They can be used these to record EMG signal from isolated frog gastrocnemius muscles. Students can then compare the relationship between the electrical activity of the muscle and the contraction force measured with the force transducer.
You can replace the chlorided silver wires and alligator clips in the Earthworm Action potential experiment. These may be inserted directly into the worm at the same positions as the chlorided wire. These electrodes often provide more reliable signal as they will not lose contact as the external wires can.
The sockets on the needle electrodes fit over the pin on the MLA2540 Bio Amp Cable.
You need to use the pin on the sticker side of the cable yoke. The opposite pin is for the shield, and is not used with these electrodes.
Here is a photo of the use of the needle electrodes with the Earthworm Action Potential experiment.