Your nervous system is responsible for two things. It either inhibits or allows conscious or unconscious motions and sensations.  A simple analogy would be to liken it to a governor. Not a governor as in the leader of a state, but one that you would find on a car engine.
In the car engine, the governor prohibits the car from reaching max speed, by limiting how much gas you can actually pump into the car. If you’ve driven a car with a governor, you can feel the pedal stop short of how far it can actually go.
Within our bodies, we have a similar mechanism of governance. These governors are what we call the Golgi Tendon Organ (GTO) and the Muscle Spindle (MS). The MS and GTO both work as inhibitors to tell your nervous system to put the brakes on a given motion. The MS is defined as
…a proprioceptor. A sense organ that receives information from muscle, that senses STRETCH and the SPEED of the stretch. When you stretch and feel the message that you are at the ENDPOINT of your stretch the spindle is sending a reflex arc signal to your spinal column telling you not to stretch any further. This sense organ protects you from overstretching or stretching too fast and hurting yourself. 
And the GTO:
…a proprioceptor, sense organ that receives information from the tendon, that senses TENSION. When you lift weights, the golgi tendon organ is the sense organ that tells you how much tension the muscle is exerting. If there is too much muscle tension the golgi tendon organ will inhibit the muscle from creating any force (via a reflex arc), thus protecting the you from injuring itself. 
Please sign in to continue reading…