What are the two major types of signaling molecules?

The two major types of signaling molecules are hormones and neurotransmitters. Hormones are released by specialized endocrine cells and travel throughout the circulatory system to attach to target cells at distant body regions during endocrine signaling. Some common examples of hormones include cortisol and melatonin, which are produced in the brain and released into the bloodstream and ultimately affect other areas of the body. 

Neurotransmitters are released from the presynaptic nerve terminal in the brain. They move across the synaptic cleft to the next neuron. Neurotransmitters bind to specific receptors and cause changes in the electrical properties of target cells, which may lead to different postsynaptic effects. Hormones and neurotransmitters both influence people’s ability to concentrate and learn. Neurotransmitters’ actions are short-term, while hormones are able to function for prolonged periods of time. Additionally, neurotransmitters can affect both voluntary and involuntary processes in the body. In contrast, hormones in the endocrine system always function involuntarily.