Q: Pacemaker cells stimulate the spontaneous contraction of cardiac muscle as a functional unit, called a what?


Read this paragraph and choose the correct option from the provided answers:

10.7 Cardiac Muscle Tissue Cardiac muscle is striated muscle that is present only in the heart. Cardiac muscle fibers have a single nucleus, are branched, and joined to one another by intercalated discs that contain gap junctions for depolarization between cells and desmosomes to hold the fibers together when the heart contracts. Contraction in each cardiac muscle fiber is triggered by Ca++ ions in a similar manner as skeletal muscle, but here the Ca++ ions come from SR and through voltage-gated calcium channels in the sarcolemma. Pacemaker cells stimulate the spontaneous contraction of cardiac muscle as a functional unit, called a syncytium.

 Choices:

- coenocyte

- tapetum

- adipocytes

- syncytium


A:
syncytium