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nmdcat.online July 28, 2026

A decrease in the diameter of the pupil in bright light is a reflex mediated by which type of muscle tissue?

A. Skeletal muscle
B. Single-unit smooth muscle
C. Multi-unit smooth muscle
✓
D. Cardiac muscle

📝 Explanation

The iris of the eye is composed of multi-unit smooth muscle. Unlike single-unit smooth muscle, the fibers in multi-unit smooth muscle are structurally independent, richly innervated by autonomic nerves, and contract in a highly localized, precise manner without gap junction transmission.

📖 Additional Information

  • Skeletal muscle
  • Single-unit smooth muscle
  • Multi-unit smooth muscle
  • Cardiac muscle

The iris of the eye is composed of multi-unit smooth muscle. Unlike single-unit smooth muscle, the fibers in multi-unit smooth muscle are structurally independent, richly innervated by autonomic nerves, and contract in a highly localized, precise manner without gap junction transmission.

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