Action Potentials + Synaptic Transmission

Question 1

what was proposed by Johannes Peter Muller?

Answer 1

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

Question 2

what is the law of specific nerve energies?

Answer 2

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

Question 3

how is the brain like an encoder?

Answer 3

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

Question 4

what is an action potential?

Answer 4

ions moving through the membrane causing changes in membrane potential

Question 5

what is a depolarized state?

Answer 5

more positive than resting potential

Question 6

what is a hyperpolarized state?

Answer 6

more negative than resting potential

Question 7

Na+/K+ ATPase

Answer 7

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

Question 8

K equilibrium potential

Answer 8

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

Question 9

steady-state potentials

Answer 9

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

Question 10

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

Answer 10

We = (zF)*V

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

Question 11

work required to change concentration equation

Answer 11

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

Question 12

what is the nernst equation @37c?

Answer 12

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

Question 13

what is the nernst equation referring to?

Answer 13

a mathematical relationship used to calculate an ionic equilibrium potential

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

Question 14

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

Answer 14

Ek, wants to be at equilibrium

Question 15

if you move resting potential more positive….

Answer 15

thats depolarization

Question 16

if you move resting potential more negative…

Answer 16

thats hyperpolarization

Question 17

when you move away from equilibrium, you create…

Answer 17

a driving force

Question 18

driving force equals?

Answer 18

membrane potential - eq potential

Question 19

Na flows in the direction that would tend to…

Answer 19

push Vm towards Eq potential

Question 20

Cl flows in the direction that would tend to…

Answer 20

push Vm towards Eq potential of Cl

Question 21

currents can go through the membrane via two distinct pathways…

Answer 21

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

Question 22

resistance is proportional to….

Answer 22

channel properties such as pore size

Question 23

resistance is the same as…?

Answer 23

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

Question 24

what is the difference between resistance and conductance?

Answer 24

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

Question 25

current depends on....

Answer 25

voltage, which is the driving force

Question 26

larger voltage =

Answer 26

larger current

Question 27

larger resistance =

Answer 27

less current

Question 28

what is ohm's law?

Answer 28

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

Question 29

what is a capacitor?

Answer 29

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

Question 30

current flow

Answer 30

flows through a resistor and capacitor set in parallel

Question 31

what does capacity depend on?

Answer 31

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

Question 32

capacitance is...

Answer 32

charge per volt (C = q/V) how much charge you can store to get a volt across the capacitor

Question 33

what is the time constant?

Answer 33

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

Question 34

how can you find capacitance with time constant and resistance?

Answer 34

Tau = R*C

Question 35

delayed electrical signals

Answer 35

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

Question 36

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

Answer 36

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

Question 37

more channels =

Answer 37

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

Question 38

capacity current equation

Answer 38

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

Question 39

voltage along an axon

Answer 39

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

Question 40

length constant equation

Answer 40

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

Question 41

what is the length constant?

Answer 41

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

Question 42

what dictates leakage?

Answer 42

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.

Question 43

action potentials

Answer 43

solves length problem: - long range communication is possible - AP continue because of active propogation - all or none events generated by voltage gated ion channels

Question 44

Na+ channels:

Answer 44

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

Question 45

activation gate

Answer 45

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

Question 46

inactivation gate

Answer 46

closes Na+ hannels by plugging the channel

Question 48

voltage gated Na channel role in AP

Answer 48

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

Question 49

K channel role in Ap

Answer 49

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

Question 50

saltatory conduction

Answer 50

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

Question 51

why doesnt the action potential go backwards?

Answer 51

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)

Question 52

AP role in sensory systeems

Answer 52

- some (mechano) use AP directly - some dont (photoreceptors would lose sensitivity)

Question 53

what is the difference between a chemical vs electrical synapse?

Answer 53

- electrical goes directly from presynaptic cell to post via connexin - chemical uses transmitter to get from pre to post

Question 54

morphological correlates for the quantum hypothesis

Answer 54

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

Question 55

what is the quantal hypothesis?

Answer 55

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

Question 56

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

Answer 56

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

Question 57

what are the steps in synaptic transmission?

Answer 57

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

Question 58

SNARE hypothesis

Answer 58

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

Question 59

molecules in SNARE

Answer 59

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

Question 60

what are the three steps involved in SNARE

Answer 60

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

Question 61

how is SNARE formed?

Answer 61

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

Question 62

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

Answer 62

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

Question 63

what happens when synaptotgamin is knocked out?

Answer 63

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