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Back in the early days of neuroscience, we didn't study the animals you might expect to learn about how brain cells communicate.

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Thanks to Skillshare for supporting  this episode of SciShow Psych.

The first 1,000 people to click  the link in the description can get a free trial of Skillshare’s Premium Membership. [♪ INTRO]. For your brain to do its job, a lot of information needs to be communicated at lightning speed.

So your brain is full of cells  that can send and receive chemical and electrical messages to  each other all the time. But we only know that this is  fundamentally how the brain works because of early neuroscience  researchers and the animals they studied. The researchers credited with first  figuring out how brain cells communicate didn’t do it by studying mice or rats.

Instead, they worked with squids and frogs. And as weird as it sounds, they were  just the right species for the job. Animal research is not taken lightly.

The use of every single experimental  animal needs to be justified to oversight committees,  research institutions, funders, and publishers before the research  reaches your eyes or ears. But needing specific reasons to  study certain animals doesn’t mean you can’t study a wide range of animals. Take Santiago Ramon y

Cajal: he  analyzed at least 58 different species in the late 19th and early 20th  centuries, from snails to oxen. He labeled some of their brain tissues with  the hottest new cell stains of the day, including Golgi staining, which highlights  only selected cells out of the crowd. This way, he was able to see how  an individual cell stretched out between two other cells, as if  they were playing telephone. His work sparked the idea  that information traveled from the end of one cell to  the beginning of the next.

But we didn’t know exactly how cells  were sending and receiving information until scientists from the  University of Cambridge observed the electricity running  through the squid’s giant axon. It’s tough to do precise experiments  on the scale of a brain cell, especially the teeny tiny  ones that some animals have. Human axons, the outstretched parts that  transmit information to the next cell, only get up to about 10 micrometers wide.

But in the squid, an axon can  be as big as 1 millimeter wide. That’s 100 times bigger! Thanks to the squid, researchers  discovered that an exchange of ions, or electrically charged atoms, generates  an electrical current within a cell.

Those ions, mainly sodium and potassium,  can flow across the cell membrane. When the cell is at rest and not sending messages, there’s more potassium inside the  cell and more sodium outside the cell. And when it initiates communication  to another cell, the membrane opens up to let sodium rush in and potassium  rush back out to reach a balance.

This ion movement gives that  part of the cell membrane a different electrical charge, which then  moves like a wave down the cell’s axon. And that’s an action potential. So the current allows one cell  to signal to another cell.

But current isn’t the only thing that changes  when an action potential is generated. Voltage also plays a role. So these researchers kept the voltage  constant using a voltage clamp that adds a counterweight to  whatever the cell generates.

And that let them focus only  on how the current changes, so they could measure how the  electricity flows in a cell. But while the squid helped take our  understanding of electrical signaling to the next level, the frog was the first animal  shown to have electricity in its body at all. Back in the 19th century,  experiments on frogs showed that their leg muscles would twitch  when stimulated with electricity.

Their large, muscley legs made them a  great animal to study in that experiment. And years later in 1921, researchers  were still studying frogs, among other organisms, to figure  out the rest of the puzzle. You see, a researcher suspected that chemicals are also involved in cell-to-cell communication.

This was because sometimes the  cell receiving the message reacts by becoming more active, but  other times it becomes subdued. And he didn’t see that kind of specific  effect being controlled by electricity alone. So he set out to test his idea  that cellular communication can be triggered by chemicals.

He studied two frog hearts that were held in individual containers of a  fancy saltwater solution. One heart still had nerves attached  to it and the other did not. He stimulated the nerves of  the heart that still had them, then transferred the solution it had  been bathing into the second heart.

The second heart responded as if the  nerves had just been stimulated because it was responding to the chemicals that the  first heart had released into its solution. Those chemical messengers are what  we now call neurotransmitters. We know today that certain neurotransmitters  lead to more communication, others lead to less, and some can lead  to either depending on the situation.

Like glutamate usually activates  a pathway within the cell that encourages sodium to flow  in and potassium to flow out. Another neurotransmitter, GABA,  usually initiates a different pathway that brings more potassium into the  cell, keeping it from sending messages. So both electricity and chemicals  are powerful signaling tools.

And because they were both found in frogs,  we know that within the same animal, cells use both electricity and  chemicals to send signals to each other. After initiating an action potential, a cell  releases neurotransmitters to the next cell. So thanks to squids, frogs,  and many other organisms, we know much more about how brain  cells communicate with each other, and how our own brains do what they do.

If you enjoyed this episode, you might enjoy learning more about your brain over on Skillshare. Skillshare is an online learning community  that empowers people to accomplish growth with classes to explore,  real projects to create, and the support of other creatives. Like, if this episode has you wanting  to learn more about how your mind works, you might like the class “Learn Psychology:  How Your Mind Works in Six Lectures.” It’s a beginner-level course that teaches you all about memory and emotions and human nature.

Skillshare is curated specifically for  learning, meaning that there are no ads, and they’re always launching new premium classes, so you can follow your curiosity and  creativity wherever it takes you. And the first 1,000 people to  click the link in the description will get a one month free  trial of Premium Membership. Thanks again for watching,  and thanks again to Skillshare for sponsoring this episode of SciShow Psych. [♪ OUTRO].