Relative Refractory Period, the voltage-gated Na+ channels can re-open, but since the resting potential is hyperpolarized (i.e. -90 mV), it is hard to stimulate it enough to reach the threshold potential (i.e. -50 mV). If a strong enough excitatory stimuli comes along at this point, however, another Action Potential will be fired.

Nernst equation for membrane potential

E(ion) = RT/FZ ln(Co/Ci) = 60mV/Z log (Co/Ci)

Compare graded potentials and action potentials

Graded Potentials • Dimmer Switch • Multidirectional • Decremental (Decreases in strength the further out the potential is from the origin) • Summate over space and time Action Potentials • All or none • Unidirectional • Non-Decremental • No Summation

How do graded potentials relate to Summation?

Graded Potentials get added together at the Trigger Zone (Axon Hillock). This adding together of Graded Potentials is known as Summation.

The resting membrane potential is said to be about -60mV measured inside of the membrane. Is that the absolute or relative membrane potential?

It is the relative membrane potential. The outside is referenced as 0mV and the inside is then the difference between the voltage on the outside and the inside. We would need to measure the outside voltage. If the outside voltage was +5mV, then we would say that the absolute resting membrane potential is -60mV + 5mV = -55mV.

Do larger diameter axons or smaller diameter axons result in faster action potentials? Why?

Larger diameter axons will result in faster action potentials because there is less resistance. In other words, there are more paths for the ions to travel down the axon, allowing them to move faster.

Myelin increases or decreases the capacitance across the membrane? What does this mean? Why is this the case?

Myelin decreases the capacitance across the membrane, meaning that less ions are lined up along the membrane. In other words, less charge is stored along the membrane. This occurs because the Myelin increases the distance between the charges, making them less attracted to each other. This decrease in capacitance will result in faster action potentials through the Myelinated regions because less ions will need to move for the propagation of an action potential in these regions.

Action potentials require less energy when the axon is myelinated. Why is this the case?

Myelin decreases the membranes permeability to ions. If less ions leave, the Na+/K+ pump will not have to use as much energy to pump these ions back to their original location.

Do myelinated or unmyelinated axons experience saltatory conduction?

Myelinated axons. The gaps between the myelin are called the nodes of ranvier. The action potential will move slower in those gaps, and faster in the myelinated regions. This creates a bit of a hop or leap along the axon. This describes saltatory conduction.

What equation relates resistance and area?

R = ρ (L/A) R = Resistance ρ = resistivity L = Length A = Area This means that for a neuron with a bigger diameter, resistance is smaller.

What is the equation for time constant for an action potential?

T = RC T = Tau, Time constant R = Resistance C = Capacitance The time constant is the amount of time it takes for voltage or current values to change approximately 63 percent from their starting values to their final values AKA the amount of time required for changing the membrane potential.

Compare Temporal Summation and Spatial Summation.

Temporal Summation is summation due to the overlapping of two or more graded potentials that occur at the same time. Spatial Summation is summation due to the overlapping of two or more graded potentials that occur close to each other.

Why is the Refractory Period essential to the propagation of an Action Potential down the Axon?

The Refractory Period prevents Action Potentials from travelling backwards up the Axon.

Describe the idea of equilibrium potential

The equilibrium potential is the membrane potential at which the electrical and chemical forces balance each other out, and there is no net movement of that specific ion in or out of the cell.

Will action potentials be able to survive a particularly long axon? Or will they decay like graded potentials?

This is one of the differences between graded potentials and action potentials. Action potentials will NOT decay throughout the length of the axon; They remain unchanged.