Muscular system: what it is, parts and functions

A summary of the characteristics of the muscular system and its functions in the body.

Humans and all other living beings on Earth navigate in a three-dimensional environment and therefore require a powerful skeletal and muscular system that allows us to respond to external stimuli and overcome the force of gravity, among many other things.

It is interesting to know that it is estimated that there are more than 650 types of muscles in the human body (according to the established definition) and that a process as apparently simple as smiling involves a total of 20 facial muscle structures to be carried out.

It is clear that we cannot live without a correct muscular system because of the psychomotor importance it harbors and, as a result, diseases such as Duchenne dystrophy (which progressively weaken this apparatus) have a long-term survival rate of about 10%. Without proper functioning of the muscle tissue, vital tasks such as breathing and Blood circulation can be severely compromised.

With these data, we wanted to highlight the extremely important functionality of this apparatus, but there are many more terms and particularities enclosed in each of our muscles and tendons. Stay with us, because in the following lines we will tell you everything you need to know about the muscular system.

What is the muscular system?

From a physiological point of view, the muscular system can be defined as the set of muscles (more than 600) that exist in the human body.. This apparatus stabilizes body position in three-dimensional space, produces the movement of bone structures, regulates the volume of organs, mobilizes substances within our body and plays an essential role in the production of heat, among many other things.

First of all, we should point out that there is a clear discordance between various bibliographical sources, since certain experts include within this system all tissue of a muscular nature, while other sources include in this definition only those muscles that can be controlled voluntarily by a living organism (skeletal musculature). For the sake of clarification, we will focus our attention on the broader and friendlier definition of the term.

The muscle: the functional unit

According to clinical sources, A muscle can be defined as a tissue made up of muscle fibers endowed with a contractile capacity..

In general, we can summarize that the basic and general physiological properties of all muscle tissue are contractibility, excitability, extensibility and elasticity.. All this allows the biomechanical action of living beings and other processes as basic as the beating of the heart or breathing.

Types of muscle groups

As we have said, if we consider the muscular tissues that are part of the organs, we can observe 3 different types of them. We will tell you about them in the following lines.

1. Smooth muscle

It is described as visceral or involuntary. It forms the walls of the hollow viscera, such as the stomach and the bladder, and those of various tubular ducts.The smooth muscles, such as the various units of the circulatory system, the respiratory system, the digestive tract, the respiratory apparatus and the reproductive organs, for example.

Generally, the smooth muscles cannot be controlled at the individual's willbut are automatically at the mercy of the nervous system. They contract slowly, are more extensible and capable of remaining in one state for a longer period of time, i.e., they do not "tire" as easily as striated muscles.

2. Striated or skeletal muscle

According to certain authors, only this type of muscle would form the muscular system per se. Unlike the smooth musculature, striated muscle is that which shapes the body and is attached to the bones, mainly in the legs, arms and legs.It is found mainly in the legs, arms, abdomen, chest, neck and face. These muscles are called "striated" because they are composed of alternating bands of light and dark tones.

These muscle fibers are innervated by cranial or spinal nerves and, as previously mentioned, are circumscribed to the voluntary government of the individual. They can be contracted rapidly and energetically, but they "tire" quickly and must therefore rest between periods of great effort.

3. Cardiac muscle

As its name suggests, the cardiac muscle is found in the heart. As you can imagine, because of its functionality, it is not under the control of the individual will, which is why it is considered automatic.. This type of muscle tissue has four basic properties:

• Rhythm, or what is the same, the capacity to generate periodic impulses.

• Conductivity, the capacity to transmit these impulses throughout the myocardial tissue.

• Irritability, the property to respond to stimuli.

• Contractility, the property to contract in response to a specific stimulus.

• Muscle nomenclature

  It is interesting to know that muscles can be classified in a very extensive terminology according to multiple parameters. For example, based on their function, a muscle can be supinator, pronator, adductor, levator and tensor. According to their shape, they are classified in terms such as triangular, square, pyramidal, rhomboid and trapezius.

  Other classificatory criteria which we will not go into here are according to size, bony relationship, direction of the fibers, number of insertions or topographical relationship. To give you a general idea, there are more than 30 muscle types based on each and every one of the parameters described above..

  The mechanism of muscular contraction

  Everything we have explained so far is really interesting, but how does it translate from a functional point of view? In the following lines we explain, in broad outline, the mechanism of muscle contraction.

  First of all, an action potential travels along a motor nerve to the end of the motor nerve, which then flows into the muscle fibers.. The signal comes from the brain which, by means of electrical impulses carried through the neurons and the release of neurotransmitters (synapses), communicates the signal to the muscle that it must perform the action for which it is prepared.

  At each end of the nerve, it releases a very special neurotransmitter: acetylcholine. To summarize a lot, we will say that acetylcholine allows the opening of sodium channels to the muscle fibers and that, indeed, the sudden concentration of this ion triggers an action potential that stimulates the muscle cells to release calcium. The release of calcium allows the reconfiguration of the muscle fibers. actin and myosin, essential globular proteins for this tissue which, with the expenditure of ATP, generate the typical movement of muscular contraction..

  Having described this, we must also point out that there are two main types of contractions:

  • Isometric: the contracted muscle fibers do not vary almost in length, but the muscle tone is intensified and no displacement occurs.
  • Isotonic: here the length of the muscle fiber is shortened by the contraction, but the muscle tone remains almost constant and displacement occurs.

  Functions of the muscular system

  We have already covered the main structures of the muscular system and their method of action but, in these last lines, we find it of special interest to elucidate the functionality of the muscular system. Among them, we find the following:

  • The production of body movement through interaction with the joints.
  • Contraction of the heart, blood vessels and the production of peristaltic movements (which allow the transport of food through the digestive tract).
  • Providing joint stability and maintaining the postural form of living beings in a three-dimensional space.
  • Providing body heat when necessary, since energy expenditure is transformed into metabolic heat.
  • Physical protection and endurance. Skeletal muscles account for 40% of the weight of an adult individual, which is why they act as protectors of organs and systems.
  • They stimulate the correct flow in blood and lymphatic vessels, with all that this entails for the homeostasis of the organism.

  In general, if we consider the muscular system in its strictest sense (only the striated or skeletal musculature), we could say that its main function is solely the production of voluntary movements in the organism in response to some type of environmental stimulus.. On the other hand, if we take into account all tissue of a muscular nature, its functionality extends to the very conception of life, since without the muscles of the heart the blood would not beat and we would simply not exist.

  Summary

  Compressing the particularities of the muscular system in a few lines is a real challenge, since each small bundle, each fiber and each globular protein included here provides enough information to write a book on its own. In any case, we have given you a general picture of this system, from the typology of its tissues to its functionality, passing through the mechanism of action at the chemical level.

  If we want you to keep one idea in mind, it is the following: in its narrowest sense, the muscular system is that which is composed of voluntary muscles, i.e. of a skeletal nature. In a broader sense, this apparatus is composed of more than 600 types of musculature, ranging from the tissues that are inserted into the bones to those that form the various organs essential for survival.

  Bibliographical references:
  • De education, t. R. R. D. O., & lomce, f. S. (2020). The muscular system. Structure and functions. Particular characteristics of the evolutionary period corresponding to the stage. Considerations to take into account in the physical education class. Summarized Thematic Summary of Physical Education Secondary Examinations (LOMCE) Volume II: Access to the body of teachers of Secondary Education.
  • Diniz, G. P. (2003). Muscular system.
  • Bones, muscles and joints. RadysChildren.org.
  • Mora, I. S. (2000). Muscular system.
  • Schoenau, E. (2006). The muscular system is the driver of skeletal development. Annales Nestlé (English ed.), 64(2): pp. 55 - 62.