To understand what a reflex arc is, we must first refer to the concept of the reflex act. A reflex act is a movement that an individual performs involuntarily, as a response to a certain stimulus. The nervous structure that is in charge of controlling this movement is called a reflex arc.
Reflex acts arise from the ability of various animals to generate a synapse in the area of the spinal cord. In this way, the body provides a response before the signal reaches the brain. Depending on which neurons are involved in the process, the reflex arc can have different characteristics.
When only two neurons (one sensory and one motor) act in the process, the reflex arc is simple. If more than one is involved, the reflex arc becomes complex. In the latter case, intercalar neurons between the sensory and the motor act.
Specifically, the reflex arc is the path that nerve impulses follow through the body. Take the case of a blow to the knee area that causes involuntary movement of the leg. The reflex arc goes from the sensory neuron that picks up the stimulus (the blow) to the motor neuron that orders the response (the movement).
It is important to distinguish, in short, between the reflex arc and the reflex act. The series of structures that make it possible to carry out the action known as the reflex act is called a reflex arc.
Reflex arc structure
Through reflex arcs the organism articulates a large number of very varied nervous processes. It is important to highlight that the reflex act is the fundamental unit of the so-called integrated nervous activity, so much so that some scholars consider it the circuit from which the other nervous structures of the body arose.
In each of these circuits or paths, which are responsible for transmitting nerve impulses and constitute the reflex arc, it is possible to notice a certain number of components, some of which are mentioned in previous paragraphs:
* sensitive receptor: they are structures that specialize in transforming stimuli into nerve impulses capable of integrating into the Central Nervous System (often mentioned by the acronym CNS). Sensory receptors can be of different types, such as chemoreceptors, mechanoreceptors, photoreceptors, and thermoreceptors;
* afferent or sensory neuron: its function is to capture the data and transport the message to the spinal cord;
* efferent or motor neuron: it has the task of carrying the nervous impulse from the spinal cord to the effector (defined below);
* interneuron: it is found in the integrating centers and is in charge of connecting the two neurons just described, the afferent and the efferent;
* effector: it is the organ that deals with generating a response, and it can be a cardiac, smooth or skeletal muscle, or a gland.
It goes without saying that the central nervous system is of vital importance for the development of our functions. The autonomous and somatic reflex arcs coexist in it, and although they are alike in certain aspects, their morphological and functional characteristics have differences that are essential to know.
The components that present a greater number of similarities between both arches are the afferents. The study of efferents, on the other hand, shows us that in the somatic reflex arc there are two neurons instead of one: the first is found in the lateral horns of the medullary gray matter, or in the brain stem and linked to nerves cranial; the second may be found in autonomic ganglia of different types, such as prevertebrales, paravertebral, intra -organic or preorgánicos. Simply put, there is a ganglion between the effector organ and the autonomic nervous center.