Motor Neuron Disease (MND)
Motor neuron disease (MND) are a small group of neurological disorders that selectively affect motor neurons, the cells that control voluntary muscle activity including speaking, walking, swallowing, and general movement of the body. They are generally progressive in nature, and cause increasing disability and, eventually, death.
Motor neuron disorders or motor neuron diseases are a larger group of disorders that include any disease that affects neurons.
What are motor neuron diseases?
The motor neuron diseases (MNDs) are a group of progressive neurological disorders that destroy motor neurons, the cells that control essential voluntary muscle activity such as speaking, walking, breathing, and swallowing. Normally, messages from nerve cells in the brain (called upper motor neurons) are transmitted to nerve cells in the brain stem and spinal cord (called lower motor neurons) and from them to particular muscles. Upper motor neurons direct the lower motor neurons to produce movements such as walking or chewing. Lower motor neurons control movement in the arms, legs, chest, face, throat, and tongue. Spinal motor neurons are also called anterior horn cells. Upper motor neurons are also called corticospinal neurons.
When there are disruptions in the signals between the lowest motor neurons and the muscle, the muscles do not work properly; the muscles gradually weaken and may begin wasting away and develop uncontrollable twitching (calledfasciculations). When there are disruptions in the signals between the upper motor neurons and the lower motor neurons, the limb muscles develop stiffness (called spasticity), movements become slow and effortful, and tendon reflexes such as knee and ankle jerks become overactive. Over time, the ability to control voluntary movement can be lost.
Who is at risk?
MNDs occur in adults and children. In children, particularly in inherited or familial forms of the disease, symptoms can be present at birth or appear before the child learns to walk. In adults, MNDs occur more commonly in men than in women, with symptoms appearing after age 40.
What causes motor neuron diseases?
Some MNDs are inherited, but the causes of most MNDs are not known. In sporadic or non inherited MNDs, environmental, toxic, viral, or genetic factors may be implicated.