Muscular system

The muscle is one of the organ systems in the body tissue of animals ( Eumetazoa all ( multicellular ) animals except the sponges and the disc animals ) and refers to the totality of the muscles. When the term is used in connection with other parts of the body, such as in the names abdominal muscles or back muscles, so the statement refers to the muscle groups of the respective body portion and their interaction.

A single muscle (Latin musculus, the little mouse ' - because a tense muscle looks like a mouse under the skin) is a contractile organ that can move internal and external structures of the organism by the sequence of contraction and sagging. This movement, both the basis of the active transport of the individual, and the shape change of the body as well as many internal functions of the body.

The basic classification of the muscles in mammals, including humans via the histological structure and mechanism of contraction. Thus, a distinction is made smooth muscle and striated muscle. The latter can be further into the heart muscle and skeletal muscle divide. Other distinguishing possibilities arise when the shape of the fiber types and functional aspects (see below). The muscle tissue is the underlying muscle tissue, which consists of the characteristic muscle cells. In skeletal muscle, the muscle cells are called muscle fibers.

3.1 Description
3.2 contraction types

4.1 Functional classification of skeletal muscle
4.2 skeletal muscle of man 4.2.1 development

Comparison of muscle types

Histology

The name of the cytological structures of muscle cells subject to a specific nomenclature for the muscles and therefore differs in part from that of other cells:

Skeletal muscles are arbitrarily controllable parts of the muscles and ensure the mobility of the animal. They are also called striped - or striated muscles, as their myofibrils are arranged very regularly in contrast to the smooth muscles and thereby produce a recognizable ring pattern of red and white myosin filaments actin filaments. All skeletal muscles are associated with the somatic musculature.
The heart muscle is working rhythmically, can not cramp, has its own conduction system, may depolarize spontaneously, contains the cardiac isoform of troponin I and T. It has the striations of skeletal muscles, but is involuntarily controlled primarily through the sinus node and thus represents a own muscle type dar.
The smooth muscle is not subject to conscious control, but innervated and controlled by the autonomic nervous system. This includes, for example, the muscles of the intestine. All smooth muscles are associated with the visceral musculature.

The striated muscle is derived from the myotomes of the somites of the body wall, the smooth from the mesoderm of the splanchnopleura, so this is also known as visceral muscles. In the region of the foregut visceral musculature is innervated by the cranial nerves and is striated, while the remaining viscera muscle consists of smooth muscle fibers.

Other possible categorizations

A muscle can be classified in various ways, and this classification is not directly and unambiguously. Often overlap the properties. Depending on the angle they are distinguished by their cell structure, form or function. Furthermore, types of muscle fibers can be distinguished, which occur mixed in a muscle.

Anatomical

Circular muscle

Hollow muscle

Spindle-shaped muscles

Spring-shaped muscles
Mehrbäuchige muscles

Multi-headed muscles

Is also divided into:

Cytologically (see above) and functional ( see below)

Classification of muscle fiber types

After enzyme activity

Type I fibers: SO ( engl. slow oxidative fibers = slow oxidative fibers ')
Type II fibers: Type II A fibers: FOG (English almost oxidative glycolytic fibers =, fast oxidative / glycolytic fibers ')
Type II X fibers: FG (English almost glycolytic fibers = fast glycolytic fibers '). There are different types ( B or C) depending on the species.

After contraction property

Extrafusale fibers (also twitch fibers = twitch ') (working muscles)

ST fibers ( slow twitch fibers = german, slow-twitch fibers ' ) are very persistent, but do not develop high forces (corresponding to SO).
Intermediate type (equivalent FOG)
FT fibers ( fast twitch fibers engl. = fast twitch fibers ') can develop high forces, but will quickly become fatigued (equivalent to FG).
Tonusfasern can only exert a slow, wormlike contraction. They are rare, for example in the extraocular muscles, the tensor tympani muscle and in muscle spindles, above.

Intrafusal fibers (muscle spindles) serve as stretch receptors and to adjust the sensitivity of the muscle spindles.

By Color

Red muscles (equivalent to SO)
White muscle (equivalent to FG) Have in many animals (but not humans ) because of the low Myoglobingehalts a bright color.

The ratio of composition of skeletal muscle from different muscle fiber types is largely genetically determined and is limited by a targeted endurance or strength training changeable. This does not change the ratio between type I and type II fibers, but probably the between Type II A and Type II -X. For many II -X fibers II -A- fibers are formed (eg in the trapezius muscle in strength training content of II-A from 27% to up to 44 % of all fibers). The distribution of the different muscle fibers in a muscle is not homogeneous, but differ in origin, insertion or in the interior and on the surface of the muscle.

Muscle contraction

Description

Contraction is a mechanical process that is triggered by a nerve impulse. Here, protein molecules into each other (actin and myosin ). This is made possible by a rapid succession of conformational changes of the chemical structure, so that the extensions of the myosin filaments - comparable with fast rudder movements - draw the myosin filaments in the actin filaments. Listen to the nerve, to supply the muscle with pulses relaxed the muscle, then one speaks of muscle relaxation.

Contraction types

Depending on the power (voltage ) and change in length of the muscle can be multiple types of contraction differ:

Isotonic ( " same tense " ): The muscle shortens without force change.
Isometric ( " same dimension" ): The force increases at a constant length of the muscle ( holding - static). In the physical sense, no work is done, since the distance traveled is equal to zero.
Auxotonisch ( " different clamped" ): Both force and length change. This is the most common type of contraction in everyday movements.

From these elementary types of contraction to contraction complex shapes can be put together. They are used in everyday life most often. These are, for example,

The Unterstützungszuckung: only isometric, then isotonic contraction. For example, lifting a weight off the floor and then angle the forearm.
The Anschlagszuckung: only isotonic, then isometric contraction. Example: chewing motion, slap.

In terms of the resulting change in length of the muscle and the speed with which this is done to contractions can be characterized as follows, for example:

Isokinetic ( " same speed " ): The resistance is overcome with a constant speed.
Concentric: muscle overcomes the resistance and becomes shorter ( positive dynamic, overcoming ). Intramuscular voltage changes, and the muscles shorten.
Eccentric: whether intentionally or not, the resistance is greater than the tension in the muscle, thus the muscle is stretched (negative, dynamically yielding ). It comes to voltage changes and extension / stretching the muscles.

Structure and function of striated skeletal muscle

Every muscle is encased by an elastic sheath of connective tissue ( fascia ), (also secondary beams ) encloses several meat fibers, which in turn with connective tissue ( perimysium externum and epimysium ) surrounded and held together, which is penetrated by nerves and blood vessels and to the fascia attached. Each meat fiber is divided into a plurality of fiber bundles (including primary beam ), which are mounted to one another so that the muscle is flexible and snugly. These fiber bundles are an association of up to twelve muscle fibers, which are united by fine connective tissue with capillaries.

Active is the muscle by tensing (contraction ) ( then relaxed again), exerts a movement and a force. A muscle contraction is triggered by electrical impulses ( action potentials ) that have been emitted by the brain or spinal cord and passed through the nerve.

In the muscle fiber is a syncytium which is a cell of a plurality of committed progenitors ( myoblasts ) is formed and, therefore, includes a plurality of cores. Muscle fiber can reach a considerable length of more than 30 cm and about 0.1 millimeters thick. She is unable to divide, which is the reason why is at a loss of fiber, no reimbursement will grow and only thickens the fiber in muscle growth. That is, from birth, the upper limit of the muscle fibers is fixed. In addition to the usual components of an animal cell mainly make myofibrils, which are finest fuzz, about 80 percent of the fiber mass. The membrane envelope of muscle fibers is called the sarcolemma.

Functional classification of skeletal muscle

With regard to their cooperation muscles are divided in to playing and interacting. Agonists ( player) and antagonist ( opponent ) each have an opposite effect. Synergists, however, have the same or similar effect and therefore cooperate in many motion sequences.

Muscles, use the extremities of the body, called adductors ( adductor ), their antagonists, the abductors ( puller), ensuring that the limbs are spread away from the body.

Example: outer and inner muscles of the thigh, with which one can straddle and merge the legs.

Flexors ( flexor ), however, bend a finger and toes, their antagonists, the extensors ( extensors ).
Rotators ( turning movements result from, for example, the forearm or the head)

Skeletal muscle of man

Every healthy person has 656 muscles, which in men about 40%, in women about 23 % of the total body mass account for the overall muscularity but depends on the lifestyle from.

The largest area of muscle of man is the latissimus dorsi ( latissimus dorsi ), which has a volume of largest muscle is the gluteus maximus (the largest buttock muscle ), the strongest of the masseter muscle (musculus masseter ), the longest of the sartorius muscle (musculus sartorius ) the most active the eye muscles and the smallest of the stirrup muscle ( stapedius muscle ). Due to the scope of mechanical work that must make the muscles, they are next to the nervous system, one of the main buyers of body energy.

Development

The newborn, the muscles are more developed in the fuselage than those in the extremities. The muscle percentage is about 21 percent of the body weight. During the growth of the muscle mass, the total body mass, however, increases in men by approximately the 32.8 - fold, but only about the 19.4 - fold. In men, muscle development completes in the period between 23 and 27, in women between 19 and 23 years of age. The muscle mass in men is about 37-57 %, while it is about 27-43 % in women.

In older age the development of muscles goes back similar to the front of the full training to a state. So this concerns mainly a reduction of the muscles in the legs.

Physiological muscle insufficiency

Due to its microscopic anatomy of a muscle can not completely retract ( the sarcomere may be shortened only by about 30 %), stretch still unlimited ( the sarcomere would otherwise tear ). This leads to two different forms of physiological insufficiency of a muscle:

Active muscle insufficiency occurs when the agonist is unable to continue to contract, because he is already contracted maximum.
Passive muscle insufficiency occurs when the agonist can not continue to contract, as his antagonist is already stretched maximum.

When two joint muscles, it is possible to counteract the muscle insufficiency (relative to the muscle effect on a joint), by stretching the muscle in the other joint (or the antagonists reduced ). Acts such as the biceps brachii with respect to its flexor force at the elbow stronger when the arm is retroverted (ie the elbow joint behind the body ) is counteracted because now the active insufficiency of the muscle by stretching the shoulder joint ( the long head of the biceps covers both joints ).

Diseases and injuries of the skeletal muscles

Botulism
Macrophagic Myofasciitis (muscle weakness disease by invading macrophages )
Muscular atrophy ( muscle wasting)
Muscle rupture ( hernia )
Muscular Dystrophy
Hamstring
Muscle hardness ( myogelosis )
Muscle tightness
Muscle myogelosis ( Myosklerose, hypertonia )
Muscle soreness
Muscle spasm
Muscle contusion
Muscle calcification
Muscle strain

Muscular imbalance
Myalgia (muscle pain)
Myasthenia (muscle weakness)
Myoclonus
Myokymia
Myopathy
Paresis
Plegia ( paralysis )
Rhabdomyolysis
Spasticity
The contracture is a stiffening of a joint due to a shortening of the muscles and tendons, caused eg by immobilization, long immobilization, lack of muscle game including among nerve damage and eventually damage in the joint space. Due to the longer inactivity it comes, first muscle breakdown.