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Bone Form and Function

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Forces Constrained by Newtons Laws of Motion 1.Law of inertia Body in motion (or at rest) tends to stay that way. 2.F = Ma a force gives a body acceleration in the direction of the force (Bemis et al. 2004). That acceleration increases with the force and decreases with the Mass of the object. 3.Equal and opposite an object receiving a force from another object, in turn, delivers an equal and opposite force.

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Center of Mass CoM = center of gravity point about which a solid body is evenly balanced. To find the Center of Mass:

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Vectors and components of force Scalar quantities values with magnitude and no direction Examples: length, mass, temperature Vector quantities* - magnitude and direction Examples: moving objects.

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Leg supporting the body Fb = downward and backward force Ground reaction force pushing back Fg = upward and forward force Fv = Fg sine(theta) Fh = Fg cosine(theta) Properties of the arrow drawings: direction and magnitude

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Corbin and Reilly, 1998 Reilly, 2000

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Amount of time foot on the ground decreases with increasing speed

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Bone juxtapositions constantly changing Hence, bones (and other materials) have to be able to respond to changing forces

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Stress and Strain Gravity acting on center of mass Strong downward force: Feet Supporting skeletal elements Joint surfaces Contraction of muscles Strong forces on attachment sites Biting or chewing Muscular attachment sites Bones (jaws and skull) Teeth (surrounding flesh and bone)

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Stress and Strain Stress measured as pressure over cross-sectional area Strain deformation in material caused by stress

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Compare elastic rubber band and rigid bone Stress-strain curve:

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Plastic region Stress (force/c.s. area) Strain (deformation) Elastic region Yield point fracture

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Connective tissues (revisited) Extracellular matrix / producing cells = High ECM HOH, Proteins, Carbs. Ex. loose fibrous CT, dense CT, Tendon, Ligament, Bone, etc. Morphology of CT: Collagen/Elastin ratio Arrangement of fibers dependent upon forces acting on the material.

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A major components of Loose, fibrous CT B Molecular structure of the material

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Arrangement of collagen fibers in dense CT A dense irregular CT (dermis of skin) B layers of a ligament C cable-like arrangement of a tendon