lecture 2

Question 1

positive/negative DF

Answer 1

positive DF- current leaving the cell
- current - flow of + particles
negative DF= current entering cell

Question 2

capacity current equation

Answer 2

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

Question 3

voltage alonx an axon

Answer 3

current will go some distance and leak out

- length constant determines how far the signal spreads in time

Question 4

length constant equation

Answer 4

lambda = Sqr (Rm/Ri)

- the easier it is to leave the axon, the lower the length constant

Question 5

action potential

Answer 5

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 6

voltage gated Na channel role in AP

Answer 6

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

Question 7

K channel role in Ap

Answer 7

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 8

saltatory conduction

Answer 8

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

Question 9

AP role in sensory systeems

Answer 9

• some (mechano) use AP directly

- some dont (photoreceptors would lose sensitivity)

Question 10

quantal hypothesis

Answer 10

postsynaptic muscle recordings made by Fatt and Katz revealed that synapse never fails
- quanta: packets of transmitter being released gives rise to MEPP

Question 11

synaptic release

Answer 11

decreasing Ca reveals the probabilistic and quantal nature of synaptic release

Question 12

steps in synaptic transmission

Answer 12

1. bring pre neuron to threshold at hillock
2. conduct down axon
3. open voltage gated Ca at terminal
4. diffuse Ca
5. exocytosis and diffusion of Ca
6. activation of receptors

Question 13

SNARE hypothesis

Answer 13

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

Question 14

molecules in SNARE

Answer 14

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

Question 15

what happens when synaptotgamin is knocked out

Answer 15

no fast synchronous release but instead slow asyonchrounous

- Ca binding leads to insertion into membrane which pulls v and t together and leads to fusion