Practical Handout: Nerve conduction

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  • 1. Year 2 Semester 1 – Nervous Control & Behaviour Module PRACTICAL ON NERVE CONDUCTION 1. Objectives: 1.1. Explain the basic principle underlying the study of nerve conduction 1.2. Explain the meaning of the following terms related to nerve conduction 1.2.1.Latency, amplitude and velocity 1.3. Determine sensory and motor conduction velocity in the upper limb after stimulation the median nerve in a volunteer. 2. Equipment: 2.1. Electromyographic (EMG) machine • Nerve conduction studies uses an EMG machine with surface electrodes to stimulate and record from human nerves and muscles. • This is useful to study nerve conduction and muscle contraction. • Following are parts of an EMG machine o Head box (to connect electrodes) o Computer (for data processing) o Monitor (to display the recordings) o Electrical stimulator (to stimulate the nerves) o Ground electrode 3. Practical activities 3.1. Draw a diagram to show the arrangements of stimulating, recording and ground electrodes. 3.2. Explain how sensory and motor nerves could be stimulated using an EMG machine. 3.3. Find out the threshold intensity of the electrical stimulus (mAmp) 3.4. Observe muscle twitch. 3.5. Find out the latency and amplitude of the compound sensory nerve action potential (SNAP) and calculate sensory conduction velocity of the median nerve. Median nerve SNAP latency (msec) distance(cm) velocity(m/s) amplitude(uV)
  • 2. 3.6. Find out the distal (terminal) latency and amplitude of the compound motor action potential (CMAP) and calculate motor conduction velocity of the median nerve. Median nerve – APB muscle CMAP distal latency (msec) proximal latency (msec) latency difference (msec) distance (cm) velocity (m/s) amplitude (mV) 3.7. Discuss among your group members what changes in the above nerve conduction tests could take place in various diseases: 3.7.1.Carpal tunnel syndrome (CTS) is a condition in which the median nerve is compressed at the carpal tunnel without any involvement of the ulnar nerve which resulted in numbness, pain and sometimes weakness of the hand. How can you confirm the diagnosis of CTS using nerve conduction studies? 3.7.2.Peripheral neuropathy (or polyneuropathy) is a disease where all peripheral sensory and motor nerves are affected with demyelination or axonal degeneration resulted in numbness, weakness of both hands and feet. This may happen as a complication of diabetic mellitus. How can you confirm the diagnosis of polyneuropathy using nerve conduction studies? © Prof. V.S. Weerasinghe, Department of Physiology, Faculty of Medicine, University of Peradeniya, Apr 2010