Can you explain how skin affects balance?
By Carol Montgomery, GCFP
It is commonly known that loss of joint range of motion in the foot, ankle, hip and spine can impact one’s balance1-3, especially when trying to walk across an uneven parking lot, the backyard, down a gravel driveway or climbing up the stairs. But how can the skin on your lower leg impact balance? And what if you have been told that you have “peripheral neuropathy” …a symptom and a disease process where sensory nerves (peripheral nervous system) transmit information from the skin and muscles in your legs and arms, to the spinal cord and brain (central nervous system), have been damaged. Radiation/chemotherapy, poor blood supply and long-standing high blood sugar levels (diabetes), vitamin deficiency, history of trauma or a chronic condition of cellulitis, a deep infection of the skin that when healed, changes the texture of the skin, all alter the pathway of sensing touch and the feeling of our skin.
“I can’t feel my feet or below my knees” is, unfortunately, a common complaint and symptom reported by many who are given the diagnosis of peripheral neuropathy. Decreased sensation, numbness, burning, and shooting pain can also be present in one or both legs or even in certain areas of one foot or lower leg. For some, this diagnosis and ongoing feeling may seem hopeless and scary. Many people do not know that peripheral nerves connecting our legs and arms to the spinal cord and brain have the capacity to regenerate. It is not a fast process, 1 mm/day and can take up to 3-4 months depending upon the extent of the damage and if certain conditions are met4: nutrition (vitamins and avoidance of certain foods), nor
mal blood sugar levels and the absence of infection are the basics. And yet for some people, nerve regeneration is not possible because they have let their condition go too long or the damage has been too great. The sensations in the lower leg can be progressively distorted from the peripheral nerve damage and can cause a person to mis-step and even fall. Falling then becomes another condition that many fear. Not just in the US, but globally, falls are a major public health problem and the financial costs from fall related injuries are significant.5
The anatomy of skin and sensation: somatosensory receptors
To help reduce the risk of fall for a person who has peripheral neuropathy we need a brief understanding of the specialized skin cells or sensory receptors that receive information from the environment and transmit that information along a predictable pathway to the spinal cord and brain. The sensory neuron is not just one nerve but many millions of nerves “packaged up” like a box of uncooked thin spaghetti noodles. Each “box” of sensory neurons is dedicated to extracting highly specific and localized information from your contact with the environment. At the end of each “spaghetti noodle”, the sensory neuron is connected to four categories of tiny specialized receptors or nerve endings: mechanoceptors (detect mechanical sensations or differences in pressure), chemoreceptors (detect chemicals that are responsible for pain and itching), photoreceptors (detect light), and thermoreceptors (detect changes in skin and blood temperature).
Mechanoreceptors play a role in keeping us upright against gravity by recognizing and feeling touch, vibration, pressure and tension in the skin. Imbedded within the skin are six different kinds of mechanoreceptors that sense changes in the skin. Normally, these mechanoreceptors work together sending their unique information along their dedicated sensory neuron to the spinal cord and then to the brain. The brain receives the message that something is touching the skin at a precise location, intensity and duration of the specific mechanoreceptor that sent the message. The brain can then make informed decisions about what should happen next, such as, pick up your foot, move away from cold, swat that fly, don’t stand on the snowy concrete in your bare feet, press down with your foot, etc.
The power of the brain lies in the parallel action of millions of cells, each doing something different; to understand the brain we need to understand how its tasks are organized and how individual neurons carry out those tasks.6 – Esther P. Gardner
Types of Skin Mechanoreceptors7:
Located in the superficial or shallow layers of skin (epidermis)
Merkel’s disks: detect light touch or pressure that allows the location of touch to be pinpointed, sense rough and change in textures
Meissner’s corpuscles: detect very fine light touch, low frequency vibration, a twist or bend in the skin, changes in pressure, motion.
Krause’s end bulb (also a thermoreceptor): detect cold.
Located in the deeper layers of skin (dermis)
Ruffini endings: detect stretch, deep pressure and warmth
Pacinian corpuscles: detect deep and transient pressure; high frequency or sudden changes in vibration, also found in the bone periosteum and joint capsules
Located all over the body: skin, muscles, fascia, joints, blood vessels, bones, and internal organs.
Nociceptors (means sensitive to harmful or painful stimuli): detect signals from damaged tissue or extreme distortion that threatens to damage tissue; their signals reach pain centers in the brain.
In peripheral neuropathy, the mechanoreceptors located in epidermis or the top layer of skin are not only less in number, but they are no longer strong, thick cables.8 It’s like the “spaghetti noodle box” has been opened and scattered on the floor. The ability to sense light pressure and find touch is markedly diminished or absent. It also takes a lot more stimulus or higher intensity to sense changes in temperature and vibration. The presence of excess glucose or sugar in the blood and chronic inflammation due to cellulitis or diabetes causes the mechanoreceptors to die and the ends of the nerves retract back down into the dermis.9
The brain and balance
In peripheral neuropathy, the mechanoreceptors in the top layer of skin that allow you to sense and discriminate light touch, texture, and temperature are gone and may not be coming back. When this happens, the brain and spinal cord do not receive accurate information about the lower leg and will not signal the muscles in the trunk, hip and lower leg to pick up the foot when there is an object on the floor, a step to clear or navigate uneven ground. The brain’s image of the foot may be interpreted as small thick tree stump and the normal reflexes, that should occur in the spinal cord that keep you from falling, will not be stimulated. The equilibrium reflex is out of your conscious control and is evident when you see someone quickly pick up their foot and place it down again as the brain’s attempt to abort a fall.
The foot feels the foot when it feels the ground. -Buddha
If you have peripheral neuropathy or you want to help a person whose sensation is markedly distorted, think DEEP PRESSURE. Understand that deep pressure DOES NOT mean “deep tissue massage”. In order to stimulate the mechanoreceptors located in the dermis of the foot and in the joints of the foot and ankle, one must apply a gradual, non-painful and sustained pressure for at least 3 seconds followed by a complete release of the pressure. This application of deep pressure is not done randomly. Using a skeletal picture of the foot and lower leg, one must “map out” the toes, foot and lower leg. In other words, the pressure applied feels like a firm, but non-painful squeeze of the skin and underlying tissue into the bone. In the brain, stimulation of the deeper layer of mechanoreceptors can transform the image of the foot from a tree stump into foot that allow the possibility of natural reflexes be activated that could keep you safe if you get off balance.
GAIT: Activating Your Human Potential
In somatic education, we use a variety of movement-based platforms that activate these deeper mechanoreceptors. In addition to the above exercise, have a look at these two videos. One is using a movement process from the Bones for Life curriculum used in our Gait for Human Potential workshops. Lying on the back one can use the foot on the wall to stimulate the deeper mechanoreceptors of the foot, leg and trunk. The same movement process can also be adapted in sitting.
The second video is a very clever way to restore the normal joint movement patterns of the trunk, hip, knee, and foot. Most people don’t know that foot numbness and poor self-image of the foot translates to poor or dysfunctional movement patterns in the hip and trunk. In this video, the stroking of the leg with the hand is not intended to re-map the foot or lower leg. But it does offer the possibility of restoring the coordinated movement patterns of the trunk and hip. Demonstrated while sitting of the floor, this same movement, with awareness can also be done in sitting and then advanced to standing.
1 Jung H, Yamasaki M. Association of lower extremity range of motion and muscle strength with physical performance of community-dwelling older women. J Physiol Anthropol. 2016;35(1):30. Published 2016 Dec 8. doi:10.1186/s40101-016-0120-8
2 Ankle dorsiflexion may play an important role in falls in women with fibromyalgia
Goes S.M., Leite N., Stefanello J.M.F., Homann D., Lynn S.K., Rodacki A.L.F.
(2015) Clinical Biomechanics, 30 (6) , pp. 593-598.
6 Kandel ER, et.al; Principles of Neuroscience 5th edition; McGraw Hill Companies:2013 p. 456.
7Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001. Mechanoreceptors Specialized to Receive Tactile Information. Available from: https://www.ncbi.nlm.nih.gov/books/NBK10895/
8 Chia‐Tung Shun, Yang‐Chyuan Chang, Huey‐Peir Wu, Song‐Chou Hsieh, Whei‐Min Lin, Yea‐Hui Lin, Tong‐Yuan Tai, Sung‐Tsang Hsieh; Skin denervation in type 2 diabetes: correlations with diabetic duration and functional impairments, Brain, Volume 127, Issue 7, 1 July 2004, Pages 1593–1605, https://doi.org/10.1093/brain/awh180
9Alsunousi, S., & Marrif, H. I. (2014). Diabetic neuropathy and the sensory apparatus “meissner corpuscle and merkel cells”. Frontiers in neuroanatomy, 8, 79. doi:10.3389/fnana.2014.00079