iWorx Physiology Names______
STRETCH RECEPTORS AND REFLEXES
The equipment should be assembled when you come into the lab. Working in pairs, choose the Subject and the Experimenter. Both of you should read the lab and be sure that you understand what you are doing before you do it.
Start the Software
o Double click the LabScribe icon on the desktop.
o Click the Settings menu.
o Select Human Nerve.
o Select AchillesStretchReflex-LS2.
Exercise 1: EMG Recording and Reflex Time
Equipment Setup
Electrode leads (Channel 1)
Plethysmograph (Channel 3)
Attach disposable electrode disks to the red, green, and black leads.
Place the Red lead at the top of the gastrocnemius, just below the knee.
Place the Black lead in the middle of the muscle, just at its widest part.
Place the Green lead just above the ankle, on the lateral side.
Attach the plethysmograph to the side of the head of the patellar hammer with its Velcro strap. When the reflex hammer strikes the tendon, the plethysmograph will emit a signal which marks the recording on the Tendon Tap channel at the point in time when the tendon was struck.
Procedure
Have the subject sit on the bench top with the legs hanging freely. An alternative is to have the subject kneel on a chair, with their knees forming a 90º angle and their ankles and feet hanging over the edge.
Tap the Achilles tendon (tendocalcaneus) with the rubber percussion hammer. After a few trials you should be able to consistently produce a reflex contraction of the gastrocnemius muscle that causes a downward movement of the foot (plantar flexion).
Click Record. Ask the Subject to move her foot slowly up and down, alternating between plantar flexion and dorsiflexion. You should see EMG bursts appearing in the top channel (CH 1).
Click Autoscale on the EMG Calf (CH 1) channel.
Tap the Achilles tendon to elicit the stretch reflex. Record 5-10 trials, using the same tapping force. Each tap on the Achilles tendon should produce a spike in the bottom channel. Each of these should be followed by a small spike in the upper EMG channel.
Click Stop.
Select Save As in the File menu, type a name for the file, and choose the Student Data folder as a destination. Designate the file type as *.iwxdata. Click Save.
Data Analysis
Click the Main icon, then use the slider bar at the bottom of the screen to scroll all the way back to the beginning, where you will see the original EMG bursts produced when the subject wiggled her foot back and forth.
Scroll forward in time until you see the first twitch in the series of experimental taps.
Click the 2-cursor icon so that 2 vertical lines appear on the graph. Position the left bar just to the left of the tap mark (bottom channel). Position the right bar just to the right of the EMG spike (top channel).
You may have to click the Zoom between Cursors button to expand the complete reaction trial to the width of the main window.
Click the Analysis icon.
Drag the left cursor to the beginning of the Tap spike. Use the point where the deflection begins to go upward. Drag the right cursor to the beginning of the EMG burst. Again, choose that point where the deflection first begins to go upward.
At the top of the EMG calf channel, you will see the T2-T1 headings. Under T2-T1 is a number that represents the time, in seconds, between the tap of the Achilles tendon and the beginning of contraction of the gastrocnemius in response. Record this value below.
Use the scroll bar at the bottom of the Analysis window and scroll forward in time to the next good recording of the tap and responding EMG. Click the 2-Cursor icon and bracket the recordings as before. Again, measure the time difference and record your data. Repeat this along the length of the experiment until you have 5 times.
TRIAL T2-T1 (seconds)
1 ______What is the average reflex time?
2 ______seconds
3 ______
4 ______
5 ______
With a tape measure, determine the distance between the center of the Subject’s calf muscle and the approximate level of the spinal cord where this reflex is integrated (L4-S3). Therefore, measure up to umbilical level on the back.
Distance (in meters) = ______
x 2 (total distance a nerve impulse must travel)
=______
Determine conduction velocity across this reflex as following:
Conduction velocity = total path length (meters) = ______meters/second
average reflex time (seconds)
Answer the following:
Given the 5 times you recorded, would you say that the Achilles tendon reflex is constant or not? Explain.
Times should be relatively constant due to the consistent length of reflex.
What conduction velocity were you expecting to find? What does your value tell you about the diameter/myelination of the nerve fibers involved in the reflex?
Spinal reflexes are very quick automatic responses because they only involve one or two synapses in the spinal cord. Conduction velocity should be fast and one would expect the nerve fibers involved in the response to be myelinated and large in diameter.
If you increased the stimulus strength, would you expect the subject’s reflex time to change with different stimulus strengths? Why does it or doesn’t it change?
No, increasing the stimulus strength would not affect the subject’s reflex time because the reflex occurs along the same path length every single time. With an increased stimulus however, you would expect an increased reflex response. This is due to the activation of more muscle spindle receptors and more neurons.
Experiment 2: Patellar Tendon (knee-jerk) Reflex
Equipment Setup
Click the Settings menu again and select the Patellar-StretchReflex file.
Place a new set of recording electrodes on the quadriceps muscle of the subject on the medial side of the thigh.
Place the Black lead on the quadriceps femoris, about 12 cm above the knee.
Place the Red lead about 10 cm above the black one.
Place the Green lead on the knee itself, on the medial side.
Procedure
Have the Subject sit on the bench top, with her leg hanging freely.
Feel the patellar tendon just below the kneecap. Place one hand on the patella, and use the other hand to tap the patellar tendon with the percussion hammer. Try to locate the best point on the tendon to elicit the knee-jerk reflex.
Click Record and record 15 or so trials, as you did in Experiment 1. The Experimenter should type in the Mark line an indication of when the
next part of the experiment begins.
The first 5 trials should be with the quadriceps relaxed.
The next 5 trials should be with the Subject voluntarily tightening the
quadriceps, trying to prevent the reflex.
The next 5 trials should occur while the Subject does the Jendrassik Maneuver (with fingers “curled” into each other and interlocked and the arms held out in front of the body, the Subject attempts to pull her hands apart). This isometric exercise develops motor activity in another part of the body while the patellar reflex is initiated.
Click Stop to halt recording.
Select Save in the File menu.
Data Analysis
Click the Main icon, and then scroll back to the beginning of the experiment. Click Autoscale in the EMG-Quad window (top channel) and in the Tap window (bottom channel), so that you can more easily see both sets of events.
Click the 2-Cursor icon, and then drag the lines to bracket the tap and following EMG recordings.
You may have to click the Zoom between Cursors button to expand the complete reaction trial to the width of the main window.
Click Analysis.
As in Experiment 1, put the left line at the beginning of the upward deflection for the tap. Put the right line at the beginning of the upward deflection for the EMG. At the top of the EMG Quad channel, you will again find the T2-T1 value.
Repeat this process through 5 consecutive trials. Do the same for the trials in which the Subject contracted her quadriceps and for when the subject did the Jendrassik Maneuver. Record all data below.
RESTING
TRIAL T2-T1 (seconds)
1 ______average reflex time = ______seconds
2 ______distance from mid-muscle to umbilical level
3 ______x2 = ______meters
4 ______
5 ______conduction velocity = ______m/sec
CONTRACTING
TRIAL T2-T1 (seconds)
6 ______average reflex time = ______seconds
7 ______distance from mid-muscle to umbilical level
8 ______x2 = ______meters
9 ______
10 ______conduction velocity = ______m/sec
VENDRASSIK
TRIAL T2-T1 (seconds)
11 ______average reflex time = ______seconds
12 ______distance from mid-muscle to umbilical level
13 ______x2 = ______meters
14 ______
15 ______conduction velocity = ______m/sec
Answer the following:
Compare the average reflex times between the Achilles and patellar tendon reflexes. What factors contribute to the difference between the two times?
One would expect that the shorter the distance the faster the response time. However, a few groups data supported a faster reflex time for the Achilles reflex which was unexpected given that the length of the reflex pathway is greater for the Achilles reflex compared to the Patellar reflex. Some explanations for this phenomenon include: Fibers may be larger in diameter and more myelinated for the Achilles reflex. Fewer neuron fibers need to be activated for the Achilles reflex as compared to the Patellar reflex. The number of muscle fibers that need to be activated in the patellar reflex to create a response is greater and therefore the response may be slower that the Achilles reflex.
Is the patellar reflex inhibited or enhanced by voluntary muscle activity in the quadriceps? Explain.
Voluntary movement in the muscles of the thigh most often inhibits the patellar reflex. . If the subject contracted the quad and also sent inhibitory signals to the leg- the subject may be able to hold the leg still and inhibit the reflex slightly. A bit of “mind over matter” Also, In order to have a good, strong reflex, the muscles of the leg need to be in a relaxed state. However, If the subject contracted the quadriceps to warm up the muscle and then did the reflex test, you may see reinforcement occur and an enhanced reflex
Is the patellar reflex inhibited or enhanced by the Jendrassik maneuver? Explain.
The Jendrassik maneuver- isometric contractions in another muscle group should enhance the response of the reflex. Often, this is used as a way to distract the patient and relax the muscles in the quadriceps.
Thinking about the times you measured during which these reflexes occurred, list in order of functional appearance all the steps involved, from tap to muscle contraction.
1. Tap from hammer on patellar ligament or calcaneal tendon.
2. Activates stretch receptor.
3. Stretch receptor associated with afferent sensory neuron
4. Sensory neuron generates action potential- cell body located in dorsal root ganglion. Axon enters dorsal root and travels to dorsal horn gray matter and then into ventral horn gray matter.
5. Sensory neuron synapses with efferent motor neuron cell body in ventral horn of gray matter.
6. Motor neuron axon exits spinal cord through ventral root and stimulates muscle cells in to contract.
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