Difference between upper & lower motor neuron lesion?
Hi,
From what i have read, it seems to me that both types of lesions affect the ventral horn - however i am incompetent to understand the difference between the two.
Can someone please clarify the physiological difference between the upper & lower motor neuron lesions?
I already know symptoms: (upper = spastic paralysis & hypertonia, lower = flaccid paralysis & muscle loss) If possible, an explanation of these would also be appreciated.
Many Thanks
Answers:
The ventral horn itself may or may not be affected. The difference comes from whether the at a tangent motor nerve is affected (the cell body for this nerve is surrounded by the ventral horn but is not always directly affected) or the upper motor neuron is affected (most cell bodies in the primary motor cortex).
If the divergent nerve is affected then you win the flaccidity and atrophy you mentioned because the input on the muscle is lost. Obviously, its the nerve that initiates contraction (strength, tone) and maintains muscle bulk (atrophy). This nerve can be artificial by hitting the cell body in the ventral horn (ALS, spinomuscular atrophy) or by hitting the nerve axon (motor neuropathy)
If only the upper upper motor rudeness is affected then you also lose normal inhibitory input to the lateral nerve body in the ventral horn. In addition to the loss of voluntary strength eventually near is overexcitation of the remaining peripheral nerve leading to the spastic picture you noted. The injury can be anywhere from the cortex to the cord but does not affect the ventral horn cell in most cases. If the ventral horn cell is affected, it will lead to a mixed upper and lower motor neuron picture.
You can also own a mixed picture...ALS being the big player there.
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From what i have read, it seems to me that both types of lesions affect the ventral horn - however i am incompetent to understand the difference between the two.
Can someone please clarify the physiological difference between the upper & lower motor neuron lesions?
I already know symptoms: (upper = spastic paralysis & hypertonia, lower = flaccid paralysis & muscle loss) If possible, an explanation of these would also be appreciated.
Many Thanks
Answers:
The ventral horn itself may or may not be affected. The difference comes from whether the at a tangent motor nerve is affected (the cell body for this nerve is surrounded by the ventral horn but is not always directly affected) or the upper motor neuron is affected (most cell bodies in the primary motor cortex).
If the divergent nerve is affected then you win the flaccidity and atrophy you mentioned because the input on the muscle is lost. Obviously, its the nerve that initiates contraction (strength, tone) and maintains muscle bulk (atrophy). This nerve can be artificial by hitting the cell body in the ventral horn (ALS, spinomuscular atrophy) or by hitting the nerve axon (motor neuropathy)
If only the upper upper motor rudeness is affected then you also lose normal inhibitory input to the lateral nerve body in the ventral horn. In addition to the loss of voluntary strength eventually near is overexcitation of the remaining peripheral nerve leading to the spastic picture you noted. The injury can be anywhere from the cortex to the cord but does not affect the ventral horn cell in most cases. If the ventral horn cell is affected, it will lead to a mixed upper and lower motor neuron picture.
You can also own a mixed picture...ALS being the big player there.
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