How do horses sleep standing up?

It is a well-known fact that a horse can sleep standing up, but why? The reason lies in its nature as an animal of prey, and as such, it must always be ready to escape.
But the reasons how it actually manages this are more complicated. One is neurological and the other is anatomical in nature.
The horse has favored the archaic parts of the brain which allow for a better control of the limbs, both when resting and in motion. It is also able to do this in a state of drowsiness.
From an anatomical point of view, we can clearly say that having four limbs instead of two helps the horse maintain its balance while looking at its skeletal structure, we can also note that the horse does not have straight legs and it’s as if they were columns.
So, the horse is able to block, through special ligaments, these joint angles and therefore overcome the force of gravity and minimise the muscle strain.