Membrane Potentials and Action Potentials Syed

Question 1

What are cell bodies?

Answer 1

• The cell body houses the nucleus and other typical cell organelles.
• The plasma membrane around the cell body is characterized by local potentials

Question 2

What are the dendrites?

Answer 2

• Dendrites are cellular extensions of the neuron
• Although variable, the number of dendrites is typically a few to many
• They are characterized by the presence of ligand (neurotransmitter)-gated ion channels
• They conduct local potentials

Question 3

What is an axon?

Answer 3

• Extension of the cell body and is typically opposite the side of the cell body where the dendrites are located
• Is covered by the plasma membrane (axolemma)
• Has voltage-gated ion channels with the ability to conduct an action potential
• Distal end of the axon has the membrane-bound vesicles

Question 4

What are the telodendria?

Answer 4

They are the branches at the end of the axon

Question 5

What causes a diffusion potential?

Answer 5

It is caused by an ion concentration difference on either side of a membrane

Question 6

What is the Nernst potential?

Answer 6

It is the diffusion potential level across a membrane that exactly opposes the net diffusion of a particular ion through the membrane.
It measures how difficult it would be for an ion to diffuse across a membrane if it was permeable

Question 7

Explain what is happening in Figure 5-1

Answer 7

The K will usually flow out, so the K diffusion potential is the force that will oppose the movement of K. Same thing for Na, but moving into the cell, so it’s positive

Question 8

Explain Figure 5-2

Answer 8

I have no idea yet

Question 9

Electrical Dipole Layer:

When both the indifferent electrode and the recording electrode are in the same fluid, what will the voltage read?

Answer 9

The voltage will be zero because there is no electrical potential there
** I think**

Question 10

Electrical Dipole Layer:

When is the only time the recording changes?

Answer 10

It only changes when we cross an electrical dipole layer

Question 11

Electrical Dipole Layer:

Why is the potential electrical difference across the cell membrane recorded as negative?

Answer 11

It’s recorded as negative because the recording electrode is inside the membrane

Question 12

What is the formula for the Nernst Equation?

Answer 12

Add the slide picture

Question 13

What is the difference between the Goldman equation and the Nernst Equation?

Answer 13

While the Nernst equation is used to determine the diffusion potential across a membrane that exactly opposes the net diffusion of a particular ion through the membrane, it can only measure the potential for one type of ion at a time
The Goldman equation can be used to measure the combined potential for more than one type of ion

Question 14

What are the assumptions for the Nernst Equation?

Answer 14

• Equation can only be used for one ion at a time
• Membrane mist be completely permeable to that ion
• Ion must be at equilibrium

Question 15

What is the simplified Nernst Equation?

Answer 15

Add picture

Question 16

Diffusion Potential:

Describe what will happen to the concentrations and the voltage difference as equilibrium is reached

Answer 16

No fucking idea

Question 17

Equilibrium Potential - Add picture

When is Equilibrium reached here?

Answer 17

Slide 27 Add Picture
Equilibrium will be reached when the electrical force driving chloride ions out of the left-hard compartment exactly balances the concentration force driving the chloride ions out of the right-hand compartment
- Equilibrium for an ion id determined not only by concentration forces but also by electrical forces (Use Nernst equation to calculate the electromotive force for Cl.

Question 18

What is the Principle of Electrical Neutrality?

Answer 18

It says that under biological conditions the sum of the concentrations of cations with any compartment must be equal to the sum of the concentrations of anions in that compartment

Question 19

What factors must be considered for equilibrium in the principle of electrical neutrality

Answer 19

Both osmotic and electrical factors must be considered

Question 20

Why is the example cell in the slide not like a real animal cell? ADD PIC Slide 29

Answer 20

• Because proteins are going to contain a charge (we assume none)
• Membrane is leaky
• The principle ion inside the cell is K, not Na
• The real cell membrane is permeable to both Na and Cl

Question 21

What does the Donnan (Gibbs-Donnan) Equilibrium say?

Answer 21

It says that if equilibrium is to be reached with two permeant ions (chloride and potassium), the electrical potential across the cell membrane must exactly balance the concentration gradients for both ions.
Because the membrane potential can only have one value, this equilibrium condition will be satisfied only when equilibrium potentials for both ions are equal

Question 22

How do you solve this cell equation? ADD PIC Slide 30

Answer 22

You would start on the right side because there is only one ? there. The + concentrations must equal the negative ones, so Cl- has to be 125. Total on left must now be 250.
When the concentrations for Cl and K are multiplied together, they must equal the same on the other side. So 125*5 = 625. So the left K and Cl must be 625 and equal to each other. Both must be 25, and P is 200

Question 23

Explain Slide 33 ADD PIC

Answer 23

Whaaa

Question 24

Read over Slide 35 and Figure 5-5 Resting membrane potential of nerves

Answer 24

idk

Question 25

What are the characteristics of an action potential?

Answer 25

• It is all-or-none: it will either occur or not occur
• It is self-propagating: Each region of depolarization serves to generate action potential on either side. - It’s not gonna keep going until it gets to the end of the axon. Each one fuels the start of the next one
• It is non-decremental: It does not decrease in strength

Question 26

What are the two types of gates for an ion channel?

Answer 26

• Ligand gated

- Voltage gated

Question 27

Explain the molecular structure of an voltage-gated sodium channel

Answer 27

• channel consists of four domains
• domains are thought to be arranged in a cylindrical configuration
• Each domain has 6 hydrophobic transmembrane segments
  S4 of each domain has a high positive charge (Na is involved)

Question 28

What are the two voltage-gated sodium channel gates and how do they work?

Answer 28

Activation gate - is closed and the inactivation gate is opened at -90mV (what the inside of the membrane being negative relative to the outside)
- Both gates are opened between -90 to +35mV
As long as one of these gate is closed, nothing will pass though (default state)
- Activation gate opens as voltage reaches -70mV to -50mC
- The activation gate is opened and the inactivation gate is closed at +35mV - -90mV

Question 29

How does the Potassium-gated channel differ from the sodium channel?

Answer 29

• Potassium-gated channels have a signle gate
• The gate is closed at a resting potential of -90mV
• Slow activation opens the gate from =35mV to -90mV

The Na is open between -90 and +35. So what’s gonna happen? K is gonna rush out. So, that means that the potential is going to drop back down and actually go below -90 because of the rush

Question 30

What are the three stages of an action potential on a neuron axon membrane and what happens in each: (think sodium)

Answer 30

Resting Stage: - 90mV
Depolarization Stage: membrane suddenly becomes permeable to sodium ions (always think in terms of Na. When gates open, we’re gonna be positive)
- Membrane potential may overshoot for large axons
Depolarization Stage - Na channels close within a few 10,00th of a second
- K channels open more than normal
**We can’t have an action potential unless it is depolarized. K will start to fly out even more, and since Na is no longer coming in, the action potential will start to go back down to the negative range
**Add in slide 47 graph and slide 48