Involuntary Muscles in the Human Body: Heart & Sphincters

Two parts of the human body that are controlled by involuntary muscles are:

1. Heart: The heart muscle, known as the myocardium, is an involuntary muscle that contracts and relaxes rhythmically to pump blood throughout the body. The heart's contractions are controlled by the electrical signals generated by the sinoatrial (SA) node and atrioventricular (AV) node, without conscious effort.

2. Sphincters: Sphincters are circular muscles that control the opening and closing of various passages in the body. For example, the esophageal sphincter regulates the passage of food from the esophagus to the stomach and prevents acid reflux. Similarly, sphincters in the urinary bladder and anal canal control the release of urine and feces, respectively. These sphincters operate involuntarily, ensuring proper bodily functions.