Skeletal System - Bone Anatomy - PDF

THE SKELETAL SYSTEM I. Bone tissue is an ever-changing, growing, developing tissue in the human body. It serves as the major support tissue for the human body. A. Osteology II. FUNCTIONS OF BONE TISSUE A. Support-bone provides a framework for the human body. It supports soft ti...

THE SKELETAL SYSTEM I. Bone tissue is an ever-changing, growing, developing tissue in the human body. It serves as the major support tissue for the human body. A. Osteology II. FUNCTIONS OF BONE TISSUE A. Support-bone provides a framework for the human body. It supports soft tissues and serves as a region for muscle attachment. B. Protection C. Movement-skeletal muscle attaches to and moves bones. D. Mineral Storage-bone is a reservoir for calcium and phosphate. On demand, bone tissue can release both of these minerals into the bloodstream for use in the human body. 1. Due to this, bone plays a key role in electrolyte balance in the body. 2. Bone tissue also helps maintain acid-base balance in the body by absorbing or releasing alkaline salts like calcium phosphate. E. Blood Cell Production 1. Hemopoiesis (hematopoiesis)-the formation/production of blood cells. This process takes place in red bone marrow. F. Energy Storage 1. Yellow Bone Marrow-associated with bone. This material is composed of adipose tissue and scattered leukocytes. The adipose tissue serves as a source of energy for the human body. G. Production of Osteocalcin-a hormone that helps regulate insulin secretion and sugar homeostasis in the body. H. Detoxification-bone absorbs heavy metals from the blood; thus, reducing their effects on body. Bone can slowly release these compounds via secretion. III. ORGANIZATION OF THE SKELETAL SYSTEM A. The human skeleton is composed of 206 bones dispersed throughout the body. These bones are classified into two major skeletal divisions: 1. The Axial Skeleton-bones located along the central axis of the body. These bones typically protect and support body structures.  2. The Appendicular Skeleton-bones of the extremities. These bones are involved in movement. B. Types of Bones in the Human Skeleton-based on shape. 1. Long Bones-are longer than they are wide. They are named for their elongated shape, not their length. a. Are typically curved. The curvature acts to increase their strength which allows them to withstand great stress; thus reducing the chance of fracture. b. The Major Parts of a Long Bone: 1) Diaphysis-the shaft of the bone. 2) Epiphyses-the ends of the bone. These are covered and protected by hyaline cartilage. 3) Metaphysis-the region in a mature bone where the diaphysis meets the epiphysis. This region of the bone contains the epiphyseal plate-region where cartilage is replaced by bone. The epiphyseal plate is involved in bone growth. 4) Hyaline (Articular) Cartilage-a layer of cartilage that covers the ends of a long bone. The cartilage serves as a shock absorber between bones. 5) Periosteum-a membrane that surrounds the surface of a bone. It is composed of 2 Layers: a) An outer fibrous layer that is composed of dense irregular connective tissue. This layer contains blood vessels, nerves and lymphatic vessels that pass into the bone. b) An inner osteogenic layer that contains elastic fibers, blood vessels and bone cells. c) Overall, the periosteum is involved in bone growth, repair and development. It also serves as a site of attachment for ligaments and tendons. d) Sharpey’s Fibers-collagen fibers that anchor the periosteum to  the bone. Some of these penetrate into the bone where they are known as Perforating Fibers. 6) Medullary (Marrow) Cavity-an open space within the diaphysis of a bone. It contains yellow bone marrow which serves as an energy source in bone. If a person becomes anemic, yellow marrow can revert to red bone marrow to aid in the production of additional red blood cells. 7) Endosteum-a membrane that covers and lines the medullary cavity of a bone. It contains 2 specialized types of bone cells: osteoprogenitor cells and osteoclasts. 2. Short Bones-are cube-shaped. Internally, these are composed of thin plates of spongy bone known as diploe. The diploe are covered by a layer of compact bone tissue. a. The carpals and tarsals are examples of short bones. 3. Flat Bones-are very thin bones. The cranial bones, sternum and ribs are flat bones. a. These are composed of 2 plates of compact bone tissue that encloses a layer of spongy bone (diploe). b. These bones provide considerable protection, and they offer a great surface area for tendon and ligament attachment. 4. Irregular Bones-have complex shapes. The vertebrae of the spinal column and some facial bones are classified as irregular bones. These are also composed of diploe. 5. Sesamoid Bones-small bones embedded in tendons in the body. The patella is an example. IV. HISTOLOGY OF BONE TISSUE A. Overall, bone tissue is composed of 5 types of cells that are embedded in a thick, hardened matrix. B. Bone Matrix-is composed of about 25% water, 25% protein (collagen), and 50% mineral salts (calcium carbonate and calcium phosphate). 1. Calcification (Mineralization)-the formation of new matrix. This occurs as the above mineral salts accumulate over collagen fibers. The collagen fibers act to provide  strength to the matrix. 2. In bone, collagen fibers are held together by sacrificial bonds that easily break and reform to dissipate energy from force on bones. C. 5 Types of Cells in Bone Tissue: 1. Osteoprogenitor (Osteogenic) cells-unspecialized cells derived from mesenchyme. These cells are capable of undergoing rapid cell division. These can develop into osteoblasts. a. Osteoprogenitor cells are located near blood vessels in the periosteum and endosteum of bone. 2. Osteoblasts-secrete collagen and other materials needed to build bone tissue. These have lost the ability to undergo cell division. These cells function by secreting new bone matrix. a. These are located on the surface of bone tissue. b. When osteoblasts are completely surrounded by matrix, they are referred to as Osteocytes. 3. Osteocytes-mature bone cells. These cells have lost the ability to divide. Osteocytes do not secrete bone matrix. They are involved in nutrient/waste exchange between bone and blood. a. These cells regulate the daily activities of bone tissue. b. These also serve as stress sensors in bone to monitor bone overload. 4. Bone Lining Cells-these are thought to help maintain the health of bone matrix. 5. Osteoclasts-are involved in bone resorption (the destruction of bone matrix). These play a key role in bone growth and repair. a. These cells release acids and enzymes that degrade bone tissue. b. Structurally they contain a ruffled border that increases surface area of the cell which increases enzyme release and bone degradation. D. 2 Types of Bone Tissue: Compact Bone and Spongy Bone. E. Compact Bone Tissue 1. Compact bone forms the external layer over all bones in the body. It also makes up the diaphysis of long bones.  2. Compact bone is composed of repeating units known as Haversian Systems (Osteons). 3. Structure of a Haversian System: a. Haversian (Central) Canals-run longitudinally in bone tissue. These contain blood vessels and nerves. b. Lamellae-rings of matrix in bone. This is composed of the mineral salts calcium carbonate and calcium phosphate. c. Volkmann’s Canals-run horizontally in bone tissue. These also contain blood vessels and nerves. d. Lacunae-small spaces in the lamellae of compact bone. Osteocytes are in these spaces. e. Canaliculi-small channels extending from lacunae. These serve as passageways through which nutrients and wastes can pass. F. Spongy Bone Tissue-contains many open spaces. 1. Spongy bone tissue is composed of thin plates of bone known as trabeculae. It does not contain Haversian Systems. 2. The spaces between trabeculae are filled with red bone marrow which is involved in blood cell production. 3. Osteocytes are located in the trabeculae. 4. Spongy bone tissue is found in: short bones, flat and irregular bones and in the epiphyses of long bones. Specifically, spongy bone is found in the sternum, ribs, skulls, and vertebrae. G. Bone contains a large supply of blood. Nutrient arteries carry blood into the diaphysis of long bones. These enter the bone through nutrient foramina. 1. Epiphyseal arteries carry blood into the epiphyses of a bone. V. BONE FORMATION (OSSIFICATION) A. Bone is a dynamic, ever-changing type of tissue. Ossification is the process by which bone forms. B. 2 Patterns of Ossification in the Human Body: 1. Intramembranous Ossification-bone formation directly on or over loose fibrous connective tissue. a. No cartilage stage is present in bones that form in this fashion.  b. This process occurs in only a few developing bones. Often times, the bones formed during intramembranous ossification are soft at birth. The skull bones, the clavicle and the mandible form in this fashion,. 2. Endochondral Ossification-bone formation over hyaline cartilage. a. Most human bones form in this manner. VI. BONE GROWTH-IN LENGTH A. Bone growth in length generally ends before the age of 25; however, bones may continue to thicken throughout a person’s life. Length growth may stop earlier in females than in males. B. Events in Length Growth of Bone: 1. Epiphyseal Plate-a layer of hyaline cartilage in the metaphysis of a growing bone. C. Final Points on Length Growth in Bones: 1. The epiphyseal plate is the only area in a bone where length growth can occur. Eventually, cells in the epiphyseal plate stop dividing. At this point, bone tissue replaces the cartilage. This produces a remnant known as the epiphyseal line. 2. Fractures of the epiphyseal plate can result in a cessation of bone growth. Due to this, a fractured bone may be shorter than its counterpart. 3. Bone growth usually stops before the age of 25. In general, length growth ends earlier in females than in males. VII. BONE GROWTH-IN THICKNESS-this occurs as osteoblasts secrete new matrix to the periosteum of a bone. VIII. HORMONAL REGULATION OF BONE GROWTH A. Human Growth Hormone (HGH)-secreted by the pituitary gland. This hormone regulates bone growth prior to puberty. Oversecretion of this hormone may lead to gigantism; whereas undersecretion may lead to dwarfism. B. At puberty, the sex hormones estrogen and testosterone stimulate changes in the human skeleton. These hormones are responsible for the growth spurt that occurs at puberty. They also stimulate the skeleton to develop into the typical male and female shape. C. Thyroid Hormones-also play a role in bone growth and development. IX. BONE REMODELING-the ongoing replacement of old bone tissue by new bone tissue.  A. Bone is an ever-changing type of tissue. Remodeling removes worn and injured bone tissue and replaces it with new, healthy bone tissue. This ensures that bone remain healthy. B. Osteoclasts-bone cells that are responsible for removing old bone matrix (bone resorption). 1. These cells breakdown matrix by secreting protein-digesting enzymes and various acids. 2. Once old bone matrix has been removed, osteoblasts secrete new matrix. C. Alkaline phosphatase-an enzyme that regulates the formation of calcium carbonate and calcium phosphate This enzyme is needed in large supplies for bone remodeling to occur. D. Vitamins and Minerals that are needed for Bone Remodeling to occur: 1. Calcium 2. Vitamin C-needed for the formation of collagen fibers. 3. Vitamin D-needed for the absorption of calcium. 4. Vitamin A-maintains a balance between bone deposit and bone resorption. X. FRACTURE-refers to any break in a bone. A. The repair of a fracture is a slow and painful process. B. Types of Fractures C. The Clavicle is the most commonly broken bone in the human body. XI. BONE AND CALCIUM HOMEOSTASIS A. Bone is the major calcium reservoir in the human body. Bones store 99% of the body’s calcium. B. Uses of Calcium in the Human Body: 1. Regulation of muscle contraction 2. Impulse formation and conduction in the nerve tissue 3. Blood clotting C. Parathyroid Hormone (PTH)-hormone that stimulates osteoclasts to release calcium into the blood under times of need. D. Calcitonin-secreted by cells in the thyroid gland. 1. When calcium levels rise above normal in the bloodstream, calcitonin responds by decreasing the activity of osteoclasts. It also increases the activity of osteoblasts. Overall, this reduces calcium levels in the bloodstream. XII. SURFACE MARKINGS-bones contain a number of surface features that serve as points of attachment, openings and depressions etc.. A. Recall that the skeleton is composed of 206 bones and it is divided into an Axial and  an Appendicular Portion. XIII. THE SKULL A. Is comprised of 2 major regions: the cranium and the facial region. B. Bones of the Cranium: 1. Frontal Bone 2. Parietal Bones-form the majority of the sides of the skull. 3. Temporal Bones- a. Temporal Squama-forms the temple. b. Zygomatic Arch-connects to the zygomatic arch to form part of jaw. c. Carotid Canal-carotid artery passes through here. Since this artery is close to the ear, you can often hear your heartrate, and you may feel a pounding sensation in this area during heavy activity. d. Jugular Foramen-jugular vein and 3 cranial nerves pass through here. e. Mandibular Fossa-forms part of the temporomandibular joint (TMJ). f. Temporomandibular joint-between temporal bone, mandible. g. Mastoid Process-bump behind the ear. Neck muscles attach here. h. Styloid Process-site for neck, tongue muscles and ligaments that hold the hyoid bone in place. 4. Occipital Bone-back of skull. a. Foramen Magnum-site where the spinal cord passes through to attach to the brain. 5. Sphenoid-forms the bat in the middle of the skull. It articulates will all cranial bones; therefore, it is often called the keystone bone of the cranium. a. Sella Turcica-surrounds and holds the pituitary gland in place. 6. Ethmoid-at front of skull, upper portion of nasal cavity, forms part of the orbits. The ethmoid connects to all of the bones of the skull and face-it essentially holds all of the bones in place. It is the most deeply situated bone of the skull. a. Cribriform Plate-forms the roof of the nasal cavity. Contains numerous holes known as the olfactory foramina through which olfactory nerves  pass. b. Perpendicular plate-forms part of the nasal septum. 7. Major Sutures of the Skull: a. Coronal suture-separates the frontal bone and the parietal bones. b. Lambdoid suture-separates the parietal bones from the occipital bone. c. Squamous suture-separates the temporal bones from the parietal bones. d. Sagittal suture-separates the parietal bones from each other 8. Developmental Aspects of the Skull a. The bones of the skull develop via intramembranous ossification. b. Due to this, the skull bones are not fully ossified at birth. Instead, the bones are composed of fontanelles (soft spots) which allow the infant’s head to be compressed during birth and they accommodate brain growth. C. Facial Bones of the Skull 1. Nasal Bones-form the bridge of the nose, are primarily cartilage in composition. 2. The Vomer-unpaired facial bone that forms part of the nasal septum. a. Nasal Septum-separates the right and left airways in the nose. b. Deviated nasal septum-physical disorder in which the vomer is pushed to one side or another. Is often caused by trauma to the face. 3. Maxillae-form the upper jaw. These paired bones hold the upper teeth in place and they form the boundaries of three cavities: the roof of the mouth, the floor of the nose and the floor of the orbits. a. Cleft palate-condition in which the maxillary bones are not completely joined. This often leads to a cleft lip. This condition is often repaired via surgery. 4. Zygomatic Bones-cheek bones. 5. The Mandible-largest and strongest bone of the face. It forms the lower jaw bone. It holds the lower teeth in place. This is the only movable skull bone. a. Mental foramen-passageway for nerves to the chin. 6. The Lacrimal Bones-smallest and most fragile bones of the face.  a. Lacrimal fossa-allows tears to drain off of the eye to the nasal cavity. 7. The Palatine Bones-form the underside of the nasal cavity and part of the orbits. 8. The Paranasal Sinuses-open spaces in some skull bones. These help filter incoming air and they provide tone to our voice. 9. The Hyoid Bone-where is this bone located? a. It serves as a movable base for the tongue. b. It is the only bone of the body that does not articulate with another bone. XIV. THE VERTEBRAL COLUMN A. Region of the Vertebral Column-How many vertebrae are in each region? 1. Cervical Region- 2. Thoracic Region- 3. Lumbar Region- 4. Sacral Region- 5. Coccygeal Region- B. Normal Curves of the Vertebral Column 1. Cervical Curve and Lumbar Curve-posteriorly concave. 2. Thoracic Curve and Sacral Curve-posteriorly convex. 3. What is the significance of these curves? C. Verebrae-bones that make up the spinal column. The major parts of a vertebra include: 1. Intervertebral Discs-cartilage pad between the vertebrae. a. Composed of an inner gelatin layer known as the nucleus pulposus which is surrounded by a strong annulus fibrosis. b. The discs serve as shock absorbers between the vertebrae. 2. Body(Centrum)-major weight-bearing structure. 3. Vertebral Arch-also bears weight. 4. Vertebral Foramen-what passes through here? 5. Intervertebral Foramina-nerves pass through these. 6. Processes on Vertebrae: Where are each of these located? a. Spinous Process b. 2 Transverse Processes c. Articular Processes E. Cervical Vertebrae-where are these located? 1. These are the smallest of the vertebrae and their spinous processes are bifid. 2. The Atlas-where is this located? It does not have a spinous process. 3. The Axis-where is this located? a. The Dens (Odontoid Process)-pivot point on the axis for skull rotation.  F. Thoracic Vertebrae-where are these located? 1. These attach to the ribs. Their vertebral foramen is circular. G. Lumbar Vertebrae-largest of the vertebrae. There are modified for support. 1. Their vertebral foramen is triangular. H. The Sacrum-triangular bone, composed of 5 fused vertebrae. 1. Sacral Foramina-holes through which nerves and blood vessels pass through. I. The Coccyx-what is this structure? 1. For the most part, it is considered to be a useless bone. XV. THE STERNUM A. Major Regions of the Sternum: 1. The Manubrium-superior portion, clavicle attaches here at the clavicular notch. a. Jugular notch-superior portion of the manubrium. 2. The Body-attaches to cartilages from ribs 2-7 3. Xiphoid Process-primarily cartilage, becomes hardened (ossified) as we age. a. Abdominal muscles attach here. b. Landmark for CPR. XVI. RIBS-everyone has 12 pairs of ribs. A. True Ribs-their cartilage attaches directly to the sternum. False Ribs- their cartilage does not attach directly to the sternum. Floating Ribs-do not attach to the sternum at all. B. Parts of a Rib 1. The Head-attaches to the vertebrae, the neck is near the head of a rib. 2. The Shaft-forms the length of a rib. Has a costal groove where nerves and blood vessels are located. XVII. THE CLAVICLE A. Acromial Extremity-site where the clavicle articulates with the acromion. XVIII. THE SCAPULA A. Acromion-upper portion of scapula, forms the Acromioclavicular joint with the clavicle. B. Glenoid Cavity-fossa where the humerus attaches to form the shoulder joint. XIX. THE HUMERUS A. The Head-articulates with the glenoid cavity to form the shoulder joint. B. The Greater Tubercle-knob, where major muscles attach. C. The Lesser Tubercle-smaller knob, major muscle also attach here. D. The Deltoid Tuberosity-site where the deltoid muscle attaches. E. The Olecranon Fossa-forms part of the elbow joint.  F. The Medial and Lateral Epidcondyles-bumps, sites of muscle attachment. XX. THE ULNA A. The Olecranon Process-prominence of the elbow. XXI. THE RADIUS A. The Head-nail-shaped structure that articulates with the ulna. B. The Radial Tuberosity-site for muscle attachment. XXII. THE HAND A. Carpals-8 bones that form the wrist. B. Metacarpals-5 bones that from the palm of the hand. C. Phalanges-14 of these in each hand, these form the fingers. XXIII. BONES OF THE PELVIC GIRDLE A. THE ILLIUM 1. Sacroiliac Joint-site where the sacrum and ilium attach. B. THE ISCHIUM 1. The Obturator Foramen-large hole, blood vessels and nerves pass through here. It is nearly closed by a fibrous membrane. 2. The Acetabulum-deep socket that receives the head of the femur or thigh bone. C. THE PUBIS BONE 1. The Pubic Symphysis-formed by the rami of the pubic bones. This symphysis is held together by fibrocartilage. The pubic symphysis forms the pubic arch. 2. The female pubis is wider in females to allow for childbirth. XXIV. THE FEMUR A. Head of the Femur-forms the pelvic girdle B. Greater and Lesser Trochanters-knobs, for major muscle attachment, including the gluteal muscles. C. The Medial and Lateral Condyles-articulate with the same structures of the tibia to form the knee joint. D. The length of the femur is approximately one-fourth of a person’s height. E. The medial portion of the femur is more pronounced in women due to their wider pelvis. This contributes to a greater incidence of knee injuries in women athletes. XXV. THE PATELLA-what is this? A. Increases leverage of the leg. Is held in place by the patellar ligament. XXVI. THE TIBIA-second largest bone of the body. A. The Medial and Lateral Condyles-articulate with femur to form knee joint. B. The Medial Malleolus-forms the medial knob of the ankle.  C. The Tibial Tuberosity-site for patellar ligament attachment. XXVII. THE FIBULA A. The Lateral Malleolus-forms the lateral side of the ankle. XXVIII. THE FOOT A. Tarsus-contains the tarsal bones which includes the calcaneus and talus. B. Metatarsus-composed of metatarsal bones. C. Phalanges-toes D. Arches of the foot-for support. XXIX. JOINTS-are defined as points of contact between bones, cartilage and bones, and teeth and bone. A. Joints serve two major functions: they provide mobility, and they hold the skeleton together. XXX. TYPES OF JOINTS A. Fibrous Joints-no synovial cavity present. The bones are held together by fibrous connective tissue. B. Cartilaginous Joints-no synovial cavity present, cartilage holds the joint together. C. Synovial Joints-have a synovial cavity. The bones are held together by ligaments. 1. Types of Synovial Joints a. Gliding joints-bones can only move side-to-side in these. b. Hinge joints-convex surface of one bone fits into the concave surface of another bone. c. Pivot joints-the rounded portion of one bone articulates with a bone/ligament ring of another bone. d. Condyloid joints-condyle of 1 bone fits into an elliptical cavity of another bone. e. Saddle joints-the articular surface of one bone is saddle- shaped and the second bone appears as a rider on the saddle. f. Ball and Socket Joints-the ball (head) of one bone fits into a depression on the second bone. XXXI. DISORDERS ASSOCIATED WITH THE SKELETAL SYSTEM A. Osteoporosis-a condition of porous bone. It is characterized by decreased bone mass and increased susceptibility to fracture. Has been treated with calcium and vitamin D  supplements. Exercise appears to reduce (an in some cases prevent) the onset of osteoporosis. Hormone replacement therapy has also been used as a means for treating osteoporosis. Osteoporosis is a form Osteomalacia-bone softening due to inadequate supplies of Vitamin D. B. Paget’s disease-accelerated remodeling. Causes weak areas in bone tissue. C. Osteoarthritis-the degeneration of hyaline cartilage. D. Rickets-a form of osteomalacia that occurs in children. Is usually associated with vitamin D deficiency. Drinking vitamin D fortified milk usually alleviates this illness. E. Herniated disc-characterized by the protrusion of the inner layer of an intervertebral disc. Can be repaired via surgery. F. Abnormal curves of the Vertebral Column: 1. Scoliosis-a lateral bending of the vertebral column, usually in the thoracic region. 2. Kyphosis-an exaggeration of the throacic curve of the vertebral column. 3. Lordosis-an exaggeration of the lumbar curve of the vertebral column.