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ANTC47 Lec 2- Sep 11.doc

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Michael Schillaci

ANTC47 Lecture 2- September 11, 2013 CHAPTER 4: Bone Biology Introduction 1) Human skeletal variation can be studied on various levels: • Population Level: skeletal variation within-and among populations o Such as population variation in stature, or craniometric variation o Mu= population average o Population distribution: Mu 1 and Mu 2 -> so talk about variation between two populations, or among three populations, etc. • Individual Level: variation between left and right limbs in measures of robusticity (how strong it is) can tell us something about handedness, or variation among muscle markings on bone can tell us something about activity patterns. • Elemental and molecular level: can tell us about genetic relationships such as paternity and even diet. 2) Bones act as the essential mechanical components of the musculoskeletal system. • They support and protect soft tissue • They anchor muscles, ligaments and tendons • They act as rigid levers upon which muscles act to produce movement • Act as production centers for blood • Storage of fat and calcium 2) The shape or morphology of bones change during growth and development, or ontogeny, through remodeling, which is the process of laying down depositing new bone in certain areas while at the same time resorbing, or removing bone in other areas. 4.1 Variation 1) Humans exhibit variation in skeletal and dental morphology, bone chemistry, and DNA. This variation is what biological anthropologists are interested in, it allows the osteologist to identify sex, age and population affinity. 2) There are four factors leading to skeletal variation: a. Ontogeny: there is a great deal of variation in size and shape during growth and development. b. Sex: Humans, like other primates, are sexually dimorphic. There is variation between males and females in size, shape and size-dependent shape. This variation allows osteologists to determine the sex of a skeleton (by looking at the variation of morphology, we can determine it’s sex). c. Geographic or population based variation: attributes of the human skeleton can vary from one location to another due to adaptations to specific environments. Example: crural index varies with latitude. Populations also vary in skeletal size and shape (Bergman’s rule: as we go higher in latitude, body size increases; Allen’s rule: the relative length of limbs decreases-> as we increase in latitude, it gets colder, so it’s an adaptation to conserve body heat, or alternatively, those who are near the equator are taller, which means they can dissipate body heat more easily) d. Individual or idiosyncratic variation: look at the symmetry of your face. 3) Understanding the normal range of skeletal variation with and among human populations, as well as with and among closely related species or subspecies is essential for identifying new species in the fossil record. A typological approach, one that employs typology (the practice of choosing one individual to characterize a whole species), without consideration of the normal range of variation can result in misguided and inaccurate taxonomies, or species identifications. -> variation is the most important component of learning evolution 4.2 Facts About Bone 1) Bone is a relatively light-weight, yet very strong, material that is a composite of collagen (which is essentially protein) and mineral (hydroxyapatite-> a form of calcium phosphate). Bone is living and dynamic tissue which is able to regenerate itself. 2) The skeleton is subjected daily to mechanical forces such as compression, bending, shear, and torsion. These forces result in bone remodeling. Bone is deposited where it is needed and resorbed where it is not (Wolff’s Law). -> laying down bone and taking bone away where it’s needed (ex. as you walk, you put mechanical forces on your skeleton, such as on your femur or back) > axial loading: depends on body weight (greater body weight means larger mechanical force) ; more axial loading means thicker bones (bone is laid down on the outside; the shape of the axial changes); it changes faster for males; as long as the diameter increases, the bone gets stronger 3) The study of these forces and how they affect morphological and structural change in bone is part of the field of biomechanics. 4.3 Bone as Elements of the Musculoskeletal System 1) A connection between different skeletal elements or bones is called a joint. These joints are articulations and connect the different bones with ligaments and cartilage. 2) Muscle attaches to bone by tendons, which are tightly-packed bundles of collagen fibers (organic component of bone). 3) The most common type of joint is a synovial joint which comprises articular cartilage (hyaline cartilage). The joint is encapsulated and contains synovial fluid which serves to reduce friction in the joint and to provide nutrients for the articular cartilage. 4) There are different types of synovial joints that are defined based on their geometry and motion, such as a spheroidal, or ball-and-socket joints (e.g., hip), hinge joints, such as the elbow, saddle-shaped (or Sellar) joints, such as the base of the thumb, and planar joints such as the ankle (tibiotalar) which allows two joint surfaces to slide across eachother. 5) Cartilaginous joints (or synchondroses) unite two bones with very little movement by means of cartilage, specifically fibrocartilage. A symphasis is a type of cartilaginous joint which incorporates some articular cartilage in association with fibrocartilage. 6
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