If someone receives a blow to the patellar ligament, they will raise their leg by reflex.
A reflex act is an involuntary movement that a person performs in response to a certain stimulus. These movements are controlled by the reflex arc : a series of structures that act as an intermediary between the sensory receptor and the effector.
We must differentiate, therefore, between the reflex act (an involuntary and stereotyped action ) and the reflex arc (the structures that drive the performance of the reflex act).
Complementary concepts
Let's see a brief definition of some of the complementary concepts of reflex action , in order to understand its use in this context:
* sensory receptor : this is a nerve ending found in the ear, tongue, nose, eyes and skin, among other sensory organs . It is responsible for receiving external and internal stimuli, then transporting the data and obtaining a response in the form of sensations and nervous impulses . This impulse is then taken to the central nervous system, where it is processed so that the individual obtains information about the characteristics of their environment and can respond appropriately;
* sensory neuron : it is also called a sensory neuron , and it is the one that is responsible for converting any external stimulus into an internal one. Its activation takes place through the action of the senses , and it 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;
* integrative neuron : also known as 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 short. 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 : it is a nerve cell that produces a response every 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.
Many actions of newborn babies are reflex actions.
How a reflex act develops
Each reflex act involves the coordination of three stages at high speed: excitation , conduction 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 coordinating the response, which develops as a reaction (third stage).
Classification according to type
According to the types of neurons that intervene 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, however, an intercalary neuron that mediates between the sensory and motor neurons is also involved.
A typical example of a reflex action is the movement we make when we receive a blow to the patellar ligament (in the knee area) and, involuntarily, raise our leg.