list of signs of lower motor neuron lession
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The effects can be limited to small groups of muscles. Recall that a motor neuron pool is a nucleus of alpha motor neurons that innervate a single muscle (link to Motor Unit Figure 2). Furthermore, nearby motor neuron pools control nearby muscles. Thus, restricted damage to lower motor neurons, either within the spinal cord or at the ventral roots, will affect only a restricted group of muscles.
Muscle atrophy. When alpha motor neurons die, the muscle fibers that they innervate become deprived of necessary trophic factors and eventually the muscle itself atrophies.
Weakness. Because of the damage to alpha motor neurons and the atrophy of muscles, weakness is profound in lower motor neuron disorders.
Fasciculation. Damaged alpha motor neurons can produce spontaneous action potentials. These spikes cause the muscle fibers that are part of that neuron’s motor unit to fire, resulting in a visible twitch (called a fasciculation) of the affected muscle
Fibrillation. With further degeneration of the alpha motor neuron, only remnants of the axons near the muscle fibers remain. These individual axon fibers can also generate spontaneous action potentials; however, these action potentials will only cause individual muscle fibers to contract. This spontaneous twitching of individual muscle fibers is called a fibrillation (Fig. 1). Fibrillations are too small to be seen as a visible muscle contraction. They can only be detected with electrophysiological recordings of the muscle activity (an electromyogram).
Hypotonia. Because alpha motor neurons are the only way to stimulate extrafusal muscle fibers, the loss of these neurons causes a decrease in muscle tone.
Hyporeflexia. The myotatic (stretch) reflex is weak or absent with lower motor neuron disorders, because the alpha motor neurons that cause muscle contraction are damaged.
Muscle atrophy. When alpha motor neurons die, the muscle fibers that they innervate become deprived of necessary trophic factors and eventually the muscle itself atrophies.
Weakness. Because of the damage to alpha motor neurons and the atrophy of muscles, weakness is profound in lower motor neuron disorders.
Fasciculation. Damaged alpha motor neurons can produce spontaneous action potentials. These spikes cause the muscle fibers that are part of that neuron’s motor unit to fire, resulting in a visible twitch (called a fasciculation) of the affected muscle
Fibrillation. With further degeneration of the alpha motor neuron, only remnants of the axons near the muscle fibers remain. These individual axon fibers can also generate spontaneous action potentials; however, these action potentials will only cause individual muscle fibers to contract. This spontaneous twitching of individual muscle fibers is called a fibrillation (Fig. 1). Fibrillations are too small to be seen as a visible muscle contraction. They can only be detected with electrophysiological recordings of the muscle activity (an electromyogram).
Hypotonia. Because alpha motor neurons are the only way to stimulate extrafusal muscle fibers, the loss of these neurons causes a decrease in muscle tone.
Hyporeflexia. The myotatic (stretch) reflex is weak or absent with lower motor neuron disorders, because the alpha motor neurons that cause muscle contraction are damaged.
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