Muscles - functions, structure and diseases

Muscles enable humans and other living creatures to move. Muscles are also responsible for the stability of the body as well as vegetative functions such as breathing and the pumping movements of the heart.

How muscles work

Muscles are contractile organs. The term "contractile" refers to their ability to contract and relax again. Many muscles resemble a mouse when tensed. This is where their name comes from (lat. musculus = little mouse). This interplay of contraction and relaxation enables both the consciously controlled movements and the unconscious functions that take place inside the body. As a result, they enable, among other things, skeletal movements or the execution of internal bodily functions.

All muscles are referred to as musculature. It can be divided into smooth muscles and striated muscles. The latter is further divided into cardiac muscles and skeletal muscles. Only the skeletal musculature can be consciously controlled.

 

© adimas / Fotolia

 

Many muscles resemble a mouse under tension. This is where their name comes from: the Latin name for little mouse is musculus.

The following video shows how a muscle bundle is structured:

 

The contraction of a muscle is triggered by nerve impulses. These trigger a series of interactions between the filaments. As a result, the myosin and actin filaments slide longitudinally into each other, causing the respective sarcomeres to shorten and the corresponding muscle fiber to contract.

Find Specialists for Sports medicine

Different types of muscle

Muscle fibers are also known as muscle fiber cells or myocytes. They form the basic cellular unit of the striated skeletal muscles and occur within a skeletal muscle in bundles of 0.1 millimetres to 1 millimetre in diameter. Their length depends on the length of the muscle.

The smallest functional unit of the muscle fibers are the sarcomeres. These consist of myosin and actin fibers, which are held together by the largest protein found in the human body (titin). In the middle of a sarcomere, the thick myosin fibers arranged parallel to each other predominate. Myosin is one of the motor proteins and converts the chemical energy ingested with food into muscle movements. Actin belongs to the structural proteins and provides elasticity and stability with its narrow filaments.

Muscle fibers have muscle fibrils (myofibrils) as functional units. These consist of several hundred sarcomeres, which are made up of myosin and actin filaments. At their ends, the sarcomeres are bounded by so-called Z-discs (intermediate discs), in which the thin actin filaments converge.

In the middle of the sarcomere, however, they meet the thicker myosin filaments. This structure results in light bands with narrow actin filaments at the ends and darker bands with thick myosin filaments in the middle of the sarcomere.

This diagram goes into more detail from top to bottom. Top: Skeletal muscle. Center: Muscle fascia. Bottom: Muscle fiber with sarcomeres

The muscle fibers of the individual muscles are usually connected to the bones of the skeleton via tendons.

The largest group of muscles are the striated skeletal muscles. A single skeletal muscle contains several meat fibers that are enclosed in an elastic fascial sheath and are attached to it via other connective tissue. A meat fiber consists of up to twelve muscle fibers that form a fiber bundle and can be moved against each other. This ensures that the muscle is elastic and supple.

Find Specialists for Orthopedics

The most important muscles

Chest muscles

The pectoral muscles consist of the pectoralis major and the pectoralis minor. The large pectoral muscle(pectoralis major muscle) supports arm movements directed in front of the body and is part of the respiratory support muscles. The small pectoral muscle(pectoralis minor muscle) is completely covered by the large pectoral muscle. It enables shoulder movements.

Back muscles

The most important part of the back musculature is the local (autochthonous) back musculature(erector spinae muscle). Its main task is to straighten and stabilize the spine.

It is supplemented by the "migrated" (allochthonous) back muscles. These include the large back muscle(latissimus dorsi muscle) and the trapezius muscle (trapezius muscle), which cover the neck and upper back area and the lower back area respectively. They lend stability to the respective regions and enable movements of the shoulders and arms, among other things.

© bilderzwerg / Fotolia

Abdominal muscles

The abdominal muscles can be divided into anterior, lateral and posterior abdominal muscles. The straight abdominal muscle(rectus abdominis muscle) belongs to the anterior abdominal muscles. It has three to four horizontal intermediate tendons, which can protrude as a "washboard" or so-called "six-pack" if the abdominal muscles are well trained. Together with the other abdominal muscles, it ensures a stable posture.

Shoulder muscles

Thedeltoid muscle is the largest shoulder muscle. It stabilizes and moves the shoulder joint. Together with the other shoulder muscles, it enables rotational movements of the arms and supports the muscles of the back.

Find Specialists for Shoulder surgery

 

 

This video clearly shows the different muscle types (explanations in English)

 

Upper and lower arm muscles

The arm muscles include a good twenty muscles, most of which are located in the forearms. However, the most prominent representatives are the biceps(biceps brachii muscle) and triceps(triceps brachii muscle) in the upper arm. The two antagonists enable the arms to bend and stretch.

Upper and lower leg muscles

Among the thigh muscles, the quadriceps(quadriceps femoris muscle) stands out in particular. It covers almost the entire front of the thigh. Its tasks include stretching and stabilizing the knees.

The lower leg muscles can be divided into the anterior and posterior muscles, which consist of extensors and flexors.

Find Specialists for Knee surgery

The human musculature

Diseases and injuries

Muscle atrophy (muscular atrophy)

Muscle atrophy, also known as muscular atrophy or muscular dystrophy, can occur as a result of inactivity or neurological diseases, for example. If there is too little movement, the body breaks down underused muscles. This can happen after a stay in hospital or be a side effect of an inactive lifestyle, for example in senior citizens. Rebuilding through training is then possible and the muscles respond again to the training stimuli. Muscle atrophy as an independent neuromuscular disease, on the other hand, requires an individual therapy concept.

Muscle pain (myalgia)

Muscle pain can occur in a wide variety of forms and with different causes. A relatively simple manifestation of muscle pain is muscle soreness (from the Greekcatarrh - literally: to flow down; meaning inflammation) after sport or unusual exertion. Tiny tears, so-called micro-ruptures, are small pieces of tissue damage that follow strong training stimuli. In this case, the muscle was overtaxed by its tasks and reacts by accumulating water in the tissue. Muscle soreness is an inflammatory process that starts about a day after the exercise stimulus and causes pain. With a little regeneration, the muscle can repair and rebuild itself. The muscle soreness subsides after a few days. An appropriate supply of nutrients, especially protein and minerals, and warmth to stimulate circulation are important.

Find Specialists for Rheumatologic orthopedics

Myalgia can also occur with infections, flu and colds or tick bites. Fibromyalgia refers to chronic fiber-muscle pain that is as yet incurable. If myalgia occurs as a symptom of another underlying disease or if pressure-sensitive trigger points are present, these causes are treated in order to counteract the muscle pain. The video shows the principle of trigger point massage:

 

 

Muscle strain, muscle fiber tear and muscle tear

Injuries that lead to muscle strain or tearing of the muscle fiber or the entire muscle under heavy strain. Muscle damage increases in this order and can occur particularly in sports with high loads, such as sudden changes of direction or twists. Insufficient warm-up before training also increases the risk of muscle injury. Muscles and joints should therefore be warmed up and prepared for training before any sporting activity. A simple basic program is to circle, twist, bend and stretch the joints according to their natural range of motion as well as loose running. Sports clothing should also be adapted to the outside temperature to avoid hypothermia.

© Henrie / Fotolia

Find Specialists for Sports traumatology

Muscle twitching (myoclonia)

Muscle twitches that occur as a side effect of neurological diseases, but also temporarily, for example during stress. They can affect the extremities and facial expressions, among other things - it is often the eyelid that affects the affected person with a fine twitch. This type of myoclonia is harmless in itself. If the twitching is more pronounced and other symptoms occur, these should be discussed with a doctor in order to rule out an underlying neurological disease.