Sciatic Nerve Flashcards
What are the 5 parts that make up a neuron (nerve cell)?
- Dendrites
- Cell body
- Hillock
- Axon
- Terminals
What is the dendrites for?
-main input; where most neurons come into contact and where it synapses
What does the cell body have?
has nucleus
Where do APs start?
Hillock
What carries APs towards other cells?
Axon
What are the terminals for?
axon branches to contact multiple cells
What is the chemical potential of the inside of the cell membrane?
[K+]= 150 mM [Na+]= 15 mM
What is the chemical potential of the outside of the cell?
[K+]= 5.5 mM [Na+]= 150 mM
How do ions move for chemical potential?
pushing ions toward the lower [ ]
How do ions move for electrical potential?
pulling the ion back
What does the Nernst Equation calculate?
The equilibrium potential of an ion (Eion)
What is the Nernst equation?
Eion = (61/z) log ( [ion]outside / [ion]inside )
What is z?
z= ion’s charge
What is the equilibrium potential for potassium?
Ek= (61/1) log (5.5/150)= Ek= -90mV
What is the equilibrium potential for sodium?
Ena= (61/1) log ( 150/15 ) Ena= +61 mV
What is the equilibrium potential of chloride?
Ecl= -70 mV
What does the Goldman equation calculate?
the membrane potential (Vm)
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) )
What is P?
P= permeability
At rest which is greater between Pk and Pna? Why?
Pk»_space; Pna
Because there are more K+ leak channels
What is the membrane potential at rest?
Vm= -70mV (closer to Ek because there is more K+ inside the cell)
What does it mean to depolarize?
Raise the membrane potential toward 0
What does repolarize mean?
return the membrane potential back to 0
What is hyperpolarize?
When the membrane potential is taken below rest
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?
- Na+ channel inactivation
- K+ channel activation
- 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?
- K+ channel deactivation
- Na+ channel deactivation
- 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
