The Wonder of Reflex Actions


The human brain is a highly complex organ that is instrumental in controlling and maintaining most body functions. It is estimated that the mind thinks of around 2,100 thoughts every hour. Millions and even billions of bits of information are processed in the conscious and subconscious minds respectively each day. That’s a lot of work for one organ, so it makes sense that not all information has to be processed in the brain before a response is given. As human beings, there are a lot of reactions that we make without consciously deciding to do so. These are known as reflex actions, and they are usually quick and protective in nature. Understanding how the central nervous system functions sheds light on the speed of reflex actions.

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Defining a Reflex Reaction

A reflex action is a rapid involuntary and automatic action by a part of the body performed in response to a stimulus. This happens without conscious thought, and the specific pathway is detailed below. If you look at the human body as a machine, then the reflex actions can be likened to an automatic preset response to a certain reading on a sensor. There are many different reflex actions that the body performs. Some are well known and others not as much.

The pupil dilation is a great example of a reflex action. When a person moves to a brighter room or spot, the light acts as the stimulus, and the response is an almost immediate widening of the pupil. Another common reflex action is moving your hand away from a hot object or a sharp item. When dust or other foreign objects pose a threat to you, some other common involuntary actions include blinking, sneezing, or coughing to protect yourself and expel the tiny particles. The knee jerk reaction is a favorite example commonly experimented with on the playground.

The Central Nervous System and the Reflex Pathway

Reflex actions are controlled by the nervous system. The central nervous system is made up of the brain and the spinal cord. For reflex actions, the spinal cord controls the movement, and it does not need to go all the way to the brain for a decision.

The pathway for a reflex action or just reflex is known as the reflex arc. There are several important components in the sequence that make the rapid automatic responses possible. Firstly, the outside stimulus must be sensed. This stimulus could be anything including light, dust, a sharp object, an insect, or a strike on the leg. The receptor is an organ that senses this stimulus or danger. This organ could be the skin in the example of someone who touches a hot object and quickly retracts their hand. Sensory neurons are long nerve cells that turn the stimulus into an electrical signal and carry it along to other neurons and through to relay neurons in the spinal cord. From there, the spinal cord sends signals to the muscles or glands to initiate the response to the perceived stimulus. These signals flow through motor neurons. In the target or effector organ, the required reflex is then performed.

Human beings have different types of reflexes. There are the myotatic reflexes or deep tendon reflexes. These are stimulated mechanically, and an example of these is the ankle reflex. Another type of reflex is one that involves the cranial nerve. These types of nerves come directly from the brain stem and not the spinal cord and relate mainly to the head and neck regions of the body. Examples of such reflexes include the jaw jerk reflex, the gag reflex, and the pupillary light reflex. Interestingly enough, newborn babies have several additional reflexes that allow them to respond to the new environment. Examples include the sucking and rooting reflexes.

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Editor's Picks

There are very few people on this planet who enjoy their work more than Aner Banner. His friends often readily admit that Aner eats, sleeps, and breaths science 24 hours a day. He is always challenging old methods, proposing new ideas, and seeking to solve difficult problems. Aner spends most of the day imparting his wisdom to the young minds of a small elementary school. Thankfully he has also mastered the art of making science come alive for the future leaders of our nation. He is loved and well respected by students, parents, and faculty alike. His motto forever remains “never stop learning.


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