Bones and Muscles PDF

Bones and Muscles Siobhán O’Connor MSc PhD Certified Athletic Therapist (CAT) Bone • Extremely hard/resilient: Tensile strength almost equal to that of cast iron, Compressive strength even greater, yet 3 times as light and 10 times as flexible • Bone is a complex, vascularized, dense connective t...

Bones and Muscles Siobhán O’Connor MSc PhD Certified Athletic Therapist (CAT) Bone • Extremely hard/resilient: Tensile strength almost equal to that of cast iron, Compressive strength even greater, yet 3 times as light and 10 times as flexible • Bone is a complex, vascularized, dense connective tissue with cells embedded in a matrix composed of organic materials (mainly collagen) and inorganic salts rich in calcium and phosphate • Organic matrix of fibrous connective tissue impinged with mineral salts • Bone is constantly changing in response to mechanical (Wolff’s law) and hormonal signals Epiphysis • end part of a long bone, initially growing separately from the shaft. Diaphysis • shaft of the bone Growth plate (physis) • area of tissue near the ends of long bones in children and teens that determines the future length and shape of the mature bone. • Each long bone has at least two growth plates Classifying Bones (Shape) • Long • Flat • Irregular • Sutural • Sesamoid Long Bone • Example - Femur • Diaphysis • Epiphyses • Periosteum - membrane of blood vessels and nerves that wraps around most of your bones • Cartilage • Epiphyseal cartilage -Layer between the diaphysis and the epiphyses that allow the shaft to continue growing until 18-25 Also called growth plate or physis Flat Bones • Example - Scapula, sternum, pelvic bones • Two layers of compact bone held together by spongy bone • They are smooth and flat to protect delicate organs and provide a large surface for muscle attachment Short bones • Example - Carpals, tarsals • Roughly cube like • Allow a wider range of movement than larger bones Irregular bones • Example - Vertebrae • Mass of spongy bone surrounded by compact bone Sutural Bones • Example - Skull • Small and Flat • Their borders are like jigsaw puzzle pieces • Structure - Similar to long bones Sesamoid bones • Example - Patella, Sesamoids • Small, flat • They develop inside tendons Bone structure • Bone/Osseous tissue - Combination of inorganic (phosphate, calcium) and organic (collagen) - Combination makes bones hard and resistant to compressive loads but brittle • Their strength depends on load mechanism • Highly adaptive material (high rate turnover) • The basic functional unit of compact bone is the OSTEON (also called the Haversian system) • Comprised of the following: - Lamellae - rings of mineralized matrix - Lacunae - small cavities within bone where the osteocytes are located - Canaliculi - small canals that link the lacunae to the blood vessels – all nutrients get to all of the osteocytes - Haversian canal - at the centre of each osteon - contains blood vessels and nerves running parallel to long axis of the bone Structure – Compact Bones • The collagen fibers are - Arranged in dense layers - Going in different directions - Allowing high resistance to tensile forces • This is the layer that gives bone its amazing strength • The lamellae and Haversian systems are– packed closely together with – only small spaces between the lamellae to house osteocytes and between each Harversian system for lymph Structure – Spongy Bone • Spongy bone differs from compact bone in that the – Haversian canals are larger and – larger gaps between the lamellae. • Trabeculae – Small flat pieces making up spongy bone • Forms Marrow Cavity – The spaces this structure creates are filled with red and yellow bone marrow, – which is a mixture of fat and red blood cells. • The spaces also help to reduce the weight of the bone. Structure – Cells of Bone • Osteocytes -mature bone cells that occupies a lacuna, a space between layers of matrix (calcium salts and protein fibres) surrounding blood vessels • Osteoblast - Formation - Osteocytes precursor • Osteoclast - Breakdown – Cells that break the bone structure removing and recycling bone matrix – Their secretion is a mix of acids and proteolytic enzymes releasing minerals Structure - Bone Growth • The balance between the opposing activities of Osteoblasts and Osteoclasts is a key factor in bone physiology • Osteoclasts > Osteoblasts – bones weaken • Osteoblasts > Osteoclasts – bones become stronger Structure – Bone Growth • Bone growth – The balance between resorption and deposition – allow the bone to self repair (when injured) and to change shape/density in response to external loading (when exposed) • Mechanical stress is important in grow and strengthen and can affect the density (overweight people, gravitational force) Function of Bone 1. Support (shape and structure) • Skeleton - Provide a support structure • Weight bearing is a fundamental part of the bone physiology • Size and shape can be modified by external load 2. Protection • Skull’s - Protect the brain - Shape is aimed at distributing a force applied to the surface • Rib cage - Protect thoracic organs Function of Bone Ctd. 3. Leverage • Long bones - Provide the levers allowing the muscular system to generate movement - Movement is limited by bone shape - The contribution to movement of the bones depends on - Structural arrangements - And/or joints architecture 4. Storage and Hematopoiesis • Bones store minerals – Calcium – Phosphate • Bones provide blood cell formation Muscles are effectors which enable movement to be carried out • Heart muscle • Also called cardiac muscle • Makes up the wall of the heart. • Smooth muscle • Found in the walls of all the hollow organs of the body (except the heart) e.g. blood vessels, airways etc • Its contraction ↓ the size of these structures. • The contraction of smooth muscle is generally not under voluntary control. • Skeletal muscle • Muscle attached to the skeleton. • Contraction of skeletal muscle is under voluntary control. Types of Muscle Muscles and the Skeleton • Skeletal muscles cause the skeleton to move at the joints • They are attached to skeleton by tendons. • Tendons transmit muscle force to the bone. • Tendons are made of collagen fibers & are very strong & stiff • Parallel e.g. sartorious • Fibres parallel to the line of pull (parallel to longitudinal axis of muscle) • Ends at either end in flat tendons (tend to be long but not very strong but good at endurance) • Fusiform e.g. biceps bracci • Fascicles nearly parallel to longitudinal axis of muscle • Terminate in flat tendons with the muscles tapering towards the tendons (diameter is less than at the belly) • Circular e.g orbicularis oculi (surrounding eyes) • Fascicles in circular arrangements form sphincter muscles that enclose an orifice (opening) • Triangular (convergent) e.g. pec major • Fascicles spread over board area converge at thick central tendon • Pennate • Short fascicles in relation to total muscle length, tendon extends nearly entire length of muscle. Powerful (more fibres packed into the same unit) • Unipennate e.g. flexor pollicis longus • Fascicles arranged on only one side of the tendon • Bipennate e.g. rectus femoris • Fascicles arranged on both sides of a centrally positioned tendon. • Multipennate e.g. deltoid • Fascicles attach obliquely from many directions to several tendons Arrangement of Fascicles Muscle Action • Concentric contraction • Muscles shorten and generate force • Eccentric contractions • Muscles elongate in response to a greater opposing force • Isometric contraction • Generate force without changing the length of the muscle Antagonistic Muscle Action • Muscles are either contracted or relaxed • When contracted the muscle exerts a pulling force, causing it to shorten (Prime mover) • Since muscles can only pull (not push), they work in pairs called antagonistic pairs • Muscles which directly oppose the prime mover are called the antagonist • Muscles which control unwanted movements associated with the action of the prime movers are called synergists • The muscle that bends the joint is called the flexor muscle • The muscle that straightens the joint is called the extensor muscle