CTCS Quiz 3

Question 0

How does rate compare to diameter of axon?

Answer 0

Larger axon = faster rate

Question 1

How does diameter of an axon affect charge?

Answer 1

Larger the charge, the less resistance.

Question 2

To double the velocity, how must the diameter change?

Answer 2

4x

Question 3

What does myelin do?

Answer 3

It reduces number of sites needed for depolarization. So it leads to larger spacing from node to node.

Question 4

How is the threshold different during relative refractory period?

Answer 4

The threshold is higher.

Question 5

When can an action potential not be fired?

Answer 5

During absolute refractory period.

Question 6

What makes acetylcholine, and what happens to it after it is degraded?

Answer 6

Acteyl CoA + Cholin > choline acetyltransferase > Acetylocholine

Acetylocholine > acetylicholinesterase > Acetic Acid and Choline

Question 7

What is the membrane resting potential of a muscle cell?

Answer 7

-90mV

Question 8

What causes the EPP?

Answer 8

ACh is released on cholinergic receptors in the muscle.

Question 9

What type of receptors does ACh bind to?

Answer 9

Nicotinic Cholinergic

Question 10

Where does the EPP happen? Close to or far away from the motor neuron?

Answer 10

Close to it.

Question 11

How many proteins make up the ACh receptor? Each subunit has how many transmembrane sections?

Answer 11

5. 4.

Question 12

What accounts for the ACh receptor’s selectivity? What makes this region?

Answer 12

Three rings of negative charge, arising from asp, glu and gln. Gln is neutral.

Question 13

What happens to the ACh receptor after it catches an ACh?

Answer 13

It flickers. Probably about 3 times in 1 or 2 ms.

Question 14

What is the resting membrane potential of a cell?

Answer 14

-70mV

Question 15

What causes the membrane potential difference?

Answer 15

It is caused by the fact that the membrane is highly permeable to K+ than it is to Na+. It is not base on the stoichiometry of the Na/K pump.

Question 16

Explain the role of Ca++ in an EPP.

Answer 16

The AP gets to the end of the neuron, it opens Ca++ gates, Ca++ goes into the neuron and causes ACh to be exocytosed out of the cell.

Question 17

What are the 7 steps of an EPP?

Answer 17

1. an APP propagates down a motor neuron to the end plate.
2. voltage gated Ca++ channels open and Ca++ goes into the neuron.
3. Ca++ causes vesicles to exocytose ACh.
4. ACh binds to receptors (2 ACh per recptor) which contain ligand gated channels.
5. the channels open.
6. Na+ ions enter muslce, and K+ leaves the muscle. the Na+ influx is greater causing the membrane potential to depolarize.
7. once membrane potential reaches a threshold, the AP propagates along the muscle.

Question 18

What breaks down ACh in the synapse?

Answer 18

Acetylcholinesterase (AChE) which breaks it down into acetic acid and choline. Choline goes back into the neuron terminal and is made back into ACh.

Question 19

What are 5 differences between the CNS and NMJ synapses?

Answer 19

1. CNS PSPs are much smaller and almost always require summation.
2. NMJ receives a signal from only one synapse. CNS uses many.
3. NMJ always uses ACh. CNS can use many neurotransmitters.
4. Different PS cation channels have different selectivities.
5. CNS synapse is often variable, helping to produce the plasticity. The NMJ is almost always a 1:1 ration of AP and muscle contraction.

Question 20

What is a fundamental concept to make the neuromuscular junction work?

Answer 20

Amplification. 2 ACh molecules start a cascade that invites 50,000 net + charges into the cell in 1-2 ms.

Question 21

What is a competitive block for ACh? What effect does it have?

Answer 21

It binds to the ACh receptor but does nothing. The effect is that it lowers the EPP amplitude.

Question 22

How does one desensitize the ACh receptor?

Answer 22

Some agonists bind to the ACh receptor, alter the conformation and prevent them from opening. These substances cannot be hydrolized by normal means.

Question 23

What is a partial ACh block?

Answer 23

An agonist that binds, but does not fully allow or prevent the EPP from happening.

Question 24

What is a miniature EPP?

Answer 24

An electrical blip that does not release a full AP. The nerve release approx. 6,000 ACh molecules at once. Maybe this is how many are in one vessicle.

Question 25

What happens to the neuromuscular APs in a low Ca++ bath?

Answer 25

The APs fire at about the same level as an MEPP. The muscular AP are Ca++ gate-regulated, and no Ca++ means the channels can’t open fully.

Question 26

Does a CNS of NMJ synapse release more vesicles?

Answer 26

NMJ.

Question 27

Which lasts longer, post-synaptic potentials or pre-synaptic potentials?

Answer 27

post-synaptic. This is important so that they can be summed.

Question 28

Is ACh always excitatory?

Answer 28

In NMJs, yes. However, in muscarinic receptors (heart) it can be inhibitory.

Question 29

What are 3 ways neurotransmitters can be coupled to channels or other synaptic actions?

Answer 29

1. receptor is a channel
2. receptor directly coupled to a G-protein which is connected to a channel.
3. receptor directly coupled to a G-protein which is indirectly coupled to a channel.

Question 30

What is an ionotropic receptor?

Answer 30

When the receptor is also the channel.

Question 31

What is a metabotropic receptor?

Answer 31

one that acts through a secondary messenger.

Question 32

What is an NMDA receptor?

Answer 32

This receptor has a lot to do with memory and plasticity. When open, it can create a membrane potential close to 0mV. It opens a non-selective ion channel. (this is somewhat right. I should look it up again.)