Action Potentials And Synaptic Transmission Review

Front 1

Significance of patch clamp technique and "feedback circuit"

Back 1

Patch clamp technique allowed measurement of membrane current
"feedback circuit" allowed measurement of current needed to maintain or change potential

Front 2

What is the flow of current across membrane dependent on?

Back 2

Driving force (Nernst potential)
Activation of channels - duration

Front 3

According to the spherical model of the cell, current has what 2 components?

Back 3

capacitive and resistance

Front 4

What determines the resistance of a neuron?

Back 4

resistance of membrane divided by volume (larger cell, more channel, less resistance)

Front 5

What is the relationship between potential, resistance, and current?

Back 5

Ohm's law - V=IR; applies when membrane is fully charged

Front 6

Describe the opening of the Na+ M gates according to the H+H model

Back 6

M gates open in response to stimulation, but open in independent fashion, causing delayed opening

Front 7

Describe the opening of the Na+ H gates according to the H+H model

Back 7

close a short time after M gates open; close in monoexponential fashion (like flipping a light switch)

Front 8

Describe characteristics of stimulus that will cause an AP

Back 8

amplitude must be above Mmax/2 and fast enough to open M gates before H gates close

Front 9

What determines the shape of an AP spike?

Back 9

sum of all membrane conductances; peak appears when I(Na+) = I(K+) + I(leak)

Front 10

What two events are occurring during the refractory period (ensuring the hyperpolarization of the membrane during that time)?

Back 10

The H gates are slowly re-opening, and the channel must be reprimed (i.e. back to the closed position)

Front 11

What is accommodation (in terms of APs)?

Back 11

increase in spike threshold when rate of change of membrane is slow

Front 12

What is anode-break excitation?

Back 12

Spike occurs after rapid removal of depolarizing stimulus

Front 13

What is the basic principle of local anesthetics?

Back 13

They depress membrane excitability

Front 14

What is the basic pattern of current flow through a dendrite or unmyelinated axon?

Back 14

Wave of depolarization followed by wave of hyperpolarization

Front 15

For an intrinsically silent neuron (classical model), why do APs begin at the axon hillock?

Back 15

At the axon hillock, spike threshold is lower

Front 16

What is an active-dendrite neuron?

Back 16

A neuron in which an AP can be initiated in the dendrite and travels to the soma

Front 17

Describe the mechanism of intrinsically firing neurons

Back 17

I(h) depolarizing current causing upward slope of resting potential, eventually leading to repetitive, intrinsic firing (T-type Ca2+ also probably involved)

Front 18

How does myelin improve signal propagation?

Back 18

lipid sheath increases length constant by increasing membrane resistance and decreases membrane capacitance for faster charging

Front 19

What is the relationship between axon radius and conduction velocity?

Back 19

Increasing axon radius increases conduction velocity

Front 20

What triggers a NT vesicle fusing with pre-synaptic membrane?

Back 20

voltage-gated Ca2+ channel opening due to local depolarization

Front 21

What is an EPSP/IPSP and what causes them?

Back 21

Excitatory post-synaptic potential
Inhibitory post-synaptic potential
Both are generated by NTs diffusing across synaptic cleft

Front 22

What role does the SNARE complex have in the synaptic transmission?

Back 22

SNARE complex involved in binding of NT vesicle to pre-synaptic membrane --> can be fusion of "kiss-and-run" process

Front 23

What is a miniature end-plate potential (generally in the context of the NMJ)?

Back 23

Spontaneous fusion of single ACh vesicle, smallest possible depolarization that can be induced in a muscle (quanta)

Front 24

What is a varicosity?

Back 24

Contact point between two neurons (many varicosities may make up synaptic connection between two neurons)

Front 25

In the NMJ, what are the roles of choline acetyltransferase and acetylecholinesterase?

Back 25

Choline acetyltransferase part of synthesis of ACh
Acetylcholinesterase breaks down ACh

Front 26

What is the major dysfunction in myasthenia gravis?

Back 26

Autoimmune disorder in which post-synaptic ACh receptors are destroyed

Front 27

What type of receptor is the nicotinic ACh recptor? Muscarinic ACh receptor?

Back 27

Nicotinic: ionotropic
Muscarinic: metabotropic

Front 28

NMDA receptor: agonists?

Back 28

Glutamate: excitatory, glycine (co-agonist)

Front 29

What is the difference in kinetics between NMDA and non-NMDA receptors?

Back 29

NMDA channels open more slowly and remain open for longer periods

Front 30

Why is the NMDA channel only active in the presence of another depolarizing stimulus?

Back 30

Mg2+ blocks transport at potentials less than -20mV

Front 31

Ca2+ current in NMDA channels suggests what?

Back 31

Channels may be involved in long-term behavioral changes

Front 32

Describe the GABA(B) receptor-induced current

Back 32

K+ current --> inhibitory

Front 33

Describe the GABA(A) current

Back 33

Cl- current
In adult, inhibitory (Cl- export predominates)
In child, excitatory (Cl- import predominates)

Front 34

Describe symmetric (type II) vs asymmetric (type I) synapses

Back 34

Symmetric: vesicles rounded, e- dense post-synaptic terminal, excitatory
Asymmetric: fewer, irregular vesicles, generally inhibitory

Front 35

What are some characteristics of gap junction synapses?

Back 35

bidirectional, share cytoplasm, no plastic, generates synchronization (increased likelihood of AP in adjacent neurons)

Front 36

In general, how would you describe the electrical signal passed via gap junction?

Back 36

Small and slow - because gap junction acts like a filter, attenuates signal