The regulated secretory pathway is a specialized transport process in which cells store soluble proteins within secretory vesicles and only release them to the cell's exterior in response to specific extracellular events or signals.

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Exocytosis is the process by which secretory vesicles move toward and fuse with the plasma membrane to release their contents outside the cell. Cells utilize exocytosis to eliminate waste products and to secrete chemical signals that other cells can receive.

Exocytosis

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SNAREs are proteins that tether. v-SNAREs are tethered to vesicles. t-SNAREs are tethered to the presynaptic membrane and attach to v-SNAREs to begin the fusion process. Synaptotagmin are attached to the vesicles and help finish the fusion process.

Proteins Involved in Exocytosis

Since exocytosis describes the release of neurotransmitters from vesicles with the help of enzymes during synaptic transmission, it is understandable that the following three things affect the rate of exocytosis: 1.) The rate of production of neurotransmitters, 2.) The rate of production of vesicles, and 3.) The activity of the neuron (i.e., the frequency of action potentials). Normally, the axon terminal contains enough neurotransmitters and vesicles to prepare itself for an action potential. These neurotransmitters and vesicles are produced in the cell body with the help of enzymes and transported to the axon terminal. 

The Rate of Exocytosis

The constitutive secretory pathway is a continuous transport process in all cells where secretory vesicles carry soluble proteins to the cell membrane and release them to the exterior without requiring external triggers.

Constitutive Secretory Pathway

Regulated Secretory Pathway

Histamine secretion by mast cells is an example of regulated secretion where these immune cells release histamine—a compound that triggers immune defense mechanisms to clear pathogens—in response to the detection of foreign objects or pathogens.

Histamine Secretion by Mast Cells

Synaptic transmission is the process by which a neuron communicates with an adjacent one. It begins when an action potential reaches the axon terminal, causing neurotransmitters to be released into the synaptic cleft. These chemicals then travel across the synapse and bind to receptors on the next neuron's dendrites. If this signal is potent enough, it will trigger a new action potential, thus propagating the nerve impulse.

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