What parts of muscle contraction are missing from the model? Describe why these parts are important to the muscle contraction process.

Explanation:

The model only shows the sensory pathway of the reflex arc and does not show the motor pathway.  The neuron loop / circuit is incomplete and therefore it does not show how Zoe would react to the nail in her leg.

When the sensory pathway carries the signal to the brain about the pain in the leg, the brain process the information and sends feedback to the muscles through motor neurons ‘telling’ the muscles how to react. The motors' neuron causes the muscle to contract in such a way that the leg moves away from the nail.

this would be called the responsiveness