Lecture 3-Membrane Potentials

Question 1

What portion of the neuron is an outgrowth of the cell body, and is the “beginning” of the axon?

Answer 1

Axon hillock

Question 2

What is “special” about the axon hillock?

Answer 2

It is where the individual A.P.s are “summed” before transmission down the axon.

Question 3

What are not typically found in the PM of the cell body?

Answer 3

Voltage gated channels (Why not?)

Question 4

The f(x) of telodendria

Answer 4

To propagate action potentials to other neurons/muscle, or to release neurotransmitters.

Question 5

What type of gated channels are found on dendrites?

Answer 5

Ligand

Question 6

Voltage gated ion channels are primarily located on what portion of the neuron?

Answer 6

Axon

Question 7

Where is the “telodendria?”

Answer 7

The presynaptic end of the neuron

Question 8

Where are dendrites found?

Answer 8

On the cell body

Question 9

Neurotransmitters terminal boutons use what type of gated channel?

Answer 9

Typically voltage gated (usually Ca2+)

Question 10

What is the diffusion potential?

Answer 10

The electrical E* that directly opposes the flow of ions down their concentration gradient

Question 11

What are the “assumptions” of the Nernst equation?

Answer 11

1) only one ion studied at a time 2) ion is at equilibrium regarding [ion]in to [ion]out 3) the P.M. must be completely permeable to the ion in question

Question 12

Nernst equation?

Answer 12

E=z(61.5) x log([ion]o/[ion]i) z= valence or “charge” on ion

Question 13

What is the “all-or-none” response in A.P. propagation?

Answer 13

The membrane reaches a threshold where it WILL fire (all). That MUST be reached. Sub-threshold changes will NOT fire an A.P. (none)

Question 14

What is the principle of “self-generation?”

Answer 14

Depolarization of an area of the cell will result in other depolarizations (“new A.P.s” on either side)

Question 15

What portion of the neuron contains the nucleus, organelles, etc.?

Answer 15

Cell body

Question 16

What is assumed in the Nernst equation?

Answer 16

That the plasma membrane is permeable to only ONE ion at any given time. Therefore, the Nernst equation can only tell you about the potential of one ion, not all the ions used in establishing the resting membrane potential.

Question 17

What are the characteristics of action potential propagation?

Answer 17

1) All-or-none: sub-threshold depolarization will NOT fire an A.P. 2) Self-propagating: depolarization will occur on either side of the local A.P. 3) Non-decremental: the A.P. does not decrease in strength over time or distance

Question 18

What is the f(x) of the S4 segment of the Na+ channel?

Answer 18

It “drives” Na+ through due to it’s highly (+) AA charge; basically “repels” Na+ through the channel

Question 19

Describe the Na+ channel activation gate (i.e. when is it closed/open?)

Answer 19

It is open from -90mV to +35 mV (allows for depolarization) Closed from +35mV to -90mV

Question 20

Describe the Na+ channel inactivation gate

Answer 20

Closed from +35mV to -90mV Open at -90mV

Question 21

Describe the Na+ “selectivity filter.”

Answer 21

The hydrophobic domains of the Na+ channel contain carbonyl groups. These groups H-bond with the water around Na+, thereby freeing it, allowing the “naked” Na+ to flow into the cell.

Question 22

Why doesn’t Na+ pass through the K+ channel?

Answer 22

Due to the K+ selectivity filter.

Question 23

Describe Fig. 5-3

Answer 23

Fit. 5-3 describes an electrode as it passes through a cell (L to right in both the cell diagram and voltage).

While in the same medium on the left, voltage is ‘0 mV.’ As the electrode pierces the cell, it reads the -mV produced by the (-) charges on the cell interior. It remains level throughout the cell as there is an even distribution of charges. As it passes through the other side of the cell, it returns to ‘0 mV.’

Question 24

Describe the difference in K+ vs Na+ selectivity

Question 25

Describe K selectivity

Answer 25

The K+ channel is line with (-) AA residues. As a result, it “pulls” the K away from its hydrating molecules. It is smaller than Na, so Na cannot move through the channel.

Question 26

Capacitance is equal to?

Answer 26

(Area of capacitors/distance between them)

Question 27

What can be done to increase the speed of an action potential?

Answer 27

Increase resistance (via myelination) and increase neuron cross section

Question 28

How do action potentials move around myelin?

Answer 28

Saltatory (jumping) conduction

Question 29

What it’s the typical neurons threshold for promoting sodium influx?

Answer 29

-61mV

Question 30

Period where a stimulus, no matter how large, will not produce another stimulus

Answer 30

Absolute refractory period

Question 31

What is the mechanism for absolute refractory period?

Answer 31

Lack of ATP to run Na/K/ATPAse results in inability to reset RMP.

Question 32

What is the refractory period where a larger than normal stimulus can creat an action potential?

Answer 32

Relative refractory period

Question 33

What is the mechanism of Relative refractory period?

Answer 33

Increased K⁺ conductance has resulted in some depolarization of the cell.

Question 34

What is the mechanism behind the relative refractory period?

Answer 34

As K leaves the cell (increased conductance of K) during repolarization, a new stimulus will cause the generation of an action potential.

In other words, the cell has become just repolarized enough that a new stimulus will depolarize it.