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Unit 4 Function: Bones protect and support body organs, serve as levers for muscles to pull on (movement), store calcium, fats, and other substances, and are the site of blood cell production. Two basic types of tissue: Compact bone = dense, looks smooth and homogenous Spongy bone = composed of small needlelike pieces of bone and lots of open space Four basic shapes: Long = typically longer than they are wide, mostly compact Short = generally cube shaped, mostly spongy Flat = thin, flattened, usually curved, two layers of compact bone sandwiching layer of spongy bone Irregular bones = do not fit one of the preceding categories (hip bone, vertebrae, etc.) A long bone is composed of a diaphysis (shaft) and two epiphyses (ends). The medullary cavity of the diaphysis contains yellow marrow, the epiphyses contain spongy bone. The epiphyseal line is the remnant of the epiphyseal plate, a flat plate of hyaline cartilage seen in young, growing bone. Periosteum (fibrous connective tissue membrane) covers the diaphysis. Endosteum lines medullary cavities and the spaces of spongy bone. Hyaline cartilage covers articular surfaces. In adults, the cavity of the shaft is primarily a storage area for adipose tissue, called the yellow marrow or medullary cavity. In infants, this area forms blood cells and red marrow is found there. In adult bones, red marrow is confined to the cavities of spongy bone in flat bone and epiphyses of some long bones. Two main kinds: Projections or processes = grow out from bone surface Depressions or cavities = indentations in the bone Indicate sites of muscle attachment, points of articulation, and sites of blood vessels and nerve passage. The structural unit of compact bone is the osteon, consisting of a central Haversian canal surrounded by concentric lamellae of bone matrix. Osteocytes (mature bone cells), embedded in lacunae (matrix), are connected to each other and the Haversian canal by canaliculi (tiny canals). Spongy bone has slender trabeculae containing irregularly arranged lamellae that enclose redmarrow filled cavities. In embryos, the skeleton is primarily made of hyaline cartilage, but in the young child most of the cartilage has been replaced with bone. Flat bones form on fibrous membranes; most other bones develop using hyaline cartilage as their “models.” Ossification (bone formation) involves two major phases 1. Hyaline cartilage model is completely covered with bone matrix by osteoblasts (bone-forming cells). 2. Enclosed hyaline cartilage is digested away, opening up a medullary cavity within the newly formed bone. By birth, most hyaline cartilage models have been converted to bone except for two regions: Articular cartilages that cover bone ends reduce friction Epiphyseal plates provide for longitudinal growth during childhood Growing bone must widen as well as lengthen increase in diameter is called appositional growth Growth of long bones is controlled by growth hormone and sex hormones (during puberty) Bone is constantly changing and remodeling due to two factors: 1. Calcium levels in blood 2. Pull of gravity and muscles A drop in calcium levels can stimulate the parathyroid glands to release parathyroid hormone (PTH) into the blood. PTH activates osteoclasts (bone destroying cells), which break down bone matrix and release calcium ions into the blood. A spike in calcium levels can result in increased bone formation as the calcium gets deposited in bone matrix and taken out of blood. http://www.youtube.com/watch?v=Hwj2idrQJYg Remodeling is essential if bones are to retain normal proportions and strength during longbone growth as the body increases in size and weight. Bones become thicker and form large projections to increase their strength in areas where bulky muscles are attached. Bones lose mass and begin to atrophy in bedridden or physically inactive people. Bones are susceptible to fractures (breaks) all through life during youth, fractures are due to exceptional trauma; during old age, fractures occur more often. Closed (or simple) fracture = bone breaks cleanly but does not penetrate the skin Open (or compound) fracture = broken bone ends penetrate skin Treated by reduction, the realignment of the broken bone ends. Closed reduction = bone ends are put back in normal position by physician’s hands Open reduction = surgery is performed and bone ends are secured with pins or wires Simple fractures heal in 6-8 weeks, longer for large bones and elderly people (poor circulation) 1. A hematoma (blood-filled swelling) is formed because blood vessels are ruptured when the bone breaks. Bone cells deprived of nutrition die. 2. The break is splinted by a fibrocartilage callus (contains cartilage matrix, bony matrix, and collagen fibers) and new capillaries form. 3. Bony callus is formed as osteoblasts and osteoclasts migrate into the area and multiply. 4. Over the next few months, the bony callus is remodeled in response to the mechanical stresses placed on it, forming a permanent “patch” at the fracture site. Can be divided into three parts: Skull Vertebral column Bony Thorax Formed by two sets of bones Cranium = encloses and protects brain, composed of eight large, flat bones Facial bones = hold eyes in anterior position, facilitate facial muscle movement, fourteen bones total All but one of the bones of the skull are joined together by sutures = interlocking, immovable joints. Mandible (jawbone) is attached by freely moveable joint Frontal bone – forms forehead, bony projections under eyebrows, and superior part of each eye’s orbit Parietal bones – paired, form most of superior and lateral walls of cranium, meet in midline of skull at sagittal suture and form coronal suture where they meet the frontal bone Temporal bones – join parietal bones at squamous sutures, bone markings: 1. External auditory meatus = canal that leads to eardrum and middle ear 2. Styloid process = needlelike projection that attaches to many neck muscles 3. Zygomatic process = bridge of bone that joins with cheekbone 4. Mastoid process = rough projection containing mastoid sinus, posterior and inferior to external auditory meatus 5. Jugular foramen = junction of occipital and temporal bones, allows jugular vein to pass through 6. Carotid canal = anterior to jugular foramen, allows internal carotid artery to pass through Occipital bone – most posterior bone of cranium, joins parietal bones at lambdoid suture Foramen magnum = “large hole,” allows brain to connect with spinal cord Occipital condyles = rest on first vertebra of spinal column Sphenoid bone – butterflyshaped, spans width of skull, forms floor of cranial cavity Sella turcica = (Turk’s Saddle) small depression in midline that holds pituitary gland in place Foramen ovale = allows fibers of cranial nerve V to pass to chewing muscles of lower jaw Ethmoid bone – anterior to sphenoid, forms roof of nasal cavity Crista galli = “cock’s comb,” projects from superior surface Cribriform plates = small holes on side, allow nerve fibers to carry impulses from olfactory receptors to brain Maxillae = (maxillary bones) fuse to form upper jaw, all facial bones except for mandible join the maxillae “keystone” bones Palantine processes form anterior part of hard palate Paranasal sinuses = lighten bones and amplify sounds we make while speaking Palatine bones = lie posterior to maxillae, form posterior part of hard palate, failure to fuse = cleft palate Zygomatic bones = cheekbones, form part of lateral walls of eye sockets Lacrimal bones = fingernail-sized, form part of medial walls of orbits, each has a groove that is a passageway for tears Nasal bones = small, rectangular, form bridge of nose Vomer bone = single bone in median line of nasal cavity, forms most of nasal septum Inferior Conchae = thin, curved bones projecting from lateral walls of nasal cavity Mandible = jawbone, largest and strongest bone on face, joins temporal bones Hyoid bone = not actually part of skull, only bone in body that does not articulate with any other bone, suspended in mid-neck region, horse-shoe shaped, serves as movable base for tongue and attachment point for neck muscles Face is small compared to cranium Skull as a whole is large compared to body length When baby is born, skull is still unfinished Some areas of hyaline cartilage still need to be ossified. Fontanels = fibrous membranes connecting cranial bones of infant “soft spots” Extends from skull, which it supports, to pelvis, where it transmits weight of body to lower limbs. Has a central cavity containing the delicate spinal cord, which it protects. Formed from 26 irregular bones (vertebrae) connected and reinforced by ligaments, resulting in a flexible, curved structure. Before birth, spine consists of 33 separate vertebrae, but 9 fuse together to form the sacrum and coccyx. Superior 7 vertebrae are cervical (C1-C7) Top two vertebrae are the atlas and axis Next 12 vertebrae are the thoracic vertebrae (T1-T12) Next 5 vertebrae are lumbar vertebrae (L1-L5) Sacrum (5 fused vertebrae) and Coccyx (4 fused vertebrae) are most inferior parts of spine Single vertebrae are separated by intervertebral discs = pads of flexible fibrocartilage that cushion the vertebrae and absorb shocks In young people, the discs have a high water content (~90%), but as people age, the water content decreases and discs become harder and less compressible. This leaves older people more susceptible to herniated discs (slipped discs), which can press on the spinal cord or spinal nerves, resulting in severe pain or numbness. The S-shape of the spine and the vertebral discs help prevent shock to the head when we walk or run. Primary curvatures = spinal curves in the thoracic and sacral regions, present at birth Secondary curvatures = cervical curvature appears when babies raise their heads, lumbar curvature appears when babies start to walk All vertebrae have a similar structure pattern Centrum (body) = disclike, weight-bearing part that faces the vertebral column anteriorly Vertebral arch = formed from the joining of all posterior extensions from the vertebral body (laminae and pedicles) Vertebral foramen = canal through which the spinal cord passes Transverse processes = two lateral projections from vertebral arch Spinous process = single projection arising from the posterior aspect of vertebral arch (actually fused laminae) Superior and inferior articular processes = paired projections lateral to vertebral foramen, allows adjacent vertebrae to form joints First two (atlas and axis) are different because they perform functions not shared by the other cervical vertebrae. Atlas has no body and has large depressions on superior surface to receive occipital condyles of skull. Axis acts as pivot for rotation of atlas and skull. It has a large, upright process (odontoid process, or dens) that acts as the pivot point. C3-C7 are the smallest, lightest vertebrae. Their spinous processes are short and divided into two branches and their transverse processes contain openings that vertebral arteries pass through on their way to the brain Larger than cervical vertebrae Body is somewhat heart-shaped with two costal demifacets (articulating surfaces) on each side that attach to heads of ribs. Spinous process is long and hooks sharply downward vertebra looks like a giraffe’s head from side Massive, blocklike bodies Short, hatchet-shaped spinous processes look like a moose head from lateral aspect Most of the stress on the vertebral column occurs in lumbar region sturdiest vertebrae Formed by the fusion of 5 vertebrae The winglike alae connect to hip bones sacroiliac joints Forms posterior wall of pelvis Median sacral crest = fused spinous processes of the sacral vertebrae Dorsal sacral foramina = holes that line each side of the median sacral crest Sacral canal = continuation of the vertebral canal Formed by the fusion of 3-5 tiny, irregularly shaped vertebrae Tailbone Sternum, ribs, and thoracic vertebrae “Thoracic cage” Breastbone – attaches to 1st seven pairs of ribs Results from the fusion of three bones – manubrium, body, and xiphoid process Three important bony landmarks: Jugular notch = concave upper border of manubrium Sternal angle = where the manubrium and the body meet at a slight angle to each other so that a transverse ridge is formed at the level of the second ribs Xiphisternal joint = point where the sternal body and xiphoid process fuse, same level as T9 vertebra Twelve pairs of ribs – males have same number as females Attached to vertebral column posteriorly, then curve downward and around toward the anterior body surface 1st seven pairs = “true ribs” because they attach to the sternum 2nd five pairs = “false ribs” because they either attach indirectly to sternum or not at all, last two pairs are “floating ribs” Intercostal spaces = spaces between ribs, filled with intercostal muscles that aid in breathing Composed of 126 bones of the limbs and the pelvic and pectoral girdles, which attach the limbs to the axial skelton Consists of 2 bones: clavicle and scapula Clavicle = “collarbone,” slender, doubly curved, attaches to manubrium of sternum and scapula, acts as brace to hold arm away from top of thorax and helps prevent shoulder dislocation Scapula = “shoulder blade,” triangular, flattened body, held loosely in place by trunk muscles, doesn’t actually attach to axial skeleton, two important processes: acromion and coracoid Acromion = enlarged end of the spine of the scapula, connects with clavicle Coracoid process = looks like a beak, points over top of shoulder and anchors some arm muscles Suprascapular notch = nerve passageway Glenoid cavity = shallow socket that receives the head of the arm bone Shoulder girdle is very light and allows upper limb to be very flexible Each shoulder girdle attaches to axial skeleton at only one point = sternoclavicular joint The loose attachment of scapula allows it to slide back and forth against thorax The glenoid cavity is shallow and shoulder joint is poorly reinforced by ligaments Great for flexibility, bad for stability very easy to dislocate 30 separate bones form each upper limb Arm, forearm, hand Upper arm is single long bone = humerus Head fits into glenoid cavity of scapula Opposite head are two bony projections = greater and lesser tubercles, attach to muscles Deltoid tuberosity = rough area in midpoint of shaft where deltoid attaches Radial groove = runs down posterior aspect of shaft, marks course of radial nerve Trochlea and capitulum = distal end of humerus, articulate with bones of forearm Coronoid fossa and olecranon fossa = depressions flanked by medial and lateral epicondyles that allow the ulna to move freely when elbow is bent and extended Radius and ulna = bones that form skeleton of forearm In anatomical position, radius is lateral bone, on the “thumb side” Bones meet at both proximal and distal ends at radioulnar joints, connected by flexible interosseous membrane Head of radius forms joint with capitulum of humerus Radial tuberosity = just below head of radius, where tendon of biceps muscle attaches Coronoid process and olecranon process = proximal end of ulna, separated by trochlear notch, grip the trochlea of humerus Carpal bones = 8 bones arranged in two irregular rows of four bones each, wrist Metacarpals = 5 bones, palm of hand, numbered 1-5 from thumb to little finger Phalanges = 14 bones, 3 in each finger (proximal, middle, and distal) except for thumb, which has 2 (proximal and distal) Two coxal bones (ossa coxae), aka hip bones Large and heavy bones, securely attached to axial skeleton Coxal bones + sacrum + coccyx = bony pelvis Hip bone is formed by the fusion of three bones: ilium, ischium, and pubis Ilium = connects to sacrum at sacroiliac joint Ischium = “sitdown bone,” forms most inferior part of coxal bone Greater sciatic notch = allows blood vessels and sciatic nerve to pass from pelvis to thigh Pubis = most anterior part of coxal bone Acetabulum = point where ilium, ischium, and pubis fuse at the deep socket, receives head of thigh bone False pelvis = superior to true pelvis, medial to flaring portion of ilia True pelvis = surrounded by bone and lies inferior to flaring parts of ilia and pelvic brim Female pelvis = inlet larger and more circular, shallower, lighter, thinner, shorter sacrum, pubic arch more rounded Carry the weight of the body when we are standing Much thicker and stronger than the bones of the upper limbs Femur = only bone in the thigh Head = “ball” that fits into hip “socket” (acetabulum) Greater and lesser trochanters = sites of muscle attachment Lateral and medial condyles = separated by intercondyle notch, articulate with tibia Patellar surface = forms joint with patella (kneecap) Two bones: tibia and fibula Tibia = shinbone, larger and more medial Medial and lateral condyles = attach to distal end of femur Tibial tuberosity = attaches to patellar ligament Medial malleolus = inner bulge of ankle Fibula = lies alongside tibia, joins at proximal and distal ends Lateral malleolus = outer part of ankle Tarsals, metatarsals, phalanges Calcaneus = heelbone Talus = between calcaneus and tibia Five metatarsals = sole of the foot 14 phalanges form toes (big toe only has 2, rest have 3) Aka “articulations” Except for the hyoid, every bone in the body forms a joint with at least one other bone Hold bones together securely, but also provide mobility Classified functionally and structurally Synarthroses = immovable joints Amphiarthroses = slightly moveable joints Diarthroses = freely moveable joints Fibrous joints = bones united by fibrous tissue Examples: sutures of the skull, syndesmoses Syndesmoses = connecting fibers are longer than those of sutures, example: joint connecting distal ends of tibia and fibula Cartilaginous joints = bones connected by cartilage Examples: pubic symphysis of pelvis, intervertebral joints of spinal column Synovial joints = bone ends separated by joint cavity containing synovial fluid Four distinguishing features: 1. Articular cartilage – covers ends of bones making joint 2. Fibrous articular capsule – joint surfaces are enclosed by a sleeve or capsule of fibrous connective tissue, which is lined with smooth synovial membrane. 3. Joint cavity – articular capsule encloses a cavity (joint cavity) which contains lubricating synovial fluid 4. Reinforcing ligaments – fibrous capsule is usually reinforced with ligaments Plane joint = articular surfaces are flat, only short slipping or gliding movements Hinge joint = cylindrical end of one bone fits into a trough-shaped surface of another bone, angular movement Pivot joint = rounded end of one bone fits into a sleeve or ring of bone (and possibly ligaments), uniaxial joints Condyloid joint = “ellipsoid joint,” egg-shaped articular surface of one bone fits into an oval concavity in another bone, move from side to side and back and forth, but cannot rotate around long axis Saddle joints = each articular surface as both convex and concave areas, essentially same movement as condyloid joints Ball-and-socket joint = spherical head of one bone fits into round socket in another, allows movement in all axes http://www.jeffsims.net/flash/skeleton.html Arthritis = over 100 different inflammatory or degenerative diseases that damage the joints, affects 1 in 7 Americans Osteoarthritis = affects the elderly, “wear and tear” arthritis, breakdown of cartilage Rheumatoid arthritis = chronic inflammatory disorder, affects 3 times as many women as men, body’s immune system tries to destroy its own tissues, inflammation of synovial membrane Gout = disease in which uric acid accumulates in the blood and is deposited in needle-shaped crystals in soft tissues of joints, incredibly painful, more common in males Osteoporosis = bone-thinning disease that affects half of women over 65 and 20% of men over 70, makes bones so fragile that a hug or sneeze could cause bones to fracture First “long bones” of fetus are formed of hyaline cartilage Cartilage gets converted to bone Epiphyseal plates of long bones continue to grow until adolescence Ratio of skull to body changes http://www.so.k12.ia.us/teacher_web/wedgem/Sites/ANATO MY/SKELETAL%20SY/Axial%20Skeleton.html
