Final answer:
A sphincterismus is a muscular spasm that affects an anatomical sphincter, which can be made of smooth or skeletal muscle responsible for involuntary or voluntary control of the opening and closing of bodily passages and hollow organs.
Step-by-step explanation:
A sphincterismus is a muscular spasm that affects an anatomical sphincter. These sphincters are rings of smooth or skeletal muscle that surround the lumen of a vessel or hollow organ, such as the internal a nal sphincter that controls the opening of the an us, or the internal urinary sphincter at the junction between the bladder and urethra. When a sphincter spasms, it contracts abnormally, which can restrict flow through the organ or vessel.
Anatomical sphincters can be either involuntary, such as the internal a nal sphincter composed of smooth muscle, or voluntary, such as the external an al sphincter composed of skeletal muscle. Smooth muscle tissue contraction is usually responsible for involuntary movements in the internal organs and forms a critical part of the digestive, urinary, and reproductive systems, as well as the airways and arteries.