The Human Skeletal System PDF

7 The Human Skeletal System By: Abdullah Munqith Bones and Joints: The human skeleton consists of about 206 bones. Junctions between neighboring bones are called Joints. Although some joints like those in the skull allow little or no movement, the majority enable for bones to move freely. These are...

7 The Human Skeletal System By: Abdullah Munqith Bones and Joints: The human skeleton consists of about 206 bones. Junctions between neighboring bones are called Joints. Although some joints like those in the skull allow little or no movement, the majority enable for bones to move freely. These are known as Synovial joints, and different types allow different types of movement. The elbow, for example, is a simple hinge, whereas the shoulder and the hip, which have a greater range of movement, are ball-and-socket joint. Bones and Joints: The bones on either side of a synovial joint are held together by ligaments. The parts of the bones that form the joint are covered with cartilage-a tough, slightly elastic material that protects the bones from damage. Friction between the layers of cartilages minimized by the presence of a lubricant known as synovial fluid. Muscles: Bones are moved by muscles which are attached to them by tendons. When a muscle contract (under the action of nerve impulses from the brain) it pulls on the bones on each side of it and causes one of them to move. Muscles cannot push and therefore to return the bone to its original position, the first muscle relaxes and a second muscle, acting in opposition to the first, contract Figure below. The two muscles are known as an antagonistic pair. Bone composition Q/What is bone made of? The outer surface of bone is called the periosteum. It's a thin, dense membrane that contains nerves and blood vessels that nourish the bone. The next layer is made up of compact bone. This part is smooth and very hard. It's the part you see when you look at a skeleton. Within the compact bone are many layers of cancellous (spongy) bone, which looks a bit like a sponge. Cancellous bone is not quite as hard as compact bone, but it is still very strong. Bone composition In many bones, the cancellous bone protects the innermost part of the bone, the bone marrow. Bone marrow is sort of like a thick jelly, and its job is to make blood cells. ✓ There are two kinds of bones Compact bone & cancellous (sponge) bone. advantage of sponge over compact bones? ❖ What is the advantage of sponge over compact bones? 1- Spongy bone under compressive forces gives the strength necessary with less material than compact bone. 2- Spongy bones are relatively flexible and can absorb more energy when large forces are involved such as walking, runing and jumping. ✓ All bones could be divided into two parts axial & appendicular Skelton Bone remolding: A continues process of destroying old bone and building new one. There are two types of cell in bone remolding. ✓ Osteoblasts Are mononucleate bone-forming cells. They are located on the surface of osteoid seams and make a protein mixture known as osteoid, which mineralizes to become bone Bone remolding: ✓ Osteoclasts Are the cells responsible for bone resorption, thus they break down bone. New bone is then formed by the osteoblasts. Bone is constantly remodeled by the resorption of osteoclasts and created by osteoblasts. Bones have about (1000g of Ca). Each day the osteoclast destroying bones containing 0.5 g of Ca, while osteoblast builds new bone using the same amount of Ca. So we have a new Skelton about every seven years Osteoporosis Osteoporosis is a disease of bone where there is reduced bone mineral density, increasing the likelihood of fractures. Osteoporosis is most common in women especially in spine and hip. Osteoporosis usually has no symptoms until a fracture occur. Up to 35 – 40 years old the activity of the osteoblast is greater than osteoclast. Over that age the process is reversed causing a gradual decrease in bone mass that continues until death. Osteoporosis ✓ Osteoporosis treatment includes advice to: 1. 2. 3. 4. 5. Stop smoking Decrease alcohol consumption Exercise regularly Have a healthy diet. Calcium supplements may also be advised, as May Vitamin D. Types of Bones Here are five types of bones in the human body: long, short, flat, irregular, and sesamoid. ✓ Long bones are characterized by a shaft, the diaphysis that is much longer than its width; and by an epiphysis, a rounded head at each end of the shaft. They are made up mostly of compact bone, with lesser amounts of marrow, located within the medullary cavity, and spongy, cancellous bone. Most bones of the limbs, including those of the fingers and toes, are long bones femur, tibia. Types of Bones ✓ Short bones Are roughly cube-shaped, and have only a thin layer of compact bone surrounding a spongy interior. The bones of the wrist and ankle are short bones. Types of Bones ✓ Flat bones Are thin and generally curved, with two parallel layers of compact bones sandwiching a layer of spongy bone. Most of the bones of the skull are flat bones, as is the sternum. Types of Bones ✓ Sesamoid bones Are bones embedded in tendons. Since they act to hold the tendon further away from the joint, the angle of the tendon is increased and thus the leverage of the muscle is increased. Examples of sesamoid bones are the patella and the pisiform. Types of Bones ✓ Irregular bones Do not fit into the above categories. They consist of thin layers of compact bone surrounding a spongy interior. As implied by the name, their shapes are irregular and complicated. Often this irregular shape is due to their many centers of ossification or because they contain bony sinuses. The bones of the spine, pelvis, and some bones of the skull are irregular bones. Examples include the ethmoid and sphenoid bones Types of Bones Q/ What could determine the bone function? 1. The bone shape. 2. The interval construction of bone. 3. The type of material to be formed. Types of Bones ✓ Bones have many functions, including the following: Shape Bone structure gives shape to the body. This shape changes as you grow, and your skeletal system determines your height, width and other factors, such as the size of your hands and feet. Body shape or type is genetically inherited. There are three main body shapes : ectomorphs (tall and thin), mesomorphs (shorter and muscular) and endomorphs (apple or pear-shaped). Types of Bones Support The skeleton provides support to the body and keeps your internal organs in their proper place. The vertebral column allows you to stand erect, while cavities hollow spaces in the skeleton are designed to hold your organs. For example, the skull holds the brain; the chest cavity holds your lungs and heart while the abdominal cavity holds your gastrointestinal organs. Additionally, the pelvis and leg bones are strong and thick to support the weight of the entire skeleton. Types of Bones Movement The skeletal bones are held together by ligaments. Tendons attach your muscles to the bones of your skeleton. The muscular and skeletal systems work together to carry out bodily movement, and together they are called the musculoskeletal system. When muscles contract, the skeleton moves. The shape of the skeletal system also impacts movement. The small bones of the foot allow for adaptation to all sorts of terrain, while the small bones in the hands allow for precise and detailed movement. Types of Bones Protection His skeleton protects vital organs from damage, encasing them within hard bones. The cranium bone --skull -- houses the brain, while the vertebral, or spinal, column protects the delicate spinal cord, which controls all bodily functions through communication with your brain. The bony thorax, comprised of the ribs and sternum, protects your heart and lungs. Types of Bones Blood Cell Production and Storage The spongy tissue inside long bones, such as the femur, or thigh bone, has two types of marrow responsible for blood cell production. On average, 2.6 million red blood cells are produced each second by the bone marrow. Types of Bones Blood Cell Production and Storage Red bone marrow gives rise to blood cells while yellow bone marrow stores fat, which turns into red bone marrow in case of severe red blood cell depletion or anemia. Skeletal bones also function as a storage bank for minerals, such as calcium and phosphorus. These minerals are necessary for vital body functions, such as nerve transmission and metabolism. Vertebral column (Spine) The spine consists of (33 vertebrae) and provides the main support for the body. Nine of the vertebrae at the base of the spine are fused, five to form the sacrum and four to form the coccyx. The top 24 are covered with cartilage and are separated from each other by tough fibrous known as discs. The discs allow the spine to bend and to twist.They also protect the vertebrae from wear and cushion them from shock. Stress–strain curve ▪ Stress strain curve is a behavior of material when it is subjected to load. ▪ In this diagram stresses are plotted along the vertical axis and as a result of these stresses, corresponding strains are plotted along the horizontal axis. ▪ From the diagram one can see the different mark points on the curve. Stress–strain curve ▪ It is because, when a ductile material like mild steel is subjected to tensile test, then it passes various stages before fracture. These stages are; 1. 2. 3. 4. 5. Proportional Limit Elastic Limit Yield Point Ultimate Stress Point Breaking Point Stress–strain curve 1- PROPORTIONAL LIMIT ✓ Proportional limit is point on the curve up to which the value of stress and strain remains proportional. From the diagram point A is the called the proportional limit point or it can also be known as limit of proportionality. The stress Up to this point can be also being known as proportional limit stress. ✓ Hook’s law of proportionality from diagram can be defined between point OA. It is so, because OA is a straight line which shows that Hook’s law of stress strain is followed up to point A. Stress–strain curve 2- ELASTIC LIMIT Elastic limit is the limiting value of stress up to which the material is perfectly elastic. From the curve, point B is the elastic limit point. Material will return back to its original position, if it is unloaded before the crossing of point B. This is so, because material is perfectly elastic up to point B. 3- YIELD STRESS POINT Yield stress is defined as the stress after which material extension takes place more quickly with no or little increase in load. Point B is the yield point on the graph and stress associated with this point is known as yield stress. Stress–strain curve 4- ULTIMATE STRESS POINT Ultimate stress point is the maximum strength that material has to bear stress before breaking. It can also be defined as the ultimate stress corresponding to the peak point on the stress strain graph. On the graph point D is the ultimate stress point. After point D material have very minute or zero strength to face further stress. Stress–strain curve 5- BREAKING STRESS (POINT OF RUPTURE) ✓ Breaking point or breaking stress is point where strength of material breaks. The stress associates with this point known as breaking strength or rupture strength. On the stress strain curve, point E is the breaking stress point. ✓ Consider a bar of cross sectional area (A) being subjected to equal and opposite forces (F) pulling at the ends so the bar is under tension. The material is experiencing a stress defined to be the ratio of the force to the cross sectional area of the bar: Stress = F/A N/m2 = Pa Stress–strain curve ✓ Now consider a force that is applied tangentially to an object. The ratio of the shearing force to the area A is called the shear stress. Or the ratio between changing in length (∆ ℓ) to the original length (ℓ). Strain = ∆ℓ/ℓ Stress–strain curve ✓ Finally, the shear modulus Y of a material is defined as the ratio of shear stress to shear strain at any point in an object made of that material. The shear modulus is also known as the torsion modulus. Y= Stress = F ℓ Strain A ∆ℓ Stress–strain curve 6- STRENGTH OF MATERIEL The ability of a material to withstand an applied load without failure or plastic deformation. Stress–strain curve 1- Compressive stress is the stress state caused by an applied load that acts to reduce the length of the material along the axis of the applied load, example pushing forces. (a) 2- Tensile stress is the stress state caused by an applied load that tends to elongate the material along the axis of the applied load, example by pulling the material. (b) 3- Shear stress is the stress state caused by the combined energy of a pair of opposing forces acting along parallel lines of action through the material , example tress caused by faces of the material sliding relative to one another. (c) Stress–strain curve Elasticity is the ability of a material to return to its previous shape after stress is released. Plasticity or plastic deformation is the opposite of elastic deformation and is defined as unrecoverable strain