When you decide you want to take a step, or lift your arm, how does this thought get converted into a movement? Once the thought enters your mind, your brain sends a signal to your muscles to contract which causes your bones to move, since they are connected to your muscles by tendons. Movements like walking or typing on a computer require a lot of different muscles to act, all at the same time. You brain has to signal to each and every muscle needed for the movement and tell those muscles what to do and when. This may sound like a pretty difficult task, but your muscles and brain have been practicing since you started moving around as a baby!

When you repeat the same movement over and over, you develop what’s called muscle memory. This is when your brain and muscles learn how to do a certain thing after lots of practice, without too much effort. It’s like they say: once you learn, you never forget how to ride a bike!

But have you ever experienced your body reacting to something without you thinking about it? Maybe a scary figure has popped out at you in a haunted house and made you jump, or you accidentally touched something hot and your hand recoiled instantly. These are a class of movements called reflexes.

Your body is always aware of what’s going on around you, and reflexes are your body’s way of responding quickly to things that might be dangerous. It’s a built-in safety system where your brain is alerted to a threat and signals to your muscles to respond accordingly without you having to process what happened first.

Say someone dressed in a scary werewolf costume is hiding in a big pile of leaves, and as you walk by, they jump out and startle you. If you’ve ever experienced something like this, you might have felt your jaw tighten, eyes close, head jerk back, shoulders and arms rise, and legs tense up. All these movements happened because your brain saw the person in the costume as a threat and signalled to your muscles to contract and move your body to positions that help you defend yourself.

Involuntary reactions like this are meant to protect us, but we also have a few reflexes that are left over from before humans even existed. Maybe you’re watching a scary movie and something really creepy happens – you might notice you got goosebumps on your skin. Goosebumps are also a reflex caused by your brain signalling to tiny muscles under your skin that contract to make all your hairs stand up straight. Although it’s not really helpful to us now, if our ancestors (who had a lot more hair on their bodies) became frightened, they would develop goosebumps too. But since they were much hairier, having all their hairs stand on end would make them look much bigger and scarier to help defend themselves against whatever they saw as a threat.

If you think about it, the musculoskeletal system is a pretty amazing thing. With direction from your brain, your muscles and bones allow you to move however you want, and keep your body safe and functioning without you having to think about it.