Muscle cells, also known as myocytes, are specialized cells responsible for the contraction and movement of muscles in the body. They are classified into three types: skeletal muscle cells, which enable voluntary movements; cardiac muscle cells, which make up the heart and function involuntarily; and smooth muscle cells, found in organs and blood vessels, also functioning involuntarily. These cells contain unique structures called myofibrils, which are made up of proteins like actin and myosin. When stimulated by nerve signals, these proteins interact to produce contractions, allowing for movement and various bodily functions. Muscle cells can also adapt to different levels of activity through growth and repair processes.