Physiology myopathy , neuropathy,

In neurology of weakness of any part of body, there are two types of general weakness upper motor neuron (Brain & spinal cord) weakness, and lower motor neuron ( Nerve) weakness. The differences are tabulated below.
The lower motor neuron refers to a peripheral nerve. The Upper motor neuron refers to the spinal cord and brain.

Lower motor neuron weakness (LMN)	Upper motor neuron weakness (UMN)
Flaccid or reduced stiffness	Spasticity or very stiff
Decreased tone	Increased tone
Decreased muscle stretch reflexes	Increased muscle stretch reflexes
Profound muscle atrophy	Minimal muscle atrophy
Fasciculations seen or twitches	Fasciculations absent
+/- sensory disturbances	+ /- sensory disturbances

Fasciculations are irregular contractions of a group of muscle fibers innervated by one axon (nerve). This appears as a small muscle twitch is common in many neurological diseases and even after exercise.

It is also customary, and very helpful, to classify LMN weakness on the basis of the anatomical station affected.

These stations are:

1. The anterior (ventral) horn cell
2. The peripheral nerve, (ventral (front) and dorsal (back) nerve roots i.e., radiculopathy (one nerve affected from the spin downwards) as in back pain. or nerve i.e., neuropathy) (usually many nerves affected but more towards hands and feet)
3. The neuromuscular junction    (where nerves meet muscles)
4. The muscle (i.e. myopathy)     (the labor force of the body)

Figure 1 The 4 anatomic stations underlying lower motor neuron weakness

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