patellar reflex

Topics: Patellar reflex, Reflexes, Reflex arc Pages: 8 (755 words) Published: November 8, 2014

Camille Martinez
Bio 217.08
Instructor: Joyce Avedesian
Environmental Stimulus and Physical Effects on Patellar Reflex May 8, 2014


The purpose of this experiment was to monitor our body’s reaction to stimulation and see how our nervous system, specifically the somatic nervous system can affect the patellar reflex. “The patellar reflex, also known as the knee jerk reflex is an example of a simple two neuron, monosynaptic reflex arc”(Marieb, Mitchell and Smith, 2014).

We tested the strength of the knee reflex activity and whether it was affected by mental distraction, muscular fatigue or simultaneous muscle activity. Our hypothesis was that our reflex response would be less vigorous with mental distraction, simultaneous muscle activity of other areas of the body, and muscle fatigue.

To test our hypothesis on patellar reflex with mental distraction we tested our subject by having her add three digit numbers undistracted. We then had her add with distraction in two trials. To test the simultaneous muscle activity, our subject sat on a bench, while grasping the edge of the bench and pulling upwards at the same time for three trials. The test for muscular fatigue, we had our subject step up and down on a stepper until she felt fatigue. We then tested her reflex response after the exercise.


The mental distraction test with no distraction (control test) resulted in a four second response to stimuli. The next two trials with mental distraction also resulted in four seconds. We noted that the response to the stimuli was consistent with this experiment. Three trials were performed for the simultaneous muscle activity. The first trial our subject did no activity, this being our control test, it resulted in a five second response to stimuli. Trial number two with the bench activity resulted in a six second response and the third trial in a seven second response to stimuli. We noted that the response to stimuli on this experiment was less vigorous. Our last experiment with the muscle fatigue test was held for three trials. The control test was inactivity from the subject resulting in no muscle fatigue that yielded a five second response to stimuli. The second trial with the bench activity, yielded a three second response and the third trial resulted in a four second response to stimuli. We noted that the muscle fatigue response was more vigorous for this experiment.

Note the chart above showing the response to stimuli for the three trials in seconds allotted

No change was detected in any of our trials for the mental distraction experiment. It did not support our hypothesis of yielding a less vigorous response. This may have been due to our subject being in expectation of her performance. We also noted that perhaps we were not hitting the patellar area correctly with our reflex hammer. If this was the case, the stimulus cannot send the impulse to motor neurons which will not cause the muscle to produce a contraction for a knee jerk. The simultaneous muscle activity experiment did support our hypothesis of a less vigorous response. This was probably due that her body was in a relaxing mode which can cause a decreased muscular reflex response. Our subject’s secular work has her multitasking often and perhaps this stimulus did not challenge her brain enough to affect her muscle activity. Strangely enough our muscle fatigue experiment did not support our hypothesis. We cannot explain why this occurred. We know that “muscle fatigue is a state of physiological inability to contract even though the muscle still may be receiving stimuli” (Marieb, Hoehn, 2013). This probably meant, we should have had our subject exercise longer or changed her exercise activity to a more strenuous one. Perhaps our hypothesis would have been supported.

In this experiment we learned that environmental...

References: Marieb, Elaine Nicpon, and Katja Hoehn. Human Anatomy & Physiology. 9th ed. Boston:
Pearson, 2013. Print
Marieb, Elaine Nicpon, Susan J. Mitchell and Lori A. Smith. Human Anatomy & Physiology Laboratory Manual. 11th ed. Glanview: Pearson, 2014. Print
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