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THE AUSTRALIAN NATIONAL UNIVERSITY

THE AUSTRALIAN NATIONAL UNIVERSITY. Introduction to Practical 4 Nerve Conduction & M uscle Response Christian Stricker ANUMS/JCSMR - ANU Christian.Stricker@anu.edu.au http:/ /stricker.jcsmr .anu.edu. au/Practical_4.pptx. Aims of the Practical. The students should

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THE AUSTRALIAN NATIONAL UNIVERSITY

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  1. THE AUSTRALIAN NATIONAL UNIVERSITY Introduction to Practical 4Nerve Conduction & Muscle ResponseChristian StrickerANUMS/JCSMR - ANUChristian.Stricker@anu.edu.auhttp://stricker.jcsmr.anu.edu.au/Practical_4.pptx

  2. Aims of the Practical The students should • understand the following concepts: • electrical nerve stimulation. • nerve conduction velocity. • neuromuscular transmission and stimulus-evoked muscle contraction.

  3. Parts of This Practical • Electromyogram and stimulus strength • Stimulus condition • Nerve conduction velocity • Nerve stimulus and muscle contraction • Summation of the muscle response

  4. Methods • Recordings of ulnar nerve easier - closer to surface. • Funny bone (elbow). • Little finger side of wrist. • Bipolar recording from muscle between two electrodes E1 and E2 against ground. • Nerve stimulation via a bar electrode either at elbow or wrist. • Recording via computer: you need to turn the box on… • Certain parameters can be changed. • Top: stimulus properties. • Right: recording conditions.

  5. Electromyogram • Normal polarisation of EMG: starts with a negative going potential. • Difference between E1 and E2 is recorded. • at the first time, AP starts on E1 causing negativity. • at the same time, no potential change at E2. • At the end, E1 with no change, but E2 with negativity; hence a positive going deflection. • If inversed, switch connec-tions around on pre-amp.

  6. EMG – Analysis • How to measure M-wave: • First negativity [µV]. • Amplitude between most negative and positive peak [µV]. • Plot amplitude of M-wave as a function of stimulus current (6 – 10 measurements). • Determine stimulus threshold and • Amplitude at supramaximal stimulation. • (Values required for subsequent stimuli)

  7. Stimulus: Anode vs. Cathode • Anode: +, i.e. where to anions (-) flow. • Cathode: -, i.e. where to cations (+) flow. • At RMP, there is a voltage difference between the inside and outside; i.e. ~ -70 mV. • If outside is made more -, transmembrane voltage drops and channels experience a depolarisation → AP. • If outside is made more +, transmembranevoltage increases and channels experience a hyperpolarisation → no AP.

  8. Stimulus Condition • Swap stimulus bar around at same location (same “grooves”). • Only one of the electrodes is effective at stimulation. • The effective electrode will generate an EMG with shortest latency and vice versa. • Determine which electrode it is.

  9. Axon Fibre Recruitment • Which fibres are recruited first? • An axon of a larger diameter will have a larger surface area → more current can be activated: • First large diameter axons and later small ones are recruited. • Normal recruitment order is the other way around: • First small cells with small axons and later increasingly larger axons: linear increase in force production with recruitment.

  10. Conduction Velocity • First stimulus at elbow (funny bone). • Second stimulus at wrist: increase stimulus current by ≥ 6 units as the nerve is deeper in tissue. • Time difference between the same two peaks.

  11. Determine Conduction Velocity • Measure time difference (on paper). • Measure using a tape the difference in distance between two recording points (marked by two pen marks on skin): keep the tape a bit loose as the nerve does not quite go in a straight line. • Determine conduction velocity as • Compare to reference value (50 – 60 m/s).

  12. Nerve Stimulus & Muscle Contraction • In addition to EMG, we now measure the pressure exerted by the muscles. • Delay between stimulus an muscle contraction. • Trials show variability. • Use average of 5 trials. • Use a very small force on transducer (no force). • Maximal contraction is at peak of contraction.

  13. Analysis of Experiment • Determine the latency between the muscle action potential and the maximal force production. • Analyse the latency of maximal force production as a function of stimulus strength: • Use sub-maximal stimuli as well. • Plot latency vs. stimulus strength. • Explain why this may be the case.

  14. Summation of Muscle Response • Two pulses are evoked on the nerve. • If interval is shortened, force is build on a not-fully relaxed first response → summation.

  15. Analysis of Summation • Determine the peak force for each stimulus interval. Note that the force is measured in relative terms; the force indicated in Newtons do not correspond to the actual value (it is hard to calibrate the pressure transducers accurately). Express the peak amplitude in respect to the value at 500 ms (C2 / C1). • Plot the relative maximal force produced with the second pulse as a function of stimulus interval. • Think of calcium homeostasis in influencing this relationship.

  16. Answer 5 Questions • Answer 5 questions for your write-up • Due 5 o’clock on Monday 26 May 2014. Other Aspects • If you want to have a copy for home, you need to print the recording out. • Print Landscape – and put a name on the file – so you can find the print-out (save the recording under your name…). • You cannot easily produce a PDF file on a PC…

  17. That’s it folks…

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