Temporal unfolding of sequences

As far as what starts a motor action - I see the need to look at this from a system point of view.
In the beginning the lizard brain explores the body through babbling in all the motor circuits.
As this process continues the cortex learns the most direct connections to the somatic cortex.
As time goes on maps between the motor and the sensory cortex starts to fill in with learned patterns.

Later, when we have explored and learned the world, we sense more of the world and this activation diffuses through the related maps.

Meanwhile - the frontal lobe has been learning body sensors and the motor programs that have resulted in rewarding activity.
This learning also spreads to related maps.

Fast forward to a critter that has explored the environment and learned the rituals that keep it alive.

Now we have the senses signaling what is around the critter. Likewise - we have the body sensors signalling internal needs. This might be thirst or hunger or sexual or shelter or boredom (need to explore some more).

As these activations spread from map to map they may meet somewhere in the middle.
One direction is feedforward and one is feedback. Where the two meet in the middle that map now has two activation signals and is strongly excited. This enhanced activation will ripple both up & down the maps, one direction to enhance attention and the other to add voting on the selected motor program and start it running.

The is the essence of the global workspace theory.