Neuromuscular Disorders Help
Introduction to Neuromuscular Disorders
We have now outlined some of the major aspects of the nervous and muscular systems. Primarily, this outline has involved basic features of their normal anatomy and physiology. To a large degree, these two systems are functionally linked due to the extremely high degree of Biological Order found in the connections between them. Hence, neuromuscular disorders, and the disease/injury states often associated with them, frequently result from the breaking or disruption of the normal connections between muscles and nerves.
Paralysis And Denervation Atrophy
Consider what happens, for instance, when part of the major motor pathway descending to the skeletal muscles is transected (tran- SEK -ted) or “cut” (sect) all the way “through” (trans-). When the motor nerve fibers from the precentral gyrus (primary motor area) are transected (cut all the way through), say, from a terrible car accident, then either partial or full paralysis (puh- RAL -uh-sis) of the body occurs. Paralysis is literally a state of “disablement,” an inability to move. The axons of the motor neurons leading from the motor areas of the cerebral cortex are unable to complete their final connection with the neuromuscular junction (motor end plate).
As a result, there is either a full or total paralysis of the skeletal muscles being supplied.
Study suggestion: If the main motor pathway leading down from the left precentral gyrus is transected, then many of the skeletal muscles on which side of the body will be paralyzed? Why?
Troph ( TROHF ) is a root that means “nourishment.” But troph means nourishment in its broadest sense, including “stimulation.” The skeletal muscle fibers, then, receive “nourishment” by the motor nerve fibers coming down to the neuromuscular junction, because they are stimulated to contract by them. In technical terms, we say that the skeletal muscle fibers are innervated ( IN -ur- vayt -ed) or have “nerve” ( nerv ) endings put “into” ( in -) them. This situation of innervation ( in -er -VAY -shun) essentially occurs at the neuromuscular junction. The skeletal muscle fibers are therefore innervated at the neuromuscular junction and receive nourishment or stimulation (troph) from them.
Denervation ( dee -ner- VAY -shun) is the “process of” (- tion ) taking “nerves” ( nerv ) “away from” ( de -) muscle fibers. If some part of the motor nerve pathway undergoes transection, then the skeletal muscle fibers ultimately being served by the pathway will suffer denervation. They will also undergo a type of atrophy ( AT -ruh- fee ) – a “condition” (- y ) “without” ( a -) “nourishment” (troph) or stimulation.
The complete phrase is denervation atrophy, which means the wasting away and degeneration of skeletal muscle fibers that have been deprived of their normal stimulation or nourishment by nerve endings. The denervated ( DEH -ner- vayt -ed) muscles become flaccid ( FLAH -sid) or “flabby” and almost useless.
Anesthesia – Loss Of Feeling Or Sensation
When the sensory nerve fibers leading from sensory receptors in muscles, joints, skin, or elsewhere are transected, then anesthesia ( an -es- THEE -zhuh) often results. Anesthesia is a “condition” (- ia ) “without” ( an -) “feeling or sensation” ( esthes ).
If, for instance, the sensory nerves leading from most of the receptors in your big toe are completely transected, then the big toe is pretty much numb, reflecting a condition of anesthesia.
Study suggestion: Assume that the main sensory nerve pathway ascending from your right big toe is completely transected. Going back and reviewing past figures in this chapter, which specific gyrus area receiving big toe sensations would be deprived? On which side of the body midline would it most likely be located?
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