THE FROG SCIATIC NERVE

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THE FROG SCIATIC NERVE

• BIOLOGY 305 LABORATORY

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ANNOUNCEMENTS

• Lab Quiz 1
• Next week in lab
• Crayfish Demo Sciatic Nerve Exercises
• Lab Report 1
• Based on next weeks lab

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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

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THE SCIATIC NERVE

• Leopard Frog
• Rana pipiens
• Sciatic Nerve
• Composed of Mixed Axons
• Sensory
• Motor
• Autonomic

www.zoo.utoronto.ca/natalie/ frogpage.html
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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

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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

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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???

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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

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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

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THE SCIATIC NERVE

• A Single Neuron
• AP propagates in ONE DIRECTION
• Due to REFRACTORY PERIOD

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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

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THE SCIATIC NERVE

• The Dissection
• Excision of Distal End

www.engin.brown.edu/.../MuscleExp/ Dissection.htm
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THE SCIATIC NERVE

• The Dissection
• Excision of Proximal
• End

www.engin.brown.edu/.../MuscleExp/ Dissection.htm
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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 Ringers

www.biopac.com/newsletter/ september/frog_nerve.ht

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THE SCIATIC NERVE

• Instrumentation Set Up
• Electrodes
• Stimulate and Record
• Response(s) from Nerve
• Types
• Stimulating
• Recording
• Ground

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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

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Recording Electrodes
Nerve Bath Chamber
Ground
Stimulating Electrodes
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THE SCIATIC NERVE

• Instrumentation Set Up
• Electrodes
• Place leads on opposite sides of bath
• Space apart by one pin
• No two electrodes should touch!

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THE SCIATIC NERVE
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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!

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THE SCIATIC NERVE

• Instrumentation Set Up
• iWORX Unit
• Digitizer
• Amplifier
• Recorder

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

• On Index Card
• Full Name
• Section Day