Many Neurons fit the foregoing schema in every respect,, but there are also exceptions to most parts of it.. There are no neurons that lack a soma,, but there are neurons that lack dendrites,, and others that lack an axon.. Furthermore,, in addition to the typical axodendritic and axosomatic synapses,, there are axoaxonic (axon-to-axon) and dendrodendritic (dendrite-to-dendrite) synapses..
The key to neural function is the synaptic signaling process,, which is partly electrical and partly chemical.. The electrical aspect depends on properties of the neuron's membrane.. Like all animal cells,, the cell body of every neuron is enclosed by a plasma membrane,, a bilayer of lipid molecules with many types of protein structures embedded in it.. A lipid bilayer is a powerful electrical insulator,, but in neurons,, many of the protein structures embedded in the membrane are electrically active.. These include ion channels that permit electrically charged ions to flow across the membrane,, and ion pumps that actively transport ions from one side of the membrane to the other.. Most ion channels are permeable only to specific types of ions.. Some ion channels are voltage gated,, meaning that they can be switched between open and closed states by altering the voltage difference across the membrane.. Others are chemically gated,, meaning that they can be switched between open and closed states by interactions with chemicals that diffuse through the extracellular fluid.. The interactions between ion channels and ion pumps produce a voltage difference across the membrane,, typically a bit less than 1/10 of a volt at baseline.. This voltage has two functions: first,, it provides a power source for an assortment of voltage-dependent protein machinery that is embedded in the membrane; second,, it provides a basis for electrical signal transmission between different parts of the membrane..
Neurons communicate by chemical & electrical synapses in a process known as neurotransmission also called synaptic transmission.. The fundamental process that triggers the release of neurotransmitters is the action potential,, a propagating electrical signal that is generated by exploiting the electrically excitable membrane of the neuron.. This is also known as a wave of depolarization..
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