Sciatic Nerve Flashcards by Frenda Garcia

What are the 5 parts that make up a neuron (nerve cell)?

Dendrites
Cell body
Hillock
Axon
Terminals

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What is the dendrites for?

-main input; where most neurons come into contact and where it synapses

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What does the cell body have?

has nucleus

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Where do APs start?

Hillock

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What carries APs towards other cells?

Axon

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What are the terminals for?

axon branches to contact multiple cells

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What is the chemical potential of the inside of the cell membrane?

[K+]= 150 mM
[Na+]= 15 mM

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What is the chemical potential of the outside of the cell?

[K+]= 5.5 mM
[Na+]= 150 mM

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How do ions move for chemical potential?

pushing ions toward the lower [ ]

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How do ions move for electrical potential?

pulling the ion back

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What does the Nernst Equation calculate?

The equilibrium potential of an ion (Eion)

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What is the Nernst equation?

Eion = (61/z) log ( [ion]outside / [ion]inside )

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What is z?

z= ion’s charge

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What is the equilibrium potential for potassium?

Ek= (61/1) log (5.5/150)=
Ek= -90mV

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What is the equilibrium potential for sodium?

Ena= (61/1) log ( 150/15 )
Ena= +61 mV

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What is the equilibrium potential of chloride?

Ecl= -70 mV

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What does the Goldman equation calculate?

the membrane potential (Vm)

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What is the Goldman equation?

Vm= (61/ |z|) log ( (Pk [K+]outside + PNa [Na+]outside + PCl [Cl-] inside) / (Pk [K+}inside + PNa [Na+]inside + PCl [Cl-] outside) )

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What is P?

P= permeability

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At rest which is greater between Pk and Pna? Why?

Pk&raquo_space; Pna

Because there are more K+ leak channels

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What is the membrane potential at rest?

Vm= -70mV (closer to Ek because there is more K+ inside the cell)

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What does it mean to depolarize?

Raise the membrane potential toward 0

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What does repolarize mean?

return the membrane potential back to 0

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What is hyperpolarize?

When the membrane potential is taken below rest

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What type of recording is used to measure the membrane potential?

Intracellular recording

What is Threshold potential?

V(T); The membrane potential (Vm) at which an action potential is initiated

APs are considered to be...?

"All or Nothing"

What does subthreshold mean?

no AP

Suprathreshold?

complete AP

What does V(T) serve as?

As a noise filter

What do neurons use to code information?

frequency modulation

What type of ion channels generate AP phases?

By voltage-gated ion channels

What does the activity of voltage-gated ion channels depend on?

Activity is dependent on the Vm (membrane potential)

What does depolarization trigger?

Na+ channel activation (opens)

Why is there a large flux of Na+ into the cell when depolarization occurs?

Because the resting Vm is very far from Ena

What are the 3 steps in Repolarization?

1. Na+ channel inactivation 2. K+ channel activation 3. K+ flows out-> rapid repolarization

What triggers Na+ channel inactivation for repolarization?

- Time dependent (occurs as soon as Na+ channel open) | - Very fast

What is the difference between inactivation and deactivation?

- Inactivation: the channel is activated (open) but something is blocking the pore - Deactivation: the pore closes, stopping the ion from going through the channel

What happens when hyperpolarization occurs?

Excess Ik (current of K+) leaving the cell

What does excess K+ leaving the cell drive?

Drives Vm below resting Vm

What are the 3 steps of Return to Vrest?

1. K+ channel deactivation 2. Na+ channel deactivation 3. Vm -> Vrest

What is K+ channel deactivation dependent and not dependent on?

- Voltage-dependent (triggered by repolarization) | - NOT time dependent

What is Na+ deactivation dependent on? What does it remove?

- Voltage-dependent | - Required to remove inactivation of Na+ channels

Which channels are the only ones activated at Vrest?

K+ leak channels are the only activated channels

What are Refractory Periods?

how long a neuron must wait before it can fire a second AP

What is Absolute Refractory Period (ARP)?

When a 2nd stimulus is fired-> no 2d AP | - Na+ channels are still inactivated

What is Relative Refractory Period (RRP)?

When a big 2nd stimulus is fired -> 2nd AP generated

Why does a 2nd AP generate during RRP?

Still have high Pk (some K+ channels haven't deactivated yet)

For conduction velocity, what size diameter causes velocity to be greater?

A bigger diameter

What is Myelination?

lipid bilayer wrapped around an axon- acts as insulation so passively spreading depolarization does not drop below V(T)

What is Saltatory conduction?

- AP "jumps" node to node (depolarization passively spreads under the myelin) - APs regenerated at the nodes (so APs don't get smaller as they spread) - APs spread much faster

What are the types of neurons?

Type A, B, and C

What are the type A subgroups?

alpha, beta, gamma, and delta fibers

Which is the fastest to slowest of the fibers? Why?

Type A> B > C - Type A are large and myelinated (20-100 m/sec) - Type B are also myelinated but have a smaller diameter - Type C are small and not myelinated

Which of the subgroups of type A are fastest to slowest?

alpha> beta> gamma> delta

What type of fibers does the Sciatic Nerve mostly made of?

Type A fibers

What are Compound nerves?

bundles of different types of axons

What is Compound Action Potential (CAP)?

summation of individual APs

What does max CAP mean?

all neurons types have been recruited

Is a CAP an "All or Nothing" AP?

No, it is the summation of the individual "All or Nothing" APs of multiple neurons

Why can't you do an intracellular recording of the sciatic nerve?

Because the sciatic nerve is made up of thousands of axons, must do extracellular recording

What is subtracted in a bipolar recording?

The voltage at the "-" electrode from the voltage at the "+" electrode

Which recording electrode records the "+" deflection?

negative recording electrode

Which electrode records the "=" deflection?

positive recording electrode

What phase of the AP are these electrodes recording?

Depolarization

Which Type A fiber has the lowest threshold?

alpha, then beta, gamma, and delta

What is Latency?

The time between the onset of the stimulus and the recording of the CAP

Changing the polarity of the stimulus can affect what two things?

Can affect both the latency and CAP amplitude

How do you calculate conduction velocity?

CV (m/sec or mm/msec) = distance traveled (mm) / time to travel this distance(msec)

What is measured for conduction velocity?

The time at CAP amplitude between two consecutive CAPS and the distance traveled (from electrode to electrode)

What is the "normal" range for conduction velocity?

20-100 msec