Sunday, September 22, 2013

Partially Accurate Science: Basic Anatomy of a Neuron

Okay, so one day when I was obviously feeling very motivated and overconfident, I thought it would be a great idea to try and explain the basic anatomy and functioning of brain cells despite the fact that I haven’t studied neurobiology in years and can’t actually find my notes. Anyway, clearly a brilliant plan, yes? I thought I’d begin by explaining the different parts of the neuron and whatnot, all of which is good stuff. I am mostly sure it is mostly true.

There are many lovely diagrams of neurons available on the internet, but because I’m afraid of copyright laws this won’t be one of them. This is something I attempted to draw on my computer but that could probably have been better rendered by monkeys. If you want to know what a neuron actually looks like, please use Google. If you want to 100% quote me on the accuracy of my science, maybe this blog isn’t for you.


In real life, neurons are much, much smaller than this

P.S. biology is fun and also gives me a headache.

The main part of your cell is the soma, or cell body. This is where the good stuff happens, the stuff that determines whether or not your lovely brain cell is going to fire a signal. When your cell receives signals from presynaptic neurons via its dendrites, those signals are integrated in the cell body. Ultimately, when the soma has received and integrated enough signals, the cell will fire and your neuron will get busy doing stuff like talking to other neurons. For now, what you need to know about the soma is that you can sort of think of it as the cell’s brain.

Inside the soma is the cell’s nucleus. As is true of other cells, the nucleus carries the DNA of the cell – the instructions that tell your cell how to produce the various proteins that allow it to function properly. If you have a disease like Huntington’s which is straightforwardly genetic, for example, and which causes mental-illness-like presentations, you know that the reason for your symptoms is a genetic defect that means your cell cannot do its job properly. Most mental illnesses are not straightforwardly genetic: there is a lot of talk about complex and varied genetic alleles (groups of genetic variations or markers), as well as problems of protein expression (epigenetic phenomena), and – most importantly – nurture/experience as expressed either epigenetically or in terms of neuroplasticity. But I digress. Stupid nucleus, throwing me off course. Some people like to think of the nucleus as the cell’s brain, but I like to think of it more like the instruction manual your cell is working with.

Your cell also has dendrites, which are short branches allowing your cell to receive signals from other ‘upstream’ presynaptic neurons; those signals are relayed electrically to the soma. Your dendrites receive signals through receptors, which are basically specialized proteins to which neurotransmitters bond. You can think of your dendrites like a massive array of antennae listening for signals from other cells and then relaying those signals to a central listening station.

The axon of a cell extends or leads away from the cell body at a swelling or juncture called the axon hillock. When your cell decides to fire, the electrical charge is dispelled or pushed down the cell’s axon to the terminal so that your cell can communicate with ‘downstream’ postsynaptic neurons. It is basically the cord responsible for transmitting the neural signal from one part of the cell to the other. The awkward bubbles I’ve drawn around it are meant to represent the myelin sheath, a protective coating that some neural cells have surrounding their axons. The myelin sheath is a protective, insulating layer keeping the electric current from leaving the axon, allowing it to travel down the cell faster. Damaged or defective myelin sheaths cause nerve damage, and signals along the neuron become degraded and lost.

The axon terminals (or terminal buttons), are where your cells finally releases the chemical signal that allows it to talk to its little friends. They branch out from the axon, and transmit the signal to other cells by means of neurotransmitters.

For reasons that currently escape me, I’ve decided that we need to take a closer look at what’s happening in the axon terminals. Probably because it’s magical.

still not a good artist; but seriously, my stick figures are amazing

Basically, your axon terminal has these little sacks in it called vesicles, which contain neurotransmitters. The type of neurotransmitter inside the vesicle will depend on what kind of cell it is. The electrical signal carried down the axon causes the sacks to merge with the outer membrane, releasing the neurotransmitter into the synaptic cleft.

The soma is, for lack of a better word, ‘surrounded’ by a cell membrane which is essentially the cell body. It keeps the outside of the cell separated from the inside of the cell. It is not the same as a cell wall, so don’t Google that by mistake. The cell membrane is semi-permeable (or selectively permeable), letting some things through and keeping other things out, as well as allowing the cell to expel things. Later, as we discuss the electrical nature of cell function, we’ll see how transmembrane protein channels and transport proteins work. But enough of that chit-chat.  

This has been fun, and maybe even a little informative. If you want to learn more about neural cell biology, pick up an introductory psychology or cell biology textbook; you could also probably just read the internet. Any of these options will net you more detailed and accurate information than you’ve seen here today. Think of this as a teaser, forcing you to either do more research or look silly at your next cocktail party.

Stay tuned for the next installment: your cell is an electrical machine (or, how your mind powers the Matrix)!

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