Which mechanism is most directly associated with reducing spasticity through decreased motor unit excitability?

• A. Facilitation
• B. Irradiation
• C. Inhibition
• D. Reciprocal inhibition

Answer: (C)

Spasticity stems from an overactive stretch reflex due to loss of normal inhibitory control over motor neurons. Reducing motor unit excitability means dampening the output of the alpha motor neurons to the muscles. Inhibition achieves this directly by suppressing or limiting the excitatory input to those motor neurons, often via spinal interneurons or descending inhibitory pathways, so motor units are less likely to fire and the overall tone decreases.

Facilitation would raise excitability, making spasticity worse. Irradiation is about the spread of activity to nearby muscles and doesn’t directly reduce motor neuron excitability. Reciprocal inhibition is a specific inhibitory process that helps coordinate movement by inhibiting antagonists, but the most direct way to lower spasticity through decreased excitability is a general inhibitory effect on the motor neurons.