Skeletal System Notes PDF

# Unit 5 - Bone ## Functions of the skeletal system: - **Support** - serves as the structural framework, provides attachment points. - **Protection** - surround the most critical organs: skull, ribcage, vertebrae. - **Assistance in movement** - muscles pull on bones to produce movement. - **Minera...

# Unit 5 - Bone ## Functions of the skeletal system: - **Support** - serves as the structural framework, provides attachment points. - **Protection** - surround the most critical organs: skull, ribcage, vertebrae. - **Assistance in movement** - muscles pull on bones to produce movement. - **Mineral storage & release** - stores strengthening minerals: calcium, phosphorus. - **Blood cell production** - long bones contain connective tissue called red bone marrow, which produces red blood cells (RBCs), white blood cells (WBCs) and platelets (hemopoiesis). - **Triglyceride storage** - stored in yellow bone marrow, adipose cells - potential chemical energy. ## Bone Facts - There are 206 bones in an adult skeleton that come in a variety of shapes and sizes. - Bones can tell a lot about an individual's life: age, size, stature, gender, health, and race. - The shape of a bone can tell about its function. Each bone has specific bumps, grooves, holes, projections, and ridges. ## Types of Bones: 1. **Long bones**: have a greater length than width, and consist of a diaphysis (shaft) and a variable number of epiphyses (ends), which are slightly curved to increase strength. - Consist mostly of compact bone tissue (dense) and some spongy bone tissue. - Examples: Humerus, Ulna, Radius, Femur, Tibia, Fibula, Medacarpals, Metatarsals, Phalanges. 2. **Short bones**: somewhat cubed shaped and nearly equal in length, width, and depth, consist of spongy bone with a thin outer compact bone layer. - Examples: Carpals & Tarsals. 3. **Flat bones**: generally thin and are composed of two nearly parallel plates of compact bone. - Examples: Cranial bones. 4. **Irregular bones**: examples are vertebrae. 5. **Sesamoid bones**: develop in the tendons of muscle where there is considerable friction, compression, and stress. - Examples: Patella. ## Diagrams - Refer to page 152/153 for diagrams. ## Anatomy of a bone 1. **Diaphysis**: bone shaft. 2. **Epiphysis**: proximal / distal end of the bone. 3. **Metaphysis**: area between diaphysis and epiphysis, allows for room to grow. - Epiphyseal plate = growth plate - Turns into epiphyseal line. 4. **Articular cartilage**: thin layer of hyaline cartilage that covers the epiphysis that forms a joint. 5. **Periosteum**: tough connective tissue sheath covering the bone that helps provide blood supply. 6. **Medullary cavity**: hollow cylindrical space where yellow/red bone marrow is located. 7. **Endosteum**: thin membrane that lines the medullary cavity. ## Bone Surface Markings - The surface of all bones are marked by a variety of bumps, grooves, indentations, projections, and holes. - These are called surface markings or osseous landmarks. - These are structural features adapted for a specific function. - Bumps, ridges, or a rough area on the bone indicate areas where soft tissue was connected: tendons attach muscle to bone. - Groove-like impressions, or holes, indicate where nerves and blood vessels pass through the bone. - Smooth surfaces indicate areas of movement between neighboring bones (joint surfaces). - In response to tension on a bone surface, new bone is deposited, resulting in raised or rough areas. - Two major types of surface markings: - Depressions and openings - Processes ## Histology of Bone Tissue - Bone contains an abundant amount of extracellular matrix that surrounds widely separated cells. - 30% collagen fibers, 55% crystallized mineral salts (calcium phosphate, calcium hydroxide hydroxyapatite) - bone building. - 15% blood, nerve, adipose. - Four types of cells are present in bone tissue: 1. **Osteogenic cells**: unspecialized bone stem cells, located along the inner portion of the periosteum. 2. **Osteoblasts**: bone-building cells: - Synthesize and secrete collagen fibers. - Initiate the process of calcification. 3. **Osteocytes**: mature bone cells. 4. **Osteoclasts**: huge cells derived of multiple monocytes and are located in the endosteum. - Release lysosomal enzymes and acids to breakdown bone. - This process, resorption, is vital to normal development, growth, maintenance, and repair. ## Compact Bone Tissue - Cortical/dense bone, located at the surface of all bones. - Provides protection and support, and helps resist stress of movement and weight. - Composed of repeating structural units called osteons or haversian systems: - Contain concentric circles of mineralized extracellular matrix (concentric lamellae) that surround blood vessels (central canal). - Spaces in osteons called lacunae contain osteocytes. - Canaliculi are small channels in the osteons that carry extracellular fluids. - Canaliculi, lacunae, and central canal are all connected. - Provides routes for nutrients, oxygen, and waste. ## Spongy Bone Tissue - Called trabecular or cancellous bone, does not contain osteons, and is located on the interior of a bone. - Contains lamellae organized irregularly around thin columns, called trabeculae. - Sites where red/ yellow bone marrow is located. - Protects red bone marrow. - Is much lighter than compact bone. ## Blood and Nerve Supply to the Bone - Bone is richly supplied with blood and nerve innervetion. - Arteries enter the bone along with nerves through openings called volkmann's canals. - Carry blood to bone. - A large nutrient artery enters compact bone through a hole called the nutrient foramen. - Enters medullary cavity and branches proximally and distally. - Veins accompany arteries and carry blood away from bones. - Nerves accompany the blood vessels that supply the bone. - Periosteum contains many sensory receptors, which give rise to pain sensation. ## Bone Formation / Growth - Embryonic skeleton is made up of mesenchyme. - Intramembranous ossification is bone forming in mesenchyme. - Endochondral ossification is bone forming in hyaline cartilage. - Bone growth occurs epiphysis and diaphysis as to close the epiphyseal plate gaps. - Bone growth in thickness occurs at the outer surface. - Bone remodeling is the ongoing replacement of old bone tissue with new bone tissue. - Resorption / deposition ## Divisions of the Skeletal System - **Axial skeleton**: 80 bones - **Skull**: 22 bones - **Cranial bones:** Frontal, parietal, temporal, occipital, sphenoid, ethmoid. - **Facial** **bones:** Nasal, maxillae, mandible, zygomatic, lacrimal, palatine, inferior nasal conchae, vomer. - Forms cranial cavity that houses the brain. - Forms smaller functional cavities: nasal, orbital, paranasal sinuses, middle/inner ear cavity. - **Foramen magnum:** opening in the occipital bone through which the spinal cord passes. - **Unique features of the skull:** - **Foramina:** openings for blood vessels, nerves, and ligaments. - **Sutures:** immovable joints between cranial bones. - **Paranasal sinuses:** cavities lined with mucous membranes that play an important role in respiration. - **Fontanels:** soft spots. - **Cranial fossa:** three regional cavities at the floor of the skull. - **Hyoid bone:** a U-shaped bone located in the anterior portion of the neck. - Does not articulate with any other bone. - Supports and provides for attachment sites for the tongue. - **Vertebral column (spine / backbone):** consists of a series of bones called vertebrae and connective tissues. - Makes up 2/5ths of an individuals height. - Contains 26 bones/vertebrae: - 7 cervical - 12 thoracic - 5 lumbar - 1 sacrum - **Vertebral curves:** - Cervical & lumbar = convex - Thoracic & sacral = concave - **Abnormal curve:** scoliosis, kyphosis, lordosis. - **Intervertebral discs:** fibrocartilage pad, found between bodies of adjacent vertebrae. - **Nucleus pulposus:** fluid -> 90% h2o - Each vertebrae consists of a vertebral arch, bodies, vertebral foramen, processes and articulating surfaces. - The cervical vertebrae are the most variable in shape and structure. - **C1 = Atlas** - **C2 = Axis** - **Thorax (chest region):** makes up the thoracic cage: - Sternum, ribs, and costal cartilage. - **Sternum:** consists of manubrium (top), sternal body (middle), and xiphoid process (bottom). - **Ribs:** attach to thoracic vertebrae (posterior) and costal cartilage to sternum (anterior). - **Appendicular skeleton:** - **Upper limb (shoulder girdle and arm)**: each limb consists of 32 bones. - **Shoulder girdle:** attaches the upper limb to the axial skeleton. - **Clavicle** (anterior): - **Scapula** (posterior) - **Arm (free upper limb):** - **Humerus** (upper arm). - **Radius** (thumb) and **ulna** (pinkie) - forearm. - **Hand:** - **Carpals** (8), **metacarpals** (5), **phalanges** (14) - **Lower limb (pelvic girdle and leg):** each lower limb consists of 31 bones. - **Pelvic girdle:** consists of two hip bones called coxal bones. - They unite anteriorly at the **pubic symphysis** and posteriorly at the **sacrum**. - Each coxal bone consists of three bones: **ilium, ischium, pubis**. - **Leg (Free lower limb)**: - **Femur** (upper leg): - **Patella** (knee cap). - **Tibia** (big toe) and **fibula** (pinkie toe) (lower leg): - **Foot:** **Tarsals** (7), **metatarsals** (5), **phalanges** (14).