There are four main types of tissues in the human body: epithelial, connective, nervous, and muscular. Epithelial tissue forms the covering or lining of structures throughout the body and in two main categories - simple and stratified. Connective tissue is made of cells separated by non-living material and includes bone, blood, cartilage and dense or loose connective tissue like areolar tissue. Nervous tissue is made up of neurons that generate and conduct nerve impulses. Muscular tissue contains specialized contractile cells called myocytes and includes skeletal, cardiac and smooth muscle.