Reflex Act Definition and Meaning
A reflex act is an involuntary movement that a person performs in response to a certain stimulus. These movements are controlled by the reflex act: a series of structures that act between the sensory receptor and the effector.
Therefore, it is necessary to differentiate between the reflex act (an involuntary and stereotyped action) and the reflex arc (the structures that drive the performance of the reflex act).
Let’s see a brief DEFINITION OF some of the complementary concepts of reflex act from Digopaul, in order to understand its use in this context:
* sensory receptor: it is a nerve ending found in the ear, tongue, nose, eyes and skin, among other sensory organs. It is in charge of receiving external and internal stimuli, to then transport the data and obtain a response in the form of sensations and a nervous impulse. This impulse is then taken to the central nervous system, where it is processed so that the individual obtains information about the characteristics of her environment and can respond appropriately;
* sensory neuron: it is also called the sensory neuron, and it is the one that is in charge of converting all external stimuli into an internal one. Its activation takes place through the action of the senses, and sends projections to the central nervous system for the subsequent transmission of information to the spinal cord or brain. A fundamental difference between this type of neuron and the one we can find in the central nervous system is that the former receives stimuli such as sound, temperature or light, and not from other neurons;
* integrating neuron: also known as the interneuron, it is part of the central nervous system, its size is small and its axon (an extension whose length determines the type of neuron) is of little extension. The interneuron does not connect with muscle fibers or sensory receptors, but does so exclusively with other neurons, and this allows it to carry out highly complex functions;
* motor neuron: another fundamental concept for understanding the reflex act, since it is the type of neuron directly involved with the movement and locomotion of vertebrates. When it transmits a nervous impulse, the muscle cell recognizes the signal thanks to the presence of receptors, which generate a response;
* effector: is a nerve cell that produces a response each time it receives a stimulus. Some of the most common are the secretion of some substance and, essential in the case of the reflex act, movement.
Each reflex act involves the coordination of three stages at high speed: excitement, driving, and reaction. The entire process begins when the receptors capture the nervous stimulus, which is conducted through the reflex arc towards the effector for the development of the response.
In other words: the nervous stimulus produces an excitation (the first stage of the reflex act), which motivates the conduction (second stage) of the message to the spinal cord. This nervous tissue is responsible for the coordination of the response, which develops as a reaction (third stage).
According to the classes of neurons involved in the reflex act, it is possible to distinguish between simple reflex acts and compound reflex acts. In simple reflex acts, only two neurons act: the sensory neuron and the motor neuron. In compound reflex acts, on the other hand, an intercalar neuron that mediates between the sensory and the motor also intervenes.
A typical example of reflex action is the movement we make when we receive a blow to the patellar ligament (in the knee area) and involuntarily raise the leg.