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Brain Blueprints: Motor Control
Moving our body is something of a magic trick; we just think about it, and it seems to happen. Usually, we don’t consciously go through all the steps needed when we aim for a certain thing or direction, and our bodies just reach out or start walking in that direction. Other times, we can be painfully aware of how difficult coordinating and producing movement is, like when learning a new skill such as playing the piano, juggling, or doing handstands.
As part of my Brain Blueprints Project I’ll try to extract the minimal system and areas related to motor control.
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The business end, muscles.
There are approximately 640 skeletal muscles in the human body that attach to bones and tendons and can be moved voluntarily or reflexively. In addition, there are smooth muscles found in internal organs and cardiac muscles found only in the heart, both of which are involuntary.
While there is enough complexity in muscles to fill a couple of books, for our purposes, we can see them as simple levers with a range of movement that imparts force or changes the attached bone, limb, or body part position.
As a simple example, here we have the deltoid muscles in your shoulder, the bone structure underneath, and the range of motion in one plane (raising your arm sideways). The muscle contracts, and due to its strategic attachment to the bone via tendons (approximated in green), movement is then generated.
The Primary motor cortex
It sure would be convenient to have a place where all these muscles could be controlled, and the primary motor cortex (PMC) seems to do just that, albeit simply. Stimulation of this area generates jerk-like movement, so it is a far cry from the smooth, controlled, and seemingly automatic movement we generate. For that, we’d need other functions and areas, but it’s not a bad place to start our system view.
