How do reflexes work? They work by using a reflex arc that bypasses the brain.
There are many different types of reflex, but they are generally meant to protect us and to allow us to move around without having to think about everything. Our brains have a limited amount of processing space and if we had to think consciously about every itch, or every step we took, we would have no processing power left for anything else. Reflexes help us to avoid this.
When you put your hand on a hot radiator, your body jerks your hand back before you are even aware that the thing you have touched is hot. When there is a loud noise, you duck and look around before you are even aware that you have heard something. When someone throws a ball at your head, you have raised your hand to block it before you are even aware that you have seen it. These are what we think of when we talk about reflexes. However, scratching when a mosquito bites us, coughing when we have something in our throat, and blinking when we have something in our eye are all reflexes and they all happen unconsciously.
So, how do reflexes work? Reflexes depend on something called the “reflex arc”. The arc begins with a stimulus. This might be the thermoreceptors in your fingers detecting the heat in the radiator you are touching
The thermoreceptors release an electrical signal when they come into contact with the hot radiator. The signal then has to be sent along the nerves to the spinal cord or the brainstem. The stimulus response is passed to a dendrite, which is the end of a nerve cell, and the dendrite passes it on to an axon. The axons are the nerve fibers, and they are very long, thin cells. The electrochemical signal passes all along the nerve fiber until it reaches the end of the nerve, which is at the spinal cord of the brainstem. This is called the integrating center because its job is to integrate and pass on the signals. It has to make sure that it sends the right signal to the right muscle. There is no point you lifting your leg if it is your hand that is burning.
As soon as the signal is received from the nerve fiber, it is rerouted down another nerve fiber to a muscle. The signal hits the muscle, makes it contract, and you pull your hand away from the radiator, hopefully avoiding a burn. And all of this happens without the brain being involved.
So, why isn’t the brain involved? We like to think that our brains are fast, but they aren’t. For example, if you were in a car crash, the airbag would fire in about 20 milliseconds, but you wouldn’t know you had even been hit by another car until about 200 milliseconds had passed. If we have to wait for our brains to process the information before we pull our hand off the hot radiator, we would badly burn ourselves. The brain is taken out of the loop so that the reaction is as close to instantaneous as the human body can get.
However, that doesn’t mean that the brain isn’t completely involved. The signal is also sent to the brain so that the brain can process what has happened and decide on the next action. Once you have pulled your hand off the radiator, the brain can come into play and decide if it needs to be run under water. If there is a loud noise and you duck, your brain can then try to tell you what the noise was and what you should do next.
Our brains sometimes do have time to interfere with a reflex. When we are walking along and we trip over, the fluid-filled vestibular apparatus in the inner ear detects acceleration. This triggers the reflex loop, and we automatically fling our arms and hands out to break the fall. This is completely unconscious. However, if you trip over and you are holding a baby, you will not drop the baby. You will not fling out both arms. You will either fling out only one arm, or you will attempt to roll over as you fall. This is because it takes longer than 200 milliseconds for you to fall and that is long enough for the brain to come online and modify the reflex.
Some of these reflexes we are born with and some we learn. When you accidentally drop a glass and catch it with the other hand without even thinking about it, you have accomplished a reflex arc, but it is a learned reflex. Dropping something usually means it breaks, which is not a good thing. We learn that from an early age. So our brain modifies a reflex for us. If we drop something, we reflexively try to catch it. You can see that this is learned because if you watch very young children, they will not attempt to catch something that they drop.
So, how do reflexes work? By using a reflex arc that allows the body to react before the brain has had time to process the information. And this is what I learned today.
Sources
https://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=1&ContentID=562
https://en.wikipedia.org/wiki/Reflex_arc
https://en.wikipedia.org/wiki/Reflex
https://kids.frontiersin.org/articles/10.3389/frym.2017.00010
https://www.bbc.co.uk/science/humanbody/body/factfiles/reflexes/reflexes.shtml
https://en.wikipedia.org/wiki/Falling_(sensation)
https://www.gclaw.com.au/news/reflexes-nar-176/
https://owlcation.com/stem/Here-is-what-happens-when-you-accidentally-touch-a-hot-pot