Read and study pages 724-730. All of Chapter 41should be read. The cells of an organism need to be able to communicate with each other so that the organism can function as a whole. Cells use either chemical or electrical signals to communicate with each other. Cells can communicate by direct transfer of electrical or chemical signals through gap junctions connecting them.
Cells can communicate by producing chemicals that diffuse locally in the extracellular fluid.
Paracrines are chemicals that are produced by one cell and act on nearby cells. Autocrines are chemicals that are produced by a cell and act on the same cell. Reflexes of the nervous system are more specific because nerves regulate specific target cells while hormones can control multiple organs and systems. The nervous system uses both electrical and chemical signals while the endocrine system uses only chemical signals. Nervous reflexes are much faster than endocrine reflexes.