Musculoskeletal System Flashcards
Functions of the skeletal system
Support Protection Movement Calcium and phosphorous reserve Haemopoiesis Fat storage
Number of bones in the axial skeleton
80
Some paired
Number of bones in the appendicular skeleton
126
All paired
Function of axial skeleton
Support
Protection
Haemopoiesis
Function of appendicular skeleton
Movement
Fat storage
Type of bone marrow in axial and appendicular skeletons
Axial - red bone marrow
Appendicular - yellow bone marrow
Importance of calcium reserve
Calcium imbalance can impact on muscle contraction and calcification of bone - reserve needed to avoid adverse effects
Importance of phosphorous reserve
Phosphorous is a building block of cells, reserve needed for repair and maintenance
Epiphysis
End of long bone
Contains red bone marrow
Metaphysis
Junction of long bone between epiphysis and diaphysis
Diaphysis
Body of long bone
Contains yellow bone marrow
Describe the forces acting on a long bone
At the epiphysis the forces acting on the long bone are perpendicular to the surface for compression
At the diaphysis the forces are parallel to the surface for structure and strength
Describe the organisation of the epiphysis
Articular cartilage on the outside surrounding thin layer of compact bone
Thick layer of spongy bone consisting of trabeculae completely covered in endosteum
Blood vessels inside compact bone and between trabeculae
Gaps formed by trabeculae network are called medullary cavities which are filled with red bone marrow
Describe the organisation of the diaphysis
Periosteum with Sharpeys fibres on the inside surround thick layer of compact bone
Thin layer of endosteum on the inside lining medullary cavity consisting of yellow bone marrow
Bone vessels and nerves are found in the periosteum
Sharpeys fibres
Perforating fibres that are incredibly strong and attach the periosteum to the bone itself
Periosteum
Outer fibrocellular sheath surrounding bone
Endosteum
Thin inner fibrocellular layer lining medullary cavity
Covers all bony surfaces
Articular cartilage
In replacement of periosteum at epiphysis, found mostly at joints
Tendons
Bundles of collagen fibres oriented in same direction to resist tension
Collagen fibre Type I
Thick and strong
Located in areas where there is lots of tension
Describe the extracellular matrix of bone
Organic fibres - 1/3 of dry weight, consist of collagen fibres type I and V, resist tension
Inorganic ground substance - 2/3 dry weight, consist of hydroxyapatite and resists compression
Osteogenic cells
Cell reserve - unspecialised stem cells
Found in periosteum and endosteum and central canals of compact bone
Can divide and supply developing bone with bone forming cells
Osteoblast cells
Bone formation
Usually in a layer under the periosteum or endosteum, wherever new bone is being formed
Synthesis, deposition and calcification of osteoid
Osteocyte cells
Bone maintenance
Trapped within lacunae inside bone
Can communicate with neighbouring cells through long cellular processes inside canniculi
Bone tissue maintenance and localised minor repair
Live lattice tissue inside bone
Rapid calcium exchange
Osteoclast cells
Bone destruction
Sites where bone resorption is occurring
Secretes acid and enzymes to dissolve mineral and organic components of bone
Hydroxyapatite
Ca10(PO4)6OH2
Crystallised and mineralised salt allowing calcium and phosphorous reserve
Osteoid
Organic extracellular matrix of bone synthesised by osteoblasts prior to mineral deposition
70% collagen, 30% proteoglycans, water and other proteins
Calcification makes the bone strong and dense
Calcification
Osteoid, a precursor matrix, is infiltrated with bone salts called hydroxyapatite making the bone strong, dense and impenetrable to nutrient diffusion via water displacement and diminishing fluid levels
Describe the process of osteogenic cell to osteocyte
Mesenchyme Osteogenic cell Osteoblast Osteocyte Fusion of monocyte progenitor cells leads to osteoclast
Canaliculi
Microscopic canals between the lacunae of ossified bone
Lacunae
A small space containing an osteocyte in bone or chondrocyte in cartilage
Processes of bone remodelling
Appositional growth
Bone resorption
Describe why bone can’t remodel by interstitial growth
Interstitial growth is a process that occurs in derfomable soft tissues. Bone is too rigid to grow by cells dividing within the tissue to make more so it can only grow by adding cells onto existing tissue
Briefly describe endochondral ossification
Growth of the epiphysis - because it’s covered in cartilage it can’t grow appositionally, i.e. put bone tissue down on top of the cartilage. Instead, the epiphysis and metaphysis come apart across the epiphyseal line where new bone tissue its put. The epiphysis moves away from the metaphysis which then tries to catch up. When they fuse again, bone growth stops.
Describe the layers of bone from the periosteum to the medullary cavity
Periosteum (fibrocellular layer) - blood vessels and nerves - osteogenic cells Mineralised bone (live lattice of bone) - osteocytes in their lacunae - osteocyte (cellular processes in canaliculi) Endosteum (fibrocellular layer) - osteogenic cells Medullary cavity and bone marrow - blood vessels
‘Resting’ periosteum or endosteum
No osteoblasts present - only dormant osteogenic cells meaning these fibrocellular levels are not currently active or growing
Describe the process of appositional growth
Periosteum becomes active when osteogenic cells which divide and differentiate into osteoblasts
Osteoblasts deposit osteoid which calcifies the bone
Some osteoblasts become trapped in the lacunae, eventually becoming osteocytes
Growth stops, osteoblasts convert back into osteogenic cells or die
Osteoid is fully calcified, periosteum becomes resting
Describe the process of bone resorption
Monocyte precursor cells leave blood vessels and fuse together on the bone surface forming a syncytium called osteoclast
Osteoclasts secrete acid and enzymes to dissolve the bone
Osteoclasts eventually undergo apoptosis, ending resorption
Blood vessels grow into the space created by the bone dissolution
Describe how bone density could be affected by bone growth
Resorption and appositional growth occur throughout the skeleton constantly but independently of each other. Because appositional growth creates new bone tissue and resorption dissolves old bone tissue, if one occurs much more than the other it can cause an increase or decrease in bone density
Describe how estrogen plays a role in bone density
Estrogen has been shown to regulate osteoclast activity. With a decrease in estrogen levels, especially during menopause, osteoclasts become rampant and dissolve bone more than they should, decreasing bone density and increasing chance of osteoporosis
Immature bone
Also known as woven bone
Common in infants, by the time a child has reached age 3 most immature bone has been replaced by mature bone
Collagen is randomly arranged meaning it is fairly pliable and not very strong
Mature bone
Also known as lamellar bone i.e. layered
Collagen fibres are put down in the same direction within a layer but between layers vary the angle to 90 degrees. This allows bone to withstand forces from many different directions making it significantly stronger
Could be spongy or compact
Spongy bone
Type of mature bone
Also known as cancellous or trabecular
Many trabeculae increases the surface area of the bone which increases the blood supply. Good supply means the bone remodels quickly
Maximum width of a trabecula is 0.4mm
Compact bone
Type of mature bone
Also known as cortical bone
Classified by containing osteons
Variable thickness but normally more than 0.4mm
Also contains interstitial and circumferential lamellae and Volkmanns canals which are perpendicular to the bone surface
Blood vessels run through
Osteon
Also called Haversian system
Contain a central/Haversian canal parallel to the surface which has blood vessels and nerves running through
Endosteum lines the insides
Alternating arrangement of collagen fibres between concentric lamellae
Periosteum in compact bone
Contains periosteal blood vessels
Outer fibrous layer and inner osteogenic layer
Primary osteon formation
Primary osteons are formed around an existing blood vessel on the surface of bone, normally in the periosteum
Osteoblasts in active periosteum either side of a blood vessel put down new bone forming ridges
Ridges fuse forming a tunnel around the blood vessel lined with endosteum
Osteoblasts in endosteum build concentric lamellae onto tunnel walls which is slowly filled inward
Bone grows outwards as osteoblasts in periosteum build new circumferential lamellae
Secondary osteon formation
Secondary osteons are created inside existing bone
Osteoclasts form and gather in an area that needs to be remodelled and starts boring its way through existing bone
Tunnel is created, osteoblasts move in and line the tunnel wall forming new active endosteum and deposit osteoid onto tunnel walls
Osteoid layer is calcified forming new lamellae and allowing a blood vessel to grow into the tunnel
Osteoblasts deposit concentric lamellae onto tunnel walls, filling it in. Some are trapped in newly deposited lamellar bone and become osteocytes
Tunnel reduces in size and remaining osteoblasts lining Haversian canal die or become bone lining osteogenic cells and contribute to resting endosteum
Cutting cone
Area where group of osteoclasts begin to bore through existing bone
Closing cone
Active area behind cutting cone where osteoblasts deposit concentric lamellae to fill in the Haversian canal
Cement line
A visible line at the junction between the outermost lamella of the new osteon and the preexisting older bone
Briefly describe the major points of spongy bone
Trabecula unit
Grows outwards
Found inside bones and epiphysis of long bones
Supplied by blood vessels in medullary cavity
Supports outer cortex of compact bone in areas where forces occur from multiple directions to help reduce the weight of bone
Rapid turnover of calcium and phosphorous
Briefly describe the major points of compact bone
Osteon unit
Grows inwards
Found in outer shell of bones and diaphysis of long bones
Supplied by vessels within Haversian and Volkmanns canals
Provides a strong dense shell of bone on the outside and thickens areas exposed to large forces
Joint
Also called articulation
Any point at which two or more bones interconnect
Synarthrosis
Immovable joint
High stability
Low movement
Commonly found in the axial skeleton
Amphiarthrosis
Slightly moveable
Medium stability
Medium movement
Mostly force transmission
Diarthrosis
Freely moveable
Low stability
High movement
Commonly found in the appendicular skeleton
Functions of joints
Movement
Force transmission
Growth
4 common features of synovial joints
Articular cartilage
Articular capsule
Joint cavity
Synovial fluid
Describe what makes synovial joints unique
They are unrestricted by the properties of a specific tissue which holds the ends of the bones tightly together
The ends of the articulating bones in a synovial joint are mostly free giving them a wide range of motion
Describe the function of articular cartilage
Specialised firm and rubbery form of hyaline cartilage to protect the ends of bones, absorb shock, support heavy loads for long periods of time and provide a smooth, near frictionless surface when combined with synovial fluid`
Describe the makeup of articular cartilage
5% cells
- Chondrocytes
95% extracellular matrix
- water (75% wet weight), glycosaminoglycans and proteoglycans (25% dry weight) make up the ground substance
- fibres (75% dry weight), mainly collagen type II
Chondrocytes
Build, repair and maintain cartilage
Live in lacunae
Can occur by themselves or in nests
Role of water in the ECM
With soluble ions, provide the mobile fluid component that can move in and out of tissue
75% wet weight
Role of glycosaminoglycans and proteoglycans in the ECM
Provides swelling and hydrating mechanism for the proper function of cartilage
Part of the solid component that is fixed inside tissue
Large hydrophilic molecules
Role of collagen type II in ECM
Structural integrity, specific zonation patterns and also part of the solid component fixed inside tissue
Collagen type II is finer and more flexible than type I
Examples of glycosaminoglycans
Keratin sulphate, chondroitin sulfate, hyaluronic acid
Example of a proteoglycan
Aggrecan
Name the different zones in articular cartilage
Surface zone Middle zone Deep zone Tide mark Calcified cartilage Osteochondral junction Sunchondral bone
Surface zone
Low proteoglycan levels
Lubricating
Densely packed collagen fibres parallel to surface
Squashed individual chondrocytes
Middle zone
40-45%
Some proteoglycans
Looser, crossing collagen fibres
Individual, uncompressed chondrocytes
Deep zone
40-45%
Lots of proteoglycans
Loosely packed collagen fibres perpendicular to surface
Chondrocyte nests appearing indicating mitotic division
Tide mark
Calcified region
Low proteoglycan levels
Calcified cartilage
Low in proteoglycans but high in hydroxyapatite
Individual chondrocytes in partially calcified lacunae
Osteochondral junction
The cement line
Collagen fibres still perpendicular to surface but do not line up with fibres in the calcified cartilage
Describe why cartilage is avascular
Cartilage is a heavily compressed tissue which would crush blood vessels and nerves
Delamination
Separation of layers causing decreased strength and stability
Glycosaminoglycan
Repeating disaccharide unit
Proteoglycan formation
Many glycosaminoglycans attach to a protein core
Negative charges on the sugar units repel each other so the glycosaminoglycans stand out from the protein core causing recoil after compression
Hyaluronic acid
A chain of glycosaminoglycans that proteoglycans can attach to
In turn the hyaluronic acid chain can attach to collagen fibres
Aggrecan formation
About 125 chondroitin sulfate molecules + about 50 keratin sulfate molecules + protein core
Describe the loading cycle of articular cartilage
Negative charges on the repeating disaccharide units in the cartilage attract positive ions such as calcium, potassium and sodium from the joint space, increasing the ion concentration in the matrix
Increased ion concentration creates an osmotic gradient drawing water (and oxygen and nutrients) into the matrix. Cartilage begins to swell
As cartilage swells, collagen is placed under increasing tension until the tension force is equal to the swelling force and it stops swelling
Load is introduced which squeezes the fluid component out of the cartilage back into the joint space and synovial fluid, lubricating the surface
Loss of fluid reduces the volume of the cartilage which pushes the negative charges together causing repulsion which helps the solid component support the compressive load
Cartilage stops shrinking and is said to be unloaded
Unloaded equilibrium
When the cartilage has swollen so much that the tension the collagen is put under is equal to the swelling force of the cartilage, stopping the swelling
Loaded equilibrium
When the compressive load on the cartilage is supported by the solid component and the repulsion of the negative charges, stopping the skrinking
Creep
Reduction of cartilage volume via fluid loss
Describe why proteoglycans are considered a swelling agent
The proteoglycans have negative charges that repel each other and attract positive charges, like those on soluble ions such as calcium, potassium and sodium
The influx of soluble ions creates a hypotonic solution in relation to the cartilage causing water to rush in to equalise it and making the cartilage swell in the process
Articular capsule
Surround the synovial joints forming a sleeve that connects the ends of contributing bones
Loose during normal range of motion but tight at extreme limits to protect from damage
Perforated by vessels and nerves and may be reinforced by ligaments
Outer fibrous layer and inner synovial membrane
Fibrous layer
Outer layer of dense connective tissue (both regular and irregular) variable in thickness
Made up of fibroblasts and parallel but interlacing bundles of collagen continuous with the periosteum of the bone
Thicker sections can be called capsular ligaments which resist tensional forces and check excessive and abnormal joint movement
Supports synovial membrane and protects the whole joint
Poorly vascularised but richly innervated by nocireceptors and proprioreceptors
Synovial membrane
Inner layer of loose connective tissue of variable thickness
Lines all non-articular surfaces inside joint cavity
Contains intima and subintima
Joint cavity
Small area between articulating surfaces
Peripheral margins filled by collapsing and in-folding of synovial membrane villi
Contains synovial fluid
Synovial fluid
A clear, slightly yellowish fluid that is an ultrafiltrate of blood plasma that leaks out of blood vessels in the subintima of the synovial membrane into the joint space
Hyaluronic acid and other lubricating proteins are also secreted by synoviocytes
Monocytes, lymphocytes, macrophages and synoviocytes can be found in low concentrations
For joint lubrication, shock absorption, chondrocyte metabolism and overall joint maintenance
Describe the makeup of the articular capsule and the adjacent cavities
Outside joint cavity (extra capsular)
Fibrous layer contains fibroblasts, nerves and some blood vessels
Subintima of synovial membrane contains adipocytes, blood vessels, marcophages and some fibroblasts
Intima of synovial membrane contains synoviocytes
Joint cavity (intra capsular) contains synovial fluid and free cells
Ligament
Dense regular connective tissue connecting bone to bone
Intima
Thin, intimate with joint space
Contains synoviocytes which secrete some components found in synovial fluid
Subintima
Highly vascular
Contains macrophages, adipocytes and fibroblasts to maintain and protect articular capsule during normal movement
5 functions of muscle
Movement Stability Communication Control of body openings and passages Heat production
Origin
Attachment that moves the least during a certain muscle contraction
Also called proximal
Insertion
Attachment that moves the most during a certain muscle contraction
Also called distal
Name the order of the layers of a muscle from big to small
Muscle Epimysium Perimysium Fascicle Endomysium Myocyte Sarcolemma Sarcoplasm Myofibril
Muscle
A bundle of fascicles
Epimysium
Dense irregular connective tissue surrounding the perimysium and the entire muscle
Perimysium
Dense irregular connective tissue surrounding the fascicles
Fascicle
A bundle of myocytes
Endomysium
Loose irregular connective tissue surrounding myocytes
Contains nerves and capillaries that supply myocytes
Myocyte
Muscle cell
A bundle of myofibrils
Sarcoplasm between myofibrils and sarcolemma surrounding
Sarcoplasm
Cytoplasm
Between myofibrils
ATP, glycogen, lipids and myoglobin
Sarcolemma
Cell membrane
Fast action potential conduction
Myofibril
Many sarcomeres
Contractile organelles
Many make up a myocyte
Deep fascia
Fibrous sheet of dense connective tissue (can be regular or irregular) underlying skin and subcutaneous tissue
Makes up outer walls of muscle compartments
Investing fascia
For example intermuscular septa and interosseous membranes
Deeper walls of muscle compartment
Fuses with periosteum when in contact with bone
Describe a muscle compartment
A muscle (dorsiflexor or plantarflexor) is surrounded by epimysium which is in turn surrounded by intermuscular septa (walls between muscles), interosseous membrane (between muscle and bone) and deep fascia (outer fibrous sheet) Also present are arteries, veins, nerves and bone
Compartment syndrome
Infection or inflammation of the tissues within a compartment causes swelling - the compartment can’t grow so the tissues become compressed which can be very painful and cause edema and other drainage disorders
Hyperplasia
Tissue or organ increases in size due to increase in cell number
Skeletal muscle cells are too big to undergo hyperplasia
Hypertrophy
Tissue or organ increases in size due to increase in individual cell size
Increase in number of myofibrils in each myocyte
Heavy resistance training and anabolic steroids can increase myocyte size
Atrophy
Tissue or organ decreases in size due to decrease in individual cell size
Decrease in number of myofibrils in each myocyte
Occurs when muscles are not used e.g. paralysis, diabetes
Muscle is replaced by fat and connective tissue
Hypoplasia
Tissue or organ decreases in size due to reduction in number of cells
Very difficult to reverse
4 functions of skeletal muscle connective tissue
Provide organisation and scaffolding for muscle construction
Provide medium for blood vessels and nerves to gain access to myocytes
Prevent excessive stretching and damage to myocytes
Distribute forces generated by muscle fibre contraction
2 structural proteins in myocytes
Desmin
Dystrophin protein complex
Desmin
A structural protein that holds myocytes together at the Z-lines
Help to align sarcomeres between myofibrils so that they shorten together and pull in unison
Protein complexes
At the surface of the myocyte the Z-lines of outside myofibrils are attached to the sarcolemma and to surrounding basement membrane and endomysium
Group of proteins forms protein complex responsible for bridge between myocyte and surrounding connective tissue
Also strengthens sarcolemma and transmits contractile forces generated by sarcomeres to surrounding endomysium
Muscular Dystrophy
Disease caused by incorrect transcription of dystrophin causing myocytes with weaker sarcolemmas that can tear easily and cause cell death
Basement membrane
Secreted by fibroblasts and myocytes
Thin, specialised sheet of connective tissue that blends with endomysium
