Biology of movement

In line with my previous posts on disabilities I thought it would be nice to explore how normal physical movement occurs.The two major systems mainly concerned with healthy movement are the skeletal and muscular system. The skeletal system comprises of bones and joints which aid movement and provide attachment points for muscle. Whilst the muscular system consists primarily of muscles.Together they form the musculo-skeletal system.ms system

Basic components of the musculoskeletal system include: collagen a fibrous protein which aids bone flexibility, hydroxyapatite made up of calcium, phosphate and hydroxyl ions (Ca5(PO4)3(OH)), bone cells that remove (osteoclasts) and replace (osteoblasts & osteocytes) weakened sections of bone, muscle cells (known as myofibers), nerves, blood vessels and connective tissue.

How the musculo-skeletal system is maintained:

In other for the musculo-skeletal system to carry out its daily action its most basic unit (the cell) must be healthy. Cells are the basic living unit of every system in the human body, certain cells differ in structure to aid their function in a particular system e.g. muscle cells, nerve cells. All cells, however, share certain characteristics in common including a need for oxygen, glucose, amino acids, regulation of homeostasis and excretion of waste products.

194px-Alveolus_diagram.svg
“Alveolus diagram” by LadyofHats – self-made(extracted from Image:Respiratory system complete.svg) (duplicate of Image:Respiratory system complete en.svg). Licensed under Public Domain via Wikimedia Commons

A cell’s oxygen supply is replenished by the respiratory and circulatory system. Oxygen is inhaled through the respiratory system, it diffuses from the tiny air sacs in the lung known as the alveoli  into the capillaries (the part of the circulatory system closet to the cells). From the capillaries it gets into the circulatory system and moved directly to the cells. Oxygen diffuses from the capillaries into the cells where it is used for cellular respiration (specifically aerobic respiration) a process that releases energy known as ATP from the breakdown of glucose and this takes place in the cells mitochondria. The respiratory system and circulatory system also eliminates carbon dioxide produced during cellular respiration. It diffuses out of the cells into the blood plasma, carried to the lungs and then exhaled.

Cells require nutrition, glucose and amino acids serve as the major source of nutrition. Dietary protein is broken down in the digestive system into amino acids and are then absorbed by the small intestine. They are released by the enterocytes (cells of the small intestine) into the circulatory system which takes them to cells where they are utilized for energy production or fatty tissue formation. A similar process occurs for the production and release of glucose from dietary carbohydrate to cells in the body. Cells of the musculoskeletal system require calcium and vitamin D to function. Our diet provides a major source of calcium and vitamin D, but, the skin/integumentary system also synthesises vitamin D. Cells also produce other waste materials, some of which are water soluble and diffuse out of the cells into the circulatory system. Which transports it to the kidney a major organ of the urinary system.

Finally, the musculo-skeletal system is made to move by a stimuli/ nerve impulse from the nervous system. The somatic nervous system specifically controls skeletal muscles; it involves the activities of motor neurones (neurones are nerve cells), sensory neurones and the brain. The brain receives a signal from the sensory neurone, which is relayed to the target muscle by the motor neurones leading to acetylcholine release at neuromuscular junction, when enough acetylcholine is released muscles contract and movement is achieved.

Certain hormones from the endocrine system also influence health movement by affecting bone and muscle mass. Parathyroid hormone, cholecalciferol and calcitonin through different mechanisms regulate calcium concentration in bones; low calcium causes weak bones and excess causes brittle bones. Increased parathyroid hormone and low cholecalciferol also lead to low muscle mass and strength all these actions will negatively affect movement.

The nervous and endocrine system also affects the musculo-skeletal system indirectly for example: the brain receives a stimulus for more calcium supply to the bones, it sends a stimulus to the digestive system to increase calcium absorption and the urinary system to decrease calcium excretion, the hormone cholecalciferol also facilitates calcium absorption by enterocytes. From there it is released into the blood stream and transported to the bones.

The musculoskeletal system is protected from harm both internally and externally by the lymphatic and integumentary system respectively. The skin is a part of the integumentary system which protects us from noxious agents. The epidermis forms a tough layer of protection, it also produces melanin which absorbs UV rays and oil glands that secrete substances which serve as barriers to harmful organisms. The lymphatic system drains fluid from tissues as well as the body of toxins, waste and other unwanted materials. Bacteria and microbes picked up in the lymphatic fluid are trapped inside lymph nodes, where they are attacked and destroyed by white blood cells.

How impairments might occur from a biological perspective:

Often times an individual might have impaired movement due to a condition in a different body system. A good example is seen in patients with cerebral palsy. Cerebral palsy is a condition that impairs muscle coordination (spastic paralysis) caused by damage to the brain (part of the nervous system) prior to or at birth. It affects the motor areas of the brain hindering its ability to coordinate posture and healthy movement. Another example is stroke a condition that occurs when the blood supply to a part of the brain is cut off. It often manifests as ataxia, dyspraxia, low muscle tone, weak muscles along with other signs; essentially it compromises healthy movement. When considered from this perspective physical disabilities might seem easy to understand and manage but nothing can ever replace proper physical and medical diagnosis. This is just to explain how we move in simple terms.

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