Unit1Lec 2-The Membrane Potential

Question 1

Membranes consist of?

Answer 1

• Phospholipids
• Proteins

Question 2

Function of Phospholipid bilayer

Answer 2

• Acts a barrier to many solutes
• Makes a seperation b/n the extra-cellular and intra-cellular environment

Question 3

Function of Transmembrane proteins

Answer 3

• Provides permeation pathway
• Acts a sensors that relay pathways

Question 4

Transmembrane protein function and regulation is the essence of what three factors?

Answer 4

1. Cellular communication
2. Changing cellular fxn by controlling what goes into and out of cell
3. Events that occur inside cell

Question 5

List the 3 mechanism that transport across the membrane occurs

Answer 5

1. Diffusion
2. Carrier Proteins
3. Ion Channels

Question 6

Explain Diffusion mechanism

Answer 6

Solute or small species can simply diffuse through the plasma membrane

Question 7

Explain Carrier Protein mechanism

Answer 7

Proteins that provide help for solutes to cross the plasma membrane b/c they are too big or charged

Question 8

Explain Ion Channel mechanism

Answer 8

Channels formed by some of the protein in the lipid bilayer, and form a water soluble channel that provides an environment for ions like Na+, K+, Cl- and Ca2+ to move from inside the cell to outside and vice versa

Question 9

What type of molecules can cross the plasma membrane easily?

Answer 9

Only small, lipophilic molecules

Question 10

What helps ions and larger molecules cross the membrane?

Answer 10

• Ion channels
• Transporters

Question 11

Ion channels vs transporters

Answer 11

• Ion channels: provide a continous aqueous space for ions to move
• Transporters: Have a receptor to bind; binding causes a confirmation change that opens up to the other side. Then looses affinity to release it.
• Ion channels are quicker than transporters

Question 12

List the major classes of ion channel

Answer 12

1. Leak
2. Stretch-activated
3. Ligand-gated
4. Voltage-gated

Question 13

Explain Leak ion channels

Answer 13

Constitutively active channels

Maintains the resting membrane potential of the cell

Question 13

Explain Streched-activated ion channels

LOW yield

Answer 13

When the plasma membrane is stretched, channel is activated

Question 14

Explain Ligand-gated ion channels

Answer 14

A molecule (i.e. neurotransmitter) binds to a protein to activate a channel

Question 15

Explain voltage-gated ion channels

Answer 15

Channel activates following a change in membrane potential

Question 16

Why does a voltage difference exists across the plasma membrane?

Answer 16

In resting state the inside of a cell is more negatively charged than its outside positively charged environment (charged gradient)

Question 17

What is the voltage difference across the membrane called?

Answer 17

Membrane potential= Em or Vm

Question 18

What creates the membrane potential (Em)?

Answer 18

Different ions concentrations across the plasma membrane, and selective permeabilites of those ions,resulting in a charged gradient

Question 19

Explain action potential

Answer 19

Trasient changes in membrane potential caused by the orchestrated opening and closing of ions cells

Question 20

At rest what is the membrane potential of neurons?

Answer 20

-70 mV

Question 21

Describe the mechanism of the activation of a action potential for a nueronal cell

Answer 21

At rest: -70 mV–>action potential causes depolarization (- to +)–>Repolarization quickly occurs after (+ to -)—>then hyperpolarization happens (past -70 mV)

Question 22

Explain the equilibrium (nerst) potential (Eeq)

HIGH yield

Answer 22

• Reflects a balance (at equilbrium) between the chemical gradient and electrical gradients for a single permeable ion

Question 23

What is the Nerst Equation?

HIGH yield

Answer 23

Eeq=58/z*log(co/ci)

z=ion charge
ci=internal concentration
co=external concentration

Question 24

What determines the direction an ion moves?

Answer 24

Knowing the equilibriun and membrane potential for that ion

Question 25

Where does membrane potential always want to go?

Answer 25

Towards equilibrium

Question 26

If Em is **less** than Eeq what is the movement for a cation (+)?

Answer 26

Moves IN the cell

Question 27

If Em is **more** than Eeq what is the movement for a cation (+)?

Answer 27

Moves OUT the cell

Question 28

if Em is **less** than Eeq what is the movement for a anion(-)?

Answer 28

Moves OUT of the cell

Question 29

if Em is **more** than Eeq what is the movement for a anion(-)?

Answer 29

Moves IN the cell

Question 30

What determines the neuronal resting membrane potential?

Answer 30

The permeabilities and concentrations of Na+, K+, and Cl

Question 31

What is the concentration of Na+, K+, and Cl- inside and outside the cell at Em=-70mV? ## Footnote Equilibrium potential

Answer 31

* Inside: 10 Na+, 30 Cl-, 140 K+ * Outside: 145 Na+, 110 Cl-, 5K+

Question 32

What is the membrane potential of Na+ for a resting neuron? ## Footnote HIGH yield

Answer 32

E(Na+)=+67 mV

Question 33

What is the membrane potential of Cl- for a resting neuron? ## Footnote HIGH yield

Answer 33

E(Cl-)=-33 mV

Question 34

What is the membrane potential of K+ for a resting neuron?

Answer 34

E(K+)= -84 mV

Question 35

What is used to calculate membrane potential?

Answer 35

The Goldman Equation

Question 36

Explain the Goldman Equation

Answer 36

Describes the resting membrane potential accounting for relative permeabilites, and concentration gradients of the three primary permeable ions

Question 37

What is the Goldman Equation

Answer 37

Em=58log{(PK[Ko+]+PNa[Nao+]+PCl[Cli-])/(PK[Ki+]+PNa[Nai+]+PCl[Clo-])}

Question 38

List the 2 mechanisms that Em can be changed by?

Answer 38

1. changing internal/external ionic concentrations (primarly K+) 2. changing the relative permeability of the ions across the plasma membrane

Question 39

What ion is the resting mammalian neuron most permeable to and why?

Answer 39

K+, thus Em is closest to the equilibrium potential of K+ Resting potential= -70mV EK+= -87 mV

Question 40

As external [K+] increase, Em becomes.....

Answer 40

Less negative (depolarization)

Question 41

As external [K+] decreases, Em becomes....

Answer 41

More negative (hyperpolarization)

Question 42

What occurs to Em when an ion increases permeability?

Answer 42

Em moves toward the equilbrium potential of the ion with increased permeability

Question 43

6. Which of the following ions would cause the most substantial change in resting membrane potential (Em) if its external concentrations were increased? A. Na+ B. Cl- C. Ca2+ D. K+

Answer 43

d. K+