True or False? All smooth muscle can contract without external stimuli.

Smooth muscle typically requires some form of external stimuli to initiate contraction. While smooth muscle can exhibit automaticity – the ability to contract on its own in response to internal pacemaker cells – it generally does not contract solely by itself without any external influences. For example, smooth muscle located in the walls of blood vessels can experience contractions triggered by factors such as hormones, neurotransmitters, or local changes in the environment (e.g., stretch).

Thus, stating that all smooth muscle can contract without external stimuli is inaccurate. There are instances where certain smooth muscles, like those found in the gastrointestinal tract, can contract rhythmically without nervous stimulation due to their intrinsic properties, but this does not apply to all smooth muscle types universally. This nuanced understanding highlights the fact that while some smooth muscle tissues have a degree of automaticity, they are not entirely devoid of external regulatory influences.