Spread of excitation in the CNS that causes contraction of synergistic muscles in a specific pattern is called what?

• A. Irradiation
• B. Proprioceptive neuromuscular facilitation (PNF)
• C. Facilitation
• D. Reciprocal inhibition

Answer: (D)

Irradiation describes the spread of excitation within the CNS to nearby motor pools, so when one muscle is activated, synergistic muscles are recruited in a coordinated pattern. This happens because neural circuits link related muscles, and activating one muscle can facilitate adjacent muscles to contract together, producing a specific, coordinated pattern of movement.

Reciprocal inhibition, by contrast, is about dampening activity in muscles that oppose the movement (antagonists) to allow smooth action of the agonists; it doesn’t describe the spread of excitation to synergists.

Proprioceptive neuromuscular facilitation is a therapeutic approach that uses patterned movements to improve neuromuscular control, not the fundamental phenomenon of excitation spreading to synergists. Facilitation is a broader term for increasing excitability, but it doesn’t specify the patterned recruitment of synergistic muscles.