Credit: via Wikipedia [see link]That's one of my favourite pictures from med school. The motor homunculus.
Control of our feet and leg muscles don't take up much brain. It's all about the hand and face. But that bit of brain is the vital processing link that keeps up upright.
Like balancing a broom on your finger. Standing upright on two feet is inherently unstable.
A modest breeze could knock us off balance if our control system switched off.
Our centre of gravity is the point at which we could balance our whole human body. Theoretically like that broom on our finger.
In most people it’s somewhere near the bottom of our spine, in the middle of our back.
Balancing makes me think more of a seesaw. Rather than us pushing straight down against gravity.
Particularly if I think of standing on one leg.
Muscles pull to balance us upright like the on two sides of a seesaw. Balancing around the pivot point of one foot (or two feet together).
A small sway from upright quickly shifts our centre of gravity beyond the outline of our feet.
Once that happens, gravity’s downward pull accelerates us quickly.
Our body races toward the centre of the Earth.
We move further from upright.
Milliseconds count.Without our control system, we very quickly fall.
And BANG, hit the ground.
The slapstick robot falls on YouTube show the moment the robot centre of mass moves outside of the robot footprint.
To stay upright, the correct part of our motor cortex must fire quickly.
That very first force must be countered.
The electricity of life fires!
Down our spinal cord.
Along super thin nerve cells.
Hitting an exact target muscle.
Muscle fibres pull.
Nerve, nerve, nerve, muscle, bone, joint...
Is it enough..?
Corrective forces push through our feet against the ground.
Milliseconds ticking by..
Further from upright = need more force.
Three possible outcomes hang in the balance:
1.
Quick enough: we adjust and stay upright. Phew! Imperceptible to our conscious brain. 1000s of micro-adjustments EVERY minute of the day.
2.
Not quite quick enough: At a certain point our legs and footprints need to move wider. Our centre of gravity MUST stay within our footprint.
3.
Too late: Our muscles can’t generate enough force. We can’t correct. We're too late. We fall. And BANG! ...hit the ground.
Tightrope walkers These guys must keep their centre of gravity balanced over the width of a rope. All 1’s, no 2’s or 3’s.
Catching ourselves is all about keeping our centre of gravity over our feet.
Our control system must act in a split second to keep us upright.
Milliseconds count.
The simple act of standing relies on our remarkably complex control system of sensors, brain and muscles.
Hopefully your day is filled with mostly
'Quick enoughs'. More 1’s than 2’s or 3’s.
