Week 3

Question 1

How is Excitatory Postsynaptic Potential achieved?

Answer 1

The activate receptor open nonselective ion channels to Na and K, as a result a lot of Na enter the cell and depolarize it to threshold.

Question 2

Describe the third step of action potential:

Answer 2

An overshoot is reached and membrane approaches but doesn’t reach Na+ equilibrium potential.

Question 3

Describe the fifth step of membrane potential:

Answer 3

The return of the membrane to a negative value cause Na+ channels to pass from inactive to closed state.

Question 4

What is an axo-axonic synapse?

Answer 4

An axon temrinal of one neuron ends on an axon terminal of another neuron.

Question 5

Why the membrane doesn’t reach the Na+ equilibrium potential?

Answer 5

Because Na+ ion channels begin to inactivate and K+ channels begins to open.

Question 6

How is Inhibitory Postsynaptic Potential Achieved?

Answer 6

Thet activate the open for Cl- ions and K+ ions and this produce either a depolarization or neutralize the effect of depolarization.

Question 7

What are the two effects that axo-axonic synapse can have?

Answer 7

1) Increase the Ca2+ concentration

2) affect the neuotransmitter synthesis.

Question 8

What is a threshold stimulus?

Answer 8

An initial stimulus that is above the threshold.

Question 9

Why does an hyperpolarization (or afterpolarization) occurs?

Answer 9

Because K+ channesl also close but slowly.

Question 10

What are the two factors that affect presynaptic strenght mechanism?

Answer 10

• The higher the concentration of calcium the more neurotransmitters are released.
• Neurotransmitter release is alsto altered by activation of membrane receptor.

Question 11

What happens to used vesicles?

Answer 11

They can be either recycled by endocytosis or may fuse briefly and reseal.

Question 12

What is a relative refractory period?

Answer 12

A period in which a second action potential is fired only if the stimulus is strong enough.

Question 13

What is an absolute refractory period?

Answer 13

During an action potential a second stimulus, no matter how strong, won’t produce any effect because Na+ chnnels are inactivated or open.

Question 14

What is postsyaptic density?

Answer 14

High density of membrane proteins on the postsynaptic cell.

Question 15

What is an overshoot?

Answer 15

A reversal in membrane potential: the inside become positive and the outside become negative.

Question 16

What is temporal summation?

Answer 16

Potential summate because a depolarization from a presynpatic cell occurs before the previous has faded away.

Question 17

Where are neurotransmitters stored?

Answer 17

Neurotransmitters are stored in small vesicles, prior to activation many vesicles are at the active zone.

Question 18

What are the two consequences of the fact that Axon hillock has a more negative threshold than soma and dendrites?

Answer 18

• It’s most responsive to small changes of membrane potential.
• It is the first region to reach threshold when EPSP summate.

Question 19

What is spatial summation?

Answer 19

Two inputs occured at different locations on the cell summate.

Question 20

What is divergence:

Answer 20

A single presynaptic cell affect many postsynaptic cells.

Question 21

What are the two types of postsynaptic receptors?

Answer 21

1) Ion channels (ionotropic receptors)

2) May indirectly influences ion channels through G proteins or second messengers (metrabotropic receptors)

Question 22

How are neurotransmitters removed?

Answer 22

1) they are actively transported back in the presynaptic axon
2) they are transported to local glia where they are degraded
2) diffuse away from the receptor site
4) are enzymatically transformed into inactive substances

Question 23

Describe the second step of action potential:

Answer 23

The membranes reaches a threshold and depolarization become a positive feedback loop (more depolarization cause more Na+ to entry).

Question 24

What is convergence:

Answer 24

Many presynaptic cells affect a single postsynaptic cell.

Question 25

Describe electrical synapses:

Answer 25

Plasma membrane of presynaptic and postsynaptic neurons are joined by gap junctions.

Question 26

How does the action potential propagate?

Answer 26

Through a sequential opening of Na+ and K+ channels along the membrane.

Question 27

Describe the two steps involved in the mechanism of neurotransmitter release:

Answer 27

1) An action potential reaches the presynaptic terminal

2) Depolarization opens Ca2+ channels and cause Ca2+ to flow into the cells and this lead to the fusion of the vesicles.

Question 28

Describe the first step of action potential:

Answer 28

An Action Potential begins with a depolarizing stimulus. This stimulates the opening of voltage-gated Na+ channels and this depolarize the membrane locally.

Question 29

Describe the fourth step of action potential:

Answer 29

Na+ permeability abruptly declines do to inactivation gating. Depolarization of the membrane open K+ channels and this cause repolarization.