Lecture 3 (Membrane potentials and AP) Flashcards by Tyler Turner

What are the basic parts of a neuron

Cell body, Dendrites, and axons

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what is housed in the cell body of a neuron

The nucleus and other typical cell organells

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Do cell body’s of neurons have voltage-gated ion channels

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the plasma membrane around the cell body is characterized by

Local potentials

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What are dendrites

Dendrites are cellular extensions of the neuron

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How many dendrites does a neuron have

ranges from few to many

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How are dendrites characterized

presence of ligand (neurotransmitter)-gated ion channels

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Do dendrites conduct local potentials

Yes

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what is an axon

extension of the cell body of a neuron that is typically on the opposite side of the cell body from the dendrites

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What is the axon covered in

plasma membrane (axolemma)

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how is the axolemma characterized

by the presence of voltage-gated ion channels and the ability to conduct an AP

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The distal end of the axon is characterized by

presence of membrane-bound vesicles filled with neurotransmitter molecules

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What is the function of the plasmalemma

functions to maintain separate intracellular and extracellular environments

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what is another name for the plasmalemma

The cell membrane

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where are sodium and chloride ions more concentrated

Outside the cell

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Where are potassium ions most concentrated

Inside the cell

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what is a diffusion potential

caused by an ion concentration difference on either side of a membrane

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What is Nernst potential

The diffusion potential level across a membrane that exactly opposes the net diffusion of a particular ion through the membrane

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what is the electrical dipole layer

dichotomous distribution of ions on either side of the membrane represents a voltage change

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When is a voltage change recorded

only when the recording electrode passes through an electrical dipole layer

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what is the Nernst equation

E=2.3RT/FlogCout/Cin
E- difference in the electrical potential between inside and outside the neuron
R- Universal gas constant
T- absolute temp
F-Faradays constant

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What is the Nernst equation used for

Measuring one type of ion at a time
- determines the diffusion potential across a membrane that exactly opposes the net diffusion of a particular ion through the membrane

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what is used to measure the combined potential for more than one type of ion

Goldman equation may be used

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What are the assumptions of the Nernst Equation

Equation can only be used for one ion at a time

membrane must be completely permeable to that ion
Ion must be at equilibrium

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EMF equation

EMF=Eion= z(61.5) x log [(ion]outside/[ion]inside) z- valence of ion it is a simplified version of the Nernst equation

How does the sodium potassium pump work

secondary active transport | pumps 3 Na out and 2K+ in

what is the resting potential caused by potassium ion alone

-94mV

What is the resting potential caused by both potassium and sodium ions

-86mV

What is the resting potential caused by sodium, potassium, and Sodium potassium pump -

-90mV

What is the resting potential caused by Na alone

+61mV

Action potential characteristics

- all-or- none, it will either occur or not occur - it is self-propagating: each region of depolarization serves to generate action potentials on either side - it is non-decremental- it does not decrease in strength

Voltage-gated sodium channels have how many domains

How are the 4 domains of voltage-gated sodium channels arranged

in a cylindrical configuration

How many hydrophobic transmembrane segments does each domain of voltage gated sodium channels have

How many total dydrophobic transmembrane segments does the voltage-gated sodium channel have

4 domains with 6 a piece = 24 in total

What are the 6 hydrophobic transmembrane segments of voltage gated sodium channels called

S1-S6

What is special about S4 segment within each of the 4 domains of Voltage gated sodium channels

has high positive charge

The inactivation gate is associated with an intracellular hydrophilic linkage between what which of the 4 domains that make up a voltage gated sodium channel

Domains 3 and 4

how many gates do voltage gated sodium channels have

What are the names of the gates in voltage gated sodium channels

activation gate and inactivation gate

which gate(s) in voltage gated sodium channels is open at -90mV

The inactivation gate

Which of the gate(s) of voltage gated sodium channels is closed at -90mV

Activation gate

When are both of the gates in voltage gated sodium channels open

between -90mV to +35mV

When does the Activation gate of Voltage gated sodium channels open

as voltage reaches -70mV to -50mV

In voltage gated sodium channels the activation gate is opened and the inactivation gate is closed at what mV

+35mV to -90mV

Explain the diameter of voltage-gated potassium channels

They are too small for hydrated potassium and hydrated sodium ions

What is near the entrance of voltage-gated potassium channels

Selectivity filter | - loops from the pore helix that are bound to carbonyl oxygens

how does the selectivity filter in voltage gated potassium ions work on hydrated sodium

Smaller hydrated ions such as sodium are not affected by the selectivity filter but are too large to pass through the potassium channel

How does the selectivity filter of voltage-gated potassium channels work on hydrated potassium

larger hydrated ions such as potassium will be dehydrated by the selectivity filter, allowing the smaller "naked" potassium ion to pass through the channel

How many gates do potassium-gated channels have

one

When is the potassium-gate closed

At resting potential of -90mV

When is the potassium-gate open

slow activation opens from +35mV to -90mV

Is the potassium gate slow or fast opening

Slow

When is the resting stage of an AP

-90mV

At what stage of an AP does the membrane suddenly become permeable to sodium ions

The depolarization stage

how fast do the sodium channels close

within a few 10,000 of a second

what happens in the repolarization stage of an AP

sodium channels close | potassium channels open more than normal

explain the positive feeback system that is in place for sodium during Ap

During AP the sodium membrane conductance increases with increase in sodium channel opening leads to larger influx and thus faster AP

Does each cell have its own threshold

Yes

what is the name of the activation gate

(m-gate)

what is the name of the H-gate

inactivation gate

which ion channels are faster potassium or sodium

Sodium

ways to increase speed of propagation of AP

``` Increasing diameter of the axon - used by invertebrates Increase membrane resistance - myelination -creates a capacitor effect ```

What is salutatory conduction

jumping of current from one node to the next

what is local potential

Caused by a ligand gated channel | often in dendrites

what is threshold

the point at which a local potential will elicit an AP | usually -65mV

What is the direction of propagation

AP travel in all directions from the point fo stimulation

what is orthodromic direction

direction normally taken (toward the distal end of the axon)

What is antidromic direction

Opposite of normal | toward the axon hillock, neuron cell body

why do AP typically travel in the orthodromic direction

because the area behind is hyperpolarized, it is an absolute refractory period

what is the principle lipid of myelin sheaths

Sphingomyelin

What are Schwann cells

Cells that form the myelin sheaths in the peripheral axons

What are the nodes of Ranvier

unmyelinated junctions between schwann cells

Why does myelination increase velocity of transmission

allows 100x less loss of ions and requires little energy fro repolarization

where do AP occur in myelinated axons

at the nodes of Ranvier

why do small diameter fibers conduct action potentials slower than large diameter fibers

Small diameter fibers have an increase internal resistance

what is the absolute refractory period

period during which a second AP cannot be elicited even with a strong stimulus

where is the energy derived during the absolute refractory period

the breakdown of ATP

what is the relative refractory period

period when a stronger than normal stimulus can cause AP

what affect do high potassium concentrations have on AP

They block sodium channels and thus make AP difficult

Which of the following types of neurons would transmit an AP the fastest

Large diameter, myelinated

salutatory conduction is characteristic of which part of a typical neuron

Axon

a selectivity filter with carbonyl oxygens is associated with what kind of ion channels

Potassium

The resting potential for a typical neuron, such as a motor neuron, is best represented by what potential

-90mV