The Stretch Reflex Lab experiment

The Stretch Reflex Lab experiment

Guidelines for writing a lab report

Download/open the LabReportTemplateStretch.docx and the data analysis ppt. presentation.  A set of data (extracted from a larger set) will appear in this presentation which includes some information about the data as well as the type of statistical analysis which has been performed on the data.  You can see the various statistical tests which have been used to analyse your data. Using the information provided for you in the data analysis ppt. presentation, you can begin writing your lab report in the LabReportTemplateStretch.docx using the guidelines listed below.

The write-up should be written in past tense and should include:

• Introduction (200 words)-Your introduction needs to set the scene and should include some background information about the subject area. What is the key research question? A minimum of two references from the past ten years need to be included (correctly cited and referenced).
• Materials and Methods (150 words)-A summary of the methods used (describing the nature of the practical and the techniques used, why they were used, and not a recipe like replication of the handout).
• Results (150 words)- A description of the key results, including a data table or graph based on whichever is the most appropriate for the dataset (legends for graphs/ tables will not be included in the word count). Report (don’t explain) your main findings using the statistical analysis which has already been performed on your unique set of data i.e. have a look at the unpaired and paired results and determine whether there is any significant difference between various parameters of interest e.g. is there a significant difference between males and females in terms of latency? Did the magnitude/latency of stretch responses during the jendrassik maneuver (JM) change when compared to the average values for magnitude/latency before and after this maneuver? Using the p values to determine whether there is a significant difference between the suggested parameters.  Keep the raw and superficial data out of your results section, (i.e. only report means, SEM, n values etc.). Make sure you also report the p values.
• Discussion (300 words)- The discussion should explain the results in the context of what is already known (ie the literature). What are your main findings? You should discuss what your findings mean in a way that can be understood by someone uninvolved in the study plus any recommendations for improvements to the practical citing relevant references (such as newer or more robust methods for gathering the data they did, or increase in sample number etc). Minimum of two references. Assignment: The Stretch Reflex Lab Experiment
• References- Use Harvard referencing system.
• Overall, write scientifically; ie don’t use I, me, we, etc and make sure you write in past tense.

Marking breakdown for the practical report

• Introduction (clear understanding of designated physiology and aims of the experiment.) – 25%
• Methods (concisely summarised and easy to follow or replicate) – 20%
• Results (appropriately stated without inference and table/graph correctly formatted/ cited) – 25%
• Discussion (standard criteria expected, including at least one recommendation, some evidence of evaluation of the experiment, relation of the findings to both current/recent research and to the wider physiology of the body and its implications for overall body function/health) – 25%
• Refs (correctly listed and cited using Harvard referencing style and cited) – 5%

These are the results

The next results are for the paired T-TEST

The Stretch Reflex

Orientation

The Stretch Reflex is a monosynaptic reflex exhibited by all skeletal muscles and which has the following chain of events…

Striking the tendon with a reflex hammer à stretches the main body of its attached muscle à stretches the muscle spindles contained within the muscle à activates the sensory endings of the 1a afferent fibres wrapped around the central part of the muscle spindles à action potentials travel up the 1a afferent axons à which enter the spinal cord by the dorsal roots à synapse onto the cell bodies of alpha-motoneurones in the ventral horn of the grey matter à stimulate action potentials which travel along the alpha-motoneurone axons, leaving the spinal cord by the ventral roots à stimulate the skeletal muscle cells of the same muscle à produce muscle action potentials (which can be recorded as EMG using surface electrodes) à muscle contraction.

Although the stretch reflex is evoked under rather unnatural conditions (ie, being struck on the tendon by an object), it should be recognised that it is in operation any time you use your muscles to make a movement; it is a fundamental mechanism by which the body regulates the behaviour of muscles, helping to ensure that the right amount of tension is produced to match the aim of the movement.

In addition to stimulating the same muscle that it stretches, there is also reciprocal inhibition of activity in the antagonistic muscle to permit the contracting muscle to move the limb. This dual effect is illustrated in the diagram of the classic patellar reflex, below.

Figure 1.

However, to make the experimental setup more straightforward, we will be looking at the reflexes evoked in the lower leg by striking the Achilles tendon.

For the classic stretch reflex, recording electrodes are placed over the gastrocnemius/soleus muscles of the calf and a single tap of the Achilles tendon evokes a single ‘spike’ of EMG (which then causes to a single twitch of the gastrocnemius/soleus muscles). The chain of events described above that form the reflex pathway takes a finite amount of time, and that time is referred to as the latency of the reflex. A plot of recorded EMG against time, with the recording ‘triggered’ by a switch in the reflex hammer, illustrates the delay (which is typically about 35 ms).

Figure 2. A, Diagram of a reflex arc in a human. When the stretch receptor is stimulated by the hammer, the action potential travels up the sensory fibers to the spinal cord and synapses on the motor fibers The action potential then travels back down the nerve to cause the muscle contraction we observe as a reflex. B, Two electrodes are placed on the calf, close to each other as shown. The third electrode is placed further down the leg, or on a bony surface such as the knee cap or ankle

Aims

• To demonstrate the simple stretch reflex and measure its latency
• To investigate the effect of the Jendrassik manoeuvre on the latency and magnitude of the simple stretch reflex, Assignment: The Stretch Reflex Lab Experiment
• To use signal averaging to produce ‘clean’ recordings

The Stretch Reflex Lab experiment

Materials & Methods

Set-up

• Measure and record the height of the subject and their leg length (hip to ankle).

• Plug the reflex hammer into CH 1 on the front of the ADI unit and the electrode lead set to the Bio Amp Connector on the front panel; ensure the PowerLab is turned on (switch is at the back).
• Attach the black, white and green lead wires (CH1 pair and Earth/Ground on the BioAmp) to the electrodes; do not attach to the subject yet.
• Run the LabChart software by double-clicking the Stretch Reflex adi-set file from Module list (PIS) tab in the Welcome centre (this settings file should launch the recording software with the correct settings).
• Click the Start button on the screen. The capture software is running in ‘triggered’ mode; ie it will not record until it receives some sort of trigger, and that trigger is the reflex hammer. Also, the software is running in ‘sweep’ mode, in which the ‘pen’ drawing the trace moves across the screen and the ‘paper’ background stays still. This approach is particularly useful for recording fast events that are initiated by some sort of external stimulus.
• With the electrodes still attached to their plastic backing strip, tap the hammer a few times on the bench.
  • Each time you do, a 50 ms recording will be triggered (with a 5 ms pre-trigger window also recorded. Q: how can the software do this when it doesn’t know when you are going to hit the bench?)
  • Click Stop. Assignment: The Stretch Reflex Lab Experiment
  • The recording electrodes are not in electrical contact as they are on non-conducting plastic, so they act as aerials and pick up 50 Hz ‘mains hum’. Make sure you know what this looks like (see below) as you do not want to confuse it with the thing you are trying to record! (Q: How can you tell it’s 50 Hz?)
• Right-click the column of pages to the left of the recording and choose Select All Pages. Press the keyboard’s Del key and choose Yes.
• Attach the electrodes to the subject (as below).

Assignment: The Stretch Reflex Lab Experiment 

• Now check that EMG can be recorded from the subject, and also that you can recognise its ‘random’ nature in contrast to 50 Hz ‘mains hum’, as follows…
  • Click Start.
  • Get the subject to stand on tip-toe while you tap the hammer on the bench.
  • Each time you tap the hammer, the screen will record 50 ms of EMG activity from the subject; this has a fairly ‘random’ appearance that differs each time you tap the hammer; learn to recognise it (see below) so you don’t confuse it with the stretch reflex, which is a fairly reproducible ‘spike’ that appears in roughly the same place each time it is induced.

• Now practise eliciting the stretch reflex as follows…
  • Get the subject to face a fixed bench, then to lean forward against the edge, then shift their weight to the non-instrumented leg, and then to lift the heel (not the toes) slightly on the instrumented leg. This helps take the ‘slack’ off the tendon without producing a lot of voluntary EMG that may swamp the stretch reflex.
  • Use the reflex hammer to tap the Achilles tendon a few cm up from its insertion point on the back of the heel (try pushing the tendon in with your thumb to find a spot where the tendon will move in when tapped)
  • Try various forces and techniques (eg holding the hammer fairly loosely) until you can reproducibly elicit a reflex (it helps to look at the tendon, not the screen; get another member of the group to say if a reflex EMG is recorded – you will see the calf muscle itself twitch slightly). A ‘typical’ reflex is shown below (at about 30 ms); note it is not a very ‘clean’ signal!
  • NB: if your subject’s stretch reflex goes down then up, simply reverse the recoding electrodes or right-click the y-axis and choose Invert Scale and Data!

Assignment: The Stretch Reflex Lab Experiment 

• Now practise ‘signal averaging’ as follows…
  • Click Stop to exit recording mode.
  • Right-click the column of pages to the left of the recording and choose Select All Pages. Press the keyboard’s Del key and choose Yes.
  • Click Start.
  • With the subject stood as before, repeatedly hit the tendon with the same force to elicit a consistent stretch reflex. Each strike will record a ‘page’ of data in the column on the left; it doesn’t matter if some pages don’t record anything.
  • Click Stop to exit recording mode.
  • Click on ‘page 1’ of the list of recordings on the left of the screen. Use the ‘down’ arrow on the keyboard to look at each recording ‘page’.
  • Find a run of ten or so recordings that look fairly good; click-drag from the first to the last one in this sequence, then right-click and choose Average; this will produce a single trace that is a composite of all of them.
  • If there are one or more pages in the sequence that were not successful, click the tiny open arrow to the left of the composite page entry (it will have the number of averaged pages in brackets to the right of its name), then click the subpage you want to delete, right-click and choose Exclude from Average.
  • Signal averaging is a very powerful technique as, by their very nature, ‘random’, noisy parts of the recording tend to cancel each other out while constant bits (eg the reflex) reinforce each other and persist. The example below is an average of 56 recordings that includes the ‘noisy’ one above.

Stretch Reflex Experiment

• Right-click the column of pages to the left of the recording and choose Select All Pages. Press the keyboard’s Del key and choose Yes.
• Click Start.
• Get the subject to face a fixed bench, then to lean forward against the edge, then shift their weight to the non-instrumented leg, and then to lift the heel (not the toes) slightly on the instrumented leg.
• Strike the Achilles tendon repeatedly and consistently to get a reproducible reflex.
• Identify a series of 10 ‘pages’ that show a consistent stretch reflex, and display them as an averaged recording.
• Place the cursor on the peak of the averaged response to determine the ‘horizontal’ latency in ms (record the ‘delta’ s value from the top right of the screen).
• Record this value in the table of results under the Stretch Reflex

Assignment: The Stretch Reflex Lab Experiment 

Jendrassik Manoeuvre Experiment

• Right-click the column of pages to the left of the recording and choose Select All Pages. Press the keyboard’s Del key and choose Yes.
• Get the subject to face a fixed bench, then to lean forward against the edge, then shift their weight to the non-instrumented leg, and then to lift the heel (not the toes) slightly on the instrumented leg.
• In addition, get the subject to hold their elbows out and fingers hooked together – but not to pull their hands apart at this stage! It is vital that the subject is nice and stable, so that when they try to pull their hands apart they will not shift their weight further down and influence the experiment.
• The idea is for the experimenter to repeatedly tap the tendon about 40 times, eliciting a nice constant response. The subject should count the taps out loud, and from taps 20-29 should pull their hands apart quite firmly; from 30-39 they should be relaxed again (but still holding their hands as before).
• Click Start and do the recording as just described.
• Once the recordings have been captured, click Stop.
• Inspect the recordings to ensure that a decent set of reflexes have been elicited. If so, do the following…
  • Highlight pages 10-19 (before JM) and average them.
  • Highlight pages 20-29 (during JM) and average them.
  • Highlight pages 30-39 (after JM) and average them.
  • For each set of subpages, eliminate ‘duds’ (if there are more than a couple, repeat the experiment)
  • For each of the averaged recordings (before, during and after JM) measure and record the latency as previously described.
  • For each of the averaged recordings (before, during and after JM) measure the magnitude of the reflex by dragging the ‘M’ tool from the bottom left of recording window and placing it on the trough (lowest point) of the response; then aligning the cursor on the peak of the response so it forms an *. Record the ‘delta’ mV value from the top right of the screen; this is the ‘vertical’ magnitude in mV (from peak to trough).
  • Record these three latencies and three magnitudes in the results sheet, under Jendrassik Manoeuvre

Results

Assignment: The Stretch Reflex Lab Experiment