Week 5: membrane potentials and action potentials

Question 1

Potassium concentrations in/out of nerve cell

Answer 1

Potassium is high concentration in nerve fiber membrane

low concentration outside cell membrane

Question 3

How does electropositivity occur outside cell membrane

Answer 3

Ions flow out and carry positive electrical charge with them

Question 4

Effect of positive ion outflow of cell membrane

Answer 4

Diffusion potential decreases (until is ceases)

Question 5

Diffusion potential at which K+ diffusion ceases (from in–>out of cell)

Answer 5

-94 mV

Question 6

Diffusion of sodium in/out of cell and overall membrane potential

Answer 6

Sodium diffuses into cell (positive charge) and creates overall potential +61mV

Question 6

Nerst equation explaination

Answer 6

Greater ration of ions = greater tendency for ion do move in one direction = greater Nerst potential REQUIRED to PREVENT additional diffusion

Question 6

The Nerst equation explores

Answer 6

The relation of diffusion potential to ion concentration difference

Question 6

Sodium concentration (inside vs outside of cell)

Answer 6

High outside of membrane, low inside

Question 7

Nerst Potential refers to inside or outside of membrane?

Answer 7

Inside of membrane

Question 8

Nerst potential assumes that potential of extracellular fluid =

Answer 8

0

Question 9

Nerst potential of a membrane is positive if

Answer 9

Ion diffusing in—>out is negative

Question 10

Nerst potential of a membrane is negative if

Answer 10

ion diffusing from inside—- out is positive

Question 11

The Goldman Equation

Answer 11

Calculates the diffusional potential when membrane is permeable to many ions

Question 12

The Nerst equation assumes that

Answer 12

A membrane is only permeable to one ion

Question 13

The Goldman Equation factors in: (3)

Answer 13

1. Polarity of electrical charge of each ion
2. Permeability of the membrane (K+ is more permeable than Na+)
3. Concentration of ions on the inside and outside

Question 14

What ions are most important for developing membrane potentials in nerve and muscle fibers?

Answer 14

Na, K, Cl

Question 15

_______ is the key for determining voltage

Answer 15

Permeability

Question 16

Which ions have changing permeability during action potentials?

Answer 16

Na and K

Question 17

Which ions have fixed permeability during action potentials

Answer 17

Cl

Question 18

Resting membrane potential of nerves(calculated from goldman equation)

Answer 18

-70 mV

Question 19

2 Factors that account for the negative membrane potential

Answer 19

1. Sodium-Potassium pump pumps more + ions out than in (3 Na out, 2 K in)
2. K+ leak channels out
   more positives out of cell than into cell = negative

Question 20

Does Na or K have a higher magnitude inside:outside ratio

Answer 20

Potassium
K+ inside: K+ outside = 35

Na+ inside: Na+ outside = 0.1

Question 21

How do neuron action potentials begin?

Answer 21

Sudden change from resting negative membrane potential —> positive potential

Question 22

Once a neuron's action potential starts, it

Answer 22

moves along the nerve fiber until the fiber's end

Question 23

Action potential stages:

Answer 23

1. Resting 2. Depolarization 3. Repolarization

Question 24

Depolarization definition and cause

Answer 24

Potential rapidly rises (becomes less negative) cause: membranes become more permeable to sodium

Question 25

Repolorization definition and cause

Answer 25

Re-establishment of normal negative resting potential Cause: Sodium channels close and potassium channels open (K+ rapidly diffuses out of cell)

Question 26

Once action potential threshold is met:

Answer 26

It always fires and always goes the length of the neuron

Question 27

Sodium permeability is facilitated by

Answer 27

Activation/Inactivation gate

Question 28

Sodium gate at rest (neuron action potentials)

Answer 28

Gate is closed, prevents entry of sodium ions into nerve fibers

Question 29

What happens to trigger activation of depolorization?

Answer 29

membrane potential becomes less negative

Question 30

What is the trigger range (mV) for depolarization

Answer 30

-70 - -50 mV

Question 31

What happens to sodium gates when action potential depolarization threshold is met?

Answer 31

It has a conformational change and Na+ permeability rapidly increases

Question 32

What causes the increase in mV that lead to activation of depolarization

Answer 32

Na+ outflow by sodium-potassium pump (3+ out, 2+ in = more positive on the outside)

Question 33

Inactivation of Na+ gate

Answer 33

Voltage quickly increases with inflow of Na+ and gate quickly shuts (happens within a few 10,000ths of a second)

Question 34

Repolorization of membrane potential

Answer 34

Sodium channels close (no more + flows in) and Potassium channels open (more + flows out)

Question 35

At rest, potassium channels are

Answer 35

Closed

Question 36

As the membrane becomes more positive, potassium channels

Answer 36

Open and potassium diffuses out

Question 37

During depolarization, __________ flows in _____

Answer 37

During depolarization, Na+ flows in rapidly

Question 38

During repolorization, ______ flows in_____

Answer 38

During repolarization, K+ flows out slower

Question 39

During conductance, at rest K concentration is ____ than sodium (inside cell)

Answer 39

greater than

Question 40

During action potential, sodium conductance _____

Answer 40

Increases 5000 fold

Question 41

How does Ca+ contribute to membrane potential becoming positive?

Answer 41

Voltage gated channels allow Ca+ to flood in, increasing overall + charge

Question 42

Deficits in Ca+ lead to______. Why?

Answer 42

highly excitable neurons Neuron can't get all the way to resting potential - it does not repolarize all the way

Question 43

What is the threshold for action potential?

Answer 43

-65 mV?

Question 44

Propagation means

Answer 44

impulse travels in all directions

Question 45

Action potentials follow an _______ principle

Answer 45

all-or-nothing

Question 46

Schwann cells create

Answer 46

myelin sheath in myelinated axons in PNS

Question 47

Myelination _____ speed of transmission

Answer 47

insulates and increases speed of tranmission

Question 48

Ions flow through _____

Answer 48

Nodes of Ranvier

Question 49

Electrical currents flow through

Answer 49

Extracellular fluid and axoplasm

Question 50

Myelination ____ velocity of nerve transmission

Answer 50

increases nerve transmission

Question 51

Oligodendroytes

Answer 51

Similar to myelination, but in central nervous system

Question 52

What factors change sodium ion diffusion/cause excitation (3)? Examples?

Answer 52

1. Mechanical (pressure distorts membrane) 2. Chemical (i.e excitatory neurotransmitters/ligands bind and open Na+ gate) 3.Electrical (membrane potential increases, action potential starts)

Question 53

Membrane stabilizing factors _____ excite ability

Answer 53

Decrease

Question 54

Examples of membrane- stabilizing factors

Answer 54

1. calcium ions 2.Procaine and tetracaine (Na channels more difficult to open)

Question 55

What can create acute local potentials?

Answer 55

Small electrical stimulations

Question 56

Refractory period

Answer 56

Membrane needs to return to resting potential before it fires again

Question 57

acute sub-threshold potentials

Answer 57

Do not trigger a full action potential

Question 58

Saltatory conduction

Answer 58

Action potentials occur node to node jumping