Question

Neurons can release neurotransmittrs or neurohormones. Are both these kinds of chemicals bound in vesicles before they are released by exocytosis? Do neurotransmitters have only one kind of effect in the target cells whereas hormones may have many different effects?

Answer 1

Molecules of neurotransmitters are stored in small "packages" called vesicles. Neurotransmitters are released from the axon terminal when their vesicles "fuse" with the membrane of the axon terminal, spilling the neurotransmitter into the synaptic cleft.

There isn't just one type of receptor for each neurotransmitter. Whether the effect of a certain neurotransmitter is excitatory or inhibitory at a given synapse depends on which of its receptor(s) are present on the postsynaptic (target) cell. Excitatory neurotransmitters encourage a target cell to take action. Inhibitory neurotransmitters decrease the chances of the target cell taking action. A hormone can have different effects depending on the target cell's location, the gender of the individual and the species. That is, hormones turn on certain genes that are preprogrammed to make specific proteins. These proteins cause a cell to respond in a new way (grow, secrete, metabolize, etc.).​​​​​​​