Lesson 3-Action Potentials

Difference between absolute and relative refractory period

The absolute period is when the sodium voltage gated channels are closed so no potential no matter the size can trigger an action potential versus with the relative the sodium voltage gated channels are active again but the neuron is hyperpolarized so a larger potential is required to reach the threshold.

What is meant by equilibrium potential

The electrical force equals the chemical force. This will always occur so the ions will be pumped until the two forces equal.

A student only uses one synapse to try to trigger an action potential but sees that no action potential is generated. Why?

The graded potentials decrease with both time and distance. Thus, as the graded potential travels from the dendrite to the axon hillox it will decrease in strength and not reach the threshold. This is why temporal and spatial summation is typically required to strengthen the signal so that when it does reach the axon hillox it will be strong enough to reach threshold.

Without the sodium potassium pump, what would happen to the resting membrane potential

The leaky channels that continue to allow potassium and sodium to move across their gradients would not allow for a stable resting potential to form.

When the __________________, the sodium voltage gated ion channel becomes closed. True or False.

+45 V. False. It does not close. It becomes inactive. Being inactive, it remains open. There is just a sphere that closes the entrance into the neuron.

When the voltage drops down to ____________ the voltage gated sodium channels become active once again.

-45 V (the threshold value.) The potassium channels become active again as well.

What would be the effect of a fast speed in the potassium voltage gated channels

1- the potassium voltage gated channel would open at the same time as the sodium so not a large depolarization 2- they would not take long to close so no hyperpolarization

Describe the three neural message transfers

1. Some neurons are silent until excited. When excited, the strength of the signal will determine the frequency of firing. 2. Some neurons are always firing regular signals themselves and then when they receive an input the frequency is either increased (excitatory) or decreased (inhibitory) 3. Some neurons are always releasing bursts of signals and then the input will affect the frequency of the bursts

Why is the equilibrium voltage of sodium not reached during an action potential?

As the voltage becomes more positive, some begin to become inactive so it stops around +45 V.

Contributing to the action potential, what type of channel does potassium have

Both leak and voltage gated

Chloride potassium symport and calcium sodium antiport play what roles in the resting membrane potential.

Chloride and Calcium do not have large impact on resting potential. both are pumped out via active transport to pump potassium out and sodium in. Chloride is both chemically and electrically driven out and It pumps the chloride out (allowing potassium to be pumped against its electrical gradient). calcium is electrically driven in but chemically driven out, through the calcium sodium antiport it is taken out to bring sodium in.

Calculate the membrane potential due to multiple ions

Do each single ion than find the average

Neurons can only receive signals via neurotransmitters. True or False.

False. Neurons can also receive sensory stimuli like light. They can also receive through receptors and those would be sensory.

The size of the action potential remains static the entire action potential. true or false.

False. The action potential decreases in size in the myelinated regions due to the decreased permeability of the membrane but then builds up its size again in the nodes of ranviar.

The speed of the action potential is static as it travels through the axon. true or false.

False. The phenomenon of saltatory conduction illustrates that the action potential travels faster in the myelinated regions and then slows down in the nodes of ranviar.

The sodium-potassium ATPase pump works via facilitated diffusion. True or False.

False. The sodium-potassium pump works via active transport because it transports the ions against their elecrochemical gradients and therefore requires ATP

The distribution of ions across the membrane is equal. True or False.

False. There is an unequal distribution of ions across the membrane because the distribution occurs until an equilibrium in terms of electrical and chemical is reached and that results in different amounts of concentrations on either side for each ion.

Pair the axon condition with the action potential speed. Fast Slow Large diameter Thick myelin Small diameter Think myelin

Fast- large diameter and thick myelin Slow-small diameter and thin myelin

Acetylcholine binds to _____________________ in the neuromuscular junction and causes the movement of ______________ ions.

It binds to a ligand-gated acetylcholine receptor. being ligand-gated, the channel is non-specific so both potassium and sodium will travel down their concentration gradients. Potassium flows out and sodium flows in, depolarizing the inside.

Describe the effect of myelin on the speed of conduction

Myelin increases the speed of conduction by decreasing the capacitance since it increases the distance. lower capacitance indicates you will not store charge allowing for the continued motion of the charge. The capacitance applies to the membrane of the neuron so think of the membrane as the 2 parallel plates so the myelination increases the distance between the two sides since it creates a thicker membrane. so you store less charge on both sides of the membrane.

Where on the axon are there the highest concentration of sodium channels?

Near the axon hillox

Calculate the membrane potential due to a single ion

Nerst equation. =RT/ZF ln (ion in/ ion out)

What happens if the threshold value is not obtained

No action potential because you need the voltage to cause the opening of the sodium voltage gated channels.

The initial resting potential is generated by

Organic anion proteins are the first proteins that form and generate the initial tiny small negative charge. They then want to chemically and electrically diffuse out but cannot diffuse out of the neuron because of imperamble membranes so you develop a -5mV resting potential.

Which ions have higher concentration on the outside of the neuron a. calcium b. chloride c. proteins' d. potassium e. sodium

Outside of the neuron: calcium, sodium, and chloride. inside: proteins and potassium

Describe the speed of the ions as they flow through the node of ranviar

SLOW because the thin membrane produced by the lack of myelin increases the capacitance so you can store charge across the membrane.

A second signal reaches the threshold value once the depolarization process has already commenced. Describe the consequence.

Since the sodium voltage gated channel is in the absolute refractory period from the moment it is activated until it becomes open again (go back down to the threshold potential) it will not fire again.

Describe the influence of myelination on ATP utilization for action potential

The myelination decreases the permeability of the membrane to ions so less ions are exchanged. Thus, when ATPase is required to go from hyperpolarized to resting potential less exchange and therefore energy is required.

Overall, why is the resting membrane potential so negative

The permeability to potassium generates a resting membrane potential that is much closer to the equilibrium potential of potassium than the equilibrium potential of the sodium. The membrane is more permeable to potassium because there are more potassium leaky channels (facilitated transport) then for sodium.

The drastic drop in resting potential comes from

The potaasium leaky channels have a huge permeability and leak potassium out of the cell since the chemical force is larger than the electrical force and this is what generates super negative inside (hyperpolarized)

The slight depolarization to go from hyper polarized to resting potential comes from

The sodium leaky channels are not as permeable as the potassium channels but due to the negative inside sodium leaks in due to the electrical force overpowering the chemical force but not much.

What allows the hyperpolarized neuron to return to the resting membrane potential?

The sodium-potassium ATPase pumps three sodium ions out and 2 potassium ions in. Also, the voltage gated potassium channels become inactive.

What drives the incoming nature of sodium into the axon?

The threshold is reached opening the voltage gated sodium channels and then the sodium will travel down both its electrical and chemical gradient into the axon.

Compare and contrast the voltage gated potassium and sodium channels

The voltage gated sodium channels open before the potassium gated voltage channels. The potassium voltage gated open up slower.

What would happen if the potassium leaky channels did not function

There would be no repolarization of the membrane as the potassium would not be able to drive down both its electrical and chemical gradient out of the neuron to make the neuron negative again.

What would happen if the sodium voltage gated channels did not become inactive?

There would not be a absolute refractory period. Another action potential would be able to be generated.

When do the voltage gated potassium channels open

They open when the threshold is reached. they do not influence the depolarization simply because they open slowly. They rapidly open when you reach the maximum depolarized state.

What type of channels are the sodium channels involved in the action potential

Voltage gated

A synapse that is closer to the axon hillox will have a greater impact on the action potential. true or false.

true because the graded potentials decay with distance so the closer the graded potential is to the axon hillox the less it has to travel so the greater its strength will be