Action Potential

Front 1

action potential

Back 1

Abrupt depolarization of the membrane for a very brief period of time that allows the neuron to communicate over long distances

Front 2

membrane potential

Back 2

the electrical charge across a cell membrane or the difference in the electrical potential inside and outside of the cell

Measured w/ respect to the outside of the cell

Front 3

resting potential

Back 3

the membrane potential of a neuron at rest or when it is not being excited or inhibited by other inputs

Normally approx –70mV

Front 4

Microelectode

Back 4

a very fine electrode that can be used to electrically stimulate or record from a neuron

Front 5

oscilloscope

Back 5

measures and shows voltage over time

Front 6

Depolarization

Back 6

reduction of the membrane potential from its normal resting potential

Towards zero

Front 7

Hyperpolarization

Back 7

increase in the membrane potential relative to the normal resting potential

More negative

Front 8

Threshold of excitation

Back 8

voltage level that triggers an action potential

Front 9

Diffusion-

Back 9

movement of molecules from regions of high concentrations to regions of low concentrations

Front 10

Molecules tend to

Back 10

distribute themselves evenly throughout the medium over time

Front 11

Electrolytes

Back 11

materials that are charged in water

Front 12

Ion-

Back 12

charged particle

Cation- positive charge
Anion- negative charge

Front 13

Cation-

Back 13

positive charge

Front 14

Anion-

Back 14

negative charge

Front 15

Electrostatic pressure

Back 15

force of attraction or repulsion between ions
Opposites attract
Like repels

Front 16

Ion channels

Back 16

channels in the cell membrane that allow for the passage of particular ions either in or out of the cell

Front 17

Voltage dependent ion channels

Back 17

ion channels that open in response to changes in membrane potential

Front 18

V-D Na+ channels require_________ to open

Back 18

depolarization

Front 19

V-D K+ channels are __________ and require ____________ to open

Back 19

less sensitive

more polarization

Front 20

What if the membrane suddenly became permeable to Na+?

Back 20

?

Front 21

Once threshold is reached Na+ channels......

Back 21

..... open and Na+ rushes into the cell

-70mV to +40mV

Front 22

The K+ channels open .....

Back 22

slightly later

Front 23

At height of AP Na+ channels become ....

Back 23

Refactory

Front 24

No more Na+ entering and K+ is still leaving the cell

Back 24

Inside of cell is now depolarized so K+ leaves the cell

Front 25

The outflow of cations returns the membrane back to resting potential

Back 25

overshoot
K+ channels close
Na+ channels reset

Front 26

The sodium - potassium pump

Back 26

Also called Na+/K+ transporter
Maintains the resting potential
Pumps 3 Na+ ions out for every 2 K+ ions into the cell
Requires energy
Membrane is somewhat leaky to Na+ & leaky to K+

Front 27

Rate Law

Back 27

variations in the intensity of a stimulus or other information transmitted in an axon are represented by variations in the firing rate

Front 28

All or none law

Back 28

an action potential once triggered is transmitted without decreasing in size to the end of the neuron

Front 29

Advantages of s

Back 29

Economy
Less Na+/K+ transporters that require energy
Speed
Transmission between nodes is very fast
Allows for faster reaction times, faster thinking
Increasing the size of the axon also increases conduction speed

Front 30

What about myelin and the nodes of Ranvier?

Back 30

Node of Ranvier is in contact with the extracellular fluid
Myelinated portion is not

Front 31

Salatary conduction

Back 31

conduction of AP’s in myelinated axons. The AP “jumps” from one node of Ranvier to the next
“jump” is a misleading term

Front 32

AP is always the same _____

Back 32

size

Front 33

AP travels one way because it starts at the_____ and also the____maintains this

Back 33

soma

Refractory period of Na+ channels

Front 34

Advantages of salutary conduction

Back 34

Economy
Less Na+/K+ transporters that require energy
Speed
Transmission between nodes is very fast

Front 35

SO basically....

Back 35

Allows for faster reaction times, faster thinking

Increasing the size of the axon also increases conduction speed

Front 36

What would happen in the AP if you flooded the extracellular space with K+?

Back 36

Excess extracellular K+ depolarizes the neuron so if it stays high then no more AP’s. A ten-fold rise in K+ eliminates the resting potential. Brain is partially protected from this by the BBB and by glia cells, particularly astrocytes, which help regulate extracellular K+ levels.

Front 37

What would happen to the membrane potential if you added Na+ into the cell?

Back 37

if you added enough Na+ to reach threshold you would elicit an AP.

Front 38

What would happen to the membrane potential if you added Cl- to the cell?

Back 38

The cell would become hyperpolarized and it would be harder to reach threshold and therefore harder to fire and AP.

Front 39

What would happen if you made the Na+/K+ pump inactive?

Back 39

The pump maintains the resting potential and if you made it inactive it could not keep the resting potential and the neuron would eventually be unable to fire and AP.

Front 40

Membrane potential is produced

Back 40

a balance between the forces of diffusion and electrostatic pressure

ions in the extracellular and intracellular fluid

Front 41

Organic anions (A-)‏

Back 41

Only intracellular
Too big to pass through membrane

Front 42

Chloride ions (Cl-)‏

Back 42

Mostly extracellular

Front 43

Sodium ions (Na+)‏

Back 43

Mostly extracellular

Front 44

Potassium (K+)‏

Back 44

Mostly intracellular

Front 45

2 forces acting on the K+ ion, do what:

Back 45

Diffusion pushes it out of the cell
Electrostatic pressure pushes it into the cell

Front 46

2 forces acting on the Cl- ion (do what)

Back 46

Diffusion = into the cells
electrostatic pressure =out of the cell

Front 47

2 forces acting on the Na+ ion ( do what)

Back 47

Diffusion = in
electrostatic pressure = in

Front 48

Absolute refactory period

Back 48

when the sodium channels are refractory and cannot open regardless of the voltage.

In this time no AP can be elicited.

Front 49

Relative refactory period

Back 49

the time immediately after the AP has fired when the resting potential has been overshot and the membrane is hyperpolarized.

In the relative refractory period the V-D Na+ channels can open but the voltage is below resting (so below –70mV) and a stronger than normal stimulus is required to fire an AP.