Hint: The above-mentioned are types of smooth muscles. Smooth muscles are the type of muscles that are used by various systems to apply pressure to vessels and organs.
Smooth muscles are of basically two types:
a. Single-unit smooth muscles: - These are also called Visceral smooth muscles. These types of muscles are found in the uterus, gastrointestinal tract, and bladder. This muscle has its muscle fibres joined by gap functions so that the muscle contracts as a single unit. Single-unit visceral muscle is myogenic, it can contract regularly without input from a motor neuron. A few of the cells in a given single-unit visceral smooth muscle (SUVSM) unit may behave as pacemaker cells, generating rhythmic action potentials due to their intrinsic electrical activity. Due to its myogenic nature, the single-unit smooth muscles are generally active, even when it is not receiving any neural stimulation.
b. Multiunit smooth muscles: - These are composed of cells that rarely possess or do not possess gap junctions, and hence are not electrically coupled. As a result, contraction does not happen from one cell to the next one, but it keeps on confined to the cell that was stimulated originally. This type of smooth muscle cell is observed in the large airways to the lungs, in the large arteries, etc.
Note: As per the names, we can get the idea about the terms as the single-unit smooth muscles mean that they function on only one cell while the other one is the multi-unit smooth muscle functions on more than one or different cells.