Why do we call our heart myogenic?
The heart is called myogenic because its normal activities are regulated intrinsically, i.e., auto-regulated by specialised muscles called the nodal tissue.
The nodal musculature has the ability to generate action potentials without any external stimuli, meaning it is auto-excitable. The sino-atrial node (SAN), located in the right upper corner of the right atrium, generates the maximum number of action potentials (70-75 per minute) and is responsible for initiating and maintaining the rhythmic contractile activity of the heart.
Since the heart's rhythmic contractions are initiated and regulated from within by its own specialised muscle tissue rather than by external neural stimulation, it is termed myogenic.
Explanation
The textbook explicitly states that 'Normal activities of the heart are regulated intrinsically, i.e., auto regulated by specialised muscles (nodal tissue), hence the heart is called myogenic.' The term 'myogenic' refers to the fact that the heart muscle itself generates the impulses for contraction, rather than requiring external neural signals. The nodal tissue, particularly the SAN, is auto-excitable and can generate action potentials spontaneously, making the heart self-regulating.