Exam 1: Membrane Potential

Question 1

What is total osmotic pressure?

Answer 1

For each mOsmo of “stuff” we have dissolved in 1 kg of water, each mOsomo can exert 19.3 mmHg of pressure where water can move around/in between

Question 2

How do you calculate total osmolarity?

Answer 2

Multiple the mOsmo of “stuff” by 19.3
Ex: If we have 280 mOsmo of “stuff” dissolved, you would multiply 280 by 19.3
280 * 19.3 = 5,404 mmHg

Question 3

Define osmoLALITY

Answer 3

Osmolality is how much “stuff” we have dissolved in 1 kg of water
Osmols or mOsmols/ 1kg H2O

Question 4

Define osmoLARITY

Answer 4

Osmolarity is how much “stuff” we have dissolved in 1L of solution
Quantity/1L of solution

Question 5

What is the difference between osmolality and osmolarity?

Answer 5

Osmolality looks at the things that are dissolved in water vs. osmolarity looks at things that are dissolved in solution
*Remember that 1L of solution is a little different than 1L of water because the 1L of solution has some solutes that displace some of the water

Question 6

What are two units that we use when talking about quantity?

Answer 6

MiliOsmols (mOsmo) and milequivalent (mEq)

Question 7

What is concentration?

Answer 7

How much stuff we have dissolved in a solution; top part of the equation

Question 8

What is quantity?

Answer 8

How much of something we have; usually expressed in grams or mols

Question 9

What is the consequence of moving 5 ions in the opposite direction when using the Na/K pump?

Answer 9

3 sodiums are lost to the outside of the cell while 2 potassium are gained within this cell; this causes an overall loss of 1 positive charge which means that every time this pump cycles, we lose 1+ charge and the net movement of + charged ions is outside of the cell, causing the inside of the cell to be negatively charged

Question 10

How does the sodium-potassium pump keep osmolarity in check?

Answer 10

By removing/cleaning out excess sodium within the cell and allowing for water to follow that excess sodium

Question 11

What consequences would occur if the sodium potassium pump were to stop working and shut down?

Answer 11

If the pump shuts down, we would not be able to pump sodium out of the cell and so sodium would increase within the cell. This would cause water to stay inside the cell with the sodium and the cell would begin to swell and become edematous. This swelling would get worse and worse until the pump started to work again.

Question 12

At rest, are cells more electronegative or positive compared to conditions outside of the cell?

Answer 12

Electronegative

Question 13

Which pump plays a major role in determining resting membrane potential?

Answer 13

The sodium potassium pump

Question 14

What dictates the charge inside of the cell?

Answer 14

Electrolytes and their gradients

Question 15

When cells are “turned on” what is their charge?

Answer 15

When cells are turned on, they change from negatively charged to positively charged for a short period of time

Question 16

What charge to proteins often carry?

Answer 16

Net negative charge

Question 17

Is there a higher concentration of proteins inside or outside of the cell? How does this affect the charge of the cell?

Answer 17

There are more proteins inside of the cell than outside; this helps contribute to the negative charge of the inside of the cell

Question 18

Why do proteins make the cell more electronegative?

Answer 18

Proteins are made from amino acids and there are more negative amino acids than positively charged amino acids; these amino acids also contribute to the polarity of the cell

Question 19

What is the Nernst equation?

Answer 19

EMF (millivolts) = +/- 61 x log (concentration inside/concentration outside)

Question 20

What does the Nernst equation tell us?

Answer 20

It tells us what the charge of the cell would be if we would allow an ion to move across the cell wall and down its concentration gradient

Question 21

How can you determine whether you would use a + or - in the Nernst equation?

Answer 21

+ for anions; - for cations

Question 22

When at rest, is the cell more permeable to sodium or potassium?

Answer 22

Potassium; potassium is 10x more permeable at rest than sodium

Question 23

What is the overall membrane potential?

Answer 23

The overall membrane potential takes into account all ions that are able to be permeable and determines the equilibrium constant for all of the ions together.

Question 24

What is the dominant electrolyte that determines resting membrane potential?

Answer 24

Potassium

Question 25

Why is the overall resting membrane potential -81?

Answer 25

Potassium has a resting charge of -91 while sodium has a resting charge of 60. Because potassium is more permeable at rest, potassium will make the overall resting membrane potential closer to -91. However, since sodium is more positive, this will skew the resting membrane potential slightly toward a more positive number but not much.

Question 26

Why is the Goldman equation important?

Answer 26

The Goldman equation takes into account all of the ions that the cell is permeable to and determines the resting membrane potential