Body processes

Contraction – Function, Task & Diseases

Contraction

The term contraction (lat. contrahere = to pull together) describes the process in which a muscle either shortens or increases its tension. There are different types of contractions with different functional importance.

What is crown traction?

A muscle can produce two mechanical effects on the human skeleton . It either stabilizes joints and areas of the body or it moves bones . In order for this to succeed, the force generated in the muscle must be transferred to the bone. The tendons take over this task .

The overall muscle consists of several subunits, such as muscle bundles, muscle fiber bundles, muscle fibers and, at the lowest level, muscle cells, also called fibrils. In addition to the cell organelles, these contain thousands of sarcomeres connected in series , the smallest functional units of a muscle. Each sarcomere can contract and thus develop strength. The total strength of a muscle therefore results from the sum of the force generation of the sarcomeres involved.

The functional center of each sarcomere are the actin-myosin complexes. Actin and myosin are proteins that are linked by cross-bridges. The thinner strands of actin are attached to the outer borders of the sarcomere, the thicker myosin molecules are each between two strands of actin.

If a nerve impulse reaches the muscle, calcium is released and the sarcomeres shorten or contract under energy consumption. The myosin units pull the actin units toward the center of the sarcomere by rowing their heads. The effect on the entire muscle depends on how many sarcomeres are contracted.

Function & task

Contractions produce 2 effects in the muscle. On the one hand, power is developed, on the other hand, heat is generated.

The musculature has a poor mechanical efficiency. Approximately 80% of the energy turnover during muscular work goes into heat development, only 20% into the generation of power. However, the heat produced makes an important contribution to regulating body temperature and optimizing metabolic processes .

The force developed by the contraction is transmitted via the tendons to the attachments to the bone and leads either to movement in the joints involved or to increased tension. Whether a movement occurs depends on the goal pursued in the movement programs in the brain and transmitted to the muscles via nerve impulses . If the goal is to carry out movement sequences, all muscle chains that are necessary for the appropriate action are automatically switched on, inhibiting influences are switched off. If a certain position is to be held, the command for the muscles, body parts and joints is to stabilize.

The interaction between agonists (acting muscles) and their opponents (antagonists) plays an important role in this process. This creates 3 possible types of contractions.

During isometric contraction, the tension in the muscle increases, but no movement occurs because the antagonists or external resistance do not allow it. Ideally, the agonists and their antagonists work together. This form of muscle work is important for all static loads, for example to stabilize the back or joints.

Concentric contractions lead to movement in the joint by shortening the active muscle and allowing the antagonists to move. This form of muscle work is mechanically the easiest and the cheapest to stimulate the muscle metabolism.

Eccentric contractions occur when the muscle controls movements that lengthen it. It has to do a lot of mechanical work because it contracts while the number of cross-bridges between actin and myosin decreases. All braking activities belong to this form of contraction.

Diseases & Ailments

A typical dysfunction of the muscle and contraction is muscle weakness (atrophy). It usually occurs because a muscle is not used enough (inactive atrophy). This phenomenon can typically be observed in bedridden patients or when limbs are immobilized ( cast ). The contractile force of the muscles and the muscle cross-section decrease, the function is impaired to a greater or lesser extent depending on the severity and duration. Another trigger for inactivity is injury or other irritation, such as painful irritation of tendon insertions. In this case, the brain switches on gentle programs that lead to muscles being used less. Inactivity atrophies can be regenerated if they don’t last too long.

The ability of muscles to contract depends on the nerve stimuli they receive from the brain. If these do not occur, no contraction can take place. Nerve conduction can be impaired either centrally (brain or spinal cord ) or peripherally ( peripheral nervous system ) or completely damaged. The result is incomplete or complete paralysis . This can be caused by injuries ( paraplegia ), herniated discs or inflammatory ( MS , poliomyelitis ) and metabolic diseases ( polyneuropathy , amyotrophic lateral sclerosis ).

Diseases that impair the ability to contract and have their origin in the muscle itself or at the transition between nerve and muscle are summarized under the term muscular dystrophy . What they all have in common is the symptoms, possibly visible atrophy , increasing weakness and rapid fatigue. In addition, there is often pain during movement as the disease progresses, since the strain on the weakened muscles increases. Also typical of muscular dystrophies is the progressive remodeling in the muscle tissue. The contractile elements are increasingly connected by connective tissuereplaced, causing not only increasing weakness but also progressive immobility (contracture).

The cause of these diseases are genetic defects that cause irreparable damage to the muscle cells, which greatly reduces or completely blocks protein formation in the muscle. Muscular dystrophies are rare diseases that cannot be cured to this day.

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.