Elements of this diagram are instances of SysML blocks that represent the use case and its associated actor(s). 

The Use-Case Block is the structural representation of a use case defined in the use-case diagram. It is used to represent the formal specification of the system behavior for the use case and acts as a location for the operations/functions that the use case employs. The Use-Case Block communicates with relevant Actor Blocks via ports and associated provided and required interfaces.

An Actor Block is the realization of an actor that was previously identified in a system use case diagram. An actor block represents a person, or system that is external to the system under development, that interacts with the system under development by providing the inputs to, and receiving outputs from the system under development.