A well-functioning nerve-muscle interaction is the basic prerequisite for the functionality of the musculoskeletal system. Disruption inevitably leads to loss of utility functions and considerable limitations in activity possibilities.
What is nerve-muscle interplay?
A well-functioning nerve-muscle interaction is the basic prerequisite for the functionality of the musculoskeletal system. Proper interaction between nerves and muscles is the basic prerequisite for the execution of well-coordinated movement actions and adequate stabilization activities. The nervous system assumes the functions of control and information transmission. The muscles are the executing organs. Movement impulses are generated in the motor centers of the cerebral cortex, where different brain areas represent and supply the various body regions. The movement commands necessary for the execution of a movement program are transmitted from there via the nerve tracts of the so-called pyramidal system to the respective segments of the spinal cord. There they are switched and sent to the periphery to the muscles responsible for execution. During dynamic actions, the antagonists are simultaneously inhibited at the spinal cord level. The nerve stimulus finally reaches the muscles via many motor end plates and is transmitted to the interior of the muscle cell via the membrane system. There, the electrical stimulus is converted into a chemical stimulus, which results in the release of calcium stored in vesicles into the interior of the cell. If the calcium concentration exceeds a certain threshold, contraction occurs under energy consumption in the muscle cell and by summation in the whole muscle.
Function and task
The generation of movement commands and the initiation of movement programs in the central nervous system are clearly goal-oriented, not muscle-oriented. The motor centers of our brain think in functional terms. Athletes therefore always focus their thoughts on the movement goal when planning movement sequences and not on the muscles that are to become active in the process. Our movement programs are designed in such a way that during movements the acting muscles (agonists) are automatically activated and the antagonists are inhibited so as not to hinder the action. In stabilization requirements, the same muscle groups can work together as synergists to stabilize joints, for example. A typical movement process in which both processes occur is walking. In the swing leg phase, the knee extensors are activated at the end while the flexors are inhibited. In the stance leg phase, both muscle groups work together to stabilize and center the knee joint during compressive loading. The contraction activity of individual muscles or muscle groups can be graded, modified and controlled in various ways. One way is through spatial and temporal control of the motor units. Each motor nerve has thousands of nerve fibers and each one of them distributes its impulses to several motor end plates, which are never all controlled simultaneously, but always with a time delay. The motor program determines which ones are activated (recruitment) and how many per unit of time (frequency). The strength of the contraction can thus be graded. The lowest level of control is taken over by the receptors in the tendons (Golgi tendon organ) and the muscle spindles. They measure changes in length and tension in the muscle and report these to the spinal cord via sensitive nerve fibers. If the signals are very strong, this means that the muscle is at risk of injury and contraction in the muscle is reduced or stopped. The extrapyramidal system, in particular the cerebellum, takes over the control and fine-tuning of muscle activity. It constantly receives information about the sequence of movement processes and compares it with stored programs and information from other brain centers. Any deviations are modified to ensure coordinated processes.
Diseases and ailments
Nerve-muscle interaction can be affected by any disease that affects either the contractility of the muscles or the nervous system.At the muscle level, these are mainly diseases that affect the supply of energy carriers or minerals or cause structural changes in tissue composition. In the context of a diabetes disease, on the one hand the uptake of glucose into the muscle cell is disturbed and on the other hand the breakdown of fats is blocked. As a result, the body does not have enough energy available for contractions when needed, which is manifested by a reduction in performance and rapid fatigue of the muscles during exertion. Muscles that are not used for a long time or are used little and meanwhile remain mainly in an approximated position gradually lose their stretching ability. Initially, this process is still reversible, but eventually it is no longer. Contractile units are immobilized and remodeled so that they acquire the same properties as connective tissue. The muscle thus loses not only its stretching ability, but also its strength. Calcium deficiency can result from reduced absorption through food or as a consequence of diseases that either impede absorption or cause increased excretion. The consequences for the muscle can be cramps because at times there is not enough calcium to resolve the contraction. Neurological diseases that damage the conduction of motor nerves have significant negative effects on muscle activity. In the case of nerve injuries, the entire nerve cable or parts of it are severed or damaged by pressure. Depending on the severity, little or no stimulation can then reach the muscle, resulting in complete or incomplete paralysis. In polyneuropathy, the insulating layer of the nerve conductors is damaged, the so-called medullary sheaths. The electrical information that is transported through this system is lost on its way to the muscles. They can develop little or no strength. Sensory disturbances also often develop in this disease because the sensitive nerve fibers are also affected. The same is true for multiple sclerosis, but it can additionally lead to coordinative disorders of muscle activity, since not only the peripheral nerves but also the central nervous system is affected.
