Peripheral Never Electrophysiolgy

Question 1

How do you measure extracellular action potentials?

Answer 1

Measure the potential difference between two extracellular electrodes

One at the site of inward current flow, and a distant reference electrode that represents no change

Question 2

What is a compound action potential?

Answer 2

Simultaneous summed action potentials from several axons

Can be measure via an electrode outside the nerve

Question 3

How are compounds action potentials created?

Answer 3

Controlled electrical stimulation of the nerve

Done by anode and cathode placement on the skin

Question 4

What is a current threshold?

Answer 4

Magnitude of extracellular current stimulation required to trigger action potential in an axon

Depends on axon diameter

Large diameter = low threshold

Question 5

What is a monphasic shape for a CAP?

Answer 5

Reference electrode is distant from the recording electrode or not over nerve (therefore not conducting)

Question 6

What is a diphasic shape for a CAP?

Answer 6

Reference electrode is near the recording electrode and over the nerve

Swings negative, then positive as the AP reaches the second electrode

Question 7

What is the CAP amplitude dependent on?

Answer 7

Varies depending on the number of axons firing

Question 8

What is an F wave?

Answer 8

Evoked by strong stimulation of motor nerves

Caused by antidromic APs that result from initial stimulation

Motor neuronal cell bodies in the spinal cord are stimulated to fire a second AP at greatly reduced amplitdue

Question 9

What is an M wave?

Answer 9

Orthodromic conduction of a motor nerve that represents the normal muscle CAP

Question 10

What are characteristics of an F wave?

Answer 10

Long latency

Smaller

Variable