EXPERIMENT 3Compound action potential of

toad sciatic nerve

Ying-ying Chen, PhDDept. of Physiology, Zhejiang University School of Medicine

bchenyy＠zju.edu.cn

EXPERIMENTAL PHYSIOLOGY

IntroductionMembrane potentials

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action potentialResting potential

Measuring the membrane potential

Intracellular recording

recording electrode

reference electrode

Extracellular recordingBiphasic action potentialMonophasic action potential

d

d

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Biphasic action potential

Positive phase

Negative phase

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1

2

stimulus

A B

A B

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3

4

A B

A B

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5

A B

d

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The duration of biphasic action potential is dependent on the distance between two recording electrodes

duration

Monophasic Action Potential

Sciatic nerve: consists of a bundle of nerve fibers

Compound action potential (CAP): resultant recording is the sum of the effect of each of the nerve fibers comprising the trunk

Cross-section of a sciatic nerve

Cell bodies Axons or nerve fibers

Spinal cord

Stimulus artifact: a passive current flow through the extracellular surface of saline-soaked nerve and detected by the recording electrodes, when a stimulus is applied to the nerve

Increase the intensity of

stimulus

threshold stimulus

suprathreshold stimulus

maximal stimulus

Stimulus artifact Action potential

Objectives

To record the CAP of the toad sciatic nerve

To examine the effect of stimulus intensity on the

magnitude of the CAP

To determine the conduction velocity of the CAP

Experimental animal: Toad

Parotoid glands

Equipment RequiredRM6240 biological signal collecting systemNerve chamber

The dissection Pith the toad

Remove the upper body and internal organs

Remove the skin from both legs

Fix the frog on the frog board with the dorsal surface uppermost

Remove the urostylePlace a thread under the root of the sciatic nerve and ligate itCut the nerve between the knot and the vertebral columnisolate the sciatic nerve

transfer the nerve to the nerve chamber

s1 s2 R1 R2 R3 R4

Stimulating electrodes Recording electrodes

stimulator

nerve

Nerve chamber

Start the softwareClick on the “RM6240USB2.0q(I)(English)” icon on the Desktop Click on the Experiment menu and select the “compound action potential”Select the “Syn trigger” on the Stimulator control panelBreadth =intensity of stimulus

Exercise 1: stimulus and response

Measure the following values:Intensity of threshold stimulus: (V)Intensity of maximal stimulus: (V)

Increase the intensity of

stimulus

threshold stimulus

suprathreshold stimulus

maximal stimulus

Record the following values in a biphasic action potential induced by maximal stimulus:Latency of action potential: (ms)

Action potential duration: (ms)

Peak amplitude of positive phase: (mV)

Peak amplitude of negative phase: (mV)

Latency Duration

Peak amplitude of positive phase

Peak amplitude of negative phase

Exercise 2: conduction velocityV=d/t = (d2-d1)/(t2-t1) (m/s)

d1 or d2: distances Between distal stimulating electrode (S2) and proximal recording electrode

t2

t1s1 s2 R1 R2 R3 R4

d1 d2

Exercise 3:monophasic action potential

Record the following values in a monophasic action potential induced by maximal stimulus : Duration: (ms) Peak amplitude: (mV)

duration

Peak amplitudes1 s2 R1 R2 R3 R4

Tips

Avoid stretching the nerveDo not touch the nerve with any object that is made of metalKeep the exposed nerve moist at all times with Ringer’s solution