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BIOL 404 > Action Potentials + Synaptic Transmission > Flashcards

Action Potentials + Synaptic Transmission Flashcards

1
Q

what was proposed by Johannes Peter Muller?

A
  • in 1835 johannes peter muller proposed the law of specific nerve energies
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2
Q

what is the law of specific nerve energies?

A

nature of perception is defined by the pathway over which the sensory information is carried
->each type of nerve has different properties that determine how we sense a stimulus

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3
Q

how is the brain like an encoder?

A

similar to morse code via action potentials
-> must be able to infer from beeps what the message is, like how APs go to the brain

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4
Q

what is an action potential?

A

ions moving through the membrane causing changes in membrane potential

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5
Q

what is a depolarized state?

A

more positive than resting potential

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6
Q

what is a hyperpolarized state?

A

more negative than resting potential

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7
Q

Na+/K+ ATPase

A

sets ionic gradients.
-> uses ATP to bring 3Na out, 2K in

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8
Q

K equilibrium potential

A

must have permeability to create potential
- when channels are introduced, K goes from high to low
1. concentration gradients push K out
2. electrostatic force pushes it back in

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9
Q

steady-state potentials

A

net inward current = net outward currnt
- net flow of all charges

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10
Q

equation for work required to move an ion in an electric field

A

We = (zF)*V

We = work required
z = valence of the ion
F = Faraday’s constant
V = voltage

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11
Q

work required to change concentration equation

A

Wc = RT*ln([X]2/[X]1)

-sum is 0 at equilibrium
- can predict what membrane potential will be for a certain ion
- nernst equation

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12
Q

what is the nernst equation @37c?

A

(61.5/z)(log([X]out/[X]in))

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13
Q

what is the nernst equation referring to?

A

a mathematical relationship used to calculate an ionic equilibrium potential

work required to change concentration = work required to move ion through electrical field

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14
Q

potassium flows in the direction that would drive Vm towards ……

A

Ek, wants to be at equilibrium

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15
Q

if you move resting potential more positive….

A

thats depolarization

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16
Q

if you move resting potential more negative…

A

thats hyperpolarization

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17
Q

when you move away from equilibrium, you create…

A

a driving force

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18
Q

driving force equals?

A

membrane potential - eq potential

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19
Q

Na flows in the direction that would tend to…

A

push Vm towards Eq potential

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20
Q

Cl flows in the direction that would tend to…

A

push Vm towards Eq potential of Cl

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21
Q

currents can go through the membrane via two distinct pathways…

A

channels (R= resistance) and the capacity of the neuron offered by the lipid bilayer membrane (C=capactiance)

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22
Q

resistance is proportional to….

A

channel properties such as pore size

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23
Q

resistance is the same as…?

A

conductance, they are inversely proportional. stronger resistance = harder to push current through

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24
Q

what is the difference between resistance and conductance?

A

resistance is how much you resist the flow of charge, conductance is how much you conduct

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25
Q

current depends on….

A

voltage, which is the driving force

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26
Q

larger voltage =

A

larger current

27
Q

larger resistance =

A

less current

28
Q

what is ohm’s law?

A

V= IR

current = conductance * voltage

net driving force tells you which direction the current will flow in
I = G*DF

29
Q

what is a capacitor?

A

two metal plates separated by an insulator and connected by a battery. the capacitor has the ability to store charge.

30
Q

current flow

A

flows through a resistor and capacitor set in parallel

31
Q

what does capacity depend on?

A

size of the plates (bigger = more charge you can store) and the gap between plates and insulator

32
Q

capacitance is…

A

charge per volt (C = q/V)

how much charge you can store to get a volt across the capacitor

33
Q

what is the time constant?

A

the amount of time required for the voltage to reach 63% of its final value

if the time constant of a neuron is 5ms, it will take 5ms for it to reach 63% of its voltage

34
Q

how can you find capacitance with time constant and resistance?

A

Tau = R*C

35
Q

delayed electrical signals

A

convey sense energies to the brain
- we live in the past
- time constant to charge the membrane

36
Q

which charges faster, a neuron with fewer channels or a neuron with more channels?

A

the one with more channels, because there is smaller resistance (less membrane)

37
Q

more channels =

A

less resistance because there are more ways for the electricity to flow through

38
Q

capacity current equation

A

C = q/V
q= CV
dq/dt= I = CdV/dt

39
Q

voltage along an axon

A

current will go some distance and leak out, length constant determines how far the signal spreads in time

40
Q

length constant equation

A

lambda = Sqr (Rm/Ri)
- the easier it is to leave the axon, the lower the length constant

41
Q

what is the length constant?

A

length constant the distance at which there is 63% of leakage; axial resistance.

aka if there is a length constant of 1mm, then 1mm away from the cell body down the axon, only 37% of the voltage magnitude remains

42
Q

what dictates leakage?

A

the ratio of resistance

if resistance is high, the current flows through the sides through the membrane resistance. the ratio of the two determines the length constant.

43
Q

action potentials

A

solves length problem:

  • long range communication is possible
  • AP continue because of active propogation
  • all or none events generated by voltage gated ion channels
44
Q

Na+ channels:

A

for an action potential to be initiated, both activation gate and inactivation gate must be clear

45
Q

activation gate

A

once open, sodium flows into the cell until its equil potential (+60mv)

46
Q

inactivation gate

A

closes Na+ hannels by plugging the channel

47
Q
A
48
Q

voltage gated Na channel role in AP

A

has an inactivation gate that turns off even even in depolarization which allows you to take AP back down

49
Q

K channel role in Ap

A

ensures unidirectional propagation:

  • K channels activate with a delay and pull membrane potential back which overshoots resting
  • activate and immediately inactivate so you cannot go backwards
50
Q

saltatory conduction

A

myelin decreases capacity current, tightens resistance and concentrates ion channels to nodes which allows current to spread faster

51
Q

why doesnt the action potential go backwards?

A

sodium inactivation gate + potassium channels being open (they have a high conductance for potassium, and there isnt a huge driving force for sodium downstream anymore)

52
Q

AP role in sensory systeems

A
  • some (mechano) use AP directly
  • some dont (photoreceptors would lose sensitivity)
53
Q

what is the difference between a chemical vs electrical synapse?

A
  • electrical goes directly from presynaptic cell to post via connexin
  • chemical uses transmitter to get from pre to post
54
Q

morphological correlates for the quantum hypothesis

A

support for chemical synapses came from being able to see the vesicles at the synaptic cleft

55
Q

what is the quantal hypothesis?

A

proposes that NTs are released in discrete packets or ‘quanta’ at synapses. it is an all or none event and the activation of postsynaptic receptors by said quanta leads to consistent, discrete responses in the postsynaptic cell

56
Q

what will decreasing calcium do to the probabilistic and quantal nature of synaptic release?

A

reducing Ca outside the EC matric will give no response or minimal response.

57
Q

what are the steps in synaptic transmission?

A
  1. bring the presynaptic neuron to threshold at the axon hillock
  2. conduction down presynaptic axon
  3. opening of voltage-gated calcium channels at the nerve terminals
  4. diffusion and action of Ca2+ at release machinery
  5. exocytosis and diffusion of transmitter in cleft
  6. activation of postsynaptic receptors
58
Q

SNARE hypothesis

A

proteins in vesicle membrane and presynaptic terminal are SNARE proteins that form complex (core) that primes vesicle for release
- requires energy

59
Q

molecules in SNARE

A
  • synaptobrevin - synaptic vesicle
  • syntaxin, snap 25 - presynaptic membrane
  • synaptotagmin - Ca sensor
  • mediate docking and priming release and retrieval
60
Q

what are the three steps involved in SNARE

A
  1. docking and priming
  2. release (exo)
  3. retrieval (endo)
61
Q

how is SNARE formed?

A

syntaxin in the membrane of the cell acts as a zipper using SNAP-25, when this complex comes together you get the SNARE complex

62
Q

what happens when Ca2+ comes in and binds to synaptotagmin?

A

it inserts itself into the transmembrane
- this pulls the v- and t- membrane together, eventually leading to the fusion of the two membranes and exo of transmitter molecules

63
Q

what happens when synaptotgamin is knocked out?

A

no fast synchronous release but instead slow asynchronous.
- Ca binding leads to insertion into the membrane which pulls v and t together and leads to fusion

BIOL 404 (20 decks)

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