5.1: Introduction to the Musculoskeletal System Flashcards by Aleksandra Kubinska

What is the MSK system

(Musculoskeletal system)
The anatomical structures that allow locomotion

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5 components of the MSK system

Bones
Joints - where 2 bones meet
Muscles
Tendons
Ligaments

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Tendons are

Cords of strong fibrous connective tissue attaching muscle to bone

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Ligaments are

Sheets of fibrous connective tissue which connect two bones

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How many bones are in the human body

206 (+sesamoids)

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How many bones are in a child’s body

270

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Appendicular skeleton consists of

Pectoral and pelvic girdle, limbs

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Axial skeleton consists of

Cranium, vertebral column, rib cage

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5 functions of the skeleton

1) rigidity / support
2) movement
3) protection for internal organs (e.g. skull, rib cage)
4) mineral storage / homeostasis (e.g. regulation of calcium and phosphate)
5) bone marrow produces blood cells

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Characteristics of bone

Not inert
Alive and undergoing continual change in response to external stresses
(therefore as a result of stroke bone undergoes demineralisation and osteoporosis)

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Bone is composed of

Cells
Extracellular matrix : (2 branches)
organic component (osteoarthritis)
inorganic component (minerals)

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2 bone cells and what they give rise to

Osteogenic cells - osteoblasts
Osteocyte - osteoclasts

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Osteogenic cell characteristics

Bone ‘stem cells’

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Osteoblast characteristics

“Bone forming”
Secretes ‘osteoid’
Catalyse mineralisation of osteoid

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Osteocyte cell characteristics
(Formation and function)

Mature bone marrow
Forms when an osteoblast becomes imbedded in its secretions
Sense mechanical strain to direct osteoclast and osteoblast activity

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Osteoclast characteristics

‘Bone breaking’
Dissolve and reabsorb bone by phagocytosis
Derived from bone marrow

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Bone mineral density (BMD) is dependent upon

Balance of osteoblasts vs osteoclast activity

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Osteoporosis arises as a result of

Low BMD

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Osteoporosis results in

Increased risk for low-impact fractures (e.g wrist, hip,lumbar spine)

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2 types of drugs used to treat osteoporosis

Drugs that :
Inhibit osteoclastic activity
Increase osteoblastic activity

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Mechanisms of fracture (3)

Trauma: low energy and high energy
Stress: abnormal stresses on normal bone
Pathological: normal stresses on abnormal bone

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5 scenarios of traumatic fractures

Falls
Road traffic accidents (RTA)
Assault
Sports
Crush injury

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5 non-traumatic diseases affecting bone

Cancer
Osteoporosis
Endocrine/metabolic diseases
Paget’s disease
Genetic diseases

Classification of joints is based upon

Structure or function

Diseases of joints is referred to as

Arthritis

Significance of joint diseases

Impact quality of life and function Affect ability to perform activities of daily living (ADLs) Limit ability to work Secondary effects on cardiovascular and metabolic systems

3 structural joint classifications

Fibrous joints Cartilaginous joints Synovial joints

3 functional joint classifications

Synarthroses Amphiarthroses Diarthroses

Characteristics of fibrous joints

No space between bones -synarthroses (e.g. sutures in skull, syndesmosis in tibia and fibula)

Characteristics of cartilaginous joints

Joints in which bones are connected by cartilage (e.g. joints between spinal vertebrae) -amphiarthroses

Characteristics of synovial joints

Space between adjoining bones filled with synovial fluid - diarthroses

Characteristic of synarthroses

Allow no movement

Characteristic of amphiarthroses

Very limited movement

Characteristic of diarthroses

Free movement of joint

4 functional types of synovial joints

Hinge (e.g knee) - monoplanar Ball and socket (e.g shoulder, hip) - multiplanar Pivot joint (e.g cervical spine) - limited rotating movements Condyloid / ellipsoidal joints (e.g. Wrist) - allow all types of movement except pivotal

Components of a synovial joint

2 bones, covered in articular cartilage, with a joint cavity containing synovial fluid

Characteristics of Synovium

1-3 cell deep lining containing macrophage like phagocytic cells and fibroblast-like cells producing hyaluronic acid Type 1 collagen

Characteristics of synovial fluid

Hyaluronic acid-rich viscous fluid

Characteristics of articular cartilage

Type 2 collagen Proteoglycan (aggrecan) Result in cartilage being strong and resistant to compression

Function of Cartilage

Provides smooth lining at a joint to allow ends of two bones to move with minimal friction

Cartilage is composed of (2)

Chondrocytes (Specialised cells) Extracellular matrix: water, collagen and proteoglycans (aggrecan) Chondroitin sulphate and keratin sulphate chains - interact with hyaluronan

Blood supply to cartilage

Avascular: no blood supply, so if injured doesn’t heal well

Aggrecan is (2)

- Proteoglycan possessing many chondroitin sulphate, and keratin sulphate chains - Characterised by ability to interact with hyaluronan (HA) to form large Proteoglycan aggregates

Two broad divisions of arthritis

Non-inflammatory : Osteoarthritis inflammatory

Osteoarthritis is

loss of articular cartilage affecting whole joint - non-inflammatory -degenerative disease

3 types of inflammatory arthritis

Immune mediated Crystal arthritis Septic arthritis (infection)

Example of autoimmune arthritis

Rheumatoid arthritis (Immune system attacks self) Psoriatic arthritis SLE (lupus) Reactive arthritis

Example of crystal arthritis

Gout (urate) and pseudogout (calcium pyrophosphate dihydrate) Crystals trigger inflammation

What is septic arthritis

Bacterial infection in the joint (medical emergency)

Function of muscles

Force generators of MSK system : move bones around a joint Respond to load (hypertrophy) V atrophy with disuse Provide protection for underlying structures

Characteristics of both ligaments and tendons (3)

Strong soft tissue structures Predominantly consist of type1 collagen Less blood supply than muscle

Characteristics of ligaments (3)

Connect bone to bone Restrict joint motion Stabil and proprioception

Characteristics of tendons (3)

Connect muscle to bone Transmit forces Collagen fibrils -> fibres

Acute injury to tendons occurs when

Force exceeds tensile strength

Chronic injury to tendons occurs when

There is a Pathological response to poor biomechanics or overuse

What cells control osteoblast and osteoclast formation

Osteocytes