Job's Body is again the source for understanding the impact of tai chi.  Chapter 8, "The Sense of Effort" will touch on several aspects of sensory feedback that accompanies movement.  I will be interested in what this might reveal about how tai chi describes the sense of energy movement during tai chi and the role of the gaze in providing feedback.  A current class mantra of "extend to open, release to loosen" might take on additional significance if applied to the muscle as a sense organ.  The sensory endings in the muscle spindles and the Golgi tendon organs are so sensitive that it may be more appropriate to describe their actions as "feeling" rather that just mechanical adjustment of muscle contraction or lengthening.
It is easy to take for granted the role of sensory feedback in the control of our biomechanics until we attempt to operate without that feedback.  Take the attempts to use your hand after you have slept on it in a way that causes it to "go to sleep" from a nerve impingement.  Your muscles and tendons are functional and you can see what you intend to do, but movements are clumsy at best.  Any action requiring "sensitivity" is impossible to do with any accuracy.  Try picking up a pin with a numb hand.
A wide variety of sensory input structures are needed to detect qualities such as color, texture, odor taste, pitch, volume, equilibrium, limb position, pressure, weight, density and many other such distinctions.  Our muscles are filled with sensory organs that give no conscious sensation, but provide us with the feedback to make the above distinctions.  Add to that the role of the cerebellum in interpreting the sensations, below the level of conscious awareness, and you have a mysterious feedback loop system that could be called a double black box.
I have marveled at the ability to reach into a bag with a wide variety of objects of different size, shape, weight, smoothness, density and material; and to be able to sort through them to find a single item, like a certain size screw or a rubber band.  Sometimes the items is obscured and sight is required to make the distinction.  A bag of similar screws or rubber bands could be to difficult to sort through only by hand to find one of a certain size.
How this sensory feedback relates to the practice of tai chi is hard to describe, but not hard to accept as essential to the feel of the movement.  In the learning process there is an initial phase where the mental activity of memorizing the movement gets in the way of "feeling" the movement.  Often we need to use our vision to see if we have in fact executed a proper bow stance.  Ultimately, correct positioning begins to be felt as we relax our conscious control of our movements and let our kinesthetic sense guide us.  Extend to open, release to loosen is more than a tension release of the muscle spindle but also a release into the subconscious sensory feedback loop that allows for the feel of the movement to take over.
When considering the role of the myofascial sheath as a support structure with tensegrity qualities, the metaphor of extend to engage, rotate and release to activate, becomes profoundly appropriate.
A principle of tai chi is that movement is continuous without interruption.  This can only be accomplished with circular movements of the limbs and torso, especially at the end point of any form.  Any straight line action would result in an end point signifying a stopping and starting point. At the end of any form position is an end point that must be an extension to open the frame (or any single joint) followed by rotational transition to releasing to loosen.  The entire myofascial connective tissue structure (including, tendons, ligaments and bones) is included in this extending to open; and it is at this point that a release of energy is expressed, in the "small circle," to rotate into release to loosen.

Reading Job's Body by Deane Juhan provides continuing illustrations of how amazing the human body is and how its systems work together to produce the actions, feelings and stable structures that we take for granted.
With tai chi, always on my mind, every chapter reveals amazing details that can explain how tai chi works.  Chapter 7, "Muscle as a Sense Organ" is no exception.  The anatomical descriptions are so detailed that I can only refer the reader to the book rather than try to summarize.  I may try to pull out some of this detail in my review of the book on this blog, but for today, I will just mention a few of the aspects that are presented to stimulate an interest in further exploration by the reader.
Muscle tissue does not have sensory receptors as does the skin, bone or connective tissue, but it does have the mechanisms to create a kinesthetic sense.  Muscle spindle receptors detecting the slightest stretch of a muscle fiber, golgi bodies detecting stretch and pressure on the tendons, the reticular formation in the brain sensing levels of arousal, the functioning of the eyes and ears in maintaining equilibrium and other systems all work together in reflex arcs and loops to control muscle tone, spatial awareness,  perception of self and much more.  The intricate relationships between a wide variety of sensation coming from muscle activity are coordinated in the cerebellum in order for us to function.
How tai chi is learned through repetition becomes anatomically clear as the muscle sensory capacity comes to light.  Repetition as the main method of instruction becomes more that just a class mantra.  It is only through this repetition that the individual can begin to benefit from the alignment, release of tension and the sense of equilibrium that, along with an awareness of body mind centering, may be the best definition of chi or life force.  My personal preference in referring to chi is to see it not as something that is created or even generated, but rather something that is released when it is not blocked.  I am reminded of a favorite reference in "Anatomy Trains" that the ancient Greek  philosopher/physician, Paracelsus believes that "all disease is caused by blockage".  In tai chi parlance it can be said that "the generation of chi is a release of blockage".