The Skeletal System Functions of the Skeletal System • Support- The skeleton forms a rigid framework to which are attached the soft tissues and organs of the body • Protection- The skull, vertebral column, rib cage, and pelvic girdle enclose and protect vital organs and sites for blood cell production is found in the protected hollows of certain bones. • Movement- Bones act as levers when muscles contract, causing movement at the joints. • Mineral Storage- The matrix of bone is composed primarily of calcium and phosphorous, with small amounts of magnesium and sodium thrown in. – About 99% of the calcium and 90% of the phosphorous found in the body is found in bones and teeth. – These minerals give bones rigidity and account for ≈ 2/3 the weight of the bone. • Hemopoiesis – Red bone marrow produces red and white blood cells and platelets in adults. Types of Bones Types of Bones • LONG BONES- have a tubular shaft and articular surface at each end. • The major bones of the arms (humerus, radius, and ulna) and the legs (the femur, tibia, and fibula) are all long bones. Phalanges are also long bones • SHORT BONES- Short bones in the human body are cubelike -- the length, width, and height measurements are all about the same. • Short bones include the carpal bones (hands, wrist) and tarsal bones (feet, ankles). Types of Bones • IRREGULAR BONES- are irregular in size and shape and are usually quite compact. They include the bones in the vertebral column, the patella (kneecap), mandible (jaw), maxilla (upper jaw). • FLAT BONES- thin and have broad surfaces. The flat bones include the scapula (wingbone), the ribs, and the sternum (breastbone) and some skull bones. • Bone is a variety of connective tissues built mainly by the deposition of calcium phosphate. The matrix also contains collagenous fibers, bone cells and a large amount of water. • osteoblasts- cells that help form bone • osteoclasts- cells that help eat away old bone. • osteocytes- mature osteoblasts that have ended their bone-forming careers and are trapped in the bone matrix. These cells engage in metabolic exchange with the blood that flows through the bones. Diaphysis- The shaft of a long bone. Compact bone tissue. Contains the Medullary cavity, which contains fatty yellow bone marrow (where fat is deposited) and is lined with endosteum (squamous epithelium). On either end of the diaphysis are the Epiphysis- the ends of the bone which consist of spongy bone surrounded by compact bone. Red bone marrow (where blood is made) is found within the pores of the spongy bone. A Typical Long Bone Separating the epiphysis from the diaphysis is the epiphyseal plate, an area of mitotic activity where linear bone growth occurs (elongation). An epiphyseal line replaces the plate when bone growth is complete. The entire bone is covered by periosteum, a connective tissue that is the site of tendon-muscle attachment and diametric bone growth (widening) A Typical Long Bone The periosteum contains collagenous fibers and many osteoblasts, which are cells that can develop into osteocytes. The ends of the epiphysis are covered with articular cartilage, a thin, smooth cartilage that facilitates the movement of the joints. A Typical Long Bone Microscopic structure • Under the microscope dense, compact bone shows a definite and characteristic pattern of arrangement. • Haversian canals- Small canals that run parallel to the long axis (shaft) of the bone. These canals are interconnected with one another and contain a blood vessel, a nerve and a lymph vessel. • Each Haversian canal is surrounded by concentric layers of bone matrix (called lamallae) and concentric rings of bone forming cells (osteoblasts). Osteoblasts and Osteocytes Bone building cells Osteoblasts synthesize and secrete collagen fibers and other organic components needed to build the matrix of the tissue Osteoblasts surround themselves with matrix, become trapped in their secretions and become osteocytes (mature bone cells) • Do not undergo Mitosis • Osteocytes - maintain metabolism • Bone cells remain alive and once they have been completely surrounded by the hard bone matrix they are called osteocytes. • The osteocytes are embedded in fluid-filled cavities within the concentric lamellae. • These cavities are known as lacunae and occur at regular intervals in these concentric layers of bone tissue. • The lacunae are connected to one another and to the Haversian canals by a system of interconnecting canals known as canaliculi. • Each Haversian canal, its concentric lamellae, lacunae with osteocytes and canaliculi forms a long cylinder and is called a Haversian system. Separate Haversian systems are joined to each other by means of interstitial lamellae. Microscopic Structure of Bone and Cartilage • Compact bone is composed of osteocytes within lacunae arranged in concentric circles called lamellae • This surrounds a central canal. The entire complex is called a Haversian system • Canaliculi connect osteocytes to central canal and to each other Spongy Bone The arrow labeled o points to an osteocyte in its lacuna. Canaliculi (not visible here) connect the lacunae of osteocytes to each other and to the marrow spaces between the trabeculae. Spongy (cancellous) bone is lighter and less dense than compact bone. Spongy bone is a network of irregularly-shaped sheets and spikes of bone (trabeculae). The spaces between the trabeculae contain red or yellow marrow, depending on a person's age and on which bone it is. The trabeculae are organized to provide maximum strength similar to braces that are used to support a building. Spongy bone is located in the hipbone and sternum of adults. A single Haversian system, or osteon, in compact bone. The Haversian canal in the center contains the blood vessel, with associated nerve. b Concentric layers of extracellular matrix (a, for example), and the osteocytes are fully encapsulated by the matrix. At the edges of the image the cement line are where one osteon meets another (b). Bone Formation and Growth • ossification- the formation of bone by the activity of osteoblasts and osteoclasts and the addition of minerals and salts. There are two types of ossification: intramembranous and endochondral. In the fetus, most of the skeleton is made up of cartilage, a tough, flexible connective tissue that has no minerals or salts. By the end of the eighth week after conception, the skeletal pattern is formed in cartilage and connective tissue membranes, and ossification begins. • The replacement of hyaline cartilage by bone is called endochondral ossification. Most of the bones of the skeleton are formed in this manner. • Intramembranous ossification involves the replacement of sheet-like connective tissue membranes with bony tissue. Certain flat bones of the skull and some of the irregular bones are formed in this manner. Endochondral Ossification • During the third month after conception, the perichondrium (the membrane of fibrous connective tissue) that surrounds the hyaline cartilage models becomes infiltrated with blood vessels and osteoblasts and changes into a periosteum. – The osteoblasts form a collar of compact bone around the diaphysis. – At the same time, the cartilage in the center of the diaphysis begins to disintegrate. – Osteoblasts penetrate the disintegrating cartilage and replace it with spongy bone. • Ossification continues from this center toward the ends of the bones. After spongy bone is formed in the diaphysis, osteoclasts break down the newly formed bone to open up the medullary cavity. • When ossification is complete, the hyaline cartilage is totally replaced by bone except in two areas. A region of hyaline cartilage remains over the surface of the epiphysis as the articular cartilage and another area of cartilage remains between the epiphysis and diaphysis. This is the epiphyseal plate or growth region. • Bone resorption is the process by which osteoclasts break down bone and release the minerals. • http://www.argosymedical.com/flash/aging_bone /landing.html • Bones grow in length at the epiphyseal plate. • The cartilage in the region of the epiphyseal plate next to the epiphysis continues to grow by mitosis. The chondrocytes (cartilage cells) in the region next to the diaphysis, age and degenerate. Osteoblasts move in and ossify the matrix to form bone. • This process continues throughout childhood and the adolescent years until the cartilage growth slows and finally stops. When cartilage growth ceases, usually in the early twenties, the epiphyseal plate completely ossifies so that only a thin epiphyseal line remains and the bones can no longer grow in length. Skeletal Formation Intramembranous ossification- the development of bone from tissue or membrane • During fetal development and infancy, the membranous bones at the top and sides of the cranium are separated by sutures –immovable joints. • There are six large areas, called fontanels, that permit the skull to undergo changes in shape during childbirth and allow rapid growth of the brain during infancy. • The fontanels close by 2 years of age. • babys-soft-spots Divisions of the Skeleton • Axial- blue • Appendicular- tan SKULL • Cranium -8 bones • face – 14 bones • middle ear- 6 bones see table on pg 131 • Sinus- a cavity inside the bones • PARANASAL sinuses – – 4 pair – sinusitis- an inflammation of the sinus membrane. 1. Cranium – 8 large, flat bones a. Frontal 1 b. Parietal – 2 c. Temporal – 2 d. Occipital – 1 e. Sphenoid – 1 f. Ethmoid – 1 These bones articulate with one another to enclose and protect the brain. The bones of the skull are held together by immovable joints called sutures Frontal Parietal Sphenoid Temporal Occipital Ethmoid Maxilla Zygomatic 2. Facial – 14 bones a. Maxillae – 2 b. Palatine – 2 c. Zygomatic – 2 Ethmoid d. Lacrimal – 2 e. Nasal – 2 Zygomatic f. Vomer – 1 g. Inferior Nasal Conchae – 2 h. Mandible – 1 Vomer Nasal Lacrimal Palatine Inferior Nasal Conchae Maxillae Mandible Sinus • a cavity inside the bones • PARANASAL sinuses – – 4 pair – sinusitis- an inflammation of the sinus membrane. Spine- vertebral column • vertebrae form a flexible curved rod. • Divided into 5 sections– – – – cervical- 7 vertebrae thoracic – 12 vertebrae lumbar- 5 vertebrae sacrum- single fused area – coccyx- single fused area cervical thoracic lumbar sacrum coccyx The vertebral column encases and protects the spinal cord, which runs from the base of the cranium down the dorsal side reaching the pelvis. Thorax • Ribs- 12 pair • Sternum • Thoracic vertebrae • All ribs attach to the vertebrae. • 10 pair attach to the sternum…7 pair with calcified bone tissue and 3 pair with cartilage. • 2 pair are “floating” APPENDICULAR SKELETON Appendicular Skeleton 1. Shoulder Girdle a. Clavicle- the main connection between the upper arm and the rest of the axial skeleton. Important site for muscle attachments. b. Scapula- an attachment site for numerous muscles which support movement and stabilization of the shoulder. c. Humerous Clavicle Scapula Humerous 2. Upper Limb 1. Arm a. Humerus 2. Forearm b. Radius c. Ulna 3. Hand a. Carpals wrist b. Metacarpals palm c. Phalanges fingers Pelvic Girdle Ilium Sacroiliac joint • The Pelvis – Hip bones • Ilium • Pubic bone • Ischium Acetabulum – Acetabulum- Each hip bone consists of an ilium, an ischium, and a pubis, all three of which in the adult are fused at the acetabulum to form a single bone. • Sacroiliac joint Pubic bone Ischium Lower Limb 1. Thigh a. Femur b. Acetabulum 2. Leg a. Tibia b. Fibula c. Patella 3. Foot a. Tarsals b. Metatarsals Joints of the Body An articulation, or joint, is where two bones come together. In terms of the amount of movement they allow, there are three types of joints: immovable, slightly movable and freely movable. Three types: • Synarthroses- immovable • Amphiarthroses - slightly movable • Diarthroses- freely movable Allow for the movement of body parts Looser fit of joint equals more movement and the converse is true. Classification of joints Synarthroses -In these joints, the bones come in very close contact and are separated only by a thin layer of fibrous connective tissue. The sutures in the skull are examples of immovable joints. Structural classification • Fibrous Joints • Two examples Fibrous connective tissue Fibula – Suture line – Fibrous connective tissue Suture line • Amphiarthroses – Slightly movable. • Structural classificationhyaline cartilage or fibrocartilage. • The ribs connected to the sternum by costal cartilages are slightly movable joints connected by hyaline cartilage. • The symphysis pubis is a slightly movable joint in which there is a fibrocartilage pad between the two bones. • The joints between the vertebrae and the intervertebral disks are also of this type. Fibrocartilage disc Vertebra Cartilage Diarthroses Most joints in the adult body are diarthroses, or freely movable joints. The ends of the opposing bones are covered with hyaline (articular) cartilage. Separated by a space called the joint cavity. The joints are enclosed in a dense fibrous joint capsule. The outer layer of the capsule consists of the ligaments that hold the bones together. The inner layer is the synovial membrane that secretes synovial fluid into the joint cavity for lubrication. Because all of these joints have a synovial membrane, they are sometimes called synovial joints. Movement of diarthrosis (synovial) joints Factors that limit movement • Bone structure – Hinge joint (elbow) – Ball and socket (hip) • Joint ligaments – Degree of tension on ligaments • Hormones – Pubic symphysis; effects of relaxin Synovial Joint Movement - saddle joint ball and socket condyloid joint Pivot joint hinge joint Gliding joint (plane joint) Characterized by flat articulating surfaces • Articulation of vertebrae with other vertebrae and bones of the ankle and wrist. • Range of Motion: least moveable Holding your forearm steady while your hand points upward and then waving side-to-side with your hand is an example of this joint's functioning. Hinge joint Permit motion only in one plane—backward and forward --- where convex surface of one bone fits into concave surface of second bone. Movements permitted: – Flexion – Extension • Ex: Movement between the humerus and ulna, phalanges. The knee and ankle joints are also hinge joints, but allow very slight side to side movement. • The articular surfaces are connected together by ligaments. Pivot Joint • Rotation of one bone around another --found in the neck, forearms, knees. • A hole in one bone fits over a pointed part of the other bone, so that one bone can turn on top of the other. Ball and Socket • The most maneuverable type of joint. • The shoulder and hip are both ball-and-socket joints. • The distal bone is capable of motion around an indefinite number of axes, which have one common center. It enables the bone to move in a 360° angle. • These joints allow for forward motion, backward motion and circular rotation. The head of the femur joins the pelvis at the acetabulum (socket). Condyloid Joint • Two bones fit together with an odd shape (e.g. an ellipse), and one bone is concave, the other convex. • Between the metacarpals of the hand and the first phalanx of the fingers Saddle Joint • Has two saddle-shaped surfaces at right angles to each other. • Found only in the thumb. Joint Type Movement at joint Examples Hinge Flexion/Extension Elbow/Knee Pivot Rotation of one bone around another Top of the neck Ball and Socket Flexion/Extension/Adduction /Abduction/Internal & External Rotation Shoulder/Hip Saddle Flexion/Extension/Adduction /Abduction/Circumduction joint of the thumb Condyloid Flexion/Extension/Adduction /Abduction/Circumduction Wrist Gliding Gliding movements Intercarpal joints Structure Anatomical terms of motion Movement- all descriptions of position and movement are based on the assumption that the body is in anatomical position • Muscles may move parts of the skeleton relatively to each other, or may move parts of internal organs relatively to each other. • Most terms of a motion have clear opposites, and are treated in pairs. • Flexion- Bending movement that decreases the angle between two parts. Bending the elbow, or clenching a hand into a fist, are examples of flexion. When sitting down, the knees are flexed. Flexion of the hip or shoulder moves the limb forward (towards the anterior side of the body). Dorsiflexion- Flexion of the entire foot superiorly, as if taking one's foot off an automobile pedal. • Extension- The opposite of flexion; a straightening movement that increases the angle between body parts. In a conventional handshake, the fingers are fully extended. When standing up, the knees are extended. Extension of the hip or shoulder moves the limb backward (towards the posterior side of the body). Plantarflexion- Flexion of the entire foot inferiorly, as if pressing an automobile pedal. Occurs at ankle. • Abduction pulls a structure or part away from the midline of the body (or, in the case of fingers and toes, spreading the digits apart, away from the centerline of the hand or foot). Raising the arms laterally, to the sides, is an example of abduction. • Adduction pulls a structure or part towards the midline of the body, or towards the midline of a limb. Dropping the arms to the sides, or bringing the knees together, are examples of adduction. In the case of the fingers or toes, adduction is closing the digits together. Additional motions without clear opposites are as follows: • Rotation - A motion that occurs when a part turns on its axis. The head rotates on the neck, as in shaking the head 'no'. • Circumduction - The circular movement of a body part, such as a ball and socket joint or the eye. It consists of a combination of flexion, extension, adduction, and abduction. "Windmilling" the arms is an example of circumductive movement. • range of motion/animations.cfm Structural differences between the male and female skeletons. • In general, male skeletons are larger and heavier than female skeletons. • The small bulge at the back of the head known as the external occipital protuberance is usually more pronounced in men. • The male jawbone or mandible is typically angular and square-shaped at the chin area, while the female jawbone tends to be more rounded and pointed. The brow ridges of men are often more prominent than those of women. • The female pelvis is smaller, shallower and wider, and the cavity is more circular in shape. The coccyx or tailbone is more movable in female skeletons. The sacrum is wider and flatter in females.