Lecture 2: Membrane potential (voltage)

Question 1

What is or are the advantages to having a membrane?

Answer 1

allows cell to maintain concentration differences

Question 2

why a phospholipid bilayer? what are the advantages?

Answer 2

we can separate out particles to keep an aqueous solution on both sides of bilayer

• lipid membrane gives opportunity to separate ions
• lipid means ions will have difficult time crossing from one side to the other

Question 3

structure of a cell membrane

Answer 3

1. phospholipid bilayer
2. cholesterol
3. variety of molecules imbedded
4. physical properties

Question 4

variety of molecules embedded in the cell membrane

Answer 4

• extrinsic- only on outtre or inner surface

- intrinsic (transmembrane) spans glycol (glycosylated) proteins

Question 5

physical properties of cell membrane

Answer 5

liquid at body temperature

Question 6

why are the differences between extra and intra cellular concentration of ions

Answer 6

• intracellular anions (proteins) are unable to migrate

- membrane semipermeable to K+ and Cl- but not to Na+

Question 7

two types of gradients or driving forces

Answer 7

chemical or concentration gradient

-electrical gradient

Question 8

the electoral gradient is _______________ to the concentration gradient

Answer 8

equal to and opposite in direction

Question 9

Na+/K+ pump

Answer 9

• 2 subunits
• binding sites
• requires ATP to go against concentration gradient
• 3Na+ moved out of the cell and 2 K+ are moved into the cell

Question 10

calculated Em from GHK eq

Answer 10

-90mV

Question 11

actually measured Em

Answer 11

-85 mV

Question 12

contribution to Em by Na+/K+ pump

Answer 12

-5 mV

Question 13

what are the unique features of neural muscle tissue

Answer 13

threshold, overshoot, hyperpolarizing afterpotential

Question 14

what did the Hodgkin and Huxley experiment with the giant squid axon suggest:

Answer 14

there was a change in membrane permeability to Na+ and K+

-too fast to be a carrier process; suggested channel or pore

Question 15

Na+ channel

Answer 15

• multiple subunits
• selectivity filter (lets Na+ through)
• voltage sensor
• inactivity gate
• domains or alpha subunit
• function during depolarization

Question 16

inactivation after ____ms depolarization clases the h gate

Answer 16

1-2

Question 17

K+ channel

Answer 17

• 1 domain x 4 subunits
• 30 types similar in muscle and nerve
• stabilizes membrane counteracts Na+

Question 18

why is the fact that depolarization spreading in all directions from the initial depol a problem?

Answer 18

in the nerve: want unidirectional depolarization

in the muscle: NMJ in middle of length of fiber

Question 19

are all nerve fibers myelinated?

Answer 19

no not c-fibers-pain (motorneurons are all myelinated though)

Question 20

salutatory conduction

Answer 20

depolarization from node to node

Question 21

what is the advantage of salutatory conduction? (depol from node to node)

Answer 21

less energy required to pump ions across membrane following depolarization

Question 22

Action potentials propagate more slowly in ______ fibers than along _____ axons

Answer 22

action potentials propagate more slowly in muscle fibers than they do along nerve axons (myelination makes it faster)