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nmdcat.online July 28, 2026

Among the following statements comparing multi-unit and single-unit smooth muscle, which is correct?

A. Single-unit smooth muscle requires nerve stimulation to contract, while multi-unit does not
B. Multi-unit smooth muscle cells are electrically coupled by gap junctions
C. Single-unit smooth muscle is found in the walls of the digestive tract and exhibits rhythmic pacemaker activity
✓
D. Multi-unit smooth muscle exhibits the stress-relaxation response

📝 Explanation

Single-unit (visceral) smooth muscle cells are linked by gap junctions, contract as a syncytium, are found in hollow organs, and often exhibit pacemaker activity. Multi-unit smooth muscle (e.g., in the iris) consists of independent fibers that require independent neural stimulation.

📖 Additional Information

  • Single-unit smooth muscle requires nerve stimulation to contract, while multi-unit does not
  • Multi-unit smooth muscle cells are electrically coupled by gap junctions
  • Single-unit smooth muscle is found in the walls of the digestive tract and exhibits rhythmic pacemaker activity
  • Multi-unit smooth muscle exhibits the stress-relaxation response

Single-unit (visceral) smooth muscle cells are linked by gap junctions, contract as a syncytium, are found in hollow organs, and often exhibit pacemaker activity. Multi-unit smooth muscle (e.g., in the iris) consists of independent fibers that require independent neural stimulation.

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