Tourette's Syndrome patient here.

The neurochemistry is still a grey area, but imagine it this way:

I often will blink my eyes, and get a nigh-irresistible compulsion to keep blinking my eyes for a few seconds. I will sometimes just "need" to move my hands in unpredictable ways. That's how tics manifest. I can temporarily suppress them, but they come out eventually.

Vocalizations are most commonly hummimg noises, occasionally a quiet, open mouth "ah" noise. It's different for different people.

Coprolalia (uncontrolled swearing) is typically the only symptom Hollywood portrays, but it's usually a symptom exclusive to cases of Tourette's much more severe than what I've got. If someone's demonstrating coprolalia, it's actually the least of their worries.

Based on my understanding, the problem isn't just that you have a glitch in the motor nerves controlling your muscles, which forces them to move. You have a glitch in the overall system in your brain that directs how and when you want to move.

Tic disorders are usually associated with some problem in the cortex (which does most of the thinking and remembering and feeling), the basal ganglia (which regulates emotional decisions and rewards), and/or the thalamus (which filters and relays nerve signals in and out of the brain). These three structures are part of the complex neural circuitry that helps you think about doing actions, decide you want to do those actions, and then tell your muscles to do those actions.

So when you have a tic disorder, something goes wrong somewhere in that circuit, causing signals to misfire and your nervous system to get confused and alarmed. You start to feel like you HAVE to do SOMETHING, because the brain parts that send the "Do Something" signal are reading error messages and sending up red flags. So then your brain grabs for some action or habit or behavior (kind of at random, and kind of based on complicated factors), and decides "This must be it! This is the Something we're supposed to Do! Quick, do this!" 

So then you do that action, and your confused nervous system calms down because it can resolve that "Do Something" signal and make it go away. And since the parts of your brain that regulate habits and release dopamine are involved, you get a strong psychological reward for doing it. And that makes your brain go "Aha, this behavior helped. I know exactly what to do next time that glitch happens." And so now that behavior is locked in as a new tic.

I'm oversimplifying a lot here, and I'm probably wrong about a lot of the specific details, but in general that's the answer. The parts of your brain that plan and control complicated actions are just picking something for you to do, so that's why it can be something complicated and specific. 

As for the words: language isn't stored in the brain as single vowels to then compose a word when speaking. It's often stored in different words, concepts, etc., which causes people with Tourette's in some cases to have full-word tics when their neurotransmitters misfire.

There's also a behavioral component to it. That's why to some extent it can be suppressed. Or why for some people it not only gets worse from stress but also is reported to help alleviate the stress.

Some interesting studies out there showing interesting rates of comorbidity with ASD, ADHD, and other similarly shared conditions.

This is a rough one to ELI5, the brain is complicated and quite a few of the mechanisms in Tourette's syndrome are not well understood (yet). One thing we do know is that there's some similarities between the underlying mechanisms of Tourette's and other disorders such as ADHD and OCD, and in some ways I think it's more intuitive to explain what's going on by comparing to ADHD/OCD symptoms (the causes and effects are similar in some ways and almost opposite in others).

I'll start off with a very simplified intro to brain anatomy, because that's kinda needed to understand the basics of how these disorders work. The brain is made up of lots of nerve cells called neurons. There's lots of different types of neurons that do different things - some send signals that activate other neurons (excitatory), some send signals that stop other neurons from being activated (inhibitory), and some send signals that have complicated effects (e.g. dopamine and serotonin).

Neurons are organised in very specific ways on a microscopic level and at a whole brain level. On the microscopic level, neurons are arranged into circuits that use loops of excitatory and inhibitory neurons to control the activity of the main neuron in the circuit that in turn connects to other neural circuits and controls what those circuits are doing. On a bigger scale, different parts of the brain have different jobs and so some neurons have long connections to other parts of the brain to link their activity together, and these need to be connected together in the right way to work as they're supposed to.

The underlying causes of Tourette's are really complex and involve several parts of the brain that process sensory information and control movement and behaviour, but one part worth calling out because of it's important role in Tourette's is the basal ganglia. The basal ganglia works as a master control centre for really important things like starting and stopping movement, decision making, and motivation, and is connected to the rest of the brain with complicated signals like dopamine (e.g. the most obvious symptom of Parkinson's disease is losing the ability to start movements, and this is caused by loss of specific cells in the basal ganglia that produce dopamine)

In people with Tourette's syndrome (and ADHD and OCD), some of the microscopic neural circuitry in the basal ganglia doesn't quite develop in the way it's supposed to. In Tourette's syndrome, research has found there's a differences in how many inhibitory cells there are in some parts of the basal ganglia - in some places there's less than normal, and there's more inhibitory cells in other parts. This causes differences in how active the microscopic neuron circuits are, and that then causes differences in what happens in other parts of the brain because everything is connected.

So this is where we get to tics, the best known symptom of Tourette's. When you boil it down, motor tics are an abnormal compulsive movement or action (compulsive = an "external" need to do something; a tick can be consciously held back to some extent, but the need won't go away until the compulsion is fulfilled). Tics happen because the basic systems that control sensory processing and action aren't working properly - the part of the brain that controls sensory information messes up and turns on the part of the brain that wants to do something (when it shouldn't), and the central control that is supposed to turn it off doesn't do it's job. The thinking part of your brain can override this if it wants to, but that means you have to think about it.

This is where the commonalities to ADHD and OCD come in. OCD is best known for causing compulsive behaviours and it's easy to see some of the similarities (afaik, compulsions in OCD involve parts of the brain that process emotions rather than movement/action, but there's a lot of overlap). In ADHD the obvious problem can be simplified to hyperactive/impulsive behaviour (impulsive = acting without thinking) and difficulty initiating AND maintaining actions (both movement and thought processes), so it's almost the opposite effect in some ways - the master control doesn't do a great job of vetoing/stopping actions when it is/is not supposed to, but also the part of the brain whose job it is to want to do something doesn't always turn on when it should, or turns off when it shouldnt.

And phew. Hope this is helpful!

CBIT therapist here. What I learned in the program was that is was akin to a faulty gait. Your basal ganglia is supposed to essentially take in environmental information and respond with appropriate motor or vocal output. However this gating mechanism gets a bit faulty or leaky. When the body starts to respond to the urge with the vocal or motor output a series of "feel good" chemicals are released reinforcing the tic. Other things like unwanted attention and/or well meaning attention can further "reinforce" and make the urge stronger. This can be confusing because most of my patients with tourettes dont want the attention And the chemical reward sounds counterintuitive especially when they are embarrassed. But that the end of the day bodies are chemicals and impulses and it doesn't know the difference between good/bad attention and just goes 'oooo attention here are some chemical rewards'.

TLDR : faulty circuitry from the basal ganglia

I have a neurological muscle disorder closely related to Tourette's. (ie. I have Tourette's without the vocal tics)

Let's just say the compulsion is irresistible. Completely irresistible. If I try to actually concentrate and resist a tic, I can do that for about 5-10 seconds before I get a bad feeling in the pit of my chest. It's a bit like the feeling when you're at the peak of a rollercoaster and you're about to do a high speed dive - it's that sort of weird feeling that is sometimes described as a feeling of impending doom

At college, I thought a girl has a crush on me because she kept winking in my direction. It turned out that she just had a twitch.

So I recently heard that tourettes actually has its roots as an autoimmune disorder.

Autoimmune disorders are when your bodies natural immune defenses, instead of attacking foreign invading pathogens, actually attack your own healthy organs. In tourettes, the immune cells attack a certain part of the brain and the damage/inflammation this causes is what leads to the tics.

I just found this out recently and thought it was super interesting.

My roommate has Tourettes and watching him try to hold it back during movies is honestly painful. You can literally see the tension building in his shoulders until he finally just lets it out.

Dude with officially diagnosed Tourette’s syndrome:

Have you ever had a really bad itch but had something in your hands so you can’t itch it right away, and the more you can’t itch it the more you WANT to itch it, nay, the more you NEED to itch it?

Well that’s how it feels to tic when you have Giles Syndrome (Tourette’s) you have this inescapable need to do… something. It could be blinking your eyes, raising your eyebrows, coughing, sniffing, twitching an arm or anything under the sun. The more you try to resist it, just like an itch the compulsion to do the thing gets bigger.

There is currently no guaranteed effective treatment, but it’s thought the condition is adjacent to OCD.

Interestingly, it seems to have a correlation with ADHD too, with up to 60% of people with Tourette’s syndrome also meeting the criteria for ADHD.

Doing finger guns sounds more like Functional Tics, not Tourette’s. They have completely different causes.