Electromyogram (EMG) Doug Foster
Author
Doug Foster CSUN/ L.A. Biohackers
Principles
Levels of organization, muscle contraction,
levers, action potentials
Standards
Old CA Standards:
7. 6. Physical principles underlie biological
structures and functions. As a basis for
understanding this concept:
Fig. 1 Bioamp and attached to laptop running Audacity
h. Students know how to compare joints in the body (wrist, shoulder, thigh) with structures used in
machines and simple devices (hinge, ball-and-socket, and sliding joints).principle applies to the
musculoskeletal system.
i. Students know how levers confer mechanical advantage and how the application of this
Materials needed
1) EMB Bioamplifier, stick-on electrodes, electrode paste (if available), craft stick probes, laptop,
Audacity app (free download : www.audacity.sourceforge.net/)
Procedure
1) Place the RCA plugs into the bioamplifier
2) Attach the stick-on electrodes to the skin over a muscle.
3) Plug in the RCA plugs
4) Attach the leads from the bioamp to arm
5) Turn on Audacity application
Explanation
Questions
The electrical spike was produced by cell in the arm. The cell is one of many that make up
_______________ tissue (name the tissue)
What kind of lever was demonstrated here?
Are there more spikes when the muscle is active or at rest?
What is a term that describes making a small signal bigger?
Everyday examples of the principles illustrated
An EKG is a much more sophisticated version of this small bioamplifier. Where this small amplifier amplifies the voltage change across groups of muscle cell in the arm (striated muscle), an EKG (electrocardiogram) amplifies changes in membrane potentials of the cells of heart muscles.
Photos
The spikes represent changes in the membrane voltages (= membrane potentials) of individual muscle cells. When a muscle contracts, huge numbers of membrane potentials change at the same time (upper red line). Small or no waveforms represent intervals of time when the muscles were at rest.
Fig. 2 Three "band" plug of cable goes to mic jack (PCs) or headphone jack (Macs)
Fig. 3 Backyard Brains workshop, Los Angeles
References
Re-inactment of famous1939 experiment by Hodgkin and Huxley. Using the giant axon from a squid, the resting potential of a nerve cell was measured for the first time. Nobel Prize stuff. HERE
Backyard Brains bioamplifier kits