This article, the second in a two-part series on the skeletal system, reviews the framework and function of the musculoskeletal system and also common pathophysiology. This article comes with a self-assessment allowing you to test your knowledge after reading it


Abstract

Understanding the structure and purpose the the musculoskeletal system enables practitioners to understand typical pathophysiology and consider the most suitable steps to enhance musculoskeletal health. This article, the 2nd in a two-part series, considers the structure and function of the musculoskeletal system, reviews the structure of muscles and also joints and also identifies several of the typical pathology arising at this structures.

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Citation: walker J (2020) Skeletal mechanism 2: framework and duty of the musculoskeletal system. Nursing Times ; 116: 3, 52-56.

Author: Jennie pedestrian is primary lecturer, Nottingham Trent University.

This write-up has to be double-blind peer reviewed

Introduction

The musculoskeletal system is comprised of bones, cartilage, ligaments, tendons and also muscles, which type a structure for the body. Tendons, ligaments and fibrous tissue bind the frameworks together to develop stability, through ligaments connecting bone come bone, and tendons connecting muscle come bone. There are 206 skeletal in the adult skeleton; male and also female skeletons are almost the same, yet the female skeleton has a more comprehensive pelvis come accommodate childbirth and also the masculine skeleton is typically taller with higher bone density. The skeleton is divided into the:


Axial skeleton – comprising the skull, vertebral column and also the rib cage;Appendicular skeleton – consists of the pelvic and also pectoral girdles, and also the upper and also lower four (Cedar, 2012).

Coordinated activity is made feasible through the combination of purposeful and also synchronised movements throughout the relevant muscles and also bones to develop articulation that the joints. The configuration of the joint surface determines the movement possible. Airplane of movement encompass flexion, extension, abduction, adduction, rotation and also circumduction (Table 1).

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Joints

The joints room the articulating surfaces between two bones and may be classified follow to exactly how much activity they allow:

Synarthrosis – a fixed, unmovable joint;Amphiarthrosis – a joint in i beg your pardon some movement is possible;Diarthrosis – a freely movable share (Moini, 2020).

They can likewise be classified follow to the components that unite the bones (such as fibrous structures, cartilaginous structures and also synovial structures), as presented below.

Fibrous joints

Fibrous joints room articulating surface linked together with tough fibrous connections. One example is the suture present in the skull, wherein bones the were originally separate have end up being fused together (synostosis) to type one bone (Danning, 2019). As the suture heat does no permit activity once fusion has occurred, this is taken into consideration to it is in a synarthrotic joint.


Syndesmoses space another form of fibrous joint, in i beg your pardon ligaments and also interosseous membrane connect the share to create a for sure structure. One instance is the worse tibiofibular joint, in i beg your pardon interosseous, tibiofibular and also transverse ligaments attach the distal tibia and also fibula the the reduced leg. One more is the radioulnar joint, whereby an intraosseous membrane associate the distal radius and ulnar bones of the forearm. This can also be classified as an amphiarthrotic joint as it patent some motion to permit for pronation and also supination the the hand and forearm.

Cartilaginous joints

These joints are associated by tough cartilage in between the bone and also can be classified as primary (synchondroses) or second (symphyses).

SynchondrosesSynchondroses room cartilaginous joints formed of hyaline cartilage, and also are mainly found in the farming skeleton together the ossification centres of cultivation bone that will certainly ossify with time (synostosis), such as the epiphyseal expansion plate.

Cartilaginous joints are usually immobile but, in a rare condition in children and adolescents, the attachments of the epiphysis loosens, enabling the femoral head come slip down the femoral neck. This is recognized as a slipped upper femoral epiphysis and also often presents v the child arising an unforeseen limp (Robson and also Syndercombe Court, 2019).

In the mature skeleton, an instance of a synchondrosis is the first sternocostal share (between the very first rib and also the manubrium); all various other sternocostal joints space synovial.


SymphysesThese are irreversible cartilaginous joints, in which the skeleton are connected through fibrocartilage; interestingly, these room all in ~ the body midline (Robson and Syndercombe Court, 2019). The intervertebral discs in between the vertebral body of the spine are an instance of bones connected by fibrocartilage. These fibrous joints allow relatively restricted movement individually but extensive movement have the right to be accomplished collectively across the entirety spine.

Another example of a symphysis is the symphysis pubis in the pelvis, i m sorry helps maintain pelvic stability. In pregnancy, the symphysis pubis is softened by hormone to permit for expansion during delivery. This, together with the unfused skeleton of the baby’s skull, permits passage of the baby’s head with the bear canal.

As symphyses enable slight movement in between the articulating surfaces, they are taken into consideration to be amphiarthroses.

Synovial joints

Synovial joints room designed to allow complimentary movement of the joint and are classified together diarthroses. Characterised by a gap in between the articulating bones, they are hosted in near proximity by a joint capsule. Contraction of the infrastructure of muscles around the share maintains movement, while stability is kept through the usage of soft organization structures, such as ligaments, labra, fat pads and menisci (Danning, 2019).

The joint has an outer fibrous capsule the encapsulates the entire joint and also is attached come the periosteum, permitting movement, keeping tensile strength and helping to avoid dislocation. Inside the capsule space sensory nerve fibres, which detect pain and identify the joint’s position (Moini, 2020). The capsule’s inner class is highly vascularised and innervated by slow/small nerve fibres that, if stimulated, may reason a diffuse burning or aching emotion (Danning, 2019). This layer likewise contains the synovial membrane (synovium), which is written of synoviocytes of i m sorry there are two types:

Type A – mediate cytokine release and are associated in generating an immune solution (Robson and also Syndercombe Court, 2019);Type B – produce the synovial fluid.

Synovial fluidThe synovial fluid helps safeguard the joint from mechanical injury and also contains hyaluronic acid and lubricin (Danning, 2019). In a healthy and balanced joint, the synovial liquid is really viscous and clear, and is one of two people colourless or a pale straw colour. Water is maybe to go into the joint really easily during inflammation but, once it mixes with hyaluronic acid, the cannot leave as quickly (Robson and also Syndercombe Court, 2019) – as such, although it might only take it a few hours for the joint to swell, it can take a few days because that that ede to subside.

The synovial liquid may come to be infected through a haematogenous (blood-borne) spread out of bacteria, extension of an nearby infection or direct inoculation adhering to trauma or one invasive procedure. This is known as septic arthritis and can damages the synovium or cartilage.

Rheumatoid arthritisThis is one autoimmune inflammation arthropathy the affects the synovium. The occurs much more often in smokers and also is 3 times much more common in females than men (Ralston and McInnes, 2014).

Clinical beginning is characterised by the abnormal manufacturing of cytokines and also inflammatory mediators such as interleukin 1, interleukin 6, interleukin 15 and tumour necrosis variable (Ralston and also McInnes, 2014). This causes the synovium to end up being inflamed and also hypertrophied therefore the synovial villi come to be thickened and also fuse together to form a pannus. The pannus invades the bordering tissue (such as the cartilage, ligaments and also joint capsule), i m sorry this can lead to progressive destruction of the joint (Danning, 2019).

Rheumatoid arthritis can also impact periarticular structures, including tendon sheaths and also bursas, and also having extra-articular manifestations.

OsteoarthritisThe articulating surface in synovial joints are coated with about 2-3mm the hyaline cartilage, which offers a smooth surface and reduces friction throughout movement. This helps distribute the weight throughout the joint, to reduce friction and damage to the bone surface ar (Robson and Syndercombe Court, 2019).

Osteoarthritis is a degenerative condition involving focal lose of the articular cartilage, therefore the cartilage i do not care less efficient at protecting the end of the bone (Ralston and McInnes, 2014). Over time, this can cause bony surface to rub together on movement, resulting in pain and audible crepitus. As the bone attempts come compensate because that the loss of articular cartilage, the produces brand-new bone to shot and stabilise the joint. This results in bone thickening under the continuing to be cartilage (sclerosis) and also formation that osteophytes in ~ the joint margins, which have the right to reduce the variety of movement of the joint.

Supporting ligamentsSynovial joints are designed come permit motion while, in ~ the same time, maintaining balance, strength and stability. They differ in structure and also the type of movement they allow – Table 2 summarises the various types.

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The security of the joint relies on that shape, the number and also position of supporting ligaments about it, their strength and also the tension they exert (Tortora and Derrickson, 2009). Supporting ligaments are defined according to their position in relationship to the capsule (extracapsular or intracapsular). Excessive tension on ligaments, together as relocating the joint beyond its functional variety of movement, can reason them to stretch and may median they sprain or tear. Ligament damages can compromise joint stability and function.

Prolonged disuse that the joint, for example as result of immobilisation in a cast or through bed rest, regularly gives reduced flexibility that the ligaments and also tendons, and also muscular atrophy (Tortora and Derrickson, 2009). This may lead to lessened mobility that joints and also difficulties with practical activity.

Muscle

There are three varieties of muscle in the body:

Smooth;Cardiac;Skeletal.

Unlike skeletal muscle, smooth and cardiac muscles room not under voluntary manage (Soames and Palastanga, 2019). Skeleton muscle is innervated through the somatic (motor) nerves to simulate voluntary movement, vice versa, cardiac and also smooth muscles are innervated by the autonomic concerned system.

Skeletal muscleThe anatomy of skeleton muscle is presented in Fig 1. Skeletal muscle fibre cells space narrow, however can be long (Danning, 2019) and also each fibre has its very own connective tissue covering called the endomysium (Soames and Palastanga, 2019). The muscle fibres are in bundles known as fascicles, i m sorry are organized together by a great of connective tissue dubbed the perimysium. These room grouped with each other to type muscles, bound by a sheath that fibrous connective tissue recognized as the epimysium. The epimysium merges v the perimysium to kind the muscle tendon, i beg your pardon attaches the muscle come the periosteum of the bone.

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The site where tendons and also ligaments insert to the bone is well-known as the enthesis; this is the website commonly influenced in seronegative spondyloarthro-pathies (for example, ankylosing spondylitis, psoriatic arthritis and reactive arthritis). Seronegative arthropathies space a form of arthritis that perform not have rheumatoid variable antibodies.

Bursas space fluid-filled sacs located at sites where there might be shearing forces, such as as soon as muscles and tendons pass over, or around the leaf of, bone – because that example, in the shoulder (subacromial bursa) or the hip (trochanteric bursa) (Robson and Syndercombe Court, 2019). Bursas allow structures to glide smoothly end each other, reducing friction throughout movement. ~ above occasion, they may end up being inflamed and painful as result of infection, arthritis or repetitive motion and ‘overuse’ the the joint, a problem known together bursitis. Common examples include prepatellar bursitis (housemaid’s knee) and olecranon bursitis (student’s elbow).

Skeletal muscles have several an essential functions, including:

Maintaining posture and also body position;Producing movement;Helping return venous blood from lower limbs to the right side of the heart (skeletal muscle pump);Converting chemical energy to mechanical energy, i beg your pardon generates heat and contributes come the body temperature (Moini, 2020; Robson and Syndercombe Court, 2019).

Many muscles are called according to their various characteristics, together as: brevis (short), longus (long), maximus (large) and also minimus (small). Your names may likewise indicate the direction that the muscle – for example, the transverse abdominus operation transversely and also the rectus abdominis muscle operation vertically (‘rectus’ way straight) – and also can additionally indicate the function; as an example, flexor pollicis longus signifies a muscle the flexes (Drake et al, 2020).

Skeletal muscles are antagonistic – they work in opposition to each various other to develop movement. Once skeletal muscle receives a signal indigenous the somatic (motor) nerve, it shortens, pulling one bone in the direction of the other. As one muscle in the pair contracts, the various other muscle relaxes; the process is then reversed to straighten the bone joint.

Skeletal muscle calls for four key properties:

Contractility – for this reason it contracts to produce forces sufficient to move bone;Extensibility – ensuring the is able to stretch without gift damaged;Elasticity – enabling it to go back to its resting state ~ being stretched or contracted;Excitability – so that is able to respond to a economic stimulation (action potential).

The neuromuscular junction is the chemical synapse formed between the nerve fibre and the muscle fibre. The nerve into the synapse in between the muscle and also the nerve fibre release acetylcholine, which acts as a chemistry neurotransmitter come convey the electrical impulse indigenous the nerve come the receptors in the muscle. Throughout surgery, the neuromuscular junction is crucial site for medicine action, as blocking the acetylcholine receptors gives a neuromuscular blockade that reasons muscle paralysis.

Skeletal muscle performs best when it is provided regularly, and the use of targeted training or exercise have the right to improve the endurance and also power. Likewise, lose of muscle mass (atrophy), such together a diminish in muscle size and also strength, might occur as result of inactivity or factors such as poor nutrition or chronic illness. Although ageing, and the accompanying reduction in mobility, deserve to reduce the top quality of the connective tissue and also cause ligaments to lose some the their adaptability (Robson and also Syndercombe Court 2019), the is essential to optimise musculoskeletal wellness by keeping a healthy diet and also continuing physical task to the finest of a person’s capability (Rowe et al, 2019).

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Conclusion

Muscles and joints are crucial part the the musculoskeletal system. The framework of articulating surfaces and also the kind of connective tissues play a significant role in the selection and aircraft of movement permitted in ~ the joint. Skeleton muscles space responsible for movement and also posture, and work ideal when offered regularly to protect against atrophy. Pathology influence the joints have the right to have a far-ranging impact on duty and range of activity – understanding just how pathology affect the musculoskeletal system permits practitioners to resolve signs and symptoms, and proactively encourage musculoskeletal health.