The "neuromuscular junction"

I didn't want to go to the gym tonight. I was tired all day. I was very unproductive. I sat and stared at my computer most of the day. I came home and collapsed onto my bed, jacket, shoes and all, and I laid there, and laid there, and I wanted to sleep. I wanted to crawl under my duvet, turn on the heating blanket and sleep until tomorrow at noon.

But I didn't. I got up, and I changed my close, got on my bike and went to the gym. I hated it all the way there. Every turn of the peddle felt like a struggle. When I got there, I put my stuff in a locker and proceeded to the cardio room and got on a treadmill. I thought, alright, I'm just gonna do a short workout because I'm tired, and I don't want to do anything. So, I set the treadmill to 5 miles knowing full well that I wasn't going to walk or run anything close to that tonight, and I started.

I walked half a mile at 5.0km/h, then I ran half a mile at 7.5km/h (I realize I'm using miles and km/h, but that's how the machines are setup... I don't know why). Then I walked again... about a 1/3 of a mile, and then I wanted to run. So I ran, for 2/3 of a mile. Then I walked for about a minute, and I wanted to run again, so I did. This time at 9km/h. I was running and I stared ahead, completely focused on an unrelated sign stuck on the wall below the tv that said "sky sports", almost mesmerized. I was so focused on it, that I started moving forward on the treadmill, as if trying to get to it, and if it weren't for the console on the front which stopped me, I would have run right off. At one point, I felt a chill wash over me. It started in my lower back, and washed right up over my head and down my front, similar to being washed over by a wave in the ocean. I kept going, and in the end, I finished the 5 miles.

Maybe that chill was just in my head, or maybe it was a physiological response in my body. As a physiologist, I would tend to lean towards the latter. But your physiology and your neurology are so intricately linked that can you really separate the two? Do you know what a neurotransmitter is? It's a small chemical, that is released, generally starting from the brain, from one nerve when that nerve is stimulated, and it binds to the next nerve in line to stimulate it, and at the end of the line there is a "motorneuron" which forms a neuromuscular junction at your heart or skeletal muscle, and the neurotransmitters released from that motorneuron stimulate the muscle to contract. So when they say "it's all in your head", it's true, literally and figuratively. And then it moves to your heart, literally and figuratively. And then it gets in your skeletal muscles, and it moves you, literally and figuratively. And in the end, it comes full circle back to your brain, because you feel good, you feel proud, you feel accomplished. Then the cycle repeats itself.