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.
Nervous control has a shorter duration than endocrine control. Stimulus intensity is represented in the nervous system by the frequency of action potentials and in the endocrine system by the amount of hormone released. A sensory receptor senses the change and sends action potentials by its afferent sensory neuron to the integration center in the brain or spinal cord. The sensory receptor is the endocrine cell or gland , there is no afferent path, the integration center is the endocrine cell or gland, the efferent path is the secretion of the hormone into the blood , the effectors are most of the cells in the body, and response is either to change the rate of an enzymatic reaction , or control transport of certain molecules across cell membranes, or to control gene expression and the making of new proteins . The term hormone means to excite or arouse .