Question

An important difference between single-unit and multiunit smooth muscle is the

A) numerous gap junctions in single-unit smooth muscle, which allow many cells to work together as a sheet.
B) longer actin and myosin filaments in multiunit smooth muscle, which allow coordination of contraction.
C) ability of single-unit fibers to change into multiunit fibers when advantageous.
D) closely controlled individual fibers in single-unit smooth muscle to allow fine control and graded contractions by selective activation.

Answer 1

Single-unit smooth muscle contains gap junctions allowing synchronized contractions, while multiunit smooth muscle lacks these and cells contract independently, controlled by the autonomic nervous system or hormones.

Step-by-step explanation:

An important difference between single-unit and multiunit smooth muscle is that single-unit smooth muscle has numerous gap junctions that allow the cells to contract synchronously as a single cohesive unit. In contrast, multiunit smooth muscle cells lack these gap junctions, leading to each cell acting independently, with contraction not spreading from one cell to the next. As a result, single-unit smooth muscle found in visceral organs can provide slow, steady contractions for processes such as moving food through the digestive tract, while multiunit smooth muscle found in areas like large blood vessels and the eyes are controlled individually by the autonomic nervous system or by hormones, providing fine-tuned responses to specific stimuli.