#10 The Nervous System, Part 3 - Synapses!

Synapse:
the meeting point between two neurons

Their purpose lies in their connections.

A single neuron in isolation might as well not exist if it doesn't have someone to listen or talk to.

The word "synapse" comes from the Greek for "to clasp or join".

It's basically a junction or a crossroads.

You've got somewhere between 100 to 1,000 trillion synapses in your brain.

Able to change and adapt in response to neuron firing patterns

Synapses are what allow you to learn and remember. They're also the root of many pasychiatric disorders.

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<Electrical vs Chemical Synapses>

Some of your synapses are electrical - that would be like an immediate group text.

Others are chemical sysnapses - they take more time to be received and read, but they're used more often and are much easier to control, sending signals to only certain recipients.

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<How Electrical Synapses Work: Gap Junctions>

They're super fast because the signal is never converted from its pure electrical state to any other kind of signal, the way it is in a chemical synapse.

One cell and one synapse can trigger thousands of other cells that can all act in synchrony.

Something similar happens in the muscle cells of your heart, where speed and team effort between cells is crucial.

An action potential in one neuron will generate an action potential in the other cells across the synapse.

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<How Chemical Synapses Work: Neurotransmitters>

Chemical Synapses:
much more abundant / slower / more precise / more selective

The main advantage chemical synapses have over electircal ones is that hey can effectively convert the signal in steps - from electrical to chemical back to electrical - which allows for different ways to contral that impulse.

At the synapse, that signal can be modified, amplified, inhibited, or split, either immediately or over longer periods of time.

The cell that's sending the signal is the presynaptic neuron, and it transmits through a knoblike structure called the presynaptic terminal, usually the axon terminal.

This terminal holds a whole bunch of tiny synaptic vesicle sacs, each loaded with thousands of molecules of a given neurotransmitter.

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<How Neurotransmitters Work>

This flow of positively-charged calcium ions causes all those tiny synaptic vesicles to fuse with the cell membrane and purge their chemical messengers.

The first neuron has managed to convert the electrical signal into a chemical one.

And depending on which particular neurotransmitter binds to which receptor, the neuron might either get excited or inhibited.

Excitatory Neurotransmitters:
Excitatory post-synaptic potentials(EPSPs): graded potentials that push the neuron closer to threshold, and make an action potential more likely.

Inhibitory Neurotransmitters:
Inhibitory Post-Synaptic Potentials(IPSPs): graded potentials that push the neuron further from threshold, make an action potential harder to achieve.

Depends on the sum of all the excitations and inhibitions in that area.

We have over a hundred different kinds of naturally-occurring neurotransmitters in our bodies that serve different functions.

But neurotransmitters don't stay bonded to their receptors for more than a few milliseconds.

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<How Cocaine Works>

These drugs can either excite or inhibit the production, release, and reuptake of neurotransmitters.

Once it hits your bloodstream, it targets three major neurotransmitters - seratonin, dopamine, norepinephrine.

Serotonin is mainly inhibitory and plays an important role in regulating mood, appetite, circadian rhythm, and sleep.

Your brain releases dopamine, which influences emotion and attention, but mostly just makes you fell awesome.

Norepinephrine amps you up by triggering your fight or flight response, increasing your heart rate, and priming muscles to engage, while an under supply of the chemical cna depress a mood.