Guidance and recording of potentials of sciatic nerve trunk action
Guidance and recording of potentials of sciatic nerve trunk action
The experimental method was obtained from the official website of the Fourth Military Medical University
Operation method
sciatic nerve trunk movement
Principle
Frogs are chosen as experimental subjects because the conditions of survival of their isolated tissues are easy to control, so they are commonly used in physiological experiments? Muscles are innervated by nerves, and when appropriate stimuli are applied to a nerve, the muscle it innervates will contract. So what is happening at the nerve? It is an excitation and an action potential. Physiological experiments often use the sciatic nerve trunk specimen to observe the excitability, the process of excitation, stimulation of some of the laws. This experiment uses an electrical stimulator? An electrical stimulus of a certain parameter is generated and applied to the sciatic nerve trunk through the stimulating electrodes, and then the signal is introduced to the amplifier of an oscilloscope by the guiding electrodes, and the phenomena occurring in the sciatic nerve trunk after the electrical stimulus can be observed on the screen of the oscilloscope. We were able to understand the concepts and meanings of subthreshold stimulation, threshold stimulation, suprathreshold stimulation, and maximal stimulation, and to understand the relationship between excitability and action potentials of the nerve trunk.
Materials and Instruments
Frog or Toad Move I. Preparation of sciatic nerve trunk specimens Caveat 1. Cut the spine in the correct position and do not pull the nerve hard. 2. Keep the nerve specimen moist frequently. 3. The nerve specimen should be in close contact with the electrode and should not be folded. 4. The stimulation intensity should not be too large. For more product details, please visit Aladdin Scientific website.
Frog Surgical Instruments Ren's Liquid
Electrical Exciter Oscilloscope Specimen Case
1. Destroy the cerebral spinal cord by taking a frog and rinsing it with tap water. Hold the frog with the left hand, press the front end of the head with the index finger so that the head is bent forward (Figure 1-1), the right hand holding a probe from the equivalent of the occipital foramen vertically into the cranial cavity, the probe will be forward into the cranial cavity. Stir the probe from side to side to destroy the brain tissue. The probe is then withdrawn back to its original position and then stabbed backward into the spinal canal to destroy the spinal cord. The sign of complete destruction of the cerebral spinal cord is that the frog's limbs are flaccid and breathing disappears. Otherwise, the spinal cord should be destroyed again in the same way as above
. 
Figure 1-1 Method of destroying the cerebral spinal cord of the toad.
Figure 1-2 Cutting off the upper part of the trunk and internal organs.
2. Cut off the upper part of the trunk and internal organs and transverse the spine at 0.5-1.0cm above the level of the sacroiliac joints, then hold the hind limbs of the frog in the left hand and press the sacrum with the thumb. Make its head and forelimbs naturally drooping, the right hand holding a thick scissors, along the spine to both sides to cut off all the internal organs and head of the frog, be careful not to injure the sciatic nerve trunk. (Figure 1-2).
3. Cut off the skin around the anus first, hold the broken end of the spine with a paper pad in the left hand, pinch the edge of the skin on it with the right hand, and peel off the skin of all the hind limbs downwards. Then place the specimen in a Petri dish containing Ren's solution: be careful to apply even pressure and keep your hands away from the specimen.
4. Wash hands and used surgical instruments.
5. Separate the lower extremity specimens of both legs and place them dorsally on the frog plate. Thread the sciatic nerve trunks on both sides and ligate as close to the spine as possible. Note that this is the lumbosacral plexus, do not miss the branch, in the ligature line of the spinal column side of the cut nerve, ligature line as a support line to gently lift the nerve, along the direction of its travel to cut off the branches of the nerve trunk on the thigh muscles. Then hold both legs, cut both sides of the platysma muscle from the dorsal stripping, and cut upwards along both sides of the spine to eliminate the spine. The thighs on both sides together with the lower limbs with bones were twisted and disarticulated relative to each other, and both thighs were cut at the center of the pubic symphysis. Place one leg back into the Petri dish.6. Free the sciatic nerve with a glass hook along the course of the nerve, through the platysma muscle and its nearby connective tissue, sciatic nerve groove, free the nerve to the slapped fossa, gently lift the nerve with a support line, and cut off the branches in the direction of its course.7. Free the tibial and peroneal nerves to cut the deep fascia at the slapping fossa, and then free the nerves to the foot.8. Clean up the specimen: place the specimen on the thigh muscle, dip cotton in Ren's solution and gently wipe away the residual tissue on the nerve trunk. The prepared specimen was then immersed in Ren's solution for a few minutes to stabilize its excitability and start the experiment.
Second, the debugging of the instrument connected
1. debugging the oscillator sensitivity lmV/Div
Input selection AC
Scanning speed lmS/Div
Trigger selection external trigger, trigger input connected to the stimulator synchronization output, in the start of the stimulator output, adjust the trigger
level to the scanning and stimulation output synchronization.
Stimulator Stimulation mode Continuous A
Stimulation frequency 16H.
Stimulation Intensity 2V block from min.
Wave Width Min.
Delay Move the stimulus artifact to the proper place.
Synchronization output Connects to oscilloscope external trigger input
2. Connections Connect the instrument according to Figure 1-3.
Experimental steps and observation items1. Prepare the shielding box by wiping all electrodes with cotton balls soaked in Ren's solution, do not leave water droplets, and wipe the inner wall, the cotton balls remain in the box to form a moist environment.2. Place the thick end of the nerve specimen on the stimulating electrode and the thin end on the recording electrode.3. Press the start button of the stimulator, adjust the delay button so that the stimulation artifacts move to the appropriate place • If there is interference, check the grounding wire of each instrument.4. Slowly increase the stimulus intensity, in the artifact after the appearance of the first up (negative phase wave) after the down (positive phase wave) potential that is biphasic action potential. The stimulus intensity at this point is the threshold intensity, and the stimulus above this intensity is the suprathreshold stimulus. The time between the artifact and the onset of the action potential is the latency.
Figure 1-3 Schematic diagram of the nerve action potential guidance device.
5. In the process of increasing the stimulus intensity, artifacts and action potentials are increased, but when the intensity is increased to a certain level (this stimulus intensity is called the maximum stimulus), the action potential is no longer increased, while the artifacts are still increased. This is one of the most reliable ways to distinguish between stimulus artifacts and action potentials.6. Clamping the nerve trunk between the poles of the recording electrode with a small camera. It is seen that the second phase of the biphasic action potential disappears, leaving only the first phase, the monophasic action potential.7. Record the amplitude, duration and latency of the biphasic and monophasic action potentials respectively, and draw their waveforms.