3 - Grover - Nerve Electrophysiology Flashcards
What are the relative charge distributions in a resting membrane?
Net positive outside
Net negative inside
How can you measure extracellular action potentials?
Extracellular recording electrode at site of inward Na+ current flow
+
Distant reference electrode
How are extravellular action potentials meaured–as in what is the relative size?
Single cells = small
Electrode outside measures summed action potentials
Compound Action Potential (CAP)
Unit Action Potential vs Compound Action Potential
Unit = 1 small action potential
CAP = Compound, summed action potential
Why must the electrical stimulation of nerves be controlled?
To ensure synchronized firing of individual axons
Anode vs Cathode
Anode (+) attracts anions
Cathode (-) attracts cations
What does effective stimulation require?
Current to:
Enter Axon
Flow through axial resistance
Exit axon and return to cathode
What type of axons are depolarized most easily and why?
Large diameter axons
Axial resistance depends on axon diameter, and is lowest in large diameter acons
Another way is saying current threshold is lowest in large diameter axons
Current Threshold
Magnitude of extracellular current stimulus required to trigger action potential in an axon
CMAP
Compound Muscle Action Potential
May be recorded for motor nerve function
Orthodromic vs Antidromic CAP
Ortho = forward
Anti = backward
***These will be relative to the nerve***
Sensory nerves travel to the CNS in an ortho direction
Motor nerves travel to the periphery in an ortho direction
Where do you want to place the recording electrodes?
Record where no muscles for sensory
Monophasic vs Diphasic CAPs
Mono = reference electrode is distant from recording electrode or not over nerve
Diphasic = reference electrode is near recording electrode and over the nerve
How do CAP amplitudes vary?
Amplitude depends on numbr of axons firing–axon size is important for the speed of the measurment
What axons will fire action potentials early following stimulus?
What will come later?
Low Current Threshold: Large diameter, fast conduction velocities (short latency)
High Current Threshold: Small diameter, slow conduction velocity (high latency)
