Exam1Lec3ActionPotential

Question 1

What is action potential?

Answer 1

rapid, transient change in membbrane potential (Vm)

Question 2

Na+ channel activation

Answer 2

responsible for transient inward current that depolarizes membrane

Question 3

K+ channel activation

Answer 3

delayed activation responsible for delayed outward current that repolarizes the membrane

Question 4

Threshold potential

Answer 4

Minimum depolarization required for an action potential to fire

Question 5

Local current flow

Answer 5

action potential propagation along un-myelinated axon

Question 6

Saltatory conduction

Answer 6

action potential propagation along myelinated axons. Much faster conduction

Question 7

AP refractory period

Answer 7

time lag between action potentials

where ion channels rest b4 another ap can re-fiire

Question 8

Multiple sclerosis

Answer 8

autoimmune, degenerative disease of axon demyelination
incr passive current flow
decr AP conduction velocity

Question 9

Action potential usuaslly initiates in ____.

Answer 9

axon hillock

axon hillock= trigger zone

Question 10

without ____ we don’t have an action potential

Answer 10

ATP

life is a neuron with a charge across membrane, and to get charge we need energy from ATP. So Na2+/K+ ATPase pumps establish and maintain membrane potential

Question 11

What is EPSPS?

Answer 11

Makes Em more dep, and make is more likely to fire

driven glutamatergic transmission

Question 12

What is IPSP?

Answer 12

Makes EM more hyperpolarized

driven by GABA

Question 13

How can Em be changed?

slide 7
What triggers the physiological changes in membrane potential?

Answer 13

Changing internal or external ionic concentrations (usually K+)

changing relative perm of the ions across the plasma membrane

Question 14

How are ionic permeabilities changed?

Answer 14

1. Ligand gated (ex Gaba, glu, 5HT)
2. Voltage-gated (Na+, K+)
3. Nucleotide-gated (cAMP, cGMP)
4. Inward rectifier “leak” channels
5. Mechananosensitive-gated (stretch)

Question 15

What are the 5 types of voltage gated ion channels?

Answer 15

Na+, Ca2+, K+, Cl-, H+

very sensitive to membrane potential

Question 16

AP depolarization is triggered by transient opening of ____

Answer 16

Na+ channel

this always happens first and then we get a delay of K+ to hyperpolarization

Question 17

mechanism of the voltage-gated Na+ channels

Na+ channels have 3 conformational states following a dep, what are they?

Answer 17

1st: open (a or m) gate state
2nd: inactive (I or H) gate
3rd: closed state

Question 18

In the inactivation stage of Na+ what predominates?

Answer 18

Efflux of K+

Question 19

K+ channel produes the delayed ____ current

Answer 19

outward

Question 20

How does K+ channel produes the delayed outward current?

Answer 20

1. Dep triggers opening of voltage gated K+ channels
2. K+ ions rush out of the cell
3. K+ ions efflux causes a transient after hyperpolarization
4. Pk remains high, causing Vm to be transiently more neg than baseline resting Vm (after hyperpol phase)

this is a built in system to prevent ap from firing too fast to prevent cell death

Question 21

What is an important component of the molecular structure of Na+ and K+ channels?

Answer 21

They have 4 subunits and the 4th one has a voltage sensing fxn with ion selectivity ( this dictates which ions can flow)

Question 22

Potassium channels are ____

Answer 22

tetramers (comprised of 4 identical subunits)

Question 23

____ segments “sense” changes in Vm, and move in response to these changes

Answer 23

S4

amino acids residues change in repsince to small mV differencees in voltage

Question 24

For a neuronal action potential we see a transient, rapid incr in ____ and a slower more stable increase in ____.

Answer 24

Pna, Pk

Question 25

Rapid activation of ____ channels causes depolarization ____ channel inactivation stops depolarization Slower activation of ____ channels contributes to repolarization

Answer 25

Na+, Na+, K+

Question 26

Action potential waveforms vary in their shape. Why?

Answer 26

Because of differences in types of activated channels and their relative times of activity ## Footnote depends on type of neuron

Question 27

Na+ channel activation enters a positive feedback loop, explain this

Answer 27

Na+ channel activation leads to a depolarization that incr probability of activation more channels

Question 28

K+ channel activation enters a slow neg feedback loop, explain this

Answer 28

Channel activation leads to a hyperpolarization that decr prob of activating more channels

Question 29

What is action potential threshold?

Answer 29

Minimum dep needed to fire an AP. AP WILL NOT fire if Vm is under threshold. *AP is an all or non phenomenon* ## Footnote NOTHING will make is fire if its under threshold.

Question 30

How does Non-propagated dep spread? ## Footnote slide 23

Answer 30

Passiviely though local current flow, this is called electronic conduction ## Footnote we are not hitting threshold at the axon hillock

Question 31

Why does the dep signal decr over distance as it moves down the axon?

Answer 31

Ionic charges dissipate within an area and charges leak out (leaky membrane)

Question 32

What is length constant?

Answer 32

the distance that 37% of vmax is reached ## Footnote vmax is the highest amplitude signal

Question 33

What factors influence length consant?

Answer 33

Membrane resistance and internal resistance within a cell ## Footnote internal resistance=interaxonal resistance

Question 34

If you have a high Rm (membeane resistance and low RI what does this mean for the length constant?

Answer 34

Larger length constant

Question 35

length constant is ____ to Rm and ____ to Ri

Answer 35

directly proportional, inversely prop

Question 36

How is AP maintained along the axon?

Answer 36

The peak membrane potential along an axon during an AP remains consistenly dep

Question 37

What is absolute refractory period?

Answer 37

A 2nd action potential can NOT fire b/c Na+ channels can not yet be re-activated-either in their open or inactivated state ## Footnote here, the mem potenital is so dep that its imposible for na+ to be reac to fire ap

Question 38

What is relative refractory period?

Answer 38

A much greater dep is required for an ap to fire. Still active voltage gated K+ channels move membrane away from threshold potential. ## Footnote mostly contributed by the activation of K+ channels openihng, K+ efflux, and hyperpol. This is after hyperpol so dep is needed for ap to take place

Question 39

What is needed in order for a charge in membrane potential?

Answer 39

Charges must be re-distributed across the membrane-the membrane must be changed

Question 40

Time needed to charge membrane to change Vm is the ?

Answer 40

rate limiting evenft for AP propagation (dictates firing propagation)

Question 41

What is time constant (t)

Answer 41

The time it takes for the change in Vm to reach 63% of its final value. ## Footnote small neurons=small memrane amt= fast charging= quick time constant opposite for large neurons

Question 42

Myelination ____ conduction velocity because Rm ____ length constant and Cm____ time constant.

Answer 42

increases, increases, decreases ## Footnote Insulating nature of myelin will incr Rm Cm decr bc or addition of membrane myelin

Question 43

Saltatory conductions: where propagation along myelinated axons where AP jumps from one node to the next. How does myelination affect Rm, Cm, Vm, Conduction velocity, and length constant

Answer 43

Incr Rm Decr Cm (at myelination site) Decr Vm Incr conduction velocity Incr Length constant ## Footnote length constant is incr bc channels can be distributed farther apart bc signal will be maintained over a greater distance

Question 44

For an unmyelinated axon it has ____ conduction because of ____

Answer 44

slower , local current flow (electrotonic conduction) ## Footnote areas of de-mye = nodes of ranvier, and this is where Na+ ions collect and where depolarization takes place to trigger dep

Question 45

For myelinated axons it has ____ conduction because of ____.

Answer 45

Faster, saltatory conduction (action potential jumps from node to node)

Question 46

What is multiple sclerosis?

Answer 46

An autoimmune degenerative disease of an axon demyelination. This causes conduction velocity to dec. Channels tend to re-distribute along the axon and action potential propagate through passive current flow whihc is much less effective

Question 47

Conduction velocity is influenced by what two things?

Answer 47

Myelination and axonal size ## Footnote Ri decr in. proportiion to the square of the axon diameter