Motor neuron lesions can be caused by physical trauma, autoimmune disease, or fetal abnormalities, leading to abnormal muscle control and movement. They can affect speech, chewing, and swallowing. Lesions are divided into upper and lower motor neuron injuries, causing spasticity and flaccid paralysis respectively. Diseases affecting motor neurons can be progressive and include cerebral palsy, multiple sclerosis, and Lou Gehrig’s disease.
A motor neuron lesion is any lesion or abnormality in the nerves responsible for controlling movement of the body. Motor neuron injuries can have many different causes, including physical trauma, autoimmune disease, and abnormalities in fetal development. They interfere with normal motor control and therefore with movement, because the damaged neurons become less effective in their job of transmitting signals between the central nervous system and the muscles. In addition to limb mobility and skills such as walking, they can also interfere with other motor functions, such as speaking, chewing and swallowing. The effects can vary enormously, from minor impairments in muscle control to total paralysis or death.
These injuries are often divided into two categories, upper motor neuron injuries and lower motor neuron injuries. Upper motor neurons begin in the motor cortex of the brain and extend down to the brainstem and spinal cord, where they meet lower motor neurons, which extend from the spine to the muscles. The effects of an injury depend on where it is. A common feature of both types of injury is abnormalities in muscle tone or tone, partial muscle contractions that occur continuously in the body. The precise nature and severity of symptoms caused by lesions depend on their size and location.
Lesions in the upper motor neurons commonly cause symptoms such as decreased strength, problems with fine motor control, and spasticity. Spasticity is a condition in which a person’s muscle tone is increased to abnormal levels, resulting in a state of constant muscle tension called hypertonia. The muscles become tighter and less flexible, in some severe cases to the point of immobility, and the sufferer may have muscle spasms or develop problems with posture or gait. Excessive muscle tension can also cause overactive reflexes or hyperreflexia.
A lower motor neuron injury commonly causes flaccid paralysis, a condition in which muscles weaken and muscle tone becomes too low, a condition called hypotonia. This can result in a partial or complete loss of mobility in the affected muscles and can ultimately result in muscle atrophy and atrophy. These injuries can also cause diminished or completely absent reflexes, called hyporeflexia, and irregular contractions called fibrillations in the skeletal muscles.
Diseases affecting motor neurons are often progressive in nature, causing more damage to the nervous system and more impairment over time, although this is not always the case. Upper motor neuron lesions are most commonly seen in people with cerebral palsy and are also the cause of primary lateral sclerosis and some forms of multiple sclerosis. Lesions of the lower motor neuron are seen in conditions such as progressive muscular atrophy, spinal muscular atrophy, and progressive bulbar palsy. Amyotrophic lateral sclerosis, commonly called Lou Gehrig’s disease, affects both upper and lower motor neurons.
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