Final answer:
Smooth muscles can maintain contractions for extended periods due to latch-bridges, which do not require continuous ATP usage.
Step-by-step explanation:
The condition that allows smooth muscle to maintain contraction for long periods of time is attributed to the presence of latch-bridges. These are a subset of myosin head and actin cross-bridges that can maintain the link between thick and thin filaments for extended periods without the continuous need for ATP.
Furthermore, smooth muscles can sustain contractions over a broad range of lengths due to their unique structural properties and are not as dependent on sarcomere organization, allowing adaptation to varying degrees of stretching within the organs they control.
The autonomic nervous system, hormones, and mechanical stretching can all influence the contraction of smooth muscle. The two major types of smooth muscle organization are single-unit and multiunit smooth muscle, with the former featuring gap junctions that synchronize contractions and are often found in the walls of visceral organs, while the latter lacks these junctions and their cells contract independently.
The muscles' structure allows for sustained contractions even when stretched, controlled by the autonomic nervous system, hormones, or mechanical stretching. Single-unit and multiunit are the two types of smooth muscle, with differing characteristics like gap junctions and independent cell contraction.