Musculoskeletal all lectures Notes PDF

Preview

Summary

Download Musculoskeletal all lectures Notes PDF

Description

Bone = Osteo (double meaning) 1. Living organs made up of different tissues 2. Tissue found in bones of skeleton Functions of the Skeletal System - Support, Protection, Movement - Calcium (99% found here) & Phosphorus (ATP, enzymes) Reserve - Haemopoiesis (Red bone marrow for RBC, WBC manufacture), Fat Storage (Yellow bone marrow) The Adult Skeleton = Axial + Appendicular - 206 bones total - more when you are born as some later fuse - Axial = 80 bones (some paired eg ribs) // Support, Protection, Haemopoiesis - Appendicular = 126 bones (paired) // Movement, Fat storage (further from axial, more yellow bone marrow) Long Bone Structure Epiphysis -In contact with other bone (articular surface) Spongy Bone -Made of Trabeculae Trabeculae -Rods of bone covered by Endosteum -Arranged to resist perpendicular force (which become parallel as it travels down DIaphysis) Diaphysis -Made of Compact bone Articular Cartilage -Covers articulating surface, slippery and shock absorbing Medullary Cavity - Contains bone marrow (Not all bones) - Bone marrow testing is painful due to poor hydration factor so won’t absorb anaesthetic Blood Vessels - Inside compact bone and between trabeculae

Compact Bone - Has storage space (medullary) - Gets narrower towards Epiphysis - Medullary space fuses with trabeculae Endosteum - Thin, inner fibro-cellular layer lining medullary cavity Periosteum - Outer fibro-cellular sheath surround the bone - Contains blood vessels and nerves Perforating Sharpey’s Fibers - Come from Periosteum and fuse with bone - Thick bundles of collagen that infuse into matrix so very strong, more likely to break bone than here Pneumatized Bone - Bone without basement membrane, has air - eg) Paranasal sinus to lighten the face Bone = Specialised Connective Tissue (CT = ECM + Cells) ECM ( = GS + Fibres)

Fibres (Organic) ⅓ dry weight Ground Substance (Inorganic) ⅔ dry weight 20-25% water

Collagen (Type I) Arranged same direction as tension F

Resists tension (stretching/pulling)

Hydroxyapatite

Resists compression (squeezing/crushing) = Resist Torsion

Cells

Osteo bone cells Poorly Hydrated

-genic -blast -cyte -clast

Types of Cells in Bone Tissue 1. Osteogenic (osteoprogenitor cells) - Precursor = Unspecialised stem cells from embryonic CT (mesenchyme) - Location = Flat cell on surface of bone under periosteum and endosteum + Central canals of compact bone

Cell reserve Bone formation Bone maintenance Bone destructure

-

Function = Only bone cells that divide and supply developing bone with bone-forming cells (under chemical signals)

2. Osteoblast - Location = In a layer under the peri or endosteum (active) wherever new bone is formed - Function = synthesis, laying down and calcification of osteoid Osteoid - 70% collagen with the remaining consisting of proteoglycans, proteins and water - Infiltrated with bone salts (hydroxyapatite - gets rid of water) = Calcification - Makes the bone strong and dense but prevents free nutrient flow due to lack of water 3. Osteocyte - Location = Sit in lacunae of bone and communicate with each other and osteoblasts via Canaliculi - Function = Bone tissue maintenance by forming live lattice in bone + localised minor repair + Rapid Ca exchange by pulling it off the walls and sending to diff parts of body 4. Osteoclast (not in lineage) - Precursor = Syncytium of monocyte progenitor cells (WBC) thus multinucleated - Location = Where bone reabsorption is occuring - Function = Secretes acid to dissolve mineral components (hydroxyapatite to expose collagen) and then enzymes which dissolve organic components (collagen). These components are endocytosed by osteoclast, neutralised, then exocytosed out the top - Clear zone - helps anchor onto bone surface and trap what is under the osteoclast - Howship’s lacunae - pit formed after bone is dissolved - Ruffled border - secrete & absorb - Die via apoptosis after 3 months

Bone Remodelling = Appositional growth + Bone resorption (can be individual processes and can occur at either peri or endosteum) - Bone remodelling is occurring all the time - Females affected more by bone resorption changes - Adult skeletal system changes 10$% each year - Age 35 and over = bone resorption mainly Appositional Growth - Signal triggers osteogenic cells to divide where some daughter cells are pushed into matrix and become osteoblasts. - Osteoblasts lay down osteoids onto the surface and calcify them. - Some osteoblasts become trapped and bury themselves in lacunae, becoming osteocytes which enables growth outwards. - Signal terminates osteoblasts by either dying or converting back to an osteogenic cell. - The new osteocytes trapped in lacunae provide bone maintenance. Bone Resorption - Monocyte progenitor cells leave blood vessel and fuse forming syncytium - Osteoclast - Osteoclasts start dissolving bone and eventually die via apoptosis - Blood vessel grows into new space Notes - Bone is too rigid to grow via Interstitial growth as this can only occur in soft tissues that deform. Int growth occurs by cells dividing and secreting more ECM and growing the tissue from within. - Long bones grow in length via Endochondral Ossification as the Epiphysis is covered in cartilage so no appositional growth. Epiphyseal plate made of hyaline cartilage which have chondrocytes that divide (int growth) and push the epiphysis away from metaphysis. The cartilage eventually dies off and osteoblasts can place new bone. Ossification rate catches up to cartilage growth. Immature/Woven Bone - Osteoblasts throw bone down quickly resulting in wavy and less collagen fibres. Bone is not strong and not dense - Precursor for mature bone Mature/Lamellar Bone - Osteoblasts deposit new bone in layers/sheets called Lamellae. The collagen fibres are in the same direction in each layer but 90 degrees between layers. This arrangement allows the bone to be strong as it can resist forces in different directions. - Two types of lamellar bone = Spongy + Compact

1. Spongy Bone/Trabecular Bone (20% skeleton) Spongy bone found more in areas with more compression. Long bone = 10% spongy, 90% compact Osteocytes trapped in lacunae of trabeculae and receive nutrients via diffusion hence 0.4mm. If trabecula is too big, osteocytes will die and trigger trabeculae to divide into two. Lamellae made of cartilage in alternating directions High surface area for osteoclasts to pull/deposit Ca2+ Trabecula lined with endosteum Osteoclast activity goes out of control by decreased estrogen levels hence during menopause = osteoporosis (porous bone as osteoclasts dissolving spongy bone) 2. Compact Bone / Cortical Bone Interstitial lamellae - between osteon Circumferential lamellae - outer, adding this when growing Concentric lamellae in osteon - alternating layers of collagen, surround BV Compact bone thickness >0.4mm because blood vessels go through it Osteon = Haversian system (unit of compact bone) Central/Haversian canal - contains blood vessels and nerves Perforating/Volkmann's canal contain blood vessels pd to surface

Periosteal blood vessels

Appositional growth= Primary osteons are formed around existing blood vessels on periosteum 1. Osteoblasts in active periosteum put down new bone forming periosteal ridges 2. Ridges fuse forming a tunnel around blood vessel where they are now lined by Endosteum 3. Osteoblasts in the endosteum build concentric lamellae on the walls of the tunnel, following it inwards forming an osteon. 4. Bone continues to grow outwards as the osteoblasts in periosteum build circumferential lamellae. Osteon formation repeats as periosteal ridges are formed around new BV Bone Remodelling= Secondary Osteons created inside existing bone 1. Osteoclasts gather in areas that need to be remodelled and bore through the bone. This area is called the ‘cutting cone’, creating a tunnel inside the bone (not on surface like primary osteons) 2. Osteoblasts move in, line the tunnel and deposit osteoid onto the walls. This osteoid layer is calcified, forming a new lamella. A blood vessel will grow into the new tunnel. 3. Osteoblasts continue depositing layers of concentric lamellae in the tunnels filling it in ‘closing cone’. Some osteoblasts become trapped in lamellae and become osteocytes. 4. Osteoblasts either die or convert back to osteogenic cells. Cement line glued by proteoglycans and GAGs is the line between the outer lamellae of new osteon and older bone.

Joints = Arthrosis = where two or more bone interconnect Joint functions - Movement - Force transmission - Growth eg) Fontanelle allow plates to open so brain can grow/seuches skull growth Functional classification of joints Type

Definition

Stability

Movement

Synarthrosis (FT& Growth)

Immovable joint

high

low

Amphiarthrosis (Vertebral column) (FT & little movement)

Slightly movable

med

med

Diarthrosis (Syanovial Joint) (not good at FT, most likely to break)

Freely movable

low

high

Simple Synovial Joints - Most common in body - Not tightly held/restricted by the properties of tissues - Have 4 common features

Aside from the articular capsule, the ends of the articulating bones in a synovial joint are mostly free. This allows a wide range of movement but also results in instability. 1. -

Articular Cartilage Specialised type of hyaline cartilage attached to the bone (1-7mm thick) Primary function is to protect ends of bones that come together to form joint Can absorb shock, support heavy loads for long times and provide frictionless surface when combined with synovial fluid Can fulfil function for entire lifespan unless arthritis

Cells 5% Chondrocytes

Build, repair, maintain cartilage Found in lacunae Either by themselves or in nests

ECM 95% Water (and soluble ions) 75% Water weight

‘Fluid component’ that can move in and out of cartilage

GAGs (HA, Chondroitin Sulphate etc)

‘Solid component’ that is fixed inside the tissue

Proteoglycans PG

Provides swelling and hydrating mechanism

Collagen - type II 75% Dry weight

Structural integrity of tissue Specific zonation patterns Also part of ‘solid component’

Surface Zone - 5-10% thickness - Densely packed with collagen fibres that run parallel to surface - Shear forces cause fibres to reorientate - Small and flat chondrocytes tightly packed in lacunae - Low in PG Middle Zone - 40-45% thickness - Thicker collagen fibres at 45 degrees to surface - Round chondrocytes are lacunae are not densely packed - PG content increases

Deep Zone - 40-45% thickness - Collagen fibres perpendicular to surface - Stacks of chondrocyte nests between collagen fibres that mitotically divide and secrete ECM, hence swelling occurs here, pushing the surface zone up Tide Mark - Boundary between cartilage and calcified cartilage - Low PG as calcified Calcified Cartilage - Chondrocyte sit in lacunae of hydroxyapatite - Low in PG as it is replaced by hydroxyapatite Osteochondral Junction - Rich in glue-like PG which sticks calcified cartilage to subchondral bone - Highly convoluted to increase SA for fibres to attach to bone, allows the shear forces to spread thus prevents delamination less likely to tear bone than this junction Notes - The collagen fibres in surface zone are anchored down to the subchondral bone resisting expansion forces - As we age, upper zones get thinner due to decrease ability to repair - Cartilage is avascular and aneural hence take long to repair - Cartilage is very hydrated Function of Articular Cartilage - GAGS and PG - Repeating disaccharides = glycosaminoglycan (CS - 125, KS - 50) - Many glycosaminoglycans attached to a protein core = proteoglycan (Aggrecan) - Since disaccharides are -ve charged, the -ve charges on GAG repel each other (good at resisting compression) - PGs attach to long HA acid chain forming large proteoglycan complex which attach to collagen fibres - PGs are hydrophilic so attract water, hence swelling

Loading Cycle of Articular Cartilage 1. -ve charges on the proteoglycan complex attached to collagen fibres will attract +ve ions to diffuse into the cartilage from the joint space, increasing ion conc in matrix 2. This creates an osmotic gradient which draws water in and the cartilage swells. This also brings in O2 and nutrients. 3. The swelling places collagen under tension (SZ moving away from subchondral bone). Eventually, swelling forces = tension forces and the cartilife stops swelling. This is an unloaded equilibrium.

4. When a load is introduced such as compression from another bone, the fluid component (water, waste and +ve ions) are squeezed out into the joint cavity containing synovial fluid, it is self lubricating 5. Loss of fluid reduces volume of cartilage = creep, pushing the -ve ions closer together. Eventually the compressive load will be supported by the solid component and repulsion of negative charges and the cartilage will stop shrinking = loaded equilibrium -

During exercise, more loading and unloading due to compressive impact hence more flushing of cartilage, providing nutrients and excreting waste leading to healthier and thicker cartilage thus joint

Osteoarthritis - Wearing away of articular cartilage where eventually bone rubs against bone due to nerve supply - Bone grows on sides of joints (bone spurs/osteophytes) - Cause inflammation 2. Articular Capsule - Joints enclosed by articular capsule around the connecting ends of the bones - Suitably loose to permit movement but can be tight at extreme unnatural limits - Perforated by blood vessels and nerves and reinforced by ligaments (dense CT connecting bone to bone) Comprised of two layers: a. Fibrous layer = outer layer of dense (ir + r) CT which is continuous with periosteum - Made up of parallel but interlacing bundles of white collagen fibres - Thicker sections are called capsular ligaments which prevent abnormal joint movement and resist tension - Supports and protects the synovial membrane and the joint - Poorly vascularised (only have transitory BV) but higher innervated - Anchored to bone by Sharpey’s fibres b. Synovial Membrane = inner layer of loose CT - Lines all of the non-articular surfaces inside joint cavity - 2 layers = intima and subintima - Intima is thin (1-3 cells thick) with synoviocytes which secrete components (HA+lubricating proteins) of synovial fluid

-

Subintima is highly vascular and contains macrophages, fat cells (padding) and fibroblasts (secrete collagen) which maintain and protect articular capsule Have villi for increase SA

3. Joint Cavity - Small area between articulating surfaces - Contains synovial fluid (2ml max) 4. Synovial Fluid - Ultrafiltrate of blood plasma that leaks out of BV from subintima of synovial membrane into joint cavity - Contains mono, lymph, synoviocytes and macrophages - Joint lubrication, shock absorption, chondrocyte metabolism Muscle = Bones are the passive levers of muscle Muscle Function - convert chemical energy (ATP) to mechanical Movement

Gut contents (smooth muscle), circulate blood (cardiac muscle)

Stability

Stabilises joints and maintaining posture by active contraction of surrounding muscles

Communication

Facial expression, body language, writing and speech

Control of body passages

Anal sphincters, eyelids, mouth muscles, gut content

Heat production

85% body heat generated by skeletal muscle

Joint reflexes - uncontrolled skeletal muscle movement Anatomy of Skeletal Muscle -

Osteotendinous Junction - very strong Sharpey’s fibres Myotendinous Junction - weak Tendon - Dense regular CT (attaches muscle to bone) Muscle belly - contracts and pulls on bone via tendon contains BV, nerves

Organisation of Skeletal Muscle

Epimysium of Muscle - Surrounds entire muscle - Dense irregular CT Perimysium of Muscle - Surrounds fascicles - Dense irregular CT Endomysium of Fascicle - Surrounds myocytes - Loose irregular CT - Contains nerves and capillaries ^These 3 layers blend but as you approach periphery they are more coarse Myocyte - Made up of myofibrils - Multinucleated (syncytium) - 10um - 100 um in diameter - mm - cm in length - Basement membrane between and secreted by myocyte and endomysium contain bv and nerves Sarcolemma of Myocyte - Surrounds Myofibrils and conduct AP Sarcoplasm of Myocyte - Contain mitochondria, lipids, glycogen, myoglobin Myofibril - 1um diameter - Made up of many sarcomeres (contractile unit) joined together by Z discs - A band - thick fil - I band - thin fil Deep Fascia and Muscle Compartments Deep fascia is dense (ir + r) CT that covers deep structures in the body beneath skin and subcutaneous tissue (superficial fascia made of fat). Muscles supplied by the same nerves can be found in the same muscle compartment. Outer walls of these compartments are made of deep fascia.

Investing Fascia - Deeper walls / septa - Intermuscular septa (between bone and muscle) and interosseous (between bone) membrane - Fuses with the bone periosteum if in contact

-

The epimysium of muscles within this compartment can move and glide under the deep fascia In other areas the deep fascia is part of muscle tendon and can act as attachment point to bone Plantar Flexor muscles (foot down) Dorsiflexors (foot up) Veins in muscle enable venous return as muscle contraction enables vein pump where swelling means drainage is affected

Size and Repair of Muscle Fibre 1. Hyperplasia - When tissue/organ increases in size due to increase in cell number. Skeletal muscle does not typically undergo this as myocytes are large and multinucleated so difficult. 2. Hypertrophy - Increase in size due to increase in size of individual myocytes from more myofibrils packed within each - There is same number of cells contributing to contraction but larger muscle size and strength - Stimulated by repetitive contraction of muscles to near maximum tension (heavy resistance training) OR use of anabolic steroids Anabolic steroids - Synthetic variants of male hormone testosterone that increase protein synthesis by targeting tissues such as skeletal muscle and bone - Other side effects include acne, hair loss/gain, liver failure, shriveled testes, infertility,, increased susceptibility to coronary artery disease and mood swings 3. Atrophy - Decrease in size due to reduction of myofibrils in myocytes - Occurs when muscles are not used / stimulated by motor neurons eg) when muscle becomes paralysed (no nerve) after long term immobilisation - Can also occur from heart failure, diabetes, cancer, AIDS - Muscle mass loss starts at age 20 and accelerates after age 50. By age 80, lost 40% muscle mass - Can be reversed if not too extreme - Muscle is replaced by fat and CT - Hypoplasia (cell loss) can also result in loss of muscle mass but this is difficult to reverse

4. Satellite Cells (Myoblasts) - Syncytium of myoblasts during embryonic stage forms myocyte - Adult have most of the myocytes you will ever have however satellite cells do have limited ability to repair damage due to old age or injury - Myocytes are large and thus unable to divide via mitosis

-

-

During formation of myocytes, some myoblasts do not fuse and become satellite cells which lie beside muscle fibres, outside of sarcolemma but within the basement membrane Only cells in muscle that can divide upon signal and fuse to form myocytes to repair damage...