| Musculoskeletal system | |
|---|---|
 Features of the human activity system from the 1911 Encyclopædia Britannica | |
| Identifiers | |
| MeSH | D009141 |
| TA2 | 351 |
| FMA | 7482 |
| Anatomical terminology | |
Thehuman musculoskeletal system (also known as thehuman locomotor system, and previously theactivity system) is anorgan system that giveshumans the ability to move using theirmuscular andskeletal systems. The musculoskeletal system provides form, support, stability, and movement to the body.
The human musculoskeletal system is made up of thebones of theskeleton,muscles,cartilage,[1]tendons,ligaments,joints, and otherconnective tissue that supports and binds tissues and organs together. The musculoskeletal system's primary functions include supporting the body, allowing motion, and protecting vital organs.[2] The skeletal portion of the system serves as the main storage system forcalcium andphosphorus and contains critical components of thehematopoietic system.[3]
This system describes how bones are connected to other bones and muscle fibers via connective tissue such as tendons and ligaments. The bones provide stability to the body. Muscles keep bones in place and also play a role in the movement of bones. To allow motion, different bones are connected by joints. Cartilage prevents the bone ends from rubbing directly onto each other. Muscles contract to move the bone attached at the joint.
There are, however, diseases and disorders that may adversely affect the function and overall effectiveness of the system. These diseases can be difficult todiagnose due to the close relation of the musculoskeletal system to other internal systems. The musculoskeletal system refers to the system having its muscles attached to an internal skeletal system and is necessary for humans to move to a more favorable position. Complex issues and injuries involving the musculoskeletal system are usually handled by aphysiatrist (specialist inphysical medicine and rehabilitation) or anorthopaedic surgeon.
The skeletal system serves many important functions; it provides the shape and form for the body, support and protection, allows bodily movement, producesblood for the body, and stores minerals.[4] The number of bones in the human skeletal system is a controversial topic. Humans are born with over 300 bones; however, many bones fuse together between birth and maturity. As a result, an average adultskeleton consists of 206 bones. The number of bones varies according to the method used to derive the count. While some consider certain structures to be a single bone with multiple parts, others may see it as a single part with multiple bones.[5] There are five general classifications of bones. These arelong bones,short bones,flat bones,irregular bones, andsesamoid bones. The human skeleton is composed of both fused and individual bones supported byligaments,tendons,muscles andcartilage. It is a complex structure with two distinct divisions; theaxial skeleton, which includes thevertebral column, and theappendicular skeleton.[6]
The skeletal system serves as a framework fortissues andorgans to attach themselves to. This system acts as a protective structure for vital organs. Major examples of this are thebrain being protected by theskull and thelungs being protected by therib cage.
Located inlong bones are two distinctions ofbone marrow (yellow and red). The yellow marrow hasfattyconnective tissue and is found in the marrowcavity. During starvation, the body uses thefat in yellow marrow for energy.[7] The red marrow of some bones is an important site forblood cell production, approximately 2.6 millionred blood cells per second in order to replace existing cells that have been destroyed by theliver.[4] Here allerythrocytes,platelets, and mostleukocytes form in adults. From the red marrow, erythrocytes, platelets, and leukocytes migrate to the blood to do their special tasks.
Another function of bones is the storage of certain minerals.Calcium andphosphorus are among the main minerals being stored. The importance of this storage "device" helps to regulatemineral balance in the bloodstream. When the fluctuation ofminerals is high, these minerals are stored in thebone; when it is low they will be withdrawn from the bone.
There are three types of muscles—cardiac,skeletal, andsmooth. Smooth muscles are used to control the flow of substances within thelumens of holloworgans, and arenot consciously controlled. Skeletal and cardiac muscles havestriations that are visible under amicroscope due to the components within their cells. Only skeletal and smooth muscles are part of the musculoskeletal system and only the muscles can move the body. Cardiac muscles are found in theheart and are used only to circulateblood; like the smooth muscles, these muscles are not under conscious control. Skeletal muscles are attached to bones and arranged in opposing groups aroundjoints.[8] Muscles are innervated, whereby nervous signals are communicated[9] bynerves, which conduct electrical currents from thecentral nervous system and cause the muscles to contract.[10]
Inmammals, when a muscle contracts, a series of reactions occur.Muscle contraction is stimulated by themotor neuron sending a message to the muscles from thesomatic nervous system.Depolarization of themotor neuron results inneurotransmitters being released from thenerve terminal. The space between the nerve terminal and the musclecell is called theneuromuscular junction. These neurotransmitters diffuse across thesynapse and bind to specific receptor sites on thecell membrane of the muscle fiber. When enough receptors are stimulated, anaction potential is generated and thepermeability of thesarcolemma is altered. This process is known as initiation.[11]
A tendon is a tough, flexible band offibrous connective tissue that connects muscles to bones.[12] The extra-cellular connective tissue between muscle fibers binds to tendons at the distal and proximal ends, and the tendon binds to theperiosteum of individual bones at the muscle's origin and insertion. As muscles contract, tendons transmit the forces to the relatively rigid bones, pulling on them and causing movement. Tendons can stretch substantially, allowing them to function as springs during locomotion, thereby saving energy.
The Joints are structures that connect individual bones and may allow bones to move against each other to cause movement. There are three divisions of joints,diarthroses which allow extensive mobility between two or more articular heads;amphiarthrosis, which is a joint that allowssome movement, and false joints orsynarthroses, joints that are immovable, that allow little or no movement and are predominantlyfibrous.Synovial joints, joints that are not directly joined, are lubricated by a solution calledsynovial fluid that is produced by thesynovial membranes. This fluid lowers thefriction between the articular surfaces and is kept within anarticular capsule, binding the joint with its taut tissue.[6]
Aligament is a small band of dense, white,fibrouselastic tissue.[6] Ligaments connect the ends of bones together in order to form a joint. Most ligaments limitdislocation, or prevent certain movements that may cause breaks. Since they are onlyelastic they increasingly lengthen when under pressure. When this occurs the ligament may be susceptible to break resulting in an unstable joint.
Ligaments may also restrict some actions: movements such ashyper extension andhyper flexion are restricted by ligaments to an extent. Also ligaments prevent certain directional movement.[13]
A bursa is a small fluid-filled sac made of whitefibrous tissue and lined withsynovial membrane. Bursa may also be formed by a synovial membrane that extends outside of thejoint capsule.[7] It provides a cushion between bones and tendons or muscles around a joint; bursa are filled withsynovial fluid and are found around almost every major joint of the body.
Because many other body systems, including thevascular,nervous, andintegumentary systems, are interrelated, disorders of one of these systems may also affect the musculoskeletal system and complicate the diagnosis of the disorder's origin. Diseases of the musculoskeletal system mostly encompass functional disorders or motion discrepancies; the level of impairment depends specifically on the problem and its severity. In a study of hospitalizations in the United States, the most common inpatient OR procedures in 2012 involved the musculoskeletal system: knee arthroplasty, laminectomy, hip replacement, and spinal fusion.[15]
Articular (of or pertaining to the joints)[16] disorders are the most common. However, also among the diagnoses are: primary muscular diseases, neurologic (related to the medical science that deals with the nervous system and disorders affecting it)[17] deficits, toxins,endocrine abnormalities,metabolic disorders, infectious diseases, blood and vascular disorders, and nutritional imbalances.
Disorders of muscles from another body system can bring about irregularities such as: impairment of ocular motion and control, respiratory dysfunction, and bladder malfunction. Completeparalysis,paresis, orataxia may be caused by primary muscular dysfunctions ofinfectious ortoxic origin; however, the primary disorder is usually related to thenervous system, with the muscular system acting as the effector organ, an organ capable of responding to a stimulus, especially a nerve impulse.[3]
One understated disorder that begins duringpregnancy ispelvic girdle pain. It is complex, multi-factorial, and likely to be also represented by a series of sub-groups driven by pain varying from peripheral or central nervous system,[18] altered laxity/stiffness of muscles,[19] laxity to injury of tendinous/ligamentous structures[20]to maladaptive body mechanics.[18]
