# Bone Form and Function - Bloomsburg University of Pennsylvania

Bone Form and Function 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. Center of Mass CoM = center of gravity point about

which a solid body is evenly balanced. To find the Center of Mass: 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. 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 pelvis a

Angles: a. hip b. knee c. ankle d. toe femur

b tibiotarsus phalanges c tarsometatarsus

off bird landmark d

Corbin and Reilly, 1998 Reilly, 2000 Amount of time foot on the ground decreases with increasing speed Bone juxtapositions constantly changing

Hence, bones (and other materials) have to be able to respond to changing forces 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) Stress and Strain Stress measured as pressure over cross-sectional area Strain deformation in material caused by stress

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

Elas t regi ic on Stress (force/c.s. area)

Plastic region Strain (deformation) 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.

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

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