The major impediment to the Expressive Transducer's function is Paralysis
Even if the structures are all present, the transducer must also be able to function. The major impediment to function is paralysis.
Two kinds of paralysis are flaccidity and spasticity. Flaccid paralysis is a loss of strength in muscle movement.
A mild example (and a temporary one, I hope) is when I sleep on my arm and find it immobile in the morning.
I couldn't even make the sign for "help" in sign language because it takes two hands.
More serious examples are Infantile paralysis (which effected President Franklin D. Roosevelt) and Amy Lateral Sclerosis (which effects Steven Hawkings today).
In the latter case, speech eventually became impossible and communication must be accomplished through a man made transducer--a computer.
NOTES: See a famous person with a severe paralysis; and hear an example of a milder case of flaccid paralysis.