Upper Motor Neuron Lesions

Muscular Atophy

"Disuse" Atrophy. Muscle atrophies b/c not being used. The muscle atrophy develops slowing and is not as severe as a lower m.n. lesion.

Why isn't it as severe? (muscle atrophy)?

Because muscle is spastic, still contracting, not totally unused even though person doesn't have "control" of muscle.

What tracts are mostly effected?

Corticospinal (where the upper m.n. reside in the primary motor cortex) and Corticobulbar tract.

What causes hyperreflexia?

Lower motor n. are hyper excitable.

Upper motor Lesion will exhibit?

Slow, mild atrophy (spasticity).

Clonus phenomenon

An upper motor lesion. A rhythmic contraction of a muscle in response to a chronic stretch. An imposing stretch continuously.

If lesion occurs between C5-T1?

C5 is where output to upper limbs. T1 below that no output to upper limbs. It will compromise upper limb function & will affect lower limb. How much upper limb function depends on what level between C5-T1. As you move down more intact.

Upper Motor Lesion will exhibit?

Clonus

Motor system consists of what?

Either upper motor neuron that originates in the cortex or brainstem that projects to the alpha or gamma lower motor neurons (or interneurons) which actually innervate the skeletal muscles.

Hyperreflexia

Exaggerated reflexes (below level of injury).

Upper Motor Lesion will exhibit?

Hyperreflexia.

If the lesion is ABOVE the pyramids what side will it affect?

It will affect the upper and lower limbs on the CONTRALATERAL sides because it is before where it crosses over.

Explain how this "clonus phenomenon" happens?

Muscle stretched-->stimulates muscle spindles-->via monosynaptic reflex arc-->this stimulates the alpha m.n.-->(*lesion in upper m.n.)-->inappropriately initiate A.P. --->contraction causes increase force generation-->this stimulates the GTO-->this disynaptically inhibits alpha m.n.-->which decrease A.P.-->causing muscle relaxation-->if person still pushing on foot-->cycle repeats itself b/c still stretching. This can happen in about 2 sec./sec.

Do upper motor lesions have fasciculations?

No fasciculations in upper motor lesions.

Upper Motor Lesion will exhibit?

Spastic paralysis. (some upper motor n. can excite the lower motor n. while others inhibit them.)

What are the pyramids?

The pyramids are where corticospinal tract crosses to the other side.

What causes the person experience spasticity?

The upper m.n. tend to suppress the activity of the lower m.n. So, if eliminate upper m.n. input -->increase excitability of lower m.n. input--> inappropriately initiate A.P.-->spasticity.

Lesions below L1?

Unaffected upper limbs, but clearly will affect the lower limbs depending on where the lesion occurs but will be ipsilateral.

Lesions between T1 - L1?

Upper limbs unaffected because all output above that point. It will affect lower limb ipsilaterally. Remember to keep tract of sides. (crossover at pyramids.)

If the lesion occurs BETWEEN the pyramids and about C5?

Will have hemiplegia on upper and lower limbs on SAME side as the lesion. (because its after the crossover).