USF Ichthyology - EMG Research

Electromyography is a procedure for measuring the electrical activity of muscles. When a muscle contracts a minute electrical charge is generated. This charge can be detected and recorded by a researcher to determine the order in which specific muscles fire. This is referred to as a "motor action pattern". Our lab is examining the motor action patterns of various shark species while they feed. Thus far we have examined lemon sharks (Negaprion brevirostris), spiny dogfish (Squalus acanthias), Atlantic guitarfish (Rhinobatos lentiginosus), bonnethead sharks (Sphyrna tiburo), nurse sharks (Ginglymostoma cirratum) and horn sharks (Heterodontus francisci).

Click here to see video featuring a nurse shark feeding during an EMG experiment.

The animal is anethestized with tricane methanesulfonate (MS-222) prior to the implantation of the EMG leads.

Bipolar leads are prepared prior to the experiment and inserted into specific muscles. Muscle position is determined via prior dissection and the use of external landmarks. Leads are inserted using 22 guage hypodermic needles.

Once the lead is implanted, the hyodermic needle is slid off and the wire is prepared for connection.

The insulation at the end of the lead is stripped, and one wire from each lead is crimped to a pin connector. As these are bipolar leads, there are two connector pins for each lead.

The pin is then inserted into a standard 25 pin connector, allowing us to implant up to 12 leads.

Once the leads are connected to the pin connector, the signal is amplified and filtered before it is recorded on a 14 channel recorder. The EMG signal is synchronized to high speed videography using an LED box. The EMG signal is recorded with a VCR with a standard VHS tape.

In addition to recording the signal on a VHS tape for later analysis, a real-time waveform output is generated using an oscilloscope.

After all of the leads are implanted, the animal is brought out of anesthesia and allowed time to recover.

We film the shark feeding in order to correlate kinematics with muscle activity. In this photo, you cna see the LED box attached to the filming window and the pin connector hanging above the tank.

The LED box has two lights in it that blink in a changing pattern, which is visible in the video footage. The box also outputs a signal to the channel recorder, which allows us to correlate video and EMG data. Also visible in this photo are the EMG leads coming off the shark's head.

After the experiment, the VHS tape is played through an analog-digital recorder, and the signal is analyzed using a computer program. The bites are synchronized with the signal from the LED box, which is visible as the square-shaped waveform on channel one.

Once the data from all recorded bites have been analyzed, the motor action pattern can be compared to the kinematic evenets that occur duing feeding. Each bar in the graph above represents the timing and duration of kinematic events recorded with the high speed camera.