16

Question 1

Which direction potassium moves to drive the cell more negative from rest?

Answer 1

Out the cell.

Question 2

Which direction sodium moves for the cell to become more positive in membrane potential?

Answer 2

Sodium moves into the cell.

Question 3

What occurs if a neurotransmitter arrives from start to end?

Answer 3

•Ligand gated Na+ channel opens: K_eq = -90 mV, Na_eq = +55 mV, Vm_rest = -70mV
•sodium will enter the cell (move in the cell) to make the membrane potential Vm = +55 mV during depolarizing.
•A graded potential occurs.
•Graded potential will spread until it reaches axon huillock
•Voltage gated Na+ channel opens when the membrane depolarizes past the threshold (Vm > -55 mV): K_eq = -90mV, Na_eq = +55mV.
•activation gate: when the Na+ channels open.
•Sodium will enter the cell since its equilibrium potential is positive. This will make the membrane potential more positive. This occurs in depolarization phase.
•The channels close before the membrane potential reaches +55 mV. The inactivation gate closes.
•the membrane starts approaching the resting membrane potential by the voltage gated potassium channels opening slowly, and potassium leaves the cell.

Question 4

Are sodium channels closed by inactive gates respond to voltage?

Answer 4

No, it must reset to the beginning.

Question 5

When does the potassium channel open in a neuron?

Answer 5

When the inactivation gate closes in the sodium pump.

Question 6

Ahsolute refractory period?

Answer 6

Inactivation gate closed, no new active potential is possible

Question 7

Relative refractory period?

Answer 7

Inactivation gate open. New action potential is possible, but less likely because neuron is hypoerpoarlized.

Question 8

Because of absolute refractory period, do action potentials sum?

Answer 8

No since no new AP is possible and prevents summation.

Question 9

Based on relative refractory period, are new AP equally or less likely?

Answer 9

Reduces sensitivity of neurons, so less likely.

Question 10

!!!!!Timing of channel opening based on refractory periods?

Question 11

!!!!!!!Is it possible to open the inactivation gate under absolute refractory period?

Answer 11

If the membrane potential passes a certain threshold.

Question 12

What causes graded potential?

Answer 12

Neurotransmitters

Question 13

Does action potential travel?

Answer 13

No, it happens in a place in space.

Question 14

How is an action potential propagated?

Answer 14

Depolarization spreads by electrotonic current flow. Essentially, the sodium that diffuses inside of the cell by a sodium potassium pump spreads to a nearby sodium potassium pump in both directions, but only the pump towards the synapses gets triggered.

Question 15

When the action potential is propagated, why does it normally travel from the cell body to the synapse?

Answer 15

Because of the refractory period.

Question 16

Myelin?

Answer 16

Formed by Schwann cells and wraps around the axon, which insulates it.

Question 17

Saltatory conduction?

Answer 17

Apparent “leaping” of action potential from node to node. This increase the spread of action potential propagation.

Question 18

!!!!!!!Electrical current flow from node to node is the fastest way to propagate action potential. But why isn’t it used often?

Question 19

Why does electrical current die of over longer distances?

Answer 19

Due to resistance inside the cell, and the leakage of ions

Question 20

Why is a large diameter neuron allow action potential propagation?

Answer 20

A large diameter neuron has lower resistance, and lower surface area to volume, so proton leaking decreases.

Question 21

!!!!!!!Why can only myelin be a certain length?

Question 22

Why myelin speeds transmission?

Answer 22

It allows the charge to spread farther down the axon without degrading (decreasing below threshold).

Question 23

!!!!!!!Initial and final sides of axon?

Question 24

Two different types of Synapses? 2•

Answer 24

•electrical synapses (almost always in central nervous system) are connected by gap junctions and electrical signal passes through the gap junction.
•Chemical synapse where neurotransmitters bind to a receptor.

Question 25

Why is chemical synapse important?

Answer 25

more regulation occurs because a depolarizing or hyperpolarizing signal can happen in the postsynaptic neuron.

Question 26

Steps of chemical synapse?

Answer 26

•action potential arise which depolarizes the presynaptic membrane.
•That depolarization opens a voltage-gated calcium channel, triggering an influx of Ca2+.
•the elevated Ca+ concentration causes Sympatric vesicles to fuse with the presynpatic membrane, releasing neurotransmitter into the synaptic deft.
•The neurotransmitter binds to ligand gated ion channels in the postsynaptic membrane.

Question 27

Are some neurotransmitters recycled?

Answer 27

Yes, they will go to the postsynaptic membrane, and then back to the presynaptic.

Question 28

!!!!!!!How does neurotransmitters get rapidly removed from the synapse?

Answer 28

•Acetylcholine (ACh) is a synapse and is made by choline and acetyl CoA.
•In the synaptic cleft ACh, is rapidly broken down by enzyme acetylcholinesterase.
•Choline is transported back into the axon terminal and is used to make more ACh.