Final answer:
Voluntary muscles like skeletal muscles can be consciously controlled but can also contract reflexively to certain stimuli, whereas involuntary muscles, such as cardiac muscles, operate without conscious control.
Step-by-step explanation:
Even voluntary muscle can contract unconsciously in a reflex, which is a response to a stereotypical or learned stimulus. Voluntary muscles such as skeletal muscles can be controlled by an individual's will, allowing us to perform actions like walking, grabbing, or speaking. However, they can also respond automatically to certain stimuli through reflexes, which are rapid, involuntary responses to specific stimuli that don't require conscious thought.
In contrast, involuntary muscles cannot be consciously controlled. These include cardiac muscles, which make up the heart, and smooth muscles found in the digestive system and other internal organs. The autonomic nervous system regulates involuntary responses, while the somatic nervous system governs voluntary responses.