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213 Terms

1
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Marrow

  • Found in nonmineralized tissue (all bones have except for ear ossicles)

  • Composed of blood vessels, nerves, and various types of cells

  • Generates the principal cells found in blood

  • More red in young people, and turns yellow with age

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Heterotopic Ossification

Building bone tissue outside of the bone organ, occurs following neurological trauma and can cause spinal cord injuries

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Trabecular bone

  • High porosity bone found in cuboidal bones, flat bones, and ends of long bones

  • Bone matrix forms plates and rods called trabeculae

  • Sometimes organized orthogonally, but often trabeculae are randomly arranged

  • More so in epiphyseal sections of long bones

  • Helps distribute load to periosteal surface

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Cortical bone

  • Dense bone found in shafts Of long bones and forming shell around vertebral bodies and other Spongy bone

  • Contains Haversian and Vokmann’s canals as well as resorption cavities

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Haversian canals

Structure in cortical bone aligned longitudinally, contain capillaries and nerves, about the size of a human hair (50 um)

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Vokmann's canals

Short transverse aligned canals in cortical bone connecting Haversian canals, contain blood vessels/nerves

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Resorption cavities

Temporary spaces created by osteoclasts during initial stage of bone remodeling

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Lamellar bone

  • Slowly formed, highly organized

  • Parallel layers of anisotropic matrix of mineral crystals and collagen fibers

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Woven bone

  • Quickly formed, poorly organized

  • Randomly arranged mineral and collagen fibers

  • Sites of fracture healing, tendon/ligament attachments

    • Bone has to 'fix' as quickly as possible and throws collagen and mineral all over site to strengthen it

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Primary bone

  • Tissue laid down de novo on existing surface (e.g., periosteal surface during growth)

  • Circumferential lamellar bone and plexiform bone

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Secondary bone

  • Bone resulting from remodeling, has been 'turned over'

  • In compact bone consists of secondary osteons

  • Most adult bone is secondary bone

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T/F bone is both a tissue and an organ

True

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Bone volume fraction (Bv)

Bv = Vm/Vt

  • Vm = volume mineral matrix

  • Vt = total volume

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Porosity (Pv)

Pv = Vv/Vt

  • Vv = void space

  • Vt = total volume

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Bone apparent density (p)

mass of a bone divided by its volume

p = bone mass/vt = (PmVm + PvVv)/ Vt

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Bone ash fraction

Degree of mineralization of bone tissue, independent of porosity

pm = (PoVo + PaVa + PwVw)/Vm

where subscripts o, a, and m = organic, mineral, and water

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Osteoclasts

  • CLEAVE

  • Multinucleated cells formed by the fusion of monocytes originating in bone marrow

    1. Demineralizes tissue with acids

    2. Resorbs collagen (organic component) by releasing enzymes

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Osteoblasts

  • BUILD

  • Mononuclear cells that produce osteoid, the organic portion of the bone matrix

    • Osteoid = organic bone tissue (collagen)

  • Differentiated from mesenchymal cells

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Osteocytes

  • Osteoblasts 'trap themselves' within bone and over time become this type of bone cell

  • They sit in cavities called lacunae and communicate with each other via dendrinic processes called canaliculi

  • Highly mechanically sensitive - respond to stress and strain

  • Responsible for orchestrating bone remodeling and adaptation and adjustments needed within those processes

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Bone lining cell

A buried osteoblast that does not become an osteocyte and instead “escapes'“

quiescent on bone surface

21
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Bone modeling

  • The independent action of osteoclasts and osteoblasts on different surfaces

  • Produces changes in bone size and shape

  • Highly active during growth and development and greatly decreases after skeletal maturity

    • Never goes away but it is easier to get larger structural adaptations during childhood/youth

  • Is highly influenced by physical activity during childhood

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Bone remodeling

  • The sequential, coupled action of osteoclast and osteoblasts

    1. Osteoclasts cleave and absorb

    2. Osteoblasts build

  • Does not usually influence bone size and shape

  • It removes a portion of old bone and replaces it with newly formed bone

  • Occurs throughout life but decreases after growth

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Trabecular remodeling

Clasts resorb a little pocket of bone along surface of the bone

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Cortical remodeling

  • No surface so the cells create a surface by tunneling through the bone marrow

  • Osteoclasts go ahead of osteoblasts

  • Older cortical bone is more porous and vascular due to this

25
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A-R-F sequence

  1. Activation: differentiation of precursor cells to produce osteoclasts (3 days)

  2. Resorption: osteoclasts resorb bone (30 days)

  3. Formation: osteoblasts build bone (3 months)

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Axial stress

  • Perpendicular to surface

  • Can be compressive or tensile

  • F/A

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Shear stress

Parallel to surface

F/A

28
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Principal stresses are ____ degrees apart

90

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Max shear stress is oriented ____ degrees between the principal stresses

45

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When axial stress is at the maximum or minimum shear stress is ___

0

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Strain

change in length / original length = F / AE

can be axial or shear and within axial category can be compressive or tensile

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Poisson’s ratio

A material loaded in one direction will undergo strains both parallel and perpendicular to the direction of load

  • V = transverse strain/axial strain

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Elastic modulus

Stress / Strain

larger modulus = more stress needed to deform an object

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Orthotropic

Material properties vary in all directions

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Characteristics of loading that affect mechanical properties of bone (4)

  1. Sample orientation

  2. Sample hydration

  3. Strain rate (viscoelasticity)

  4. Loading mode

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Viscoelasticity

 Time-dependent mechanical behaviour

  • all biological materials are viscoelastic

  • faster loading = stiffer and stronger(but more brittle)

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What are the 3 toughening mechanisms of bone?

  1. Collagen fibers create bridges between cracks

  2. Uncracked ligaments create bridging between cracks

  3. Microcracks (energy release via heat)

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Stress by bending formula

Mx/I

  • M = moment

  • x = position

  • I = areal moment of inertia

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Normal stress due to axial force and bending

= (F/A) + (Mx/I)

40
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What is beam theory?

  • Used to calculate normal and shear stresses and strains acting on a cross section of bone

  • 3 primary assumptions:

    1. The beam has a constant cross sectional geometry

    2. The beam has a longitudinal plane of symmetry

    3. The beam is made of homogeneous material

41
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What are the 3 types of cartilage?

  • Hyaline

  • Elastic

  • Fibrocartilage

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Hyaline cartilage

  • Most prevalent cartilage found in adults

  • Includes articular cartilage that covers joint surfaces

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Elastic cartilage

  • Found in external ear, eustachian tubes, and epiglottis.

  • More flexible and elastic than hyaline

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Fibrocartilage

  • Found in intervertebral disks, meniscus, tendon-bone attachments

  • Can form when hyaline cartilage is damaged

45
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T/F Cartilage has blood and nerve supply

False, it has neither

46
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Extracellular matrix

  • produced by chondrocytes

  • mostly type II collagen and proteoglycans (aggrecan), rest is interstitial fluid

  • responsible for mechanical properties of cartilage

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Chondrocytes

  • Live in lacunae like osteocytes, but do not have cell to cell connections

  • Metabolically active (synthesis and degradation of ECM)

    • mechanical compression = signal for metabolic activity

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Proteoglycans

  • Negatively-charged, mutual repulsion

  • Provide high compressive strength

    • (Cartilage would have no compressive strength without PGs!!!)

  • Most common PG = aggrecan

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Interaction between PGs and collagens

  • Collagens form fibrillar network

    • Hold water in

  • PGs bind to collagen fibrillar network

    • Push water away

  • Water fills this molecular framework

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What are the 3 things that vary with depth in cartilage?

  • Amount of collagen/PGs

  • Orientation of collagen fibers

  • Shape and size of chondrocytes

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What are the 4 zones of articular cartilage?

  • Superficial Tangential Zone (STZ)

  • Middle zone

  • Deep zone

  • Calcified zone

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Superficial Tangential Zone (STZ)

  • Tangential fibres

  • 10-20% of tissue thickness

  • Highest collagen and water content

  • Lowest PG content

  • Collagen fibers oriented parallel to surface

  • Chondrocytes are elliptical with their axes aligned with the surface

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Middle zone

  • 40-60% of the thickness

  • Randomly arranged collagen orientation

  • Chondrocytes are round and randomly distributed

  • Highest proteoglycan content

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Deep zone

  • 30% of the thickness

  • Collagen oriented perpendicular to the surface

  • Chondrocytes are arranged in a columnar fashion perpendicular to the calcified cartilage

  • "anchored" into calcified cartilage

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Calcified zone

A layer of calcified cartilage anchored to underlying subchondral bone

56
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Functions of cartilage

  • Transfers and distributes loads between bones, thereby lowering joint stress

  • Allows load-bearing surfaces to articulate with very low friction

  • Its is "not" a shock absorber as is frequently stated

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Mechanical properties of cartilage (4)

  • Inhomogeneous

  • Biphasic

  • Viscoelastic

  • Anisotropic

58
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Biphasic

  • Articular cartilage is considered a fluid-filled biphasic porous permeable material

  • Fluid-saturated porous material

  • Two phases: fluid (interstitial fluid) and solid (collagens, PGs, and cells)

59
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Viscoelasticity is dependent on:

  • Time

  • Internal friction (high internal friction=water doesn’t escape)

60
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Creep

When a fixed amount of stress is applied and held, strain will rapidly increase and then slowly increase until a certain point

61
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At equilibrium, load is balanced by the _____ phase alone

Solid

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Stress relaxation

Under constant strain, stress slowly decreases over time due to fluid escaping ECM (like a wet sponge)

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Creep mechanism in cartilage

  • Fluid exudation is most rapid initially (initial rapid rate of deformation)

  • Fluid exudation decreases gradually until it completely ceases

  • Load is equilibrated by solid matrix and the fluid friction

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Permeability ________ when strain increases

decreases

65
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What are the 3 regions of tendon?

  • External (free) tendon

  • Aponeurosis (internal tendon)

    • Attachment area for muscle fibers (myotendinous junction)

  • Bone-tendon junction (osteotendinous junction)

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Rupture is most common in this area of tendon

Free tendon

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Myotendinous Junction

  • Muscle joins with tendon:

  • Increased surface/contact area:

    • Decreased stress

    • Changes form of stress:

      • Tensile -> Shear

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Osteotendinous junction

  • Tendon joins with bone. Gradual transition:

    • From tendon -> fibrocartilage

    • Fibrocartilage -> mineralized fibrocartilage

    • Mineralized fibrocartilage -> bone

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Viscoelasticity in tendon is a combination of:

  • Viscous properties: Fluids resistance to fluid flow

    • 55-70% of a tendon is water

    • Internal frictional forces between adjacent collagen fibers/fibrils/fascicles etc.

  • Elastic properties: Ability to return to original shape once unloaded

    • Collagen Triple Helix structure

    • Crimp

    • Elastin

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Fatigue life

The number of cycles of submaximal stress/strain a material can withstand before failure

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Material properties

Independent of size and shape

  • ex. elastic and shear modulus

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Structural properties

Dependent on size, shape and CSA

  • ex. stress, force, displacement

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Homogeneity

Material acts the same throughout regardless of location

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Isotropy

Material acts the same throughout regardless of direction

(does not exist in real life)

75
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Describe the organizational scales of muscle from smallest to largest

  1. Sarcomere

  2. Myofibril (contractile unit)

  3. Fiber (cell)

  4. Fascicle

  5. Whole muscle

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Epimysium

Surrounds whole muscle

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Perimysium

Surrounds muscle fascicles

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Endomysium

Surrounds muscle fibers

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Unipennate muscle

A muscle with one pennation angle

  • ex. medial gastrocnemius

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Bipennate muscle

A muscle with 2 pennation angles

  • ex. tibialis anterior

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Aponeurosis

A continuation of distal and proximal tendons onto the muscle

  • more randomly arranged collagen fibrils than in tendon

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T/F aponeurosis is stiffest in the longitudinal direction and overall less stiff than tendon

True

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Fascicle

A bundle of fibers surrounded by perimysium

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Muscle Fiber

A single cell formed during development from the fusion of several undifferentiated immature cells known as myoblasts

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Fiber bundles promote muscle _____

Stiffness

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Myofibrils

  • Contractile machinery of muscle

  • Repeating units of sarcomeres with a characteristic striation pattern

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Describe the anatomy of a sarcomere

  • Z-line

    • outer bounds

  • M-line

    • myosin tails

  • A-band

    • length of myosin

  • I-band

    • region of only actin

  • H-zone

    • region of only myosin

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Z-line

  • Defines outer bounds of each sarcomere

  • Attachment of actin/thin filaments

  • Appears as dark lines on electron micrograph

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M-line

  • Attachment of myosin filaments

90
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A-band

  • Does NOT change in length

  • Length of myosin/thick filament

  • Referred to as "Anisotropic band" due to how it polarizes light under an electron micrograph

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I-band

  • Shortens with contraction

  • Region of only actin filaments

  • Referred to as "Isotropic band" due to how it does not polarize light under an electron micrograph

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H-zone

  • Shortens with contraction

  • Region of only myosin filaments

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Titin

  • Largest protein found

  • Links thick myosin filaments to Z-disc

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Motor Unit

A single motor neuron and all the muscle fibers it innervates

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Innervation

Acetylcholine (Ach) is released at the neuromuscular junction and travels across the synaptic cleft to the motor end plate

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Excitation

This generates an action potential (AP) along the fibre in nerves, APS can only travel in one direction, but in muscle, they can travel in both directions

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Activation

Action potential causes release of calcium into the cell which triggers cross-bridge cycling

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What are the steps involved in cross-bridge cycling?

  1. Active site on actin is exposed as Ca2+ binds troponin

  2. Myosin head forms cross bridge with actin

  3. During power stroke, myosin head bends, and ADP and Pi are released

  4. A new ATP molecule binds to myosin head, causing cross-bridge to detach

  5. ATP hydrolyzes to ADP and Pi which returns myosin to "cocked" position

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T/F The biceps brachii is an example of a unipennate muscle

False, it is a fusiform muscle

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T/F Human muscles are each composed of a single fiber type

False