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Overview for Musculoskeletal System
Skeletal System
Function – support, protection, storage, blood cell production
Structure – osseous tissue = 2/3 calcium phosphate, 1/3 collagen, 2% osteocytes
1. Macroscopic
Shapes
Long bone
Central shaft (Diaphysis)
Bone marrow – surrounded by shaft
Epiphyses – bone ends covered by articular cartilage
Short bone
Flat bone
Irregular bone
Types bone
Compact - solid
Spongy – network with spaces
Periosteium – outer surface tendons & ligaments attach
Fibrous outer layer
Cellular inner layer
Endosteum – lines marrow cavity; active in growth & repair
2. Microscopic
Osteocytes (osteon) – bone cells
Lacunae – small pockets that contain bone cells
Lamellae – narrow sheets of calcified matrix where lacunae lie
circular & parallel to long axis of central canal
Canaliculi – small channels radiate through matrix & connect
lacunae & link to blood vessels
3. Microscopic Compact – covers bone surfaces except at joints; heavy stress
Haversian canal (central canal) – osteon arranged around canal that
has blood vessels
Perforating canals – passageways for linking blood vessels to central
canal
4. Microscopic Spongy – no stress; lighter
No osteons
Trabeculae – rods or plates creating open network
protect and support cells of red bone marrow
Canaliculi communicate with spongy and transport wastes
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5. Cells
Osteocytes – mature bone cells
Osteoclasts – bone eaters with acids & enzymes dissolve matrix;
help regulate Ca & PO4 levels
Osteoblasts – bone builders; build new matrix via osteogensis;
promote calcium salt deposits;
Osteoblast become osteocytes when completely surrounded by
matrix
Formation & Growth
1. Intramembranous Ossification – osteoblasts differentiate in fetus
occurs in deep dermis; stem cells secrete matrix = calcified
Ossification Center – place where ossification first occurs
vessels grow with needs for nutrients & trapped in new bone
2. Endochondral ossification – ossification of hyaline cartilage forms most bone
Chondrocytes enlarge in calcifying matrix
Bone formation at surface with invasion into perichondrium &
cells differentiate to osteoblasts = new bone matrix
Blood vessels invade to form spongy bone; center of shaft –
primary center of ossification; bone develops towards ends
Osteoclasts break down spongy & create marrow; epiphyseal cartilage on
ends continues to grow; bone added in front advancing osteoblasts
Epiphyses center begin to calcify = secondary centers of ossification
Articular cartilage – thin cap at end in joint cavity
(puberty – bone growth faster than cartilage expansion – end )
Appositional growth – bone deposited on outer surface countered by
osteoclasts inner surface = marrow enlarges
3. Requirements for growth
Vitamin D3 – converted to calcitriol in kidney aids in Ca absorption GI
Vitamin A
Vitamin C
Growth hormone
Thyroid hormone
Sex hormones
Calcium metabolism hormones
Remodeling
1. Role – turnover = adaptability (more stress – thicker & stronger)
2. Homeostasis & Mineral (bones store calcium)
Calcium – vital bones, nerves, muscles
Parathyroid hormone & calcitriol – elevate Ca levels
Calcitonin – depress calcium levels in fluids
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Injury & Repair
1. Stages
Fracture hematoma
External callus & internal callus
Spongy bone bridge
Remodeling
2. Types injuries
Sprain – stretch or tear ligaments with acute pain, swelling
Subluxation – separation bone ends in joint capsule
Dislocation – complete dislocation of bone ends from normal joint
position
Fracture – structural integrity disruption
Comminuted, impacted, greenstick, oblique, spiral, torus,
transverse, segmental & open or closed
Growth plate injury – Salter Harris grading (1-5 with 5 worst)
3. Aging – Osteopenia= inadequate ossification
Divisions
1. Axial – skull (29), thoracic (24 ribs & sternum), vertebral column (26)
Protections vital organs, respiration, stabilize Appendicular skeletal
Cranium- facial (14), auditory ossicles (6), hyoid bone
Frontal – forehead
Parietal – posterior to frontal & sides of skull
Occipital – inferior & posterior skull
Temporal – sides & base cranium
Sphenoid – floor of cranium; bridge cranium & facial bones
(bat with wings extended)
Ethmoid – anterior to sphenoid with honeycombed masses
(sinuses)
Facial – maxillary, palatine (roof of mouth), vomer (nasal septum),
zygomatic, nasal bone (bridge nose), lacrimal (move
with frontal, ethmoid, maxillary bones), nasal complex
inferior nasal conchae (superior, middle, inferior),
mandible, hyoid (ligament supported, larynx muscles)
Vertebral column (curves = primary – thoracic & sacral = fetal
secondary – cervical & lumbar = post birth)
Cervical (7)
Thoracic (12)
Lumbar (5)
Sacrum (1) – formed from 5 fused fetal bones
Coccyx
2. Appendicular – limb bones, pectoral, pelvic girdles (126 total)
31 lower limbs & 32 upper limbs
Pectoral – scapulae, clavicles (connect with manubrium of sternum)
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Humerus, radial, ulna, metacarpal, phalanges, pollex (thumb)
Pelvic girdle – coxae, ilium, ischium, sacroiliac joint, acetabulum
Lower limb – femur, patella, tibia (shinbone- larger, medial), fibula,
tarsal (ankle= 7), metatarsal, phalanges
Joints
1. Types movement
Gliding – clavicle & sternum – sliding
Hinge – elbow, knee, ankle, phalageal joints
Pivot – rotation head (axis & atlas)
Ellipsoidal – phalanges
Saddle – thumb base
Ball –and-socket – shoulder & hip
Muscles
Function – movement of skeleton, maintain posture & position, support soft tissue
guard entrances & exits, maintain body temperature
Macroanatomy
Epimysium – surround entire muscle; layer of collagen fibers
Perimysium – connective tissue that divides skeletal muscle into bundles
Fascicles – bundles of muscle fibers
Endomysium – surrounds each muscle fiber & joins adjacent fibers
Tendon – collagen fibers of epimysium, perimysium & endomysium come
together at ends to form bundle that connects muscle to bone
Blood Vessels & Nerves – come through the epimysium & perimysium
Voluntary muscles via axon nerve fibers
Microanatomy
Sarcolemma – cell membrane surrounding muscle fiber
Sarcoplasm – cytoplasm of muscle fiber
Transverse tubules or T tubules – openings across surface Sarcolemma
series of tunnels assist in muscle contractions
Myofibrils – circular structure that contain myofilaments containing
actin (thin) & myosin (thick)
Sacroplasmic reticulum – binds T tubule to membranes (smooth endoplasmic);
surround myofibril & between T tubules
Terminal cisternae – lies either side T tubules; high calcium concentration
stored calcium from here & to sacroplasmic reticulum starts
muscle contraction
Triad – T tubules & terminal cisternae
Sarcomere – repeating functional units of myofilaments
Z lines
M lines
A bands
I bands
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Myofilaments – sliding theory
Thin – actin –bead covered with tropomyosin
Thick – myosin - head
Tropomyosin – protein covers actin
Troponin – bound to actin hold Tropomyosin in place
Calcium unlocks system, activates troponin to move
Tropomyosin allows actin & myosin connection =
MUSCLE CONTRACTION
Neuromuscular Junction
Motor Neuron – nerve cells that control skeletal muscles attach to by
perimysium come together at synaptic terminal
Synaptic terminal – end point
Acetylcholine (Ach) – neurotransmitter
Synaptic cleft – narrow space separates synaptic terminal from Sarcolemma
Motor end plate – portion membrane contains Ach receptors
Acetylcholinesterase (AChE) – enzyme breaks down Ach
Muscle Mechanics
Tension – active force of pull on collagen fibers
Resistance – passive force resists or opposes movement
Compression – push applied to object
Frequency
Twitch – single contraction
Phases
Latent – begin stimulation with action potential sweep
Contraction - tension rises to peak
Relaxation – muscle tension falls, calcium levels drop, cross
bridges disconnect
Motor Unit – muscle fibers controlled by single motor neuron
Iotonic – change in muscle length & tension remains same -lifting
Isometric – length unchanged but tension increases – pushing
Energy
ATP – transfer energy in muscle contraction more than needed transferred to
Creatine leading to Creatine phosphate
Creatine phosphokinase (CPK) – enzyme converts energy back; muscle
damage leads to CPK leakage
Aerobic metabolism – normal O2 intake usually enough when resting
Anaerobic – glycolysis = main ATP source – pyruvic acid = lactic acid
Muscle fatigue – muscle can not contract due to build up of lactic acid despite
neural stimulation
Muscle Performance
Fast fibers – contract fast, fatigue fast, white in color
Slow fibers – slower contraction, red pigment Myoglobin, red muscle,
extensive capillary supply with oxygen
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Types of Muscles
Cardiac – small, centrally placed nucleus, found in heart, intercalated disc
pacemaker cells, automatic, longer contraction, aerobic
metabolism, calcium from sarcoplamic reticulum &
increases in cell membrane permeability to extracellular ion,
Contract WITHOUT neural stimulation
Skeletal – larger, multinucleated, short contraction, nervous system stimulation
aerobic & anaerobic metabolism, voluntary
Smooth – small, single nucleus, sphincter regulate movement in GI, GU,blood
vessels, spindle shaped, NO striations, lack myofibrils, sarcomeres,
thin & thick filaments attach different, calcium enters differently
(extracellular), contract automatically or hormonally, neuron
control is NOT voluntary