graded potentials and action potentials (lec 4)

Question 1

excitability

Answer 1

• ability to produce an electrical signal that can transmit information between different regions of the membrane
• their membrane is called excitable membrane

Question 2

polarized

Answer 2

resting membrane potential : -70mV

Question 3

depolarization

Answer 3

-cell is getting more positive following resting state

Question 4

overshoot

Answer 4

inside cell is more positive because K+ channels have not begun to open yet (slow)

Question 5

repolarization

Answer 5

• coming back to -70 mV
• K+ channels are finally open

Question 6

hyperpolarized

Answer 6

potassium channels slow to close so cell becomes more negative than normal polarized cell

Question 7

graded potentials

Answer 7

• a small, local change in membrane potential
• can occur in depolarizing or hyperpolarizing direction
• are graded
• are decremental
• can be summed
• have no threshold

Question 8

action potentials

Answer 8

• can be sustained nerve signaling over longer distances
• are large alterations in membrane potential
• are rapid and have a high frequency
• need voltage gated channels to occur
• 1-2ms duration
• all-or-none
• cannot be summed
• has refractory period

Question 9

na+ and K+ voltage gated channels

Answer 9

• activated by a change in electrical membrane potential
• important for action potentials
• both channels open at -55 mV
• K has only activation gate, Na has activation and inactivation gates

Question 10

ligand gated channels

Answer 10

• open in response to the binding of a chemical messenger
• important for graded potentials

Question 11

mechanically gated channels

Answer 11

• open in response to physical deformation
• important for graded potentials

Question 12

action potential 3 phases

Answer 12

action potentials occur at action hillock

-rising (depolarization)

stimulus occurs to get to -55mV

voltage-gated Na+ channels open at ciritcal threshold -55mV

-falling (repolarization)

Na channels closed

voltage gated k+ channels triggered open at -55 but very slowly

-after-hyperpolarization

K+ channels slow to close = hyperpolarized

Question 13

true or false : action potentials are all-or-none phenomenon

Answer 13

true

-once it hits -55mV action potential happens automatically

Question 14

Na+ channels : resting state

Answer 14

• activation gate is closed
• inactivation gate is open

Question 15

see lect 4 for specific openings and closing of channels

DRAW IT OUT

Question 16

lidocaine and tetrodotoxin

Answer 16

• prevents action potentials by blocking voltage-gated Na+ channels
• poison produced by puffer fish that blocks Na+ voltage gated channels

Question 17

threshold stimulus

Answer 17

• just strong enough to depolarize the membrane to this level
• usually 15 mV less negative than resting membrane potential

Question 18

absolute refractory period

Answer 18

• second action potential cannot be triggered
• AP will not fire
• sodium channels already open during rising and during falling there is an inactivation gate inhibiting from firing

Question 19

relative refractory period

Answer 19

larger than normal stimulus is required to trigger another action potential

-AP can fire

Question 20

AP

Answer 20

• 1 sec ~ 10 million ions can diffuse through 1 ion channel
• 50 million ions to change membrane potential by 100 mV
• one AP WILL NOT AFFECT concentration gradients

Question 21

DO graded or action potentials lose strength with distance

Answer 21

• graded potentials lose strength with distance
• AP do not

Question 22

why doesnt action potential propagate backward?

Answer 22

-refractory period prevents firing of another AP

Question 23

saltatory conduction

Answer 23

• action potentials jump from node to node as they propogate along a myelinated fiber
• dont actually jump, are generated at each node
• at nodes of ranvier

Question 24

what do myelin on axons help with?

Answer 24

• sends info faster than an axon without myelin
• faster and with minimal leak
• greater myelination and diameter = faster conduction