L7 Action Potentials

Question 1

K+ equilibrium potential

Answer 1

-90mV

Big conc gradient favors efflux
\+
Small electrical gradient favors influx 
=
Weak outward driving force
but w/ high permeability

Question 2

Na+ equilibrium potential

Answer 2

+65mV

Big conc and electrical gradients favor influx
=strong inward driving force
But with low permeability

Question 3

What would happen if permeability to Na+ suddenly increased? And then permeability to K+ increased?

Answer 3

Drives it right toward its equilibrium potential (65) very quickly, depolarize

Drives it back towards its equilibrium potential (-90) very quickly, repolarizes

Question 4

Action potentials are always the _____ magnitude and move in what direction?

Answer 4

SAME

only move in one direction

Question 5

Action potentials take place as a result of?

Answer 5

A triggered opening and subsequent closing of two specific channels

All are triggered at the same threshold!
Over or under -55mV

Question 6

What are the triggered channels involved in action potentials?

Answer 6

Voltage gated Na+ activation gate
Voltage gated Na+ inactivation gate
K+ voltage gated channel

Question 7

Na+ activation gate

Answer 7

Opens to allow Na+ to move outside in initially when triggered by -55mV

Opens rapidly

is open from threshold to peak (-55 to +30mV)

At rest , it’s closed

Question 8

Na+ inactivation gate

Answer 8

Stops further influx of Na+ when triggered by -55mV (same time as activation)

Closes slowly
Is closed from peak to resting (30mV to -70mV)
Doesn’t completely close until peak is reached

At rest, it’s open

Question 9

K+ voltage gated channel

Answer 9

Triggered at threshold to open (-55mV)

Delayed opening
Not fully opened until peak (30mV)

Open through peak to after hyperpolization (30 to -80)

Question 10

Positive-feedback cycle for opening of Na+ channels at threshold

Answer 10

The passive spread of current from adjacent site that’s already depolarized spreads down membrane causing further depolarization/decrease in membrane potential because moving further away from threshold point and can’t reset to rest to trigger another action potential

Question 11

Refractory period

Answer 11

Ensures one way propagation of action potential

Limits frequency (impossible to get two at same time)

Question 12

Absolute refractory period

Answer 12

Interval during which NO stimulus can elicit an action potential

Most voltage gated Na+ channels are inactivated

Question 13

Relative refractory period

Answer 13

Interval when a SUPRANORMAL stimulus is required to elicit an action potential ( in hyperpolarized state)

Just have generate more depolarization (-80 to -55 instead of -70 to -55)

Due to elevated gK coupled with the residual inactivation of voltage gated Na+ channels

Question 14

Hyperkalemia

Answer 14

Depolarizes, so it’s easier to get an action potential because it’s closer to -55mV

Question 15

If hyperkalemia is severe what happens

Answer 15

membrane depolarizes so much and Can’t back get to threshold (-55mV) and stuck in absolute refractory period

Paralysis- permanent or periodic

In periodic- Na+-K+ ATPase pump can reset levels to below -55mV and action potentials can fire again

Question 16

What factors determine speed of conduction?

Answer 16

Diameter

Myelination

Question 17

What’s the relationship between diameter of fiber and speed of conduction?

Answer 17

Larger diameter=less resistance =rapid fibers
Motorneurons

Smaller diameter=more resistance=slow fibers
   Internal organs (gut, glands)

Question 18

Myelination

Answer 18

Lipid insulator

Keeps charges inside axon and greatly increases the conduction velocity

Question 19

Myelinated vs unmyelinated fibers

Answer 19

Myelinated axons are always faster

Even with smaller diameter

Question 20

Contiguous conduction

Answer 20

Conduction in unmylienated fibers

Action potential spreads along every portion of the membrane

Takes a long time

Question 21

Saltatory conduction

Answer 21

50x faster

Impulses jump over sections of fiber covered with insulating myelin

Action potential jumping from one node of ranvier to next

Question 22

All or nothing principle

If a stimulus exceeds threshold

Answer 22

An action potential will be initiated

An action potential will always be same magnitude because they only have one trigger

Either triggered or not

Question 23

Stimulus strength is produced by

Answer 23

Rate of stimulus, NOT magnitude

Lower amplitude of graded potentials = slower rate of action potentials= weaker stimulus

Higher amplitude of graded potentials= high rate of action potentials = stronger stimulus