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Basic Background in Reflex Physiology

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Basic Background in Reflex Physiology JOURNAL OF MOLECULAR PATHOPHYSIOLOGY, 2020 VOL 9, NO. 1, PAGE 1–8 10.5455/jmp.20200107080528 MINI REVIEW Open Access Basic background in reflex physiology André Felipe Breda Andrade Costaa, Ana Paula da Veiga Argusb, Franciele Prestel Pisettac, Alberto Gonçalves Evangelistad aCenter for Agri-Veterinary Sciences, Santa Catarina State University, Lages, Brazil bVeterinary Hospital, Federal University of Paraná, Curitiba, Brazil cVeterinarian, Joinville, Brazil dSchool of Life Sciences, Pontifical Catholic University of Paraná, Curitiba, Brazil ABSTRACT ARTICLE HISTORY Reflexes are a fundamental part of nervous system analysis. Various pathologies man- Received January 07, 2020 ifest themselves by disrupting the basic reflex functions inherent in the individual, and Accepted May 14, 2020 some of them are fully developed at birth. For a complete clinical analysis, knowledge Published May 26, 2020 of the basic mechanisms of its functioning is required. This review aims to demonstrate KEYWORDS the mechanism of some of the main reflexes present in individuals in a simplified way, consolidating knowledge of great importance to the area. The focus is not on detailing Physiology; reflexes; the specifics of each reflex but on the use of recent advances in research to accurately nervous system; health care determine its visual effects as well as its effects in the organism, observed through clin- ical examinations. Introduction - - retinal receptors transduce light, and muscle spin A reflex can be defined as an involuntary, quali dle receptors transduce the stretch. Several types of tatively invariable nervous system response to a- receptors are known, with different capacities for stimulus. A reflex arc is defined as the movement stimulus transduction [4,5]. - described from the stimulus to the central or periph In transduction, action potentials are generated- eral nervous system and its return to the stimulus along the sensory nerves at a frequency propor site, with a function. The reflex arc is a fundamental tional to the transduced energy [6]. This propor part of the physiology of posture and locomotion, as- tionality between the intensity, by which a receptor well as for the clinical examination of the nervous is stimulated, and the frequency of action potentials system [1,2]. Reflexes have the function of main resulting in a sensory nerve is called the coding taining the homeostasis of the organism, as well as frequency and is how the receptor communicates- preserving the physical integrity of the individual to the nervous system about the intensity of light, [3]. We can quote from the increase in blood flow heat, muscle stretch, and so forth, which he trans during exercise to coughing and sneezing. They are duced [7]. important survival mechanisms, and many of the The sensory nerve, also called as the afferent mechanisms fully developed at birth. nerve, conducts the action potential generated at- Reflexes have five basic components involved the receptor to the nervous system, penetrating in the physiological response: receptors, sensory the spinal cord through the dorsal roots. On enter nerves, synapses, motor nerves, and target organs. ing the nervous system, synapses occur to generate Receptors vary widely within the body, but they a response to the stimulus. For most of the reflex- all share a common function: to translate some- arcs, more than one synapse occurs. Few reflexes environmental energy received into the stimulus are monosynaptic, such as those from muscle spin form into action potential so that they can prop dles. The response is driven by the motor nerve, Contactagate through Alberto Gonçalves the sensory Evangelista nerves. [email protected] For example, or efferent School nerve, of Life bringing Sciences, the Pontifical action Catholicpotentials University of of Paraná, Curitiba, Brazil. © 2020 The Authors. This is an open access article under the terms of the Creative Commons Attribution NonCommercial ShareAlike 4.0 (https://creativecommons.org/licenses/by-nc-sa/4.0/). André Felipe Breda Andrade Costa, Ana Paula da Veiga Argus, Franciele Prestel Pisetta, Alberto Gonçalves Evangelista Muscle stretch reflex the nervous system to the target organ, an effector of the response. The motor nerves leave the spinal - To perform a response, receptors capable of cord through the ventral roots [8,9]. detecting the result of the contraction of the mus It is in the target organ that the reflex response - cles to the central nervous system, as well as their will be fulfilled, with variations in its activity extension over the body, are required. The recep according to its usual function. As an example, we tors involved are the muscle spindles and the Golgi can mention the quadriceps muscle of the leg, in - tendon organ [17]. The spindles can contract and the case of the patellar reflex (muscle stretch), and - indicate muscle length as they have parallel skel the smooth muscle of the iris when in the pupillary etal fibers. The Golgi tendon organ is an encap reflex, triggered by light [10,11]. Reflex Physiology sulated structure located at the muscle–tendon - junction, where the collagen fibers of the tendon join the ends of the extrafusal muscle fibers. The Reflexes can be segmental or intersegmental. A seg stretching of the fibers also stretches the tendon mental reflex is one in which the reflex arc passes organ. These compresses and stretches the nerve- through a small segment of the nervous system endings, causing their depolarization. Tendon- [11]. In an intersegmental reflex, multiple segments organs are very sensitive to changes in muscle ten of the nervous system are used [12]. The reflex sion, unlike muscle spindles which are more sensi analysis is very important for diagnosis, treatment, tive to changes in muscle length. When the muscle and prognosis of diseases of the nervous system,- contracts, the frequency of depolarization of the but a well-performed analysis can also determine tendon organs increases markedly, whereas that of pathologies in other systems, such as musculoskel the muscle spindles decreases or even disappears- etal systems [13]. - [18,19]. The autonomous nervous system guarantees The spindle is encapsulated and contains special adequate responses to emergency or stress situ ized skeletal muscle fibers, intrafusal muscle fibers, ations that require rapid and intense responses, and extrafusal muscle fibers. The intrafusal fibers being the main responsible for reflexes. It is the part- can contract at their polar end, whereas, at their- of the nervous system responsible for regulating- apolar end, there is no contraction, being encased neurovegetative functions whose control is invol by the motor neuron itself and gamma motor neu untary: respiratory, cardiovascular, renal, diges rons themselves. The extrafusal muscle fibers can tive, and endocrine systems. It plays a major role in physically shorten the muscle and receive nerve maintaining homeostasis at all times in the face of supply within their motor unit, which is the alpha different environmental situations and challenges, motor neurons [18]. innervating various organs, glands, blood vessels, The way to generate an action potential is- and smooth and cardiac muscles. It is divided into through muscle stretching, with stretching of the- the sympathetic and parasympathetic autonomic- equatorial segment and opening of the ion chan nervous system [14,15]. nels, causing membrane depolarization, and gener- The sympathetic system innervates all the vis- ating the action potential [20]. The ability to send cera of the body, preparing the body for the fight- information to the central nervous system is deter or-flight response. Among its functions, pupil dila- mined through the muscle spindle, which informs tion, increase in heart/respiratory rate and blood the length of the muscle. Both the stretch receptors- pressure, bronchodilation, and decrease in diges provide the nervous system with information on tive peristalsis, among others, are highlighted. The length and tension, which is essential for coordina parasympathetic system has a function contrary to- tion in posture and locomotion [21]. - the sympathetic system in a large part of the body, This reflex can happen in any muscles of the which can cite the functions of reducing heart/respi body; however, some are more important for clin ratory rate, emptying the bladder, and increasing ical analysis and diagnosis. The reflex mostly used the peristalsis of the digestive system. The balance in the analysis of the patient is the patellar reflex.- of function between the two autonomous systems In this reflex, the action potentials are generated in makes the body in an ideal health condition [14,16]. the spindle sensory nerve at a frequency propor- In the course of this review, we will present the tional to the degree of stretching of the equatorial basics fundamentals of the reflexes of the greatest region of the spindle. Once transmitted to the cen clinical importance. tral nervous system, a monosynaptic and excitatory 2 J Mol Pathophysiol • 2020 • Vol 9 • Issue 1 Basic background in reflex physiology connection occurs with the motor neuron that through the optic nerve, where through various returns to the extrafusal fibers of the same muscle interneurons, and cholinergic parasympathetic [13,22]. neurons stimulate the muscle that contracts the- The patellar reflex is generated by percussion of iris, with a decrease in the pupil [30]. the patellar tendon (quadriceps muscle insertion).-
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