8/20/2019 LEB03_0266

1/325PHYWE Systeme GmbH & Co. KG · D-37070 Göttingen Laboratory Experiments, Biology

LEB 03 Musculature

Muscle stretch reflex and determination of conducting velocity 03.02

Principle and tasks:

To trigger a stretch reflex in thelower leg musculature by tappingthe Achilles tendon (Achilles tendonreflex). To record the compoundaction potential and determine thereflex latency and the conductionvelocity.

Attaching the electrodes

Cobra3 Basic Unit 12150.00 1

Power supply, 12 V 12151.99 1

RS232 data cable 14602.00 1Cobra3 Universal Recorder software 14504.61 1

Bio-amplifier 65961.93 1

EMG electrodes, 3 off 65981.02 1

Electrode collecting cable 65981.03 1

Electrode cream, tube 65981.05 1

Reflex hammer, triggering 65981.10 1

Connecting cord, 32 A, l  = 25 cm, red 07360.01 1

Connecting cord, 32 A, l  = 25 cm, blue 07360.04 1

Roll of adhesive tape (e.g. Elastoplast)

PC, Windows® 95 or higher

What you need:

Muscle stretch reflex and determinationof conducting velocity P4030211

What you can learn about

Electromyogram

Muscle stretch reflex

Achilles tendon

Reflex latency

Conduction velocity

Jendrassik effect

Facilitation

Typical result

8/20/2019 LEB03_0266

2/3

Related topics

Electromyogram, muscle stretch reflex, Achilles tendon,

reflex latency, conduction velocity, Jendrassik effect, facil-

itation

Principle and task

To trigger a stretch reflex in the lower leg musculature by

tapping the Achilles tendon (Achilles tendon reflex). To

record the compound action potential and determine the

reflex latency and the conduction velocity.

Equipment

Cobra3 Basic Unit 12150.00 1

Power supply, 12 V 12151.99 1

RS232 data cable 14602.00 1

Cobra3 Universal Recorder software 14504.61 1

Bio-amplifier 65961.93 1EMG electrodes, 3 off 65981.02 1

Electrode collecting cable 65981.03 1

Electrode cream, tube 65981.05 1

Reflex hammer, triggering 65981.10 1

Connecting cord, 32 A, l = 25 cm, red 07360.01 1

Connecting cord, 32 A, l = 25 cm, blue 07360.04 1

Roll of adhesive tape (e.g. Elastoplast)

PC, Windows®

Set-up

— Connect the instruments as shown in Fig. 1.

— Connect the bio-amplifier  A MPLIFIER OUT to Cobra3

 A NALOG IN 2 (red to + and blue to -)

— Connect the electrode collecting cable to the bio-

amplifier A MPLIFIER IN

— Connect one plug of the reflex hammer to the yellow

 A NALOG IN 1 socket of the Cobra3 interface and the

other plug to the red voltage output OUT socket

Procedure

— Call up the COBRA 3 MEASURE programme in Windows

— Select the UNIVERSAL WRITER as measuring instrument

Phywe Series of publication • Laboratory Experiments Biology • © PHYWE SYSTEME GMBH & Co. KG • D-37070 Göttingen 40302 35

LEB

03.02Muscle stretch reflex and determination of conducting velocity 

Fig. 1: Experimental set-up

Fig. 2: Attaching the electrodes

8/20/2019 LEB03_0266

3/3

— Put a little electrode cream on the electrodes and use

adhesive tape to attach them firmly to the inside of the

lower leg, above the Gastrocnemius muscle, in the

succession as shown (Fig. 2)

— Do not allow the green cable to hang down, but (to

reduce the interfering radiation) gather it together and

stick it firmly to the ankle (with the other cables)

— Set the bio-amplifier to 1000 times amplification and

EMG

— Set the measurement parameters (see Fig. 3) and go

to measurement with CONTINUE

— Hold the bended lower leg of the (standing) test per-

son with the left hand. Socks should be left on for bet-

ter isolation; relax all muscles as much as possible

— Tap the achilles tendon with the reflex hammer to

simultaneously trigger off the muscle stretch reflex

and the measurement— Save the result and prepare for a new measurement

— Have the test person stretch his arm musculature; he

should do this by hooking his hands together and

strongly pulling them against each other as if to force

them apart. Repeat the action potential measurement

as described above

Results and evaluation

— The reflex latency (= the interval between the stimula-

tion and the muscle action potential) is approximately

40 ms. With a nerve tract length (Achilles tendon –

spinal cord – muscle) of 2 m, the conduction velocity

is 50 m/s (Fig. 4)

— The amplitude of the muscle action potential is higher

with tensed arm musculature than with relaxed arm

musculature (approx. 3 mV compared to approx.

2 mV). The cause of this so-called Jendrassik effect is

that, as a result of the tensing of the arm musculature,

the other motoneurons of the spinal cord are innervat-

ed (facilitation).

Note

— Analog in 1 is only required for the triggering of themeasurement procedure with the reflex hammer. This

(disturbing) channel can be removed from the dia-

gram:

Change A NALOG CHANNEL 2 to NO Y A  XIS,

and change A NALOG CHANNEL 1 to A NALOG CHANNEL 2.

Phywe Series of publication • Laboratory Experiments Biology • © PHYWE SYSTEME GMBH & Co. KG • D-37070 Göttingen4030236

LEB

03.02Muscle stretch reflex and determination of conducting velocity 

Fig 3: Measurement parameters

Fig. 4: Typical result