Nerve Conduction Lab Lecture (Week 1--Schweizer and Tripp) Flashcards Preview

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Flashcards in Nerve Conduction Lab Lecture (Week 1--Schweizer and Tripp) Deck (12)
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Action potential (AP) vs. compound action potential (CAP)

Action potential is in a single axon/cell; can have subthreshold responses with increasing amplitude then suprathreshold responses with AP then as strength increases, AP occurs earlier; different wave form shape depending on size of stimulus

Compound action potential is multiple axons/cells in a nerve bundle; increasing stimulation strength leads to recruiting increased number of axons to fire AP; maximal amplitude of wave form reached once all axons have been recruited; wave is always same shape just larger version of itself


Nerve conduction lab

Stimulated motor nerve and calculated muscle response

Latency is a TIME (ms) that includes synaptic transmission, etc


When we stimulated the nerve, how did we know when all the muscle fibers had been recruited?

When we turned the stimulating voltage up and the wave form did not get bigger, that's when we knew all the muscle fibers had already been recruited


Where is the median nerve in the wrist?

Between the palmaris longus and the flexor carpi radialis


Compound motor action potential (CMAP)

Electrical discharge of the muscle fibers resulting from stimulation of the motor nerve

Derived from all the muscle fibers from all the individual motor nerve fibers in that muscle (motor units) which fire in a nearly synchronous fashion due to the electrical stimulus


Information we collected

Latency: time from stimulus to response; stimulus to first negative (upward on the screen) deflection

Amplitude: vertical height of evoked response; baseline to peak of wave

Duration: time-duration of negative portion of response

Waveform (shape): biphasic usually


How do we calculate conduction velocity

Calculated between stimulus sites (not from distal site to muscle)

MNCV (m/s) = D/(Latency1 - Latency2)


Wallerian degeneration

Portion of nerve distal to injury degenerates after complete axonal disruption


Segmental demyelination

Loss of myelin from variety of injuries (disease, compression)

Axon is still intact


Axonal degeneration

Dying back of axon from distal portion

Form of axonal neuropathy

Looks like Wallerian degeneration in picture, but is going distal to proximal (as opposed to proximal to distal as in Wallerian degeneration)


Conduction speed of fully myelinated nerve compared to non-myelinated nerve

Fully myelinated motor nerve conducts 50-60 m/s

Completely non-myelinated nerve can conduct as slow as 2 m/s (but usually just something <50 m/s)


NCS abnormal responses and causes

Prolonged latency due to myelin loss

Slow velocity due to myelin loss

Low amplitude due to axon loss

Temporal dispersion due to myelin status variable

Prolonged latency and low amplitude due to myelin loss and axon loss

Conduction block due to segmental myelin loss

Abnormal shape due to wrong nerve, muscle, stimulation site, or variable myelin and/or axon loss

Decks in Block 5: Neuroscience Class (43):