Week 3: More Neurophysiology

Question 1

Action Potential

Answer 1

1. Large depolarizing wave
2. Actively propagates itself down the axon
3. Does not lose amplitude

Question 2

Potential Sensitive Channel

Answer 2

Begin at the axon hillock

Open and close in response to the value of VM

Potential sensitive Na+ channels
Potential sensitive K+ channels
- both open to depolarization

Question 3

Voltage Clamp

Answer 3

1. Measures the VM
2. Changes the VM to any determined value
3. Adds current to either side of the membrane to maintain the given VM

Question 4

Tetrodotoxin (TTX)

Answer 4

Binds to and clogs Na+ potential sensitive channels (Not passive Na+ channels).

This allows for the study of K+ potential sensitive channels

Question 5

Tetraethylammonium (TEA)

Answer 5

Binds to and clogs K+ potential sensitive channels (not passive K+ channels).

This allows for the study of Na+ potential sensitive channels.

Question 6

Similarities between K+ and Na+ Channels

Answer 6

1. Both open to depolarization

2. Both have a greater (population) response the greater the depolarization

Question 7

Dissimilarities between K+ and Na+ Channels

Answer 7

1. Na+ channels open more rapidly then K+ channels open
2. If the depolarization persists, Na+ channels close, K+ do not
3. Na+ channels are faster to close/K+ channels are slower to close

Question 8

g

Answer 8

Conductance: flow of ions

Question 9

3 States on Na+ Potential Sensitive Channels

Answer 9

1. Closed (ready to open)
2. Open
3. Closed (refractory)

Question 10

Refractory

Answer 10

The brief period that follows an action potential where the neuron cannot fire again
Due to the closed state of the Na+ channels

Question 11

Absolute Refractory

Answer 11

immediately following an action potential during which the neuron cannot be fired because the Na+ channels are all locked closed

Question 12

Relative Refractory

Answer 12

Right after the absolute refractory period when an action potential can be fired only if the stimulus is stronger than usual

May be due to the fact that Na+ channels become ready have different thresholds

Question 13

Accomodation

Answer 13

When a slow depolarization raises the VM well past a normally observed threshold before the neuron will generate an action potential

Question 14

Types of K+ Potential Sensitive (Voltage gated) Channels

Answer 14

1. Slowly activated (delayed rectifier)
2. Ca++ activated K+ channel
3. A-Type - fast, transient activated by depolarization
4. M-type - activated by depolarization, but inactivated by ACh (acetylcholine)

Question 15

General effects of Ca++ Influx

Answer 15

1. Contributes directly to the depolarization of the action potential
2. Contirubutes to hyperpolarization of the neuron

Question 16

2 Factors Ca++ Hyperpolarization is due to

Answer 16

1. Ca++ will activate K+ channels causing K+ efflux (leaving)
2. Ca++ will decrease it’s own influx by blocking channels

Question 17

Hyperpolarization can lead to

Answer 17

1. a decrease in sensitivity to depolarization
   OR
2. an increase in sensitivity to depolarization (i.e., Ca2+ channels being open again)

Question 18

Plasticity

Answer 18

Being able to vary the outcome of processing information

Question 19

What types of potential sensitive channels do NG2+ glia have?

Answer 19

Na+
Ca2+
K+

Question 20

Where are NG2+ located?

Answer 20

Hippocampus
Cerebral cortex
Cerebellum

Question 21

After Potential

Answer 21

The period of hyperpolarization following the action potential

Due to the slow closing of the K+ potential sensitive channels

Question 22

Threshold (VT)

Answer 22

The value of VM when the net ionic current changes from outward to inward

Question 23

What is mediating the Action Potential?

Answer 23

Not Na+ or K+

Ca2+ AT THE AXON TERMINAL is the critical factor

Question 24

Ca2+ Potential Sensitive Channels

Answer 24

Only populate the axon terminal

Open to (slight) depolarization

Question 25

Types of Ca2+ Potential Sensitive Channels

Answer 25

L Type - not in the active zone, but still in the terminal | N Type - in the active zone

Question 26

L Type Ca2+ Potential Sensitive Channels

Answer 26

Slow, not located where the NT is released

Question 27

N Type Ca2+ Potential Sensitive Channels

Answer 27

Fast, associated with the release on NT

Question 28

End Plate

Answer 28

Post synaptic Surface

Question 29

End Plate Potential

Answer 29

the PSP

Question 30

Miniature End Plate Potentials

Answer 30

Very small end plate potentials that occur randomly in the absence of an action potential ~.5mV Appear to be the result of one vesicle releasing into the synapse

Question 31

Quantal Hypothesis

Answer 31

1. under normal conditions, the end plate potential of about 70mV is due to about 150 vesicles dumping into the synapse 2. variations in end plate potentials are the result of varying amounts of vesicles dumping

Question 32

Dense Bar

Answer 32

Thickening on the inner surface of the presynaptic membrane with Ca2+ channels lining either side Located directly opposite the postsynaptic receptor sites Vesicles collect in rows along the top sides on the dense bars

Question 33

Active Zone

Answer 33

Dense bars and the vesicles Essentially where the NT release occurs

Question 34

Exocytosis

Answer 34

The process whereby the synaptic vesicles in the axon terminal release their molecule NT's into the synapse

Question 35

Endocytosis

Answer 35

The recycling process where the vesicles are recaptured

Question 36

Clathrin

Answer 36

Mark vesicle membranes for recapturing

Question 37

Kiss and Run

Answer 37

The vesicle briefly touches and opens to the synapse releasing some on its NT

Question 38

Process of Exocytosis

Answer 38

1. restraining the vesicles to the area above the active zone 2. herding the available vesicles to the active zone 3. docking the vesicles 4. mediating exocytosis 5. endocytosis

Question 39

Synapsins

Answer 39

Keep vesicles attached to filaments Synaptobrevin - in vesicle Synaptotagmin - in vesicle Syntaxin - on membrane SNAP-25 - on membrane

Question 40

Rab

Answer 40

Proteins that bring vesicles into the active zone

Question 41

Synaptobrevin

Answer 41

Binds to Syntaxin and SNAP-25 On the vesicle Serves a receptor for clathrin

Question 42

Synaptic Plasticity

Answer 42

the process whereby neurotransmission can change its effectiveness How the resulting PSP can vary (via Ca2+)

Question 43

Intrinsic synaptic plasticity

Answer 43

Potentiation?

Question 44

Potentiation?

Answer 44

Facilitation the increase in size of a PSP resulting from the tetanus/tetanic stimulation

Question 45

Tetanus/tetanic stimulation

Answer 45

the high frequency firing of a neuron

Question 46

Post-tetanic potentiation

Answer 46

potentiation that persists after the tetenic stimulation May last for hours or days Likely due to accumulation Ca2+ in the terminal