A Matter of Time

Think Fast: A Look at Reflexes

"Rational behavior requires theory. Reactive behavior requires only reflex action." W. Edwards Deming

Have you ever been to a doctor’s appointment and had your reflexes checked?  The doctor takes out an instrument with a hard, triangular rubber knob on the end, and taps it right below your kneecap.  Do you know what should happen as a result?  Your reflexes should react to this tap by causing your leg to jump upwards slightly from its downward hanging position.  This is known as the patellar reflex.  “It is also known as a deep tendon reflex (DTR) because the doctor is actually tapping on a tendon called the patellar tendon. This tap stretches the tendon and the muscle in the thigh that connects to it. A message then gets sent to the spinal cord that the muscle has been stretched." (“What Are Reflexes?”).  This message eventually gets to the brain as well, but reflexes and spinal cord messages often have to travel faster than the messages to the brain.  That is why reflexes are defined as instantaneous or “involuntary” reactions.

Reflexes also come into play in the world of sports.  Athletes often are prided for having quick reflexes, which ultimately translates into fast reaction time.  Reaction time is the time that passes between the introduction of a stimulus and when the reflex kicks in.  For example, when a runner hears a gunshot fired to signify the start of the race, his reflexes must kick in so he can react to the gunshot, move his legs, and start running.  A swimmer deals with the same situation when they are waiting for the start signal.  As the swimmer crouches over the block, prepared to dive in, the signal sounds.  The swimmer’s reflexes determine his reaction time. That is, his reflexes determine how much time passes between the actual sounding of the signal and the point in time when the swimmer explodes off of the block and splashes into the pool.  Reflexes and human reaction times are directly related.

A dictionary defines reflexes as “…an involuntary action or response, as a sneeze, blink, or hiccup…” and “…an unlearned or instinctive response to a stimulus…” (Webster’s II).  The main reason that humans have reflexes is to provide protection.  Reflexes protect us from things that are potentially dangerous, before these things have a chance to harm us (“What Are Reflexes?”).  So many of the biological processes we experience every day employ reflexes: blinking, pupil enlargement and reduction, and jumping or twitching.  We blink to keep dangerous materials in the air out of our eyes.  Our pupils enlarge or get smaller to control the amount of light reaching our highly sensitive eyes (“Reflexes”).  The patellar reflex is an example of a jumping or twitching reflex often used in sports to avoid injury or get a jump start out of a gate or off a block in a sporting event. What would have helped a cave man escape from a marauding, fanged predator?  Reflexes!  As soon as he heard the predator rustling about in the bushes, the cave man’s reflexes would kick in, forcing the muscles in his legs to react in a split second, and allowing him to escape and run away.

Just how fast are human reflexes and reaction times?  Most times they only amount to fractions of a second.  It is difficult to be more precise however because reflex time varies from person to person.  How fast a person’s reflex or reaction time is also depends on how often that person’s brain is made to react.  In other words, reflexes can be trained because the more practice your reflexes get, the faster they become (Kelly).  When driving a vehicle, humans typically should have a reaction time of about 0.75 to 1.5 seconds on average to ensure safe driving (“Rule 4: Don’t Speed!”).  Still, factors such as age, disability, and as we have seen, practice can alter reaction times.

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