Section 3

Question 2

Describe the relationship between concentration and electrical gradients using an K+ as an example.

Question 3

Define depolarization and hyperpolarization.

Question 4

What are electrical gradients?

Answer 4

A difference in the concentrations of anions and cations across a barrier creates a separation of charge. Opposites charges attract, and this separation of charges creates an electrical potential across the membrane (aka membrane potential, measured in volts).

Question 5

Define what is meant by an excitable cell.

Answer 5

Some cells such as nerves and muscle cells are what we call excitable cells and make use of the electrical potential for their functional role in the body.

Question 6

What is Ohm’s Law?

Answer 6

The relationship between membrane potential and ionic currents

Equation:
V = IR
where V is voltage (the membrane potential), I is the current (ions moving across the membrane), and R is resistance (the ability of the plasma membrane to resist ion movement across it)

Question 7

How do ions move across the plasma membrane?

Answer 7

Ion channels

Question 8

What are the four main classes of ion channels?

Answer 8

Voltage-gated, chemically gated, mechanically gated, and thermally gated

Question 9

Describe briefly how voltage gated ion channels work.

Answer 9

They open and close in response to changes in the membrane potential.

Question 10

Describe briefly how chemically gated ion channels work. What is a common place they’re found?

Answer 10

They open when a specific chemical messenger (known as a ligand) interacts with it.

They can be found in the dendrites in neurons.

Question 11

Describe briefly how mechanically gated ion channels work. Provide an example.

Answer 11

They open in response to mechanical deformations such as stretch.

Example is those in the cochlea of the ear.

Question 12

Describe briefly how thermally gated ion channels work. Provide an example.

Answer 12

They respond to changes in temperature.

They are present in specialized neurons that project to the skin to act as temperature detectors.

Question 13

What is the electrochemical gradient?

Answer 13

It is a combination of the concentration and electrical gradients. They can work together or in opposition.

Question 14

What is the Nernst equation used for?

Answer 14

used to calculate the equilibrium potential (E) which is aka the reversal potential. This is the membrane potential at which there is no net flow of an ion across the membrane due to a balance between the electrical and chemical gradients

Question 15

Know the equation for Nernst equation?

Question 16

What are E values important for?

Answer 16

In determining if the net driving forces move ions into or out of a cell.

The net flow will always be in the direction that brings the membrane potential to its E. Because of this, the equilibrium potential of an ion can also be called its reversal potential

e.g, if the membrane potential is higher than the E value, this means the conc gradient is strong than the elec gradient and positive ions will flow out of the cell to make its membrane potential more negative.
The opposite is true as well

Question 17

What is the resting membrane potential?

Answer 17

(RMP)
it is the electrical potential across its membrane

Question 18

What is the resting membrane potential dependent upon?

Answer 18

the types of ions channels in a membrane, the concentration of ions on both sides of the membrane and their relative permeabilities at that time

Question 19

When the cells RMP is negative, what does that mean in relation to the charges on the inside/outside of the cell.

Answer 19

If the RMP is negative, the inside of the cell is negative relative to the outside

Question 20

When there are both K+ and Na+ channels present, will the RMP:

a) settle at the RMP for Na+
b) settle at the RMP for K+
c) settle at a RMP value between the two

Answer 20

c) And you would have to calculate this using the Goldman equation

Question 21

Which one of the following can be calculated using the Nernst equation:

a) EP
b) RMP

Answer 21

EP

Question 22

Which one of the following is dependant partly upon the types of ion channels in a membrane:

a) EP
b) RMP

Answer 22

RMP

Question 23

Which one of the following applies to an ion:

a) EP
b) RMP

Answer 23

EP

Question 24

Which one of the following is also called reversal potential:

a) EP
b) RMP

Answer 24

EP

Question 25

Which one of the following is a measure of the electrical potential across the membrane:

a) EP
b) RMP

Answer 25

RMP

Question 26

Which one of the followings value determines if the net driving forces move ions into or out of a cell:

a) EP
b) RMP

Answer 26

EP

Question 27

Which one of the following can be calculated using the Goldman equation:

a) EP
b) RMP

Answer 27

RMP

Question 28

What is depolarization?

Answer 28

When the magnitude of the polarization decreases (moves towards 0 mV)

Question 29

What is repolarization?

Answer 29

After either a depolarization or a hyperpolarization, once the polarizing begins to return towards the RMP then it is said to be repolarizing

Question 30

What is hyperpolarization?

Answer 30

When the magnitude of the polarization increases (moves even more negative than the RMP)

Question 31

For excitable cells, if the membrane depolarizes enough it will fire what we call ___________.

Answer 31

an action potential

Question 32

What are graded potentials?

Answer 32

Local changes in membrane potential that are used for short distance signalling.

Typically small in magnitude,
but can change in magnitude or strength.

The magnitude and duration of a graded potential depend directly on the strength and duration of the triggering stimulus.

Question 33

What are graded potentials generally caused by?

Answer 33

Triggering events that make voltage-gated ion channels open

Question 34

Why do graded potentials not move far along the membrane/not last long?

Answer 34

Because as the wave of depolarization moves along the membrane, there is a loss of charge. The magnitude of the graded potential decreases as it moves away from the site of the initial triggering event until it eventually disappears.