Why are there so many different neurotransmitters if nerves only communicate in a binary action potential language?
I mean different kinds of nerves are united to only their similar kind, so what is the use of having so many different chemical 'languages'?
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If there were only one kind of transmitter how would cocaine produce a different effect than barbiturates?
It's so you can have different mututally exclusive signals without having a type of neuron for every one of these signals.
How does that work? Whether it's X transmitter or Y or Z, the neuron will only communicate either a 1 or a 0. You could literally just have two neurotransmitters for the entire body.
One* even
To elaborate that OP, think of a thalamo-cortical connection like a power source connecting to a TV screen. The TV is using a binary YES/NO electrical language, but the cords in it are insulated and coded different colors, despite all of them being copper on the inside. The copper core is the common interneuron mixture in your brain, while the color-coded wire insulation is, effectively, the utility of neurotransmitters and neuromodulating peptides. Organisms are just much more efficient at "insulating" signals and communicating in this way.
If the brain only used GABA and glutamate to initiate action potentials, it would not have the ability to contain and control its electrical signals, and would require substantially more differentiated cells with unique microbiological properties. Basically, thinking of the brain like a wet CPU doesn't work, because interneuron and glial cells are more similar to each other than the discrete inorganic metals, plastics, rubbers and forms of glass used in any mechanical computer.
Action potentials are not binary. When a neuron gets a stimulus, its potential goes up by some amount. There is an internal threshold that must be reached in order for a neuron to spike. This means that the output is binary, but the internals can be binary, linear, or even non-linear and thresholds for spiking can change with different neurotransmitter levels.
The brain does not communicate in 1s or 0s.
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> There are no big or small action potentials in one nerve cell - all action potentials are the same size. Therefore, the neuron either does not reach the threshold or a full action potential is fired - this is the "ALL OR NONE" principle.