Skeletal System

Divisions of Skeletal System Axial skeleton – bones of the skull, vertebral column, and rib cage Appendicular skeleton – bones of the upper and lower limbs, shoulder, and hip

Axial Skeleton 80 bones Consist of bones in the: Skull Vertebral Column Thorax Hyoid

Appendicular 126 bones Bones in the: Shoulders Upper limbs Lower limbs Pelvic girdle

Classification of Bones: By Shape Long bones – longer than they are wide (e.g., humerus) Figure 6.2a

Classification of Bones: By Shape Short bones Cube-shaped bones of the wrist and ankle Bones that form within tendons (e.g., patella) Figure 6.2b

Classification of Bones: By Shape Flat bones – thin, flattened, and a bit curved (e.g., sternum, and most skull bones) Figure 6.2c

Classification of Bones: By Shape Irregular bones – bones with complicated shapes (e.g., vertebrae and hip bones) Figure 6.2d

Function of Bones Support – form the framework Protection – provide a protective case for the brain, spinal cord, and vital organs Movement – provide levers for muscles

Function of Bones Mineral storage – reservoir for minerals, especially calcium and phosphorus Blood cell formation – (hematopoiesis) occurs within the marrow cavities of bones

Gross Anatomy of Bones: Bone Textures Compact bone – dense outer layer Spongy bone – honeycomb of trabeculae filled with yellow bone marrow

Spongy Bone Does NOT contain osteons Made up of trabeculae (irregular latticework) Btw. spaces of trabeculae is filled with red bone marrow Only site of RED bone marrow: Vertebrae Skull Hips Ribs Sternum Ends of long bones

Bone Structure – Typical Long Bone Diaphysis = shaft, yellow bone marrow produced here Epiphyses = distal & proximal ends Epiphyseal line = remnant of epiphyseal plate Periosteum = outer, fibrous, protective covering, essential for bone growth & diameter Endosteum = inner lining of medullary cavity, contains bone forming cells Articular cartilage = pad of hyaline cartilage on the epiphyses where long bones articulate or join, reduces friction, absorbs shock Medullary cavity=space w/in diaphysis that contains fatty yellow marrow

Typical Long Bone Structure

Structure of Long Bone Figure 6.3

Structure of Long Bone Figure 6.3a

Structure of Long Bone Figure 6.3b

Structure of Long Bone Figure 6.3c

Bone Tissue Bone is made up of an inorganic component (mineral salt) making them hard Also made up of an organic component (collagen fibers) giving it strength

Bone Surface Markings Depressions & Openings Foramen HOLE through which blood vessels, nerves, or ligaments pass through (ex. Foramen magnum) Meatus PASSAGE extending within a bone (ex. External auditory meatus) Fossa DITCH or shallow depression on a bone (ex. Mandibular fossa of temporal bone)

Processes that form joints Condyle large rounded prominence forming a joint Head rounded projection that forms a joint & supported (ex. Head of femur) Facet smooth, flat surface (ex. Facet of vertebrae)

Processes to which tendons, ligaments, & other connective tissues attach Tuberosity large rounded projection with a rough surface (ex. Deltoid tuberosity of humerous) Spinous process sharp, slender projection (on vertebrae) Crest Prominent ridge (ex. illiac crest of pelvic bone) Trochanter large, blunt projection (only on femur)

Microscopic Structure of Bone: Compact Bone Haversian system, or osteon – the structural unit of compact bone Lamella – weight-bearing, column-like matrix tubes composed mainly of collagen Haversian, or central canal – central channel containing blood vessels and nerves Volkmann’s canals – channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal

Microscopic Structure of Bone: Compact Bone Osteocytes – mature bone cells Lacunae – small cavities in bone that contain osteocytes Canaliculi – hairlike canals that connect lacunae to each other and the central canal

Microscopic Structure of Bone: Compact Bone Figure 6.6a, b

Microscopic Structure of Bone: Compact Bone Figure 6.6a

Microscopic Structure of Bone: Compact Bone Figure 6.6b

Microscopic Structure of Bone: Compact Bone Figure 6.6c

Chemical Composition of Bone: Organic Osteoblasts – bone-forming cells Osteocytes – mature bone cells Osteoclasts – large cells that resorb or break down bone matrix

Functional Zones in Long Bone Growth Growth zone – cartilage cells undergo mitosis, pushing the epiphysis away from the diaphysis Transformation zone – older cells enlarge, the matrix becomes calcified, cartilage cells die, and the matrix begins to deteriorate Osteogenic zone – new bone formation occurs

Long Bone Growth and Remodeling Growth in length – cartilage continually grows and is replaced by bone as shown Remodeling – bone is resorbed and added by appositional growth as shown

Long Bone Growth and Remodeling Figure 6.10

Bone Deposition Occurs where bone is injured or added strength is needed Requires a diet rich in protein, vitamins C, D, and A, calcium, phosphorus, magnesium, and manganese

Importance of Ionic Calcium in the Body Calcium is necessary for: Transmission of nerve impulses Muscle contraction Blood coagulation Secretion by glands and nerve cells Cell division

Homeostasis of Bone Tissue Nutrition Vitamin D absorbs calcium in small intestine Vitamin A bone resorption Vitamin C Hardens bones Hormones Growth Hormone (from pituitary gland) stimulates growth Parathyroid  Can increase or decrease calcium levels Thyroid Promotes normal bone growth

Developmental Aspects of Bones By age 25, nearly all bones are completely ossified In old age, bone resorption predominates Until age of 25 osteoblasts dominate Mid-old age osteoclasts dominate

Hyoid Bone Not actually part of the skull, but lies just inferior to the mandible in the anterior neck Only bone of the body that does not articulate directly with another bone Attachment point for neck muscles that raise and lower the larynx during swallowing and speech

Vertebral Column Formed from 26 irregular bones (vertebrae) connected in such a way that a flexible curved structure results Cervical vertebrae – 7 bones of the neck C1=Atlas C2=Axis Thoracic vertebrae – 12 bones of the torso Lumbar vertebrae – 5 bones of the lower back Sacrum – bone inferior to the lumbar vertebrae that articulates with the hip bones

Vertebral Column Figure 7.13

Bony Thorax (Thoracic Cage) Functions Forms a protective cage around the heart, lungs, and great blood vessels Supports the shoulder girdles and upper limbs Provides attachment for many neck, back, chest, and shoulder muscles Uses intercostal muscles to lift and depress the thorax during breathing

Bony Thorax (Thoracic Cage) Figure 7.19a

Comparison of Male and Female Pelves Table 7.4.1

Comparison of Male and Female Pelves Table 7.4.2

Developmental Aspects: Fetal Skull Infant skull has more bones than the adult skull At birth, fetal skull bones are incomplete and connected by fontanels Fontanels Unossified remnants of fibrous membranes between fetal skull bones The four fontanels are anterior, posterior, mastoid, and sphenoid

Developmental Aspects: Fetal Skull Skull bones such as the mandible and maxilla are unfused Figure 7.33

Developmental Aspects: Old Age Intervertebral discs become thin, less hydrated, and less elastic Risk of disc herniation increases Loss of stature by several centimeters is common after age 55 Costal cartilages ossify causing the thorax to become rigid All bones lose mass

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