Final answer:
Hormones are the substances released from neurosecretory cells that travel through the bloodstream to reach their target tissues, contrasting with neurotransmitters that are released at synapses.
Step-by-step explanation:
Neurosecretory Cells and Their Signaling Molecules
Substances that are released from neurosecretory cells but travel through the bloodstream to target tissues are known as hormones. These cells, such as the chromaffin cells of the adrenal medulla, release signaling molecules directly into the circulation. This is in contrast to neurotransmitters, which are released at synapses. An example of this is norepinephrine, which acts as a neurotransmitter when released from postganglionic sympathetic fibers, but is considered a hormone when released by the adrenal medulla into the bloodstream. Both types of signaling molecules are essential for body functions, but their release and mode of action distinguish them as either neurotransmitters or hormones.