MNB.1 Skeleton, Bone, Ossification, Somatic Skeleton PDF

Musculoskeletal System, Nervous System & Bioelectricity MNB.1 Skeleton, Bone, Ossification, Somatic Skeleton N A M E : D r. To m H o d g k i n s o n DAT E : 2 4 t h S e p t e m b e r 2 0 2 4 Learning outcomes At the end of this lecture, the learner will be able to Discuss the structure of...

Musculoskeletal System, Nervous System & Bioelectricity MNB.1 Skeleton, Bone, Ossification, Somatic Skeleton N A M E : D r. To m H o d g k i n s o n DAT E : 2 4 t h S e p t e m b e r 2 0 2 4 Learning outcomes At the end of this lecture, the learner will be able to Discuss the structure of bone and cartilage. Outline the different categories of skeleton. Describe endochondral ossification. Recall the main elements of the axial and appendicular skeleton, vertebrae, girdles, limbs. Discuss the structure of different types of joints. Describe the detailed structure of the vertebral column. M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 2 Introduction to Bone Biology M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 3  The Skeleton The skeleton in the vertebrates is composed of bone and cartilage - mechanical support to the body. Bone Can be divided into two types - spongy and compact. Compact - dense and hard and forms outside of the long bones. It is composed of Haversian systems - central Haversian Canal containing blood vessels which branch through the bone. Surrounding the canal are concentrically arranged lacunae which contain the osteocytes. Spongy (or cancellous) - found in the interior medullary cavity of long and other bones where it forms a network of trabeculae between the marrow. M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 4 Haversian System Osteon Note cross connecting Volkmann canal M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 5 Bone Structure The lacunae are connected together by a system of radiating canaliculi which allow the supply of nutrients to the osteocytes. Bone is in a constant state of remodelling and adaptation. Bone cells called osteoclasts are present in small numbers which can cause bone erosion or resorption (remove damaged bone). Osteoblasts important cell type that secrete the new bone extracellular matrix. This extracellular matrix is composed of about 80% calcium phosphate in the form of calcium hydroxyapatite crystals. Other 20% organic largely protein, mainly type I collagen. M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 6 M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 7 Bone Remodelling The lifelong cycle of bone maintenance (repair) and resorption is called bone remodelling. During development of the skeleton bone growth occurs independent of osteoclast removal of bone in a process called bone modelling. M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 8 Periosteum and Endosteum Periosteum Endosteum Dense layer of vascular Lines the inner surface connective tissue enveloping of the medullary cavity of bone except at joints. all long bones. Outer fibrous layer Thin vascular (containing fibroblasts). membrane of connective tissue. Inner osteogenic layer (containing progenitor cells Osteoclasts resorption of that differentiate into bone occurs from osteoblasts). endosteal side Contains nerves endings that make it very sensitive. M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 9 Cartilage Cartilage locations in the body Functions of cartilage: - Support soft tissues - Provide low friction surface for bone articulation at joints - Enable growth of the long bones. Three types of cartilage: – Hyaline- Most Common. Moderate amount of collagen fibres (e.g., Articulating surfaces of joints). – Elastic- Contains elastic fibres in addition to collagen (e.g., external ear) – Fibrocartilage – Very low number of cells, high collagen fibre content (e.g., Intervertebral disc) There are no blood vessels (avascular), lymphatics or nerves. M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 10  Cartilage Structure More flexible than bone but confers insufficient rigidity to withstand gravity. Semi-rigid supporting structure largely made of an extracellular ground substance of: - proteoglycans (e.g., Aggrecan), - glycosaminoglycans (e.g., chondroitin sulphate, hyaluronic acid) - collagen (e.g., type II collagen) and in some types of cartilage elastic fibres. The spaces in cartilage are called Lacunae and contain Chondrocytes. Some cartilages remain unchanged, others ossify. M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 11 Structure of the skeleton DERMAL SKELETON VISCERAL ENDOSKELETON AXIAL SOMATIC APPENDICULAR The skeleton may be classified into dermal and endoskeleton. The dermal skeleton develops differently to the endoskeleton. In dermal bones osteoblasts from the periosteum convert foetal connective tissue (mesenchyme cells) to bone. This is called Intramembranous ossification. Dermal bones are found in the skull, jaw and pectoral girdle. M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 12  Structure of the skeleton - Endoskeleton DERMAL SKELETON VISCERAL ENDOSKELETON AXIAL SOMATIC APPENDICULAR Endoskeleton is always preformed of cartilage and forms the rest of the skeleton. It is divided into two further categories; 1. Visceral skeleton only found in larynx, tracheal cartilages, ossicles. 2. Somatic skeleton - all the rest! M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 13 Somatic Skeleton Axial skeleton highlighted in green The somatic skeleton is divided into two parts the axial skeleton and the appendicular skeleton. Axial: skull, vertebral column (including the sacrum), ribs, and sternum. M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 14 Axial Skeleton - Vertebrae Divided into five regions: Cervical Vertebrae (C1-C7): Smaller, with transverse foramina and bifid spinous processes. Thoracic Vertebrae (T1-T12): Larger, with long spinous processes and facets for rib articulation. Lumbar Vertebrae (L1-L5): Largest, with short, blunt spinous processes. Sacrum (S1-S5): Fused into a triangular bone. Caudal (4 fused as Coccyx): Small, fused vertebrae forming the tailbone. M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 15 Vertebral Column Spinous Process (1): A single projection that extends posteriorly from the vertebral arch. It serves as an attachment point for muscles and ligaments. Transverse Processes (2): Two lateral projections, one on each side of the vertebra. They serve as attachment points for muscles and ligaments and, in the thoracic region, for ribs. Superior Articular Processes (2): Two projections that extend upward. They articulate with the inferior articular processes of the vertebra above them. Inferior Articular Processes (2): Two projections that extend downward. They articulate with the superior articular processes of the vertebra below them. M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 16 Somatic Skeleton Appendicular: all the rest including – Pectoral girdle: clavicle, scapula. Upper limb: humerus, radius, ulna, carpal bones, metacarpals, phalanges. Pelvic girdle: hip bone (ilium, ischium, pubis). Lower limb: femur, tibia, fibula, tarsal bones, metatarsals, phalanges. Sesamoid bones: develop in tendons as they turn corners, the patella or knee-cap is an example. M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 17  Endochondral Ossification In the foetus, cartilage models the shape of A B C D E the future adult bone (A). May persist for months or years before being invaded by osteoblasts for conversion to bone with laying down of minerals, calcium and phosphate (B, C D and E). Ends of bone - epiphyses - the last parts of a long bone to ossify (epiphyseal plate, E). Until ossification is complete the epiphysis remains separated from the shaft (the diaphysis) by the epiphyseal plate of hyaline cartilage (E). M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 18 Endochondral Ossification Epiphyseal (growth) plates are not penetrated by blood vessels, so nutrient artery of the diaphysis contributes no supply to the epiphyses of long bone Avascular until after epiphyseal plate has disappeared. growth plate Damage to the blood supply can result in death (necrosis) of the bony tissue and if this affects the growing end of a bone in children, normal development is delayed or prevented. M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 19 When Endochondral Ossification does not proceed as typical During endochondral bone growth the bone shaft is thickened by the addition of perichondral bone. This is formed like membrane (dermal) bone in successive layers. Too much natural growth hormone (eg pituitary tumour) before the epiphyses have united leads to gigantism. Robert Wadlow M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 8ft 11in (2.72m) 20 When Endochondral Ossification does not proceed as typical Too much natural growth hormone (eg pituitary tumour) after the epiphyses have united leads to acromegaly (large extremities). Growth hormone abuse by young athletes delays fusion of the epiphyses. Sultan Kösen Current Worlds Tallest man M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 21  Endochondral Ossification- Genetic Condition Achondroplasia is a genetic condition due to a rare autosomal dominant mutation. Failure of long bone endochondral ossification, especially humerus and femur. Typical Bone Growth Achondroplasia M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 22 Joints Joints are junction sites of two or more bones of the body. Two basic types non-synovial and synovial. Non-Synovial Fibrous joints Bone - fibrous tissue – bone e.g., inferior tibiofibular, sutures of skull. Little movement, except that fetal skull bones move during birth. Cartilaginous joint Two types are found. As age advances, cartilaginous joints may ossify. Primary cartilaginous: Bone - hyaline cartilage – Bone All ossify except first rib-sternum. Secondary cartilaginous: Bone - Hyaline - Fibrocartilaginous disc - Hyaline – Bone Symphyses. 23 Joints Synovial Joints Freedom of movement. Articular surfaces covered by articular cartilage and between them is the synovial cavity. Synovial membrane does not cover articular surfaces themselves. Synovium is specialised tissue that produces synovial fluid for lubrication. Also found outside joints in places where friction resistance is necessary: bursas and synovial sheaths. A disease of the synovium is rheumatoid arthritis. M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 24 Learning outcomes review After learning this lecture material, you should be able to: Discuss the structure of bone and cartilage. Outline the different categories of skeleton. Describe endochondral ossification. Recall the main elements of the axial and appendicular skeleton, vertebrae, girdles, limbs. Discuss the structure of different types of joints. Describe the detailed structure of the vertebral column. M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 25 Useful Reading Chapter 40 (838-842) Biology, Solomon Chapter 39 on tissue types also. Chapter 10 (204-209) Human Biology, Chiras M N B. 1 S k e l e t o n , B o n e , O s s i fi c a t i o n , S o m a t i c S k e l e t o n 26 Thank you F O R M O R E I N F O R M AT I O N P L E A S E C O N TA N T N A M E : D r. G o b i n a t h R a m a c h a w o l r a n E M A I L : r. g o b i n a t h @ r c s i u c d. e d u. m y 27