Module 3: Lecture 1

Question 1

what separates the intra and extra cellular fluid?

Answer 1

the plasma membrane
- restricts the flow of molecules

Question 2

what does saying “the membrane has been polarized” mean?

Answer 2

there is a separation of charge across the membrane

Question 3

what is the fundamental basis for cellular communication in nervous and muscle tissues?

Answer 3

when we allow ions to somehow mix and traverse across the membrane
- the separation of charge that allows your nervous system to communicate

Question 4

the plasma membranes of all living cells are polarized _________.

Answer 4

electrically
- forms a ‘membrane potential’

Question 5

what are the key factors regarding membrane potential?

Answer 5

• it is defined by the separation of charge
• difference in the relative number/concentration of cations and anions in the ICF and ECF
• difference in permeability of key ions
• therefore: ion movement (membrane potential) is influenced by both ion concentration and membrane permeability

Question 6

what is membrane potential measured by?

Answer 6

Volt or millivolt (mV)

Question 7

the movement of ions across a membrane are determined by?

Answer 7

• concentration gradient (high to low)
• electrical gradient (opposites attract, similar charges repulse)
• combined effects = the electrochemical gradient

Question 8

whether the ion moves across the membrane or not depends on?

Answer 8

whether the membrane is permeable to that ion
- cell membranes are very restrictive to the flow of ions across it

Question 9

what makes a membrane have a ‘potential’?

Answer 9

when there is an unequal distribution of electrical forces
- hence, a membrane potential has been generated
- exists because of an unequal + and - on both sides

Question 10

is the membrane itself charged?

Answer 10

no

Question 11

why are the ECF and ICF neutral?

Answer 11

because the net charge of cations is balanced by the net charge of anions

Question 12

the magnitude of the potential (mV) depends on?

Answer 12

the number of opposite NET charges that are separated
- ex. difference between -8 and +8 is 16 which is greater than -3 and +3 which is 6. the membrane with 16 has a greater magnitude of potential, more net difference of the charge

Question 13

do all cells have a membrane potential?

Answer 13

yes

Question 14

what are the two different cell types on whether they can utilize the cellular potential?

Answer 14

• non-excitable cells
• excitable cells
• they have a ‘resting membrane potential’ that is relatively constant

Question 15

what are excitable cells?

Answer 15

• nerve or muscle cells that can produce rapid and transient changes in their resting membrane potential when excited (called electrical signal (communicaton))

Question 16

what are key ions in membrane potential?

Answer 16

• sodium (Na+)
• potassium (K+)
• negatively charged intracellular proteins (A-)

Question 17

do we have more sodium ions in extra or intracellular fluid?

Answer 17

extracellular

Question 18

do we have more potassium ions in extra or intracellular fluid?

Answer 18

intracellular

Question 19

where are negatively charged intracellular proteins more concentrated, ICF or ECF? and why can’t they flow down their concentration gradient?

Answer 19

• ICF
• because they have no permeability; they are only going to be contributing to the membrane potential within the inside of the cell

Question 20

is the cell membrane more permeable to potassium or sodium?

Answer 20

potassium

Question 21

a lot more potassium can _____ the cell than sodium can ____ the cell at rest for a nerve cell

Answer 21

1. leave
2. enter

Question 22

since ions like Na and K are water-soluble, they cannot diffuse across the lipid-rich plasma membrane. so how do they pass through the membrane?

Answer 22

they can move through ion channels
- they are protein channels embedded into the bilipid membrane that allow the ions to traverse across it
- PASSIVE channels. NOT active transport
- sometimes referred to as Leak ions

Question 23

are protein (leak) channels selective?

Answer 23

• yes
• you have sodium leak channels and potassium leak channels

Question 24

what happens to the charge of the ICF and ECF when potassium ions move out of ICF and into ECF?

Answer 24

ICF becomes for negative and ECF becomes more positive

Question 25

why is the ICF more negatively charged than the ECF?

Answer 25

because the membrane is impermeable to large proteins (A-)

Question 26

when are the electrical gradients and the concentration gradients completely balanced? (equilibrium potential)

Answer 26

when there is no further NET movement of K+
- when the inward electrical gradient exactly counterbalances the outward concentration gradient

Question 26

what pushes potassium into the cell and what pushes potassium out of the cell?

Answer 26

out of the cell: the concentration (chemical) gradient
into the cell: the electrical gradient (A- ions make the inside more negative so that potassium will be attracted to the inside)

Question 27

what has happened once the potassium equilibrium potential of -90mV has been reached?

Answer 27

• the plasma membrane has a potential
• no net movement of K+ across the membrane
• a large concentration of K+ still exists inside the cell

Question 27

inside the cell, relative to the outside of the cell, at equilibrium what is the membrane potential? (potassium equilibrium potential)

Answer 27

-90mV

Question 28

why do we talk about the inside of the cell as -90mV rather than the outside being +90mv?

Answer 28

• random convention so we all utilize the same language
• we always reference the inside of the cell with respect to the outside of the cell

Question 28

what is the -90mV dictated by?

Answer 28

• the intracellular protein membrane potentials
• key- the concentration differences

Question 29

how do we measure the -90mV?

Answer 29

the Nernst equation:

E= 61 log Co/Ci

E= equilibrium constant for the ion in mV
61= constant
Co= concentration of the ion outside the cell
Ci= concentration of the ion inside the cell

Question 30

what is the equilibrium potential for sodium?

Answer 30

+65mV