Exercise Science and Sports Medicine Unit 3 A SKELETAL SYSTEM Lecture notes I. Introduction a. The skeletal system is defined as the framework of bones, cartilage, ligaments and other connective tissues in the human body. b. Normally, the human skeleton is composed of 206 bones that give form to the body and, with the joints, allow body motion. c. Bones must be rigid and unyielding to fulfill their function, but they must also grow and adapt as the human being grows. As a rule, bone growth is complete by late teens. d. Bones are just as much living tissue as muscle and skin. A rich blood supply constantly provides the oxygen and nutrients that bones require. Each bone also has an extensive nerve supply. II. Functions of the skeletal system a. Support: Bones are as strong as or stronger than reinforced concrete. The skeletal system provides structural support for the entire body. b. Protection: Delicate tissues and organs are surrounded by skeletal elements. i. The skull protects the brain. ii. The vertebral column protects the spinal cord. iii. The ribs and sternum protect the heart and lungs. iv. The pelvis protects the digestive and reproductive organs. c. Movement: Bones work together with muscles to produce controlled, precise movements. The bones serve as points of attachment for muscle tendons. Bones act as levers that convert muscle action to movement. d. Storage: Bones store minerals that can be distributed to other parts of the body upon demand. Calcium and phosphorus are the main minerals that are stored in bones. In addition, lipids are stored as energy reserves in the yellow bone marrow. e. Hemopoiesis (production of blood cells): Red bone marrow produces red blood cells, white blood cells, and platelets. III. Classification of Bones a. The bones of the human skeleton have four general shapes: long, short, flat, and irregular. b. Long – are longer than they are wide. i. Examples – humerus, femur, ulna, metacarpals, metatarsals, phalanges, tibia, and fibula. c. Short – are nearly equal in length and width; are somewhat cube shaped. i. Examples – carpals, tarsals. d. Flat – are thin and relatively broad; have a large surface area for muscle attachment. i. Examples – scapula, cranial bones, sternum, ribs. Unit 3 A– Skeletal System 1 draft copy Exercise Science and Sports Medicine e. Irregular – have complex shapes that do not fit easily into any other category. i. Examples – facial bones, vertebrae. f. Sesamoid – sesamoid bones are small bones that are situated within tendons. They are also called floating bones. i. Example – patella. IV. Structure of the Skeletal System a. The typical features of a long bone such as the humerus. i. Diaphysis – the long central shaft of bone; contains the yellow bone marrow; made of compact (or dense, relatively solid) bone. ii. Epiphysis – the expanded ends of the bone; contains the red bone marrow; made of spongy (lighter) bone. iii. Epiphyseal line – also known as the growth plate, this is the area where the diaphysis meets the epiphysis. In growing bone, it is the region where cartilage is reinforced and then replaced by bone. iv. Articular Cartilage – a thin layer of cartilage covering the epiphysis or ends of the bone. It provides a smooth gliding surface for a joint and helps to protect the ends of the bone. v. Periosteum – a dense fibrous covering around the surface of the bone. It is essential for bone growth, repair, and nutrition. It also functions as a point of attachment for ligaments and tendons. V. Skeletal Terminology a. Each of the bones in the human skeleton not only has a distinctive shape but also has distinctive external features. b. These external landmarks are called bone markings or surface features. i. Foramen – a tunnel or hole for blood vessels and/or nerves. (examples – pelvis, skull.) ii. Fossa – a shallow depression. (example – pelvis.) iii. Condyle – a smooth, rounded articular process; knuckle like projection. (examples – femur, humerus.) iv. Tuberosity – a small, rough projection. (examples – tibia, pelvis.) v. Crest – a prominent ridge. (example – pelvis.) vi. Sinus – a chamber within a bone, normally filled with air. (example – skull.) VI. Skeletal Divisions a. The skeletal system consists of 206 separate bones and is divided into the axial and appendicular divisions. b. Axial Skeleton i. Forms the longitudinal axis of the body. ii. The 80 bones of the axial skeleton can be subdivided into: 1. The 22 bones of the skull plus associated ones (6 auditory bones and the hyoid bone). 2. The 26 bones of the vertebral column. Unit 3 A– Skeletal System 2 draft copy Exercise Science and Sports Medicine 3. The 24 ribs and the sternum. c. Appendicular Skeleton i. Forms the limbs and the pectoral and pelvic girdles. ii. Altogether there are 126 appendicular bones; 32 are associated with each upper limb and 31 with each lower limb. VII. Bones a. The following bones should be located and memorized by students (these are not all of the bones in the human skeleton): i. Skull 1. Parietal 2. Occipital 3. Temporal (Mastoid Process) 4. Frontal 5. Zygomatic 6. Mandible 7. Maxilla 8. Nasal ii. Vertebral Column 1. Note – spinous & transverse processes, body, and vertebral foramen 2. 7 Cervical (Atlas & Axis) 3. 12 Thoracic 4. 5 Lumbar 5. 5 Sacral 6. 4 Coccyx iii. Sternum: lies in front of the heart; distal tip is known as the xiphoid process. iv. Hyoid: located in neck; provides attachment for tongue and voice box muscles. v. Ribs (12 pairs) 1. First 7 pairs: connected by cartilage to sternum; known as true ribs. 2. Pairs 8-10: attach indirectly to the sternum; known as false ribs. 3. Pairs 11-12 are also known as floating ribs as they have no attachment to the sternum. vi. Upper Extremity 1. Clavicle (collar bone) 2. Scapula (shoulder blade) 3. Humerus (Epicondyles) 4. Radius 5. Ulna 6. 8 Carpals 7. 5 Metacarpals 8. 14 Phalanges (proximal, middle, and distal) Unit 3 A– Skeletal System 3 draft copy Exercise Science and Sports Medicine vii. Pelvis 1. Illium 2. Ischium 3. Pubis viii. Lower Extremity 1. Femur 2. Tibia 3. Fibula 4. Patella 5. 7 Tarsals (Calcaneus) 6. 5 Metatarsals 7. 14 Phalanges (proximal, middle, and distal) VIII. Joints a. Joints or articulations exist wherever two bones meet. The function of each joint depends on its anatomy. Each joint reflects a workable compromise between the need for strength and the need for mobility. b. Ligaments – connect bone to bone. c. Bursa – fluid filled sacs that reduces friction between soft tissue and bones; also act as shock absorbers. d. Meniscus – a cartilage disc between some complex joints for shock absorption, cushioning, and stability. e. Types of Movement i. Students should understand the terminology and practical movements associated with the following terms: 1. Flexion 2. Extension 3. Abduction 4. Adduction 5. Circumduction 6. Rotation, including Internal Rotation and External Rotation 7. Pronation 8. Supination 9. Inversion 10. Eversion 11. Dorsiflexion 12. Plantar Flexion 13. Opposition 14. Protraction 15. Retraction 16. Elevation 17. Depression Unit 3 A– Skeletal System 4 draft copy Exercise Science and Sports Medicine f. Joint Classification i. Joints can be classified according to the range of motion they permit. ii. Synarthrotic Joints 1. Immovable joints. 2. Bones are connected by fibrous tissue or cartilage. 3. Examples: sutures – found between bones in the skull. iii. Amphiarthrotic Joints 1. Slightly moveable joints. 2. Examples: Joint between tibia and fibula, joints between vertebrae. iv. Diarthrotic Joints 1. Freely moveable joints permitting a wide range of motion. 2. Ends of the bones in diarthrotic joints are covered by cartilage and held together by synovial capsules filled with synovial fluid. This fluid helps to lubricate the joint and permits smooth movement. 3. Categories a. Gliding joints – have relatively flattened articular surfaces which slide across each other. The amount of movement is relatively small. Examples – between the tarsal and carpal bones, between the clavicle and sternum. b. Hinge joints – permit motion in a single plane, like the opening and closing of a door. Examples – elbow, knee, ankle, and interphalangeal joints. c. Pivot joints – permit only rotation. Examples – between radius and ulna permitting supination/pronation, between atlas and axis. d. Saddle joints – articular surfaces that resemble saddles and opposing surfaces nest together. This permits angular motion including circumduction, but prevents rotation. Example – carpometacarpal joint at the base of the thumb. e. Ball and Socket joints – the round head of one bone rests within a cup-shaped depression in another. All combinations of movements, including circumduction and rotation, can be performed at these joints. Examples – shoulder and hip joints. IX. Exercise and the Skeletal System a. Bone is dynamic and changes with the stress put on it. Bone has the ability to alter its strength in response to stress placed on it. b. Bones that are positively stressed will increase their density and become stronger over a period of time. Conversely, bones that are adversely stressed will become weakened over time. Unit 3 A– Skeletal System 5 draft copy Exercise Science and Sports Medicine c. Exercise enables bone to i. Increase its deposition of mineral salts and collagen fibers. ii. Become considerably stronger than bones of sedentary individuals. iii. Maintain its strength and integrity. d. Wolff’s Law says that function determines form. Bone responds to physical stresses or the lack of them. Bone is deposited on areas subjected to stress and reabsorbed from areas where little stress is present. X. Common Disorders of the Skeletal System a. Osteoporosis i. A condition that produces a reduction in bone mass great enough to compromise normal function. Because bones are more fragile, they break easily and do not repair well.