Human Impact

Skeletal SystemUnit 4BonesFunction: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.Classification of BonesTwo basic types of tissue:Compact bone = dense, looks smooth and homogenousSpongy bone = composed of small needlelike pieces of bone and lots of open space

Classification of BonesFour basic shapes:Long = typically longer than they are wide, mostly compactShort = generally cube shaped, mostly spongyFlat = thin, flattened, usually curved, two layers of compact bone sandwiching layer of spongy boneIrregular bones = do not fit one of the preceding categories (hip bone, vertebrae, etc.)

Structure of a Long BoneA 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.Structure of a Long BonePeriosteum (fibrous connective tissue membrane) covers the diaphysis.Endosteum lines medullary cavities and the spaces of spongy bone.Hyaline cartilage covers articular surfaces.

Structure of a Long BoneIn 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.Bone MarkingsTwo main kinds:Projections or processes = grow out from bone surfaceDepressions or cavities = indentations in the boneIndicate sites of muscle attachment, points of articulation, and sites of blood vessels and nerve passage.Microscopic AnatomyThe 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).

Microscopic AnatomySpongy bone has slender trabeculae containing irregularly arranged lamellae that enclose red-marrow filled cavities.Bone Formation, Growth, and RemodelingIn 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.Bone Formation, Growth, and RemodelingOssification (bone formation) involves two major phases1. 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.Bone Formation, Growth, and RemodelingBy birth, most hyaline cartilage models have been converted to bone except for two regions:Articular cartilages that cover bone ends reduce frictionEpiphyseal plates provide for longitudinal growth during childhoodBone Formation, Growth, and RemodelingGrowing bone must widen as well as lengthen increase in diameter is called appositional growthGrowth 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 blood2. Pull of gravity and musclesBone Formation, Growth, and RemodelingA 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 Bone Formation, Growth, and RemodelingRemodeling is essential if bones are to retain normal proportions and strength during long-bone 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.Bone FracturesBones 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 skinOpen (or compound) fracture = broken bone ends penetrate skinBone Fractures

Bone FracturesTreated by reduction, the realignment of the broken bone ends.Closed reduction = bone ends are put back in normal position by physicians handsOpen reduction = surgery is performed and bone ends are secured with pins or wiresSimple fractures heal in 6-8 weeks, longer for large bones and elderly people (poor circulation)Repairing Bone Fractures1. 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.

The Axial SkeletonAxial SkeltonCan be divided into three parts:SkullVertebral columnBony ThoraxSkullFormed by two sets of bonesCranium = encloses and protects brain, composed of eight large, flat bonesFacial bones = hold eyes in anterior position, facilitate facial muscle movement, fourteen bones totalAll but one of the bones of the skull are joined together by sutures = interlocking, immovable joints.Mandible (jawbone) is attached by freely moveable jointCraniumFrontal bone forms forehead, bony projections under eyebrows, and superior part of each eyes orbitParietal 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

CraniumTemporal bones join parietal bones at squamous sutures, bone markings:1. External auditory meatus = canal that leads to eardrum and middle ear2. Styloid process = needlelike projection that attaches to many neck muscles3. Zygomatic process = bridge of bone that joins with cheekbone4. Mastoid process = rough projection containing mastoid sinus, posterior and inferior to external auditory meatus5. Jugular foramen = junction of occipital and temporal bones, allows jugular vein to pass through6. Carotid canal = anterior to jugular foramen, allows internal carotid artery to pass through

CraniumOccipital bone most posterior bone of cranium, joins parietal bones at lambdoid sutureForamen magnum = large hole, allows brain to connect with spinal cordOccipital condyles = rest on first vertebra of spinal column

CraniumSphenoid bone butterfly-shaped, spans width of skull, forms floor of cranial cavitySella turcica = (Turks Saddle) small depression in midline that holds pituitary gland in placeForamen ovale = allows fibers of cranial nerve V to pass to chewing muscles of lower jawEthmoid bone anterior to sphenoid, forms roof of nasal cavityCrista galli = cocks comb, projects from superior surfaceCribriform plates = small holes on side, allow nerve fibers to carry impulses from olfactory receptors to brain

Facial BonesMaxillae = (maxillary bones) fuse to form upper jaw, all facial bones except for mandible join the maxillae keystone bonesPalantine processes form anterior part of hard palateParanasal sinuses = lighten bones and amplify sounds we make while speaking

Facial BonesPalatine bones = lie posterior to maxillae, form posterior part of hard palate, failure to fuse = cleft palateZygomatic bones = cheekbones, form part of lateral walls of eye socketsLacrimal bones = fingernail-sized, form part of medial walls of orbits, each has a groove that is a passageway for tears

Facial BonesNasal bones = small, rectangular, form bridge of noseVomer bone = single bone in median line of nasal cavity, forms most of nasal septumInferior Conchae = thin, curved bones projecting from lateral walls of nasal cavity

Facial BonesMandible = jawbone, largest and strongest bone on face, joins temporal bonesHyoid 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

Fetal SkullFace is small compared to craniumSkull as a whole is large compared to body lengthWhen baby is born, skull is still unfinishedSome areas of hyaline cartilage still need to be ossified.Fontanels = fibrous membranes connecting cranial bones of infant soft spotsVertebral Column (Spine)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.Vertebral Column (Spine)Superior 7 vertebrae are cervical (C1-C7)Top two vertebrae are the atlas and axisNext 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

Vertebral Column (Spine)Single vertebrae are separated by intervertebral discs = pads of flexible fibrocartilage that cushion the vertebrae and absorb shocksIn 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.Vertebral Column (Spine)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 birthSecondary curvatures = cervical curvature appears when babies raise their heads, lumbar curvature appears when babies start to walkAbnormal Spinal Curvatures

VertebraeAll vertebrae have a similar structure patternCentrum (body) = disclike, weight-bearing part that faces the vertebral column anteriorlyVertebral arch = formed from the joining of all posterior extensions from the vertebral body (laminae and pedicles)Vertebral foramen = canal through which the spinal cord passesTransverse processes = two lateral projections from vertebral archSpinous 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

Cervical VertebraeFirst 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 brainThoracic VertebraeLarger than cervical vertebraeBody 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 giraffes head from sideLumbar VertebraeMassive, blocklike bodiesShort, hatchet-shaped spinous processes look like a moose head from lateral aspectMost of the stress on the vertebral column occurs in lumbar region sturdiest vertebrae

SacrumFormed by the fusion of 5 vertebraeThe winglike alae connect to hip bones sacroiliac jointsForms posterior wall of pelvisMedian sacral crest = fused spinous processes of the sacral vertebraeDorsal sacral foramina = holes that line each side of the median sacral crestSacral canal = continuation of the vertebral canalCoccyxFormed by the fusion of 3-5 tiny, irregularly shaped vertebraeTailbone

Bony ThoraxSternum, ribs, and thoracic vertebraeThoracic cage

SternumBreastbone attaches to 1st seven pairs of ribsResults from the fusion of three bones manubrium, body, and xiphoid processThree important bony landmarks:Jugular notch = concave upper border of manubriumSternal 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 ribsXiphisternal joint = point where the sternal body and xiphoid process fuse, same level as T9 vertebra

RibsTwelve pairs of ribs males have same number as femalesAttached to vertebral column posteriorly, then curve downward and around toward the anterior body surface1st seven pairs = true ribs because they attach to the sternum2nd five pairs = false ribs because they either attach indirectly to sternum or not at all, last two pairs are floating ribsIntercostal spaces = spaces between ribs, filled with intercostal muscles that aid in breathingAppendicular SkeletonAppendicular SkeletonComposed of 126 bones of the limbs and the pelvic and pectoral girdles, which attach the limbs to the axial skelton

Bones of the Shoulder GirdleConsists of 2 bones: clavicle and scapulaClavicle = 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 dislocationScapula = shoulder blade, triangular, flattened body, held loosely in place by trunk muscles, doesnt actually attach to axial skeleton, two important processes: acromion and coracoidBones of the Shoulder GirdleAcromion = enlarged end of the spine of the scapula, connects with clavicleCoracoid process = looks like a beak, points over top of shoulder and anchors some arm musclesSuprascapular notch = nerve passagewayGlenoid cavity = shallow socket that receives the head of the arm boneBones of the Shoulder GirdleShoulder girdle is very light and allows upper limb to be very flexibleEach shoulder girdle attaches to axial skeleton at only one point = sternoclavicular jointThe loose attachment of scapula allows it to slide back and forth against thoraxThe glenoid cavity is shallow and shoulder joint is poorly reinforced by ligamentsGreat for flexibility, bad for stability very easy to dislocate

Bones of the Upper Limbs30 separate bones form each upper limbArm, forearm, handArmUpper arm is single long bone = humerusHead fits into glenoid cavity of scapulaOpposite head are two bony projections = greater and lesser tubercles, attach to musclesDeltoid tuberosity = rough area in midpoint of shaft where deltoid attaches

ArmRadial groove = runs down posterior aspect of shaft, marks course of radial nerveTrochlea and capitulum = distal end of humerus, articulate with bones of forearmCoronoid fossa and olecranon fossa = depressions flanked by medial and lateral epicondyles that allow the ulna to move freely when elbow is bent and extended

ForearmRadius and ulna = bones that form skeleton of forearmIn anatomical position, radius is lateral bone, on the thumb sideBones meet at both proximal and distal ends at radioulnar joints, connected by flexible interosseous membrane

ForearmHead of radius forms joint with capitulum of humerusRadial tuberosity = just below head of radius, where tendon of biceps muscle attachesCoronoid process and olecranon process = proximal end of ulna, separated by trochlear notch, grip the trochlea of humerus

HandCarpal bones = 8 bones arranged in two irregular rows of four bones each, wristMetacarpals = 5 bones, palm of hand, numbered 1-5 from thumb to little fingerPhalanges = 14 bones, 3 in each finger (proximal, middle, and distal) except for thumb, which has 2 (proximal and distal)

Bones of the Pelvic GirdleTwo coxal bones (ossa coxae), aka hip bonesLarge and heavy bones, securely attached to axial skeletonCoxal bones + sacrum + coccyx = bony pelvisHip bone is formed by the fusion of three bones: ilium, ischium, and pubis

Bones of the Pelvic GirdleIlium = connects to sacrum at sacroiliac jointIschium = sitdown bone, forms most inferior part of coxal boneGreater sciatic notch = allows blood vessels and sciatic nerve to pass from pelvis to thighPubis = most anterior part of coxal boneAcetabulum = point where ilium, ischium, and pubis fuse at the deep socket, receives head of thigh boneBones of the Pelvic GirdleFalse pelvis = superior to true pelvis, medial to flaring portion of iliaTrue pelvis = surrounded by bone and lies inferior to flaring parts of ilia and pelvic brimFemale pelvis = inlet larger and more circular, shallower, lighter, thinner, shorter sacrum, pubic arch more rounded

Bones of the Lower LimbsCarry the weight of the body when we are standingMuch thicker and stronger than the bones of the upper limbsThighFemur = only bone in the thighHead = ball that fits into hip socket (acetabulum) Greater and lesser trochanters = sites of muscle attachmentLateral and medial condyles = separated by intercondyle notch, articulate with tibiaPatellar surface = forms joint with patella (kneecap)

LegTwo bones: tibia and fibulaTibia = shinbone, larger and more medialMedial and lateral condyles = attach to distal end of femurTibial tuberosity = attaches to patellar ligamentMedial malleolus = inner bulge of ankle

LegFibula = lies alongside tibia, joins at proximal and distal endsLateral malleolus = outer part of ankle

FootTarsals, metatarsals, phalangesCalcaneus = heelboneTalus = between calcaneus and tibiaFive metatarsals = sole of the foot14 phalanges form toes (big toe only has 2, rest have 3)

JointsJointsAka articulationsExcept for the hyoid, every bone in the body forms a joint with at least one other boneHold bones together securely, but also provide mobilityClassified functionally and structurallyJointsSynarthroses = immovable jointsAmphiarthroses = slightly moveable jointsDiarthroses = freely moveable joints

Fibrous jointsFibrous joints = bones united by fibrous tissueExamples: sutures of the skull, syndesmosesSyndesmoses = connecting fibers are longer than those of sutures, example: joint connecting distal ends of tibia and fibula

Cartilaginous jointsCartilaginous joints = bones connected by cartilageExamples: pubic symphysis of pelvis, intervertebral joints of spinal column

Synovial jointsSynovial joints = bone ends separated by joint cavity containing synovial fluidFour distinguishing features:1. Articular cartilage covers ends of bones making joint2. 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 fluid4. Reinforcing ligaments fibrous capsule is usually reinforced with ligamentsTypes of Synovial Joints Based on ShapePlane joint = articular surfaces are flat, only short slipping or gliding movementsHinge joint = cylindrical end of one bone fits into a trough-shaped surface of another bone, angular movement

Types of Synovial Joints Based on ShapePivot joint = rounded end of one bone fits into a sleeve or ring of bone (and possibly ligaments), uniaxial jointsCondyloid 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

Types of Synovial Joints Based on ShapeSaddle joints = each articular surface as both convex and concave areas, essentially same movement as condyloid jointsBall-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 DisordersArthritis = over 100 different inflammatory or degenerative diseases that damage the joints, affects 1 in 7 AmericansOsteoarthritis = affects the elderly, wear and tear arthritis, breakdown of cartilageRheumatoid arthritis = chronic inflammatory disorder, affects 3 times as many women as men, bodys immune system tries to destroy its own tissues, inflammation of synovial membrane

DisordersGout = 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 malesOsteoporosis = 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

Developmental Aspects of SkeletonFirst long bones of fetus are formed of hyaline cartilageCartilage gets converted to boneEpiphyseal plates of long bones continue to grow until adolescenceRatio of skull to body changes

http://www.s-o.k12.ia.us/teacher_web/wedgem/Sites/ANATOMY/SKELETAL%20SY/Axial%20Skeleton.html