Final answer:
The statement that single-unit smooth muscle cells are arranged in opposing sheets and exhibit a stress-relaxation response is true. These cells, found in visceral organs, are connected by gap junctions which facilitate coordinated actions necessary for the function of organs like the stomach and bladder.
Step-by-step explanation:
It is true that single-unit smooth muscle cells are arranged in opposing sheets and exhibit a stress-relaxation response. Single-unit smooth muscle, often found in the walls of visceral organs, contracts as a single entity due to the connections formed by gap junctions. This arrangement facilitates coordinated contractions and relaxations necessary for the proper functioning of organs. The stress-relaxation response allows these muscles to stretch and then immediately relax in response to filling, which is vital for organs like the stomach and urinary bladder that expand and contract as substances move through our body.
The autonomic nervous system or hormones generally control these muscles' contractions, but they can also contract spontaneously or in response to stretching. Unlike in multiunit smooth muscle, the contraction in single-unit smooth muscle spreads from one cell to the next, making a coordinated contraction of the whole muscle mass possible.