Human tissues are groups of cells that work together to perform specific functions in the body. There are four main types of tissues: epithelial tissue, which covers surfaces and lines cavities; connective tissue, which supports and binds other tissues; muscle tissue, which enables movement; and nervous tissue, which transmits signals throughout the body. Each type of tissue has unique characteristics and roles. For example, muscle tissue can be further divided into three types: skeletal muscle, which moves bones; cardiac muscle, which makes up the heart; and smooth muscle, which controls involuntary movements in organs. Together, these tissues form organs and systems that maintain the body's functions.