Fluids and equilibrim

Question 1

What is the typical cell membrane potential?

Answer 1

-70mV

Question 2

What is electrical neutrality?

Answer 2

Is the equal distribution of cations and anions in any compartment.

Question 3

How are cells able to create a negative membrane potential?

Answer 3

They are able to alter their charge distribution between ECF and ICF causing a few charges to move without altering the bulk concentrations

Question 4

The inside of a membrane is always what?

Answer 4

Slightly more negative inside than outside.

Question 5

What is the principle of electrical neutrality?

Answer 5

Small changes in the number of ions creates a large potential difference across the membrane without affecting the bulk concentrations of ion.

Question 6

What is membrane potential?

What is it generated by?

Answer 6

The voltage across the membrane at any moment.

It is generated by the movement of ions across the membrane

Question 7

What is the membrane potential governed by?

Answer 7

It is governed by the chemical concentration gradient and electrical potential difference

Question 8

What establishes the electrochemical gradient?

Answer 8

Leak and voltage gated ion channels.

Question 9

How is electrochemical equilibrium achieved?

Answer 9

It is achieved when there is a balance in the concentration gradient and electrical gradient.

Question 10

Describe how electrochemical equilibrium is achieved using K+?

Answer 10

membranes are permeable to K+ which causes it to leave the cell through Na/K pump into the ECF, this leaves a negative charge in the cell. This electrochemical gradient draws K+ back into the cell.

Question 11

What is used to maintain the equilibrium?

Answer 11

ATP is used to create and maintain Na+/K+ gradients via Na+/K+ ATPase pump.

Question 12

What are the three reasons that ATP is important?

Answer 12

ATP maintains normal ionic concentrations.
Indirectly determines the cellular gradients of other ions and molecules
Basis of membrane potentials.

Question 13

What does the Nernst equation measure?

Answer 13

It measures the voltage difference across the membrane for a single ion in mV.

Question 14

At equilibrium potential what is the net movement of ions?

Answer 14

Net movement of ions is zero.

Question 15

What is Ek with respect to mV?

Answer 15

Ek is negative with respect to mV, so K+ will move out of the ICF into the ECF until the membrane potential reaches -90mV and the electrochemical gradient equilibrates.

Question 16

What is ENa and ECa in respect to mV?

Answer 16

ENa and ECa are positive with respect to mV, so when allowed Na+ and Ca+ will enter the cell until mV becomes positive.

Question 17

How can you determine if the membrane potential will be positive?

Answer 17

The membrane potential will be positive if the [ECF] is higher than the [ICF].

Question 18

Is the membrane only permeable to Na+ and K+?

Answer 18

No, membrane is permeable to many ions but Na+ and K+ are most considered.

Question 19

What equation do we use to calculate resting membrane potential considering all ions?

Answer 19

The Goldman equation, which takes into consideration the permeability of each ion as well concentration gradients.

Question 20

What is the major determinant of membrane potential?

Answer 20

K+ efflux through K+ ion channels

Question 21

What effect does extracellular [K+] have ?

Answer 21

[K+] below 3.5mmol/L is considered Hypokalaemia

[K+] above 5.5mmol/L is considered Hyperkalaemia

Question 22

What effect does Hypokalaemia have on excitable cells?

Answer 22

Hypokalaemia causes the resting membrane potential to become more negative, making an action potential more harder to achieve. Hyperpolarising the cell.

Question 23

What effect does Hyperkalaemia have on excitable cells?

Answer 23

Causes the resting membrane potential to be more positive, making an action potential easier to achieve. Depolarisation more likely to occur.

Question 24

Why are membrane potentials so important?

Answer 24

They are the basis of action potentials.