Somesthesia, Yoga -- Physiological aspects, Sensory receptors, Sensorimotor integration
Most of us must learn to feel, as an artist learns to see in order to draw. All of the physiological processes of feeling and seeing can happen with no awareness at all, when the mind is wandering elsewhere. Essential to the learning process is awareness, prajna. With no awareness, we have unconscious sensations, not conscious perceptions.
The light striking the retina of the eye is the first step in seeing. A great deal more happens in the visual part of the cerebral cortex, at the back of the head, and along the pathways to it. The conscious experience of seeing is typically correlated with neural activity in the visual part of the cerebral cortex. Probably the whole brain is re-organized in the process of becoming an artist.
Similarly, body-feeling or somatosensation starts in receptors in the skin, muscles, tendons, ligaments, and joints. Pathways through the spinal cord to the brain communicate sensations. At the same time, the neural activity is combined, as light sensations are combined into lines and shapes before we see a scene. The process of learning to feel brings awareness, prajna, to these combinations of body sensations and to the whole experience of feeling.
We each learn individually how an asana feels. For example, in tadasana, I feel the pressure on the soles of my feet, the muscle feel of straightening the hips and lifting the chest, and the skin stretch in the arms and hands. What do you feel? To stand upright, we also use vision, aligning ourselves to the trees or walls around us. The receptors of the inner ear communicate further gravitational information along pathways to the eyes, neck, and spinal cord.
Practicing the various asanas provides a framework for learning to feel, as drawing provides a framework for learning to see. An asana is typically experienced as a whole, rather than as a scattering of sensations. That whole experience is formed as the body sensations are combined in spinal pathways, the brainstem, and the brain. We will start with the receptors in the skin, familiar as touch, because their separate qualities tend to be easier to perceive.
McCollum, Gin, "Body Sensations: Neurobiology, Learning to Feel, and Sensory Teamwork" (2015). Mathematics and Statistics Faculty Publications and Presentations. 190.