Muscle spindles- sensory organs of our muscles

Our muscle spindles are the sensory organs of our muscles; they literally "set the tone" of our body and therefore we can say that we are:
holding generational memory in our muscle spindles.
Families can often be "of one tone" and tone can be described as a readiness to move.

When our muscle contract and release the muscle spindles are affected and they contract, when our muscles are resting and release when the muscle fibers are contracting! Each spindle senses a bundle of fibers at once.
If , say we were to tune into our spindles and tone them( higher tone), this would release the muscle fibers - and were we to bring their tone down, it affects the muscles, by bringing up their readiness. So a calming, centering preparation, before an action, actually supports the strength and responsiveness of the muscles ( as say in Aikido).
Visualisation is a technique that employs this awesome organ: without moving, one prepares and tracks possible movement in the body/through the muscles, one changes tone. In Body-Mind Centering we differentiate visualizations that use the visual cortex to imagine and these tonal changes.
Next time, as you prepare to sit for meditation or begin your Yoga practice - tune into the spindles situated between the muscle fibers and instead of relaxing your muscles- tone these spindles and feel your body adjust it's tone; through the spindles you will facilitate balancing your tone.

http://www.neurosoma.com/musclespindle.html