Neurotransmitters are recognized in the synapse. In the event wherein a nerve action potential triggers the release of neurotransmitter containing synaptic vesicles from the axon of a nerve, the dendrites of the receiving nerve will recognize these neurotransmitters and trigger specific actions (i.e. excitatory or inhibitory). For instance, the release of glutamate from the synapse will trigger an excitatory response (depolarization) while the release of GABA will trigger an inhibitory response (hyperpolarization).
Target cells respond to specific hormones. Hormones are endocrine molecules that trigger specific cellular functions such as glucose uptake, urine secretion and reabsorption, etc. Hormones bind to either (1) specific hormone receptor (i.e. insulin receptors), (2) cytoplasmic receptors (i.e. thyroid hormone receptor), and (3) nuclear receptors (i.e. steroid hormones). All of which will trigger a cascade that will eventually lead to new protein synthesis (or the inhibition of such). For example, insulin binds to insulin receptors in muscle cells wherein it would trigger the synthesis of glucose channels which will facilitate the uptake of glucose.
