What are the different types of cell signaling molecules?

The four main types of cell signaling molecules are hormones, pheromones, neurotransmitters, and local transmitters. Hormones are chemical messengers that travel through the bloodstream to utilize their effects. These hormones include: insulin, estrogen, testosterone, and antidiuretic hormone. Pheromones are secreted or excreted chemical factors which produce a social response in members of the same species. These signaling molecules cause an instant and specific behavior response, such as being attracted to a potential mating partner. Neurotransmitters carry chemical signals from one neuron to the next target cell, which can be another neuron, a muscle cell, or a gland. As a signal travels along a nerve cell, the electrical charge of the signal causes the vesicle of the neurotransmitters to fuse with the nerve cell membrane. The neurotransmitters are then released from the axon terminal into a fluid-filled space between one neuron and the next target cell. Local transmitters function over short distances by diffusion. They play a role in processes such as blood pressure regulation, reproduction, and nervous system functions. Local transmitters function in cells which are close to one another, such as paracrine signals. They are also involved in the body’s immune responses and differentiation.