Voluntary Muscle Control and Motor Neuron Disease

November 12, 2012

Voluntary Muscle Control and Motor Neuron Disease

Motor neuron disease involves neurological problems that affect the activity of voluntary muscle function. Voluntary muscle groups are skeletal muscles that you willfully control to walk, speak, breath or any other movement of the body under your control. Motor neuron disease tends to be progressive and there is very little that can be done other than support the individual and their needs.

Symptoms of motor neuron disease are are far and wide but generally show up in mid life and progressively worsens with age. Often, muscle weakness is observed followed by muscle loss. Stiffness in arms and legs can be observed sometimes with spastic movements. Tendon reflexes often become overactive. It’s not unusual to see a patient dragging a foot or having slurred speech. There are two groups of motor neurons that are involved with voluntary muscle control. One is upper motor neurons and the other group is lower motor neurons. Upper motor neurons are found in the frontal lobe of the neocortex and lower motor neurons are found in the spinal column. There are different motor deficits depending on which group of neurons are affected. For example, upper motor neuron damge presents with spastic muscle movements, sudden reflexes in the hands, fingers and feet and lower motor neuron damage tends to present with muscle weakness, twitching and muscle wasting (atrophy). All of your skeletal muscles require both upper and lower motor neuron control. Individuals who have motor neuron disease can demonstrate cognitive disorders such as certain forms of dementia that bring about personality changes with a lack of constraint (uncontrolled, lacking in social graces) or they can have problems with naming objects or executing complex tasks that require a sequence of steps including initiation, inhibition, sustaining and switching attention. This can be seen when an individual has difficulty in doing finances or driving a car. Individuals that have PLS often present with pseudobulbar palsy which causes a pathological form of laughter and crying.

Causes of motor neuron disease are generally unknown. In most cases, individuals who have ALS (amyotrophic lateral sclerosis) a motor neuon disease which involves both upper and lower motor neurons, the cause is unknown. Most of these individuals have no family history of it. On the other hand, ten percent of ALS patients have a family history and also test postive for genetic markers known to be associated with this disease. There are a number of mutations involved however, one that is common is the gene that codes for super oxide dismutase (SOD). It is reported that there are over 100 different mutations in SOD that can give rise to ALS motor neuron disease. These mutations are thought to make SOD produce proteins that are toxic to neurons in stead of removing free radicals the way they are supposed to.

Motor neuron disease occurs in the neocortex and the spinal column where motor neurons in these regions are malfunctioning. These motor neurons are responsible for voluntary control of skeletal muscle that lets us get around to to the things we want to such a walk, run, throw a ball and type for example. When these systems are damaged muscle weakness sets in, spastic movements occur, muscle is loss by wasting and tendon reflexes become overactive. These damaged systems can also affect cognition exhibiting memory loss, inability to do complex tasks and behavioral changes.


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