How does my body balance itself so I can do what I want to do without falling to the ground?
Gravity is the force that makes all things fall toward the earth. An object’s center of gravity is a theoretical point about which its weight is evenly distributed. For an object that has a uniform density with a regular and symmetrical shape, such as a square piece of solid wood, the center of gravity is at its geometric center. Everyone knows that if you push a square solid wooden block slowly off the edge of a table it will fall to the ground when its center of gravity is no longer on the table.
The human body is made of muscles, organs, fat and bone, each with a different density. Although the physical outline of the body is symmetrical from side to side, its shape is very irregular. The center of gravity for most people, while standing or lying with their arms at their sides is in the midline near their belly button (umbilicus). To be able to stay standing the body’s center of gravity must remain between its two feet, both from side to side and back to front, otherwise it falls to the ground. Movement of the arms or legs away from the body or bending the spine in any direction changes the body’s center of gravity. Moreover, carrying an object, especially at a distance from the body, will also change its center of gravity. Finally, for our earliest ancestors to survive within the laws of nature they not only had to stay balanced while standing, but also walking, with only one foot, and running, with neither foot, in contact with the ground. In other words, the human body is an inherently unstable object so it needs to take control to stay balanced.
It’s the job of the neuromuscular system to keep the body in position while balancing itself against gravity. Although the spinal cord provides reflexes that help it maintain its posture, it’s mainly the brain, particularly the brainstem and the cerebellum, that provides the coordinated motor patterns needed to maintain its balance. To be able to make ongoing adjustments the brain receives sensory information from mainly four sources; the pressure sensors in the feet, the sensors in the muscles, tendons and joints (proprioceptors) in the neck and the rest of the spinal column, the vestibular apparatus within the inner ear and the vision provided by the eyes.
The pressure sensors in the feet tell your brain about your body’s weight distribution relative to its center of gravity. Stand up and lean from side to side, and back and forth. Notice the difference in the pressure sensations felt from each foot with these movements, the feeling of imbalance and the immediate adjustments that must be made for you to stay standing.
The sensors in the muscles, tendons and joints (proprioceptors) in the neck and the rest of the spinal column provide your brain with information about the relative position of your head and the rest of your body. Bend your neck forward and backward and then bend from your waist in any direction. You’ll see that wherever your neck and spinal column goes so goes your head and the rest of your body as well. Notice the feeling of imbalance as your center of gravity moves away from being between your feet and how you quickly have to adjust to prevent from falling to the ground.
The vestibular apparatus within the inner ear consists of the semicircular canals, the utricle and the saccule. They send information to the brain about the speed and direction of the angular motion of your head and neck, the position of your head with respect to gravity and your motion back to front, side to side and up and down (like in an elevator). In addition, the vestibular apparatus sends information to your brain that helps to stabilize the retinal image through the vestibulo-ocular reflex. Twist your head around in different directions and you’ll feel a bit dizzy and unbalanced. Now move your body back and forth, side to side and jump up and down and you’ll see how you have to automatically compensate to stay balanced. Now, look into a mirror and focus on your eyes as you rotate your head from side to side, up and down and then in any direction and then do it as fast as you can. Notice how your eyes automatically move in the opposite direction of your head so you can keep them in focus. This is also called the doll's eye reflex (vestibulo-ocular reflex) and is used by physicians (along with the corneal and pupillary light reflex) to assess brainstem function.
Vision from the eyes provides the brain with an image of the surroundings in which the body is located. Clinical experience teaches us that with concentration, training and slow movement, vision, by itself, can often help maintain the body's balance without information from the pressure sensors, proprioceptors and vestibular apparatus. Close your eyes and begin to walk, progressively increasing the speed as able. Notice how difficult it is to maintain your balance. This is because, closing your eyes makes you totally dependent on the pressure sensors in the feet, the proprioceptors of the spine and limbs and the vestibular apparatus. Now do this exercise again, but this time with your eyes open and you’ll verify that visual cues makes it a lot easier to maintain your balance.
One of the first indications that a person may have a problem with their balance is when they accidentally fall in the shower. While taking a shower most people close their eyes to shampoo their hair and then quickly turn their head and neck and whole body to rinse off. In doing this maneuver (with their eyes closed) their brain can no longer use visual cues to maintain their balance. If a person has a condition like a sensory neuropathy (common in diabetics) which limits the reception of the sensory data from the feet, or Multiple Sclerosis, which slows the nerve impulse velocity in the brainstem, or degeneration of the cerebellum, which causes poor coordination, then they will come to realize how important their vision is for maintaining their balance when they take that first fall.
So, by using information from the pressure sensors in your feet, the proprioceptors in your neck and the rest of your spine, the vestibular apparatus in your inner ears and the vision from your eyes, your brain works to maintain your balance so you can do what you want to do without falling to the ground.
Three Questions for Mr. Darwin
- How did my body anticipate its need for and where did it obtain the information to produce and place exactly where needed, the pressure sensors in my feet, the proprioceptors in my neck and the rest of my spine, the vestibular apparatus in my inner ears and the light-sensitive tissue in my eyes so I could stay balanced?
- Even though, with much effort, the body can stay balanced with just vision, clinical experience tells us that this would not have been adequate for the survival of our earliest ancestors, so in what order did each of these sensory devices come into being while allowing them to survive?
- Where did my brain get the knowledge to know what to do with the sensory information it needs and then send out messages to my muscles to keep me balanced?
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Howard Glicksman M. D. graduated from the University of Toronto in 1978. He practiced primary care medicine for almost 25 yrs in Oakville, Ontario and Spring Hill, Florida. He now practices palliative medicine for a Hospice organization in his community. He has a special interest in how the ethos of our culture has been influenced by modern science’s understanding and promotion of what it means to be a human being.
Copyright 2018 Dr. Howard Glicksman. All rights reserved. International copyright secured.
