Here is a diagram of the apparatus used in this experiment.

Trigger Lead
The trigger lead co-ordinates delivery of the stimulus to the muscle with the start of the trace (beam) moving across the oscilloscope screen. Without this lead you would not be able to see the muscle contraction or CNAP.

Isolated Stimulator
The stimulator will deliver electrical pulses via stimulating electrodes to the nerve or muscle. Controls allow the stimulus parameters to be varied; voltage (V), duration (ms), frequency (Hz) and number (single or paired stimuli with a variable interval between them).

Stimulating Electrodes 1
These are used to electrically activate nerve fibres in the sciatic nerve – to produce the compound nerve action potential.

Recording Electrodes
These are used to record the compound nerve action potential of the sciatic nerve evoked by electrical stimulation.

Stimulating Electrodes 2
These are used to electrically activate the gastrocnemius muscle directly.

Cathode Ray Oscilloscope
The cathode ray oscilloscope displays the output of both amplifiers. The upper trace shows the strain gauge output (muscle tension), the lower trace the voltage (compound nerve action potential) recorded from the sciatic nerve.

AC Amplifier
The AC amplifier increases the size of the voltage recorded by the recording electrodes. In this experiment the amplifier gain is set at x100.

DC Amplifier
The DC amplifier increases the size of the voltage output of the strain gauge transducer. To convert this voltage to tension the strain gauge will need to be calibrated.

Strain Gauge
The muscle tendon is attached via a ligature thread to the strain gauge. When the muscle contracts tension is applied and the strain gauge converts this tension change to a DC voltage. The voltage output is then amplified and displayed on the oscilloscope.