Musculoskeletal System Functions and Anatomy

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The musculoskeletal system is the body's support structure. It is a matrix of bones, muscles, and joints that provides stability and protection and allows you to move. The musculoskeletal system is dynamic and constantly remodeling itself to keep you healthy.

Research shows that up to 40% of the musculoskeletal system's load-bearing capacity is lost within weeks of inactivity. The musculoskeletal system weakens with age, too, increasing the risk of injuries and musculoskeletal diseases like osteoarthritis. Regular exercise throughout your life is crucial for keeping your musculoskeletal system healthy.

This article takes a closer look at the function and anatomy of the musculoskeletal system. It details a variety of conditions that can affect this system, along with tips to keep your musculoskeletal system healthy.

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What Is the Musculoskeletal System?

The musculoskeletal system, also known as the human locomotor system, is the framework of the body. It is controlled by the nervous system, and comprised of bones, muscles, joints, and the many connective tissues that bind them together.

Among its many important functions, the musculoskeletal system:

  • Gives your body shape
  • Supports the body's weight
  • Allows you to move
  • Shields vital organs from impact damage
  • Stores essential minerals like calcium and phosphorus, which are crucial for bone and cell maintenance
  • Produces red and white blood cells via bone marrow
  • Operates breathing (respiration) via muscle contractions

The musculoskeletal system is constantly regenerating throughout your life, and its health is profoundly influenced by physical activity. Living an active lifestyle not only enhances musculoskeletal functions, but also protects against musculoskeletal diseases.

Anatomy of the Musculoskeletal System

The musculoskeletal system is an interconnected network of features that each boast their own structures, functions, and roles. To understand how the musculoskeletal system works as a whole, you will need to be familiar with its parts.

Bones

There are 206 bones in the adult human body. Bones consist of a hard outer part made of proteins (mostly collagen) and hydroxyapatite (mostly calcium and other minerals). The inner portion of bone, called trabecular bone, is softer than the hard outer cortical bone, but it still is necessary for maintaining bone strength.

While the structure of all bone is the same, the bones perform various functions in the body:

  • Bones provide structural support for the body.
  • Bones form a protective armor around organs.
  • Bones store the majority of calcium and phosphorus, which are essential for bone, teeth, and cell health.
  • Bones have an inner cavity that contains bone marrow, where red blood cells, white blood cells, and other components of blood are produced.

Bones undergo a process that is known as remodeling. Bone remodeling is a continuous process whereby old bone is gradually replaced by new bone. About 25% of trabecular bone and 3% of cortical bone are removed and replaced through the remodeling process each year.

Muscles

There are two kinds of muscle that are part of the musculoskeletal system: skeletal muscles and smooth muscles. The third type of muscle, cardiac muscle, is not part of the musculoskeletal system.

Skeletal muscles are:

  • Bundles of contractile fibers, meaning that they move various parts of the body by contracting
  • Attached to bones and positioned in opposing groups around the joints. For example, muscles that bend the elbow are positioned opposite muscles that straighten the elbow.
  • Controlled by the brain, operating voluntarily under a person's conscious direction

Smooth muscles are:

  • Involved in certain bodily functions that are not under a person's control
  • Located around some of the arteries and contract to adjust blood flow
  • Located around the intestines and contract to move food and feces along the digestive tract
  • Controlled by the brain, but not voluntarily. The engagement of smooth muscle is based on bodily needs, not conscious control.

There's more to muscles than keeping you strong. When you exercise, your skeletal muscles emit proteins called myokines that:

  • Regulate body weight
  • Reduce inflammation
  • Increase insulin sensitivity
  • Suppress tumor growth
  • Improve cognitive function

Cartilage

The ends of the bone that form a joint are covered with a connective tissue called cartilage. Normal cartilage is smooth, flexible, and tough. Cartilage is composed of collagen, water, and proteins called proteoglycans.

Cartilage serves to:

  • Absorb shock during activities like running, jumping, and other forms of impact
  • Reduce friction with the movement of a joint, preventing bones from rubbing together
  • Enhance the resilience of bones and protect them from wearing down

Cartilage lacks lymph nodes, blood vessels, and nervous tissue. While this makes cartilage resilient, the limited blood flow makes it less capable of repairing and renewing itself. Thus, disorders marked by the breakdown of cartilage, like osteoarthritis, can be severely painful and disabling.

Joints

The joints are where the ends of two or more bones come together. While there are joints that do not move, such as the joints between the plates of the skull, most joints are capable of facilitating movement. There are two types of joints that facilitate movement: synovial joints and cartilaginous joints.

Synovial joints are:

  • The most common joint in humans
  • Able to slide without friction, due to the slippery, lubricated cartilage that covers the ends of each bone at the joint
  • Numerous in form and include ball-and-socket, condyloid, gliding, hinge, pivot, and saddle joints. The elbow joint and hip joint are examples of synovial joints.

Cartilaginous joints are:

  • Completely united by cartilage where the two bones meet
  • More rigid than synovial joints. Cartilaginous joints lack a joint cavity, which limits their movements. The pelvis is an example of a cartilaginous joint.
  • Able to withstand high-impact activities like running and jumping due to the cushioning cartilage provides

Joints are enclosed in a joint capsule which has a lining (synovium). Cells of the synovium produce synovial fluid which nourishes the cartilage and helps to reduce friction during movement.

Ligaments

Ligaments are tough, fibrous bands of tissue that connect bone to bone. They are composed of collagen and elastic fibers, which give them a rubberband-like stretchability.

Ligaments:

  • Surround and support the joints, allowing movement in specific directions
  • Ensure the bones in a joint do not dislocate or twist too much
  • Contain sensory nerves that monitor data from movements, and help regulate the stiffness of joints based on that data

Ligaments are particularly vulnerable to damage caused by overuse, trauma, and disease. While they are capable of self-healing after an injury, the process tends to be slower compared to muscles and bones.

Tendons

Tendons are similar to ligaments, except rather than connecting bone to bone, tendons connect muscle to bone. These tough, fibrous bands of tissue are primarily made of collagen.

Tendon's primarily perform the following functions:

  • Absorb the forces that muscles generate upon impact
  • Evenly transfer those forces to bones
  • Protect muscles from injury

Tendons are usually found within a sheath (the tendon sheath), which allows them to move friction-free. A tendon sheath has two layers: the supportive and protective fibrous tendon sheath, and the synovial sheath, which produces synovial fluid to lubricate joints.

Bursae

Bursae (the plural form of bursa) are small, fluid-filled sacs that:

  • Cushion the spaces between the bones, tendons, and muscles near joints
  • Are mostly found next to large joints, such as shoulder, elbow, hip, and knee joints
  • Minimize friction between these structures
  • Help absorb shock upon impact

Bursae vary in size depending on their location. The largest bursa in the body is the subacromial respective subdeltoid bursa, located between the acromion, deltoid, and the rotator cuff tendons of the shoulder.

What Health Conditions Affect the Musculoskeletal System?

Musculoskeletal conditions are the leading cause of disability worldwide, affecting at least 1.7 billion people. There are more than 150 musculoskeletal conditions, including the following:

Conditions Affecting Bones

Musculoskeletal conditions affecting bones include the following:

Osteoporosis is a condition in which bone density decreases, resulting in weak, brittle bones. People with osteoporosis have a greater risk of bone fractures. Most people with osteoporosis are post-menopausal women and men with low testosterone.

Osteopenia is another condition marked by low bone density. Unlike osteoporosis, in which bone density decreases over time, most people with osteopenia never developed peak bone density to begin with. This may be due to genetic reasons, or conditions like celiac disease that affect the body's ability to absorb calcium.

Fragility fractures affect roughly half of all women and one-quarter of all men at some point in life. Fragility fractures are fractures that occur when a person falls from standing height or less. An injury like this means that your bones are weaker than normal, typically due to another underlying condition like osteoporosis. The hip, spine, and wrist are the most common sites of fragility fractures.

Traumatic fractures are fractures caused by force. They can happen to any person of any age, not just people with low bone density. Traumatic bone fractures are commonly caused by falls from higher heights, motor vehicle accidents, and direct blows. Traumatic fractures can happen suddenly, or they can occur over time (stress fractures) due to activities like running.

Conditions Affecting Muscles

The following musculoskeletal conditions affect muscles:

Sarcopenia is the involuntary loss of muscle strength and mass, most often due to aging and lack of physical activity. Beginning at age 30, the body naturally starts to lose about 3% to 5% of muscle mass each decade. While this is normal, poor nutrition and lack of exercise can expedite muscle loss and result in sarcopenia.

Muscle strain occurs when a muscle is overstretched, causing muscle fibers to tear. This is often called a "pulled muscle." Muscle strains range from mild, in which the muscle is tender but has not lost strength, to severe, in which the muscle separates from the tendon and loses function. Muscle strains most often occur during contact sports like football, and sports that require quick starts, like tennis.

Muscular dystrophy is a group of genetic muscular diseases that causes progressive muscle loss. Muscular dystrophies worsen over time. Eventually, many people with muscular dystrophy lose their ability to walk. Some muscular dystrophies appear in childhood, while others start later in life.

Conditions Affecting Joints

Various musculoskeletal conditions affect joints:

Rheumatoid arthritis is a chronic inflammatory disease in which the immune system attacks its own tissues, causing inflammation around joints and sometimes organs. The condition causes pain, stiffness, and swelling in the joints. Most people with rheumatoid arthritis start to notice symptoms in their 30s to 50s.

Psoriatic arthritis is another form of inflammatory arthritis that affects some people with psoriasis, an autoimmune skin and nail disease. Psoriatic arthritis causes joint pain, stiffness, and swelling, most commonly in the fingers and toes. There are several forms of psoriatic arthritis, such as symmetrical polyarthritis, which closely resembles rheumatoid arthritis.

Gout is an inflammatory disease that occurs when there is too much uric acid in the body. This causes uric acid crystals to build up in joints. Usually, flares affect one joint at a time. Gout flares usually start suddenly and last for days to weeks at a time. Flares are followed by remission when there are no symptoms.

What Is the Most Common Musculoskeletal Condition?

Low back pain is the most common musculoskeletal condition, affecting at least 619 million people worldwide. It is the leading cause of disability and is most prevalent in women ages 50 to 55 years. Low back pain may begin suddenly or develop gradually. The exact cause of low back pain is unclear in about 90% of cases.

Keeping Your Musculoskeletal System Healthy

You can't prevent every musculoskeletal injury or disease. But you can take steps to keep your musculoskeletal system strong and reduce your risk of preventable conditions:

  • Quit smoking: Smoking is linked to numerous musculoskeletal conditions, including low bone density, increased fracture risk, and increased risk of rheumatoid arthritis and other joint diseases.
  • Stretch: Stretching reduces muscle tension, making your muscles, joints, and ligaments more resilient to stress and reducing your risk of injuries. Stretching also increases blood flow, helping your muscles rebound quicker from injury, inflammation, and exercise.
  • Strength train: Strength training increases bone density and muscle mass and reduces the risk of osteoporosis. Strength training also improves balance, reducing the risk of falls.
  • Keep blood pressure and cholesterol at safe levels: Cardiovascular and musculoskeletal health are closely intertwined. Having high blood pressure and high cholesterol both prolongs inflammation and makes it difficult for the body to recover from it.
  • Maintain a healthy weight: People with increased body mass indexes (BMIs) have a greater risk of lower limb injuries, especially to the knees and ankles. They are also less likely to engage in regular exercise, which further increases the risk of poor cardiovascular health and widespread inflammation.
  • Get proper sleep: Poor sleep is a common problem in people experiencing musculoskeletal conditions. Research shows that people with both musculoskeletal conditions and sleep issues experience more severe pain, greater disability, and are less physically active compared to people with musculoskeletal conditions who get good sleep.
  • Practice good posture: Poor posture can have a profoundly negative impact on your musculoskeletal health over time. People with poor posture are more likely to have back pain, spinal dysfunction, and joint degeneration.
  • Protect your body: Preventable injuries due to vehicular and workplace accidents are a major cause of musculoskeletal injury. Wear a helmet when doing activities like horse riding, rock climbing, or bicycling, and wear a seatbelt any time you are in a vehicle.
  • Ask about your medications: Many medications can result in bone loss over time, and increase the risk of osteoporosis. When prescribed a medication, ask your provider if it is associated with bone loss. If so, your provider may also prescribe a medication that increases the rate of bone formation in the body.

Summary

The musculoskeletal system is an intricate network of bones, muscles, tendons, ligaments, and other connective tissues. In addition to giving your body its shape, the musculoskeletal system functions like armor, protecting your organs and preventing injuries. Some musculoskeletal conditions, like osteopenia, cannot be prevented. Others, like osteoporosis, can be slowed or prevented by keeping your musculoskeletal system healthy.

You can reduce your risk of musculoskeletal issues by making lifestyle changes like exercising regularly, getting good sleep, and practicing good posture.

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Carol Eustice

By Carol Eustice
Carol Eustice is a writer covering arthritis and chronic illness, who herself has been diagnosed with both rheumatoid arthritis and osteoarthritis.