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THE FROG SCIATIC NERVE

THE FROG SCIATIC NERVE. BIOLOGY 305 LABORATORY. ANNOUNCEMENTS. Lab Quiz #1: Next week in lab Crayfish Demo & Sciatic Nerve Exercises Lab Report #1: Based on next week’s lab. REVIEW OF THIS WEEK: MUSCLE RECEPTOR ORGAN OF CRAYFISH. MRO 1 : Response (f) is function of stimulus intensity

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THE FROG SCIATIC NERVE

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  1. THE FROG SCIATIC NERVE BIOLOGY 305 LABORATORY

  2. ANNOUNCEMENTS • Lab Quiz #1: • Next week in lab • Crayfish Demo & Sciatic Nerve Exercises • Lab Report #1: • Based on next week’s lab

  3. REVIEW OF THIS WEEK: MUSCLE RECEPTOR ORGAN OF CRAYFISH • MRO1: • Response (f) is function of stimulus intensity • MRO2s: • Elicited by sudden, high intensity stimulus • Amplitude differs from MRO1 • Sensory Adaptation: • Decreased response (f) to long duration stimulus of fixed intensity • Rate of change may be influenced by stimulus intensity

  4. THE SCIATIC NERVE • Leopard Frog: • Rana pipiens • Sciatic Nerve: • Composed of Mixed Axons: • Sensory • Motor • Autonomic www.zoo.utoronto.ca/natalie/ frogpage.html

  5. THE SCIATIC NERVE • Goals Include: • Measure compound APs in Sciatic Nerve • Determine threshold for AP firing • Observe axon recruitment • Measure AP conduction velocity • Determine directionality of signal

  6. THE SCIATIC NERVE Compound Action Potentials: • Summation of axons in nerve firing simultaneously • Direction of response (+ or --) depends on configuration of electrodes • Some traces are bipolar

  7. THE SCIATIC NERVE The Stimulus Artifact: • Deflection caused by application of voltage to nerve • If applied voltage exceeds 0 Volts, you should see a stimulus on trace • May not see response. WHY???

  8. THE SCIATIC NERVE Threshold: • Voltage at which neuron sufficiently stimulated (depolarized) to fire AP • If you apply a stimulus with increasing voltage: • NO RESPONSE to sub threshold stimulus • Greater amplitude response as more neurons reach threshold

  9. THE SCIATIC NERVE Maximum Response: • At some stimulus voltage, all neurons reach threshold • All fire APs • Further increase in stimulus will NOT recruit more axons to fire

  10. THE SCIATIC NERVE • A Single Neuron • AP propagates in ONE DIRECTION • Due to REFRACTORY PERIOD

  11. THE SCIATIC NERVE A Mixed Nerve: • Intact: • Sensory neurons (axons) send signal from PNS to CNS • Motor neurons send signal from CNS to PNS • Excised: • Axons In Nerve Act Like a Wire • Injected current travels in any direction from pt. of origin

  12. THE SCIATIC NERVE The Dissection: • Excision of Distal End www.engin.brown.edu/.../MuscleExp/ Dissection.htm

  13. THE SCIATIC NERVE The Dissection: • Excision of Proximal End www.engin.brown.edu/.../MuscleExp/ Dissection.htm

  14. THE SCIATIC NERVE Instrumentation & Set Up: • The Nerve Bath Chamber: • Keep track of which end is which • Anterior versus posterior • To retain blood supply, tie off anterior end (spine) last • Cut longest section possible • Be gentle! • Try not to stretch nerve • Keep frog/ nerve bathed in Ringer’s www.biopac.com/newsletter/ september/frog_nerve.ht

  15. THE SCIATIC NERVE Instrumentation & Set Up: • Electrodes • Stimulate and Record Response(s) from Nerve • Types • Stimulating • Recording • Ground

  16. THE SCIATIC NERVE Instrumentation & Set Up: • Electrodes • Stimulating Electrode (+ & -): • Connect to one end of nerve bath • Recording Electrode (+ & -): • Connect to other end • Ground: • Placed in- between

  17. Recording Electrodes Nerve Bath Chamber Ground Stimulating Electrodes

  18. THE SCIATIC NERVE Instrumentation & Set Up: • Electrodes • Place + & – leads on opposite sides of bath • Space apart by one pin • No two electrodes should touch!

  19. THE SCIATIC NERVE

  20. THE SCIATIC NERVE Instrumentation & Set Up • Electrode Tips: • Confirm everything is plugged in • Confirm good electrical contact • Confirm electrodes connect to pins in contact with nerve!

  21. THE SCIATIC NERVE Instrumentation & Set Up: • iWORX Unit • Digitizer • Amplifier • Recorder

  22. THE SCIATIC NERVE iWorx Stimulator Panel (OUTPUT) iWorx Recording Channels (INPUT)

  23. ATTENDANCE • On Index Card: • Full Name • Section Day

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