======Human Reflexes======


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**Alternative titles:** Reflex Action Demonstrations
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====Summary====                   
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====Procedure====  
  - For the **knee-jerk reflex**: Have a student sit with legs dangling. Gently tap the tendon just below the kneecap with the side of your hand or a soft object. Watch for the leg to kick forward.  
  - For the **pupillary light reflex**: Have a student cover one eye with their hand for about 30 seconds, then quickly remove it while observing the pupil in a mirror or with a partner’s help. Notice the pupil constricting in response to light.  
  - For the **blink reflex**: Move your hand quickly but safely toward a student’s eyes (without touching). Observe the automatic blink.



====Links==== 
How Reflexes Work (Knee jerk and eye blink) - Interactive Biology: 
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====Variations====
  * Measure reaction time with the [[demonstrations:dropping_ruler_reaction_time|Dropping Ruler Reaction Time]] experiment.



====Safety Precautions====
  * Ensure no hard or sharp objects are near the eyes during the blink reflex test.  
  * Tap the knee tendon gently to avoid discomfort.  
  * Use caution when dropping the ruler to avoid hitting fingers.




====Questions to Consider====
  * How is a reflex different from a voluntary movement? (Reflexes are automatic and involve the spinal cord, while voluntary movements require brain input.)  
  * Why does the knee move when the tendon is tapped? (The tap stretches the tendon, triggering a spinal reflex that contracts the thigh muscle.)  
  * What does the pupil’s reaction to light show about the nervous system? (It demonstrates automatic control by the brainstem.)  
  * Why might your reaction time change if you are distracted? (Attention and brain processing affect voluntary reactions but not reflexes.)