pierre - for future reference, when your urine looks like red wine, time to go to the doctor. get better.
allison - GTOs are proprioceptors in the musculotendinous junction--they fire off electrical signals to the spinal cord in regards to tension in the muscle in question. when that tension reaches a certain threshold, they cause inhibition of the motor neurons in that muscle to reduce the tension, presumably to prevent injury from excessive tension. they're basically mechanical opposites of muscle spindles/intrafusal fibers, which initiate the myotatic reflex, i.e. respond to rapid stretching of a muscle with an involuntary contraction of that muscle.