As niels said, they have all induction motors, some advanced kitchen equipments has also a safety coupling.
For instance if you want crush nuts on your smoothie but the nuts are too hard to crush by the baldes, safety coupling (automatic engagement) disengage the motor and the driven shaft to protect sensitive components of motor, baldes or ... .
They also have another coupling in serie with the safety coupling, it is called the magnetic coupling (only in recent applications) to couple the motor and the driven shaft, as far as you keep pressing the button, friction disc of magnetic coupling get engage with driving shaft (motor) and the driven shaft (blades). Old food processors use another type of conventional coupling. If you can drive the motor manually by rotating it with your hand it's not a magnetic coupling.
At the driven end of magnetic coupling there is a crown wiel (negative or female) and a male part at the top of driven shaft which is connected via a polymer rod to the baldes, this maple and female part fit together to complete the the torque transmission.
There exist many variants of mechanisms, but they share the same principal. All of them have at least an induction motor, a coupling and blades.