Cells are the units of structure and function of all living things, as stated in the cell theory. However, cells are highly specialized to perform various jobs in a multicellular organism. Types of cells include, muscle cells which are able to contract and relax leading to movement, bone cells which provide the material to produce the skeleton, a framework for the body. Epithelial cells are for protection of the organism, fat cells can store fat for energy use when needed. Neurons or nerve cells are specialized for conducting nerve impulses to and from the spinal cord and brain. Blood cells are specialized for different functions--red corpuscles transport oxygen, white corpuscles are part of the immune system and are for defense against foreign cells. These are just a few examples of how specialized cells work together to maintain homeostasis in the body.