10-25-2007, 01:51 PM
we see UMN lesion in lower limb and LMN lesion in upper limb, why?
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Can anyone explain ALS - nabil
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10-25-2007, 02:56 PM
10-25-2007, 03:18 PM
The muscle-controlling nerve cells, or motor neurons, are divided into two types. The upper motor neurons are located in the upper part of the brain and exert some control over the lower motor neurons, which are in the brainstem and the spinal cord.
In ALS, upper and lower motor neurons degenerate. Upper motor neurons normally send signals to lower motor neurons, which send signals to muscles. The lower motor neurons are directly attached to muscles through "wires" called axons. Bundles of these axons leave the spinal cord and extend out to the muscles. It's these bundles that doctors are referring to when they talk about the "nerves." The function of lower motor neurons is straightforward. They send "go" signals to muscles. When these cells gradually die, as in ALS, muscles become progressively weaker and eventually unable to move (paralyzed). The lower motor neurons that control most of the body are in the spinal cord. Those that control the muscles of speaking, swallowing and facial expression are in the brainstem. They're sometimes called bulbar motor neurons, because the part of the brainstem that houses them has a bulblike shape. The term bulbar involvement means that the muscles of the face, mouth and throat are involved in the disease. The upper motor neurons have more complex functions. It's harder to study them, and not as much is understood about them, although new techniques are changing that. These cells seem to exert complex control over the lower motor neurons that allow movements to be smooth, directed and varied in intensity. (For instance, they're part of an elaborate system that allows a person to aim a hand at a glass of water, pick it up, estimate its weight, use the right amount of force for its weight, and lift it to his or her mouth, all while thinking about something else.) When upper motor neurons are lost and lower motor neurons remain, movements are still possible but can become "tight" (doctors use the word spastic for this) and less precise. In ALS, a combination of these effects is usually seen because both upper and lower motor neurons are dying. People with ALS can have weak and wasted muscles with tightness (spasticity). Muscle twitches and cramps are common; they occur because degenerating axons (nerves) become "irritable." THANKS A LOT JOHN FOR THIS. I AM CLEAR WHY THERE IS UMN TYPE OF LESION IN LOWER LIMB, BECAUSE THERE IS NO CONTROL OF UMN THERE. BUT I AM NOT CLEAR WHY THERE IS LMN LESION IN UPPER LIMB, IS IT BECAUSE THERE WAS NO CONTROL OF UPPER MOTOR NEURON OVER LMN IN UPPER LIMB? THANKS AGAIN.
10-25-2007, 03:20 PM
THANKS A LOT JOHN FOR THIS. I AM CLEAR WHY THERE IS UMN TYPE OF LESION IN LOWER LIMB, BECAUSE THERE IS NO MORE CONTROL OF UMN THERE.
BUT I AM NOT CLEAR WHY THERE IS LMN LESION IN UPPER LIMB, IS IT BECAUSE THERE WAS NEVER CONTROL OF UPPER MOTOR NEURON OVER LMN IN UPPER LIMB? THANKS AGAIN.
10-25-2007, 03:30 PM
NEVER CAN NEVER HAPPEN, THERE HAS 2 BE INNERVATION OF UM WITH LM.
10-25-2007, 03:31 PM
STILL CUIRIOUS TO KNOW WHY THERE IS LMN LESION IN UPPER LIMB?
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