Which statement best differentiates phasic and tonic smooth muscle contractions?

• A. Phasic smooth muscle contracts rapidly and rhythmically; tonic smooth muscle contracts more slowly and sustains contraction.
• B. Phasic smooth muscle contracts slowly and sustains contraction; tonic contracts rapidly.
• C. Phasic smooth muscle is only in vascular walls; tonic is in intestines.
• D. Phasic smooth muscle is innervated by autonomic nerves; tonic by somatic nerves.

Answer: (A)