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A clear decrease in muscle strength, up to complete paralysis, is a symptom of damage to the nervous system within the so-called the motor pathway that leads nerve impulses from the cortex of the brain to the muscles. Depending on the site of damage, the resulting limb paresis will vary in extent and with different characteristics.
Weakness (paresis) of the limbs – formation
There are four main places where the traffic road may be damaged:
- neuromuscular contact,
- peripheral nerve,
- brain and spinal cord,
- muscle.
Damage to the brain and spinal cord leads to paresis called central. It is characterized by excessive muscle tension of the pocket knife type (getting rid of this tension requires considerable strength at the beginning of the movement, and then clearly less). A reduction in muscle tone (flaccid muscles that do not offer any resistance during passive movement) is characteristic of peripheral paresisie for damage to peripheral nerves and muscles. Diseases of the peripheral nerves and muscles, apart from flaccid paresis, are also characterized by rapid and extensive muscle atrophy (the so-called denervation). In central paresis decay also occurs, but is much smaller and progresses more slowly. It occurs because of a lack of activity that can be counteracted by undergoing passive or active rehabilitation.
Based on the extent of the paresis and the presence of symptoms other than motor symptoms, it is possible to conclude not only in which part (at what level) of the nervous system the pathological process causing its damage develops, but also more precisely about the location of this damage.
If the weakness (paresis) of the limbs affects only one right limb and is accompanied by a speech disorder of the aphasia type, the pathological process is probably located in the cortex, on the surface of the left hemisphere of the brain. If this weakness of strength affects both the arm and the leg on the same side of the body (hemiparesis), the cause of its formation is a pathology located deep in the hemisphere of the brain. Paresis of all four limbs (tetraparesis) results from damage to the brain stem and both lower limbs (paraparesis) – most often the spinal cord. The accompanying symptoms of cranial nerve damage facilitate a more precise localization of the damage in the brainstem, and the sensory disturbances – in the spinal cord.
The paresis resulting from damage to the peripheral nerves may be limited to the innervation of one nerve (mononeuropathy) or attack the limbs on both sides symmetrically, as a rule exclusively or much more clearly, in their peripheral sections (polyneuropathy). In the first case, the cause is usually an injury or a disease process related to the nerve site, e.g. an overgrown ligament causing its compression. In the latter case, it is most often a generalized disease process, such as diabetes or uremia.
The type of damage can also be inferred from the time when paresis appears. If paresis develops suddenly, within minutes or hours, it is usually caused by vascular damage to the brain, i.e. a stroke. However, if the paresis develops slowly – the cause is probably a brain tumor.
The weakness occurring in diseases of the neuromuscular junction, e.g. in myasthenia gravis, looks slightly different from typical paresis. It consists in increased fatigue of muscles, sometimes all, and more often only some of their groups, e.g. the eye muscles, which develops simultaneously with the number of repeated movements and disappears after rest.