Here's why:
* Self-excitable cells are also known as autorhythmic cells. These cells have the unique ability to generate their own electrical impulses, which trigger muscle contraction without any external stimulation.
* Cardiac muscle is found in the heart. It needs to contract rhythmically and consistently to pump blood throughout the body. The autorhythmic cells in the heart's sinoatrial (SA) node act as the natural pacemaker, generating the electrical signals that coordinate the heart's contractions.
Other muscle types:
* Skeletal muscle requires nerve stimulation to contract. It's responsible for voluntary movement.
* Smooth muscle is found in the walls of organs and blood vessels. It's typically controlled by the autonomic nervous system. While some smooth muscle can display spontaneous contractions, they are not truly self-excitable like cardiac muscle cells.
