Why does a medical doctor often tests the knee for reflexes? What is it really testing for ? Surely not that single area for a single purpose (reflex). What am I missing?
In: Biology
Causing a reflex provokes a movement. Said movement requires several different systems to work together (muscles, nerves that carry information to the body, spine/brain, nerves that carry a response to the muscles involved, etc…)
At the same time, all of these different systems depend on a multitude of conditions to work properly – e.g. structural integrity, nutrients, etc…
Therefore, testing different reflexes can test many of these components and how they work together at the same time. This is a quick way to narrow down initial complaints which often can mean various different things (e.g. “my arm feels numb” could be due to hundreds of different things, but exaggerated arm reflexes will point you in one direction, decreased reflexes in another)
Under some conditions, some reflexes can appear or disappear, which are very useful diagnostic clues. In some cases, these clues can greatly narrow down what could be causing the issue (if you’re curious, look up the Babinski reflex)
Also, comparing reflexes (involuntary movements) to voluntary movements is useful in many situations – eg if someone has erectile dysfunction, if they can achieve a full, involuntary erection while asleep (reflex erection), this is a pretty good sign that there is nothing physically wrong with said dong.
Bonus: next time you have a male human (possibly yourself) you feel comfortable with while naked in front of you, stroke the inner part of his thigh while he is relaxed (can’t be looking down). You will see the testicle on that side go up. This is called the cremasteric reflex, after the cremasteric muscle which causes the testicle to rise. If someone comes to the ER with testicular pain and an absent cremasteric reflex, you can be pretty sure that the person has testicular torsion (though nowadays it’s better to diagnose using other, more refined means – this is a “classic” sign)
How did I do for ELI5? Am currently a tired and stressed out medical student studying for exams 🙂 Also, I know the examples aren’t your typical knee-jerk reflex, but everyone knows about that one!
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