Background: The neuron's membrane resting potential is maintained at a certain voltage. The neuron has a lipid bilayer with certain protein channels which allow the movement of ions in both directions (in and out). Some of these protein channels are gated by:
1) mechanical changes (stretching, pressure, etc)
2) voltage changes- regulated by electrical signals (transport of Na+, K+ through protein channels)
3) Ligands (neurotransmitters, etc)
(Guyton and Hall, Textbook of Medical Physiology, 2016)
Question: If action potentials are brought about by voltage-gated channels which are activated by the change in voltage, what brings about this change in voltage which activates voltage-gated channels?
It sounds a bit convoluted. Here's a quote from Wikipedia's Membrane Potential page:
Because voltage-gated ion channels are controlled by the membrane potential, while the membrane potential itself is influenced by these same ion channels, feedback loops that allow for complex temporal dynamics arise, including oscillations and regenerative events such as action potentials.
Hopefully this quote will help to communicate my confusion.