Man is a sun;
and his senses are the planets.
The previous two senses observed the body's boundaries, the body's internal state and the space it takes up. The sense of movement, or of muscles, enables you to perceive your body's movements and posture. Your body – limbs, eyes, mouth, tongue, forehead, chest – is never still. All these movements are perceived, and very accurately, too. You can perceive a 0.038 degree turn of the elbow. Not only do you perceive your movements, you are also aware of the exact position of your limbs and all the other moving parts of your body. At any given moment, you know exactly where your arms and feet are. This is essential information; if you are going to execute a new movement, you have to know where the movement is to begin. You don't even have to think about this, the sense of movement is always present.
The muscle sense is situated in spindle-shaped receptors in the muscles, which measure the degree of tension in the muscle fibres. There are similar receptors in the tendons. The bending and stretching of the limbs is perceived by receptors in the joint tendons and in the surrounding tissue.
Your sense of movement is primarily focused on perceiving your own body, but you often also use it to observe things around you. In observing moving objects, your sense of movement works together with your sense of sight, so that you can see the type of movement taking place and estimate the speed of the moving object. In order to determine the object's shape, your eyes follow the outline of the object and shift to and from details that attract your attention. Painters use this roving habit of eyes to guide you through their painting along a chosen course. The movements and shapes are observed by the movement sense in the eye muscles, but the eye itself only observes the colours.
You can also perceive the movement of a branch in a tree with your muscle sense, by imitating the movement with your arms. You could also imagine the movement, and imagine how your eyes or arms would likewise move. This is called sensorial fantasy or muscular imagery, and you can apply it whenever you want to observe and imitate shapes and movements. Think about: the gait of a horse, how a cow or a pig lies down, the motions of leaves, the arrangement of branches in different trees, and so on. Movement and feeling are connected. This is evident in our body language: the welcome indicated by open arms, the dismissal expressed by a throw-away wave of the hand, and so on.
The muscle spindle: the muscle sense organ
Take a piece of paper and a pencil. Close your eyes, or ask someone to blindfold you. Draw a house, or a three-master. The first time, draw it as you would normally draw, occasionally lifting your pencil off the paper. Then draw it again, but keep the pencil on the paper all the time. You could also do this exercise on a blackboard, so that others can observe you as you draw.
Ask someone to blindfold you and to put your arm in a certain position. Describe the exact position of your arm, which muscles are activated and which are not. Then let someone change the position of your arm just slightly. Again, describe the position of your arm and the muscles used, and describe the changes that you perceive in your arm.
Split into two groups. Form rows, facing each other, and put your hands flat against the hands of the person opposite you. Make circles and other movements with your hands, varying the pressure on the other's hands. Describe what you feel: the pressure, tension, relaxation and movements.
Describe the motion of a moving organism, either human or animal. What is the motion like, which parts of the organism are moving, could you imitate the movement?
Stand in front of a large object and observe it while someone else observes your eyes. Ask this person to describe your eye movements.