Muscular system. In human anatomy, the muscular system is the set of the more than 650 muscles of the body, whose main function is to generate movement, either voluntary or involuntary – skeletal and visceral muscles, respectively. Some of the muscles can be threaded in both ways, which is why they are often categorized as mixed.
The muscular system allows the skeleton to move, maintain its stability and the shape of the body. In vertebrates it is controlled through the nervous system, although some muscles (such as the heart) can function autonomously. Approximately 40% of the human body is made up of muscles, that is to say that for each kg of total weight, 400 g correspond to muscle tissue.
- Classification according to the way they are controlled
- The shape of the muscles
- Care of the muscular system
The muscular system is responsible for:
- Locomotion: carry out the movement of blood and the movement of the extremities.
- Motor activity of the internal organs: the muscular system is in charge of making all our organs perform their functions, helping other systems such as the cardiovascular system.
- Information on the physiological state: for example, renal colic causes strong contractions of the smooth muscle generating strong pain, a sign of the colic itself.
- Mimicry: the set of facial actions, also known as gestures, that serve to express what we feel and perceive.
- Stability: the muscles together with the bones allow the body to remain stable, while remaining active.
- Posture: control of the positions performed by the body in a resting state.
- Heat production: producing muscle contractions generates caloric energy.
- Shape: The muscles and tendons give the typical appearance of the body.
- Protection: the muscular system serves as protection for the proper functioning of the digestive system and for vital organs.
- Skeletal muscles of the arm, during a contraction: biceps brachii – left, to the left – and triceps brachii – right, to the right. The first flexes the arm, and the second extends it. They are antagonistic muscles.
The main function of the muscles is to contract, in order to generate movement and perform vital functions. Three muscle groups are distinguished, according to their arrangement:
- Skeletal muscle
- Smooth muscle
- Heart muscle
Striated (skeletal) muscle
Striated muscle is a type of muscle that has the sarcomere as its fundamental unit, and which presents, when viewed through a microscope, striae that are formed by the alternating light and dark bands of the sarcomere. It is made up of spindle-shaped muscle fibers, with very sharp ends, and shorter than smooth muscle. These fibers have the property of plasticity, that is, they change their length when they are stretched, and they are able to regain their original shape. To improve the plasticity of the muscles, stretching is useful. It is in charge of the movement of the axial and appendicular skeletons and the maintenance of posture or body position. In addition, the skeletal muscle of the eye performs the most precise movements of the eyes.
The musculoskeletal tissue is made up of very long (up to 30 cm), cylindrical and multinucleated cell bundles, which contain abundant filaments, the myofibrils. The diameter of skeletal striated muscle fibers ranges from 10 to 100 microns. These fibers originate in the embryo by the fusion of elongated cells called myoblasts. In skeletal muscle fibers, the numerous nuclei are located on the periphery, near the sarcolemma. This characteristic localization helps to differentiate skeletal muscle from cardiac muscle because both show striations but in the heart muscle the nuclei are central.
Smooth muscle, also known as visceral or involuntary, is made up of spindle-shaped cells that have a central nucleus that resembles the shape of the cell that contains it, they lack transverse striations although they show slightly longitudinal striae. The stimulus for smooth muscle contraction is mediated by the autonomic vegetative nervous system. Smooth muscle is located in the reproductive and excretory systems, in blood vessels, in the skin, and internal organs.
There are smooth unit muscles, which contract rapidly (no innervation is triggered), and smooth multi-unit muscles, in which the contractions depend on nerve stimulation. Unitary smooth muscles are like those of the uterus, ureter, gastrointestinal tract, etc.; and multiunit smooth muscles are those found in the iris, nictitating membrane of the eye, trachea, etc.
Smooth muscle also has, like striated muscle, actin and myosin proteins.
Cardiac muscle (myocardium) is a type of striated muscle found in the heart. Its function is to pump blood through the circulatory system by contraction. The heart muscle generally works involuntarily and rhythmically, without nerve stimulation. It is a myogenic muscle, that is, self-excitable. The striated and branched fibers of the heart muscle form an interconnected network on the wall of the heart. The heart muscle automatically contracts at its own rate, about 100,000 times a day. It cannot be consciously controlled, however its rate of contraction is regulated by the autonomic nervous system depending on whether the body is active or at rest.
Classification according to the way they are controlled
- Volunteers: Controlled by the individual
- Involuntary or visceral: Directed by the central nervous system
- Autonomous: Its function is to contract regularly without stopping.
- Mixed: Muscles controlled by the individual and by the nervous system, for example the eyelids.
Muscles are made of a protein called myosin, it is found throughout the animal kingdom and even in some vegetables that have the ability to move. Muscle tissue is made up of a series of fibers grouped into bundles or primary masses and wrapped by the fascia, a kind of protective sheath or membrane, which prevents the movement of the muscle. The muscle fibers have abundant intraprotoplasmic filaments, called myofibrils, which are located parallel to the long axis of the cell and occupy almost the entire cell mass. The myofibrils of smooth muscle fibers are apparently homogeneous, but those of striated muscle present zones of different refringence, which is due to the distribution of the main components of myofibrils, the proteins of myosin and actin.
The shape of the muscles
Each muscle has a certain structure, depending on the function they perform, among them we find:
- Fusiform spindle-shaped muscles. Being thick in its central part and thin at the ends.
- Flat and wide, they are those found in the chest (abdominals), and protect the vital organs located in the rib cage.
- Abanicoides or fan, the pectoral muscles or the temporal muscles of the jaw.
- Circular, ring-shaped muscles. They are found in many organs, to open and close ducts. for example the pylorus or the anal opening.
- Orbicular, spindle-like muscles, but with a hole in the center, serve to close and open other organs. For example lips and eyes.
Muscles are generally associated with obvious functions such as movement, but in reality they are also what allow us to push food through the digestive system, breathe, and circulate blood.
The functioning of the muscular system can be divided into 3 processes, one voluntary in charge of the skeletal muscles, the other involuntary carried out by the visceral muscles and the last duty process of the cardiac muscles and autonomously functioning.
The skeletal muscles allow walking, running, jumping, in short, they empower a multitude of voluntary activities. Except for reflexes, which are the involuntary responses generated as a result of a stimulus. As for involuntary functioning muscles, it can be specified that they perform independently of our will but are supervised and controlled by the nervous system, it is in charge of generating pressure for the transfer of fluids and the transport of substances throughout the organism with the help of peristaltic movements (such as food, during the digestion and excretion process).
The autonomous process takes place in the heart, an organ made of heart muscles. The primary function of this muscle tissue is to contract regularly, millions of times, having to endure fatigue and tiredness, or else the heart would stop.
Care of the muscular system
To keep the muscular system in optimal conditions, a balanced diet must be kept in mind, with just doses of glucose which is the main energy source of our muscles. Avoid excess fat consumption, since they are not completely metabolized, producing overweight. For prolonged physical exercise routines, they need a diet rich in sugars and vitamins.
In addition to a healthy diet, physical exercise is recommended, muscular exercise causes muscles to work, developing by increasing their strength and volume, acquiring elasticity and contractility, better resisting fatigue. It also benefits the development of the skeleton because it strengthens, strengthens and models it, due to the traction that the muscles exert on the bones, if the exercises are correctly practiced, they perfect the harmony of the lines and curves.
Exercise helps to the performance of the organs. Increases chest volume, improves breathing and blood circulation, expanding the size of the lungs and heart. Another effect of physical exercise is that it causes a considerable increase in appetite, favoring digestion and assimilation of food.
Diseases that affect the muscular system can be produced by some viruses that directly attack the muscle, ailments are also experienced due to muscle fatigue, improper postures, sudden exercises or accidents. Some diseases and ailments that affect the muscular system are:
- Tear: breakdown of muscle tissue.
- Cramp: involuntary spasmodic contraction, affecting the superficial muscles.
- Sprain: injury caused by moderate or total damage to muscle fibers.
- Muscular dystrophy: degeneration of skeletal muscles.
- Atrophy: loss or decrease of muscle tissue.
- Hypertrophy: abnormal growth or development of the muscles, producing in some cases serious deformations. However, controlled muscle hypertrophy is one of the goals of bodybuilding.
- Poliomyelitis: Commonly known as polio. It is a disease caused by a virus, which attacks the central nervous system, causing nerve impulses to not be transmitted and limbs to atrophy.
- Myasthenia gravis: it is a neuromuscular disorder, it is characterized by a weakness of the muscular tissue and the muscular istema is an acid component.
- Bodybuilding (from the French bodybuilding) is a discipline used for the development of the fibers of the muscular system, through the combination of physical exercise such as weight lifting, increased caloric intake and rest to develop great muscles and a well-defined body and bulky.
- To achieve relaxation of the body and relieve contractures and tensions of the muscular system, there are numerous massage techniques, which in many countries are studied at the university level under the title of kinesiology.
- In the male human body muscles represent 40 to 50% of body weight, in women it represents 30% to 40%. The largest muscle is the Trapezius and Latissimus Dorsi of the back in equal parts, and the smallest is the abutment (bone) in the auditory system. The longest is the Sartorius Originated in the anterior superior iliac spine and becoming inserted in the anterior surface of the tibia up to the tubercle of the tibia. When we walk, we use more than 200 different muscles at the same time. The fastest muscle in the body is the eyelids, capable of opening and closing them up to 5 times per second. The strongest muscle is the masseter, which although it only measures 5 cm can develop a force of more than 4 kN. The muscle that develops the most is the myometrium,
- Muscle fatigue originates from the production of lactic acid, in addition to excessive muscle work, which implies higher glucose and oxygen requirements.
- A fundamental mineral in muscle work is magnesium, whose daily requirement in an adult ranges from 310 to 420 mg. Although the excess of magnesium is toxic, its lack produces inconveniences in the muscular functioning, which usually present their first symptoms through cramps. The essential mineral in muscle contraction is “Calcium” since without ATP it does not dissociate into ADP and Pyrophosphate and Myosin is not anchored to Actin (contractile cycle).
- Although we tend to associate muscles with movement, we generally think of obvious functions; in fact they are also the ones that allow us to push food through the digestive system, breathe and circulate blood.
- A unique technique – and on the other hand free of risks – to reduce the symptoms of a cramp is to hold for a few seconds a pinch on the mouth, on the upper lip.  This may be related to manipulation of the nervous system practiced by techniques such as the digit puncture.