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Chapter 5 The Skeletal System skeletal system - consists of: bones joints cartilage ligaments skelton - composed of 206 bones 2 divisions of the skeleton: axial skeleton - longitudinal axis of body appendicular skeletal - bones of limbs and girdles functions of the bones: support protection movement storage blood formation - internal framework - supports and anchors all soft organs - bones protect soft body organs - skeletal muscles attach to bone by tendons and use the bones as levers to move body - fat is stored in bone cavities - bone tissue stores minerals (calcium, phosphorus, etc.) - calcium ions (Ca2+) needed in blood for the nervous system to transmit messages, for muscles to contract, and for blood to clot - hormones control movement of calcium to & from bones - hematopoiesis (formation of blood cells) occurs in bone marrow cavities 2 types of osseous (bone) tissue: compact - dense; looks smooth spongy - made of needlelike bone pieces; has lots of open space 4 groups of bones (based on shape): long bones - longer than they are wide - shaft with heads at both ends - made mostly of compact bone - examples: all bones of limbs (except wrist & ankle bones) short bones - generally cube-shaped - made mostly of spongy bone - examples: wrist & ankle bones sesamoid bones - special type of short bone - form within tendons - example: patella (kneecap) flat bones - thin, flat, and usually curved - composed of spongy bone sandwiched by 2 thin layers of compact bone - examples: most skull bones, ribs, and sternum (breastbone) irregular bones - don’t fit in a preceding group - examples: vertebrae, hip bones long bone structure diaphysis periosteum Sharpey’s fibers epiphyses articular cartilage epiphyseal line epiphyseal plate medullary cavity bone markings - shaft - made of compact bone - fibrous CT membrane which covers the diaphysis - AKA perforating fibers - CT fibers that attach periosteum to bone - ends of long bones - composed of spongy bone enclosed by a thin layer of compact bone - covers epiphyses (no periosteum) - hyaline cartilage - smooth, slippery surface; decreases friction at joints - thin line separating epiphysis from diaphysis - remnant of the epiphyseal plate - AKA growth plate - plate of hyaline cartilage in a young growing bone - lengthwise growth of a long bone occurs here - by end of puberty, they are replaced by bone leaving epiphyseal lines - cavity of the shaft - primarily stores adipose tissue (yellow marrow) - contains red marrow in infants (blood cells made) - in adults red marrow is confined to spongy bone cavities - bumps, holes, and ridges - reveal where muscles, tendons, and ligaments were attached and where nerves and blood vessels passed - 2 types: projections - grow out from bone surface depressions - indentations in the bone microscopic long bone structure osteocytes - bone cells; found in lacunae lacunae - tiny cavities in bone matrix which contain osteocytes lamellae - concentric circles of bone tissue containing lacunae - surround central canals central canals - AKA Haversian canals - run lengthwise through matrix - contain blood vessels and nerves osteon - AKA Haversian system - consists of central canal and surrounding rings (lamellae) canaliculi - tiny canals that radiate outward from central canals to lacunae - allow bone cells to receive nutrients perforating canals - AKA Volkmann’s canals - run at right angles to the shaft - allow communication between inside and outside of bone bone tissue - very hard (due to calcium salts) - flexible (due to collagen fibers) bone formation embryo skeleton young child - mostly hyaline cartilage - cartilage has been replaced by bone - hyaline cartilage is “ossified” into bone - 2 phases: * hyaline cartilage is covered with a bone matrix by osteoblasts (bone-forming cells) * cartilage is digested away forming medullary cavity ossification long bone growth - controlled by hormones (growth hormone, sex hormone) - ends during adolescence (epiphyseal plates completely converted to bone) parathyroid hormone (PTH) - produced by parathyroid glands when blood levels of calcium are low - activate osteoclasts (bone-destroying cells) osteoclasts - break down bone matrix and release calcium into blood stresses of muscle pull and gravity physically inactive people - cause bones to become thicker and form projections to increase their strength - bones loses mass & atrophy because they are no longer subjected to stress rickets - disease of children - bones don’t calcify due to lack of calcium or vitamin D (needed for calcium absorption) - bones soften and legs become bowed bone fractures - breaks - during youth, most result from trauma during sports or car accidents - more frequent in old age closed (simple) fracture open (compound) fracture common fractures: comminuted compression depressed impacted spiral greenstick - bone breaks cleanly; doesn’t penetrate the skin - ends of bone penetrate skin - bone breaks into fragments (common in old age) - bone is crushed (common in old age) - broken bone portion is pushed inward (typical in skull fractures) - ends of broken bones are pushed into each other - common when trying to break a fall with outstretched arms - excessive twisting forces cause a ragged break (common in sports) - incomplete break, like a green twig (common in children) treatment of a broken bone reduction - bone is realigned - doctor uses his hands with closed fractures - surgery necessary with open fractures immobilization - cast or traction healing time for a simple fracture bone healing hematoma forms fibrocartilage callus forms bony callus forms bone remodeling occurs axial skeleton - 3 parts: - 6-8 weeks (longer for larger bones and in the elderly) - due to broken blood vessels - contains cartilage and bone matrix and cartilage fibers - made by CT cells - closes the gap and “splints” the bone - made of spongy bone by osteoblasts - replaces fibrocartilage callus - bony callus remodeled into a strong permanent patch skull vertebral column bony thorax skull - cranium encloses and protects brain - facial bones hold eyes in place and allow facial muscles to produce facial expressions most bones joined together by sutures (immovable joints) sinuses - air spaces in bone cranium - composed of 8 flat bones: frontal bone - forms forehead and superior part of each orbit (eye socket) parietal bones - paired bones - form most of superior and lateral walls of cranium temporal bones - paired bones - inferior to parietal bones on each side - important markings: external acoustic meatus - ear canal styloid process - needlelike just below EAM - many neck muscles attach here zygomatic process - joins cheek bone mastoid process - below and behind EAM - neck muscles attach here jugular foramen - where occipital and temporal bones meet - jugular vein passes through carotid canal - anterior to jugular foramen - carotid artery passes through occipital bone - forms floor and back wall of skull - important markings: foramen magnum - large opening at base of occipital bone - spinal cord passes through occipital condyles - rockerlike projections - rest on first vertebrae sphenoid bone - butterfly-shaped - forms part of cranial floor and eye orbits - important markings: sella turcica - depression that holds pituitary gland optic canals - optic nerve passes from brain to eyes ethmoid bone - anterior to sphenoid - forms roof of nasal cavity and part of orbits facial bones - 14 bones (12 are paired) maxillary bones - form upper jaw and anterior hard palate - carry the upper teeth - paranasal sinuses - drain into nasal passages - throat infections can spread here causing sinusitis palantine bones - form posterior hard palate - cleft palate zygomatic bones - cheekbones - also form part of orbits lacrimal bones - form part of orbits (fingernail size) - each has a groove for the passage of tears nasal bones - form bridge of nose vomer bone - forms nasal septum inferior nasal conchae - part of nasal cavity mandible - lower jaw - joins temporal bones on sides of face - carries the lower teeth hyoid bone - “Adam’s apple” - not really part of skull - suspended in midneck region - moveable base for tongue and attachment point for neck muscles that raise and lower larynx when we swallow or speak fontanels - soft spots in fetal skull - fibrous membranes not yet turned to bone - allow skull to be compressed during birth - also allow for brain growth vertebral column - AKA spine - flexible, curved structure extending from skull to pelvis - made of 26 irregular bones connected by ligaments - spinal cord runs through its central cavity vertebrae - 24 of them intervertebral discs - pads of fibrocartilage - cushion vertebrae and absorb shocks - herniated disc (slipped disc) - intervertebral disc protrudes - may cause numbness and excruciating pain vertebrae structure: body - disklike; bears weight arch - arch extending from the body foramen - spinal cord passes through transverse processes - lateral projections from arch spinous process - projection from posterior part of arch articular processes - allow vertebra to form joints with adjacent vertebrae cervical vertebrae - 7 of them C1 – C7 (think: breakfast at 7AM) - form neck region of spine atlas (C1) - holds skull - no body axis (C2) - acts as a pivot for atlas - has odontoid process (pivot point) thoracic vertebrae - 12 of them T1 – T12 (think: lunch at 12 noon) lumbar vertebrae - 5 of them L1 – L5 (think: dinner at 5 PM) sacrum - formed by the fusion of 5 vertebrae - joins with L12 above and the coccyx below - forms posterior wall of pelvis - joins with hip bones (sacroiliac joints) coccyx - formed by the fusion of 3-5 vertebrae - “tailbone” bony thorax - made of sternum, ribs, and thoracic vertebrae - AKA thoracic cage sternum - breastbone - forms from the fusion of 3 bones: manubrium - superior body - middle xiphoid process - inferior - bony landmarks: jugular notch - concave upper border of manubrium sternal angle - manubrium and body meet at a slight angle xiphisternal joint - where body & xiphoid process meet ribs - 12 pairs - forms wall of bony thorax - all attach to vertebral column and then curve downward and toward anterior body true ribs - first 7 pairs - attached to sternum by costal cartilages false ribs - next 5 pairs - attached to sternum indirectly by cartilage floating ribs - last 2 pairs - not attached to sternum appendicular skeleton - bones of the shoulder girdle, upper limbs, pelvic girdle, and lower limbs shoulder girdle (pectoral girdle) very flexible yet easily dislocated consists of: clavicle scapula - collarbone - attaches to manubrium of sternum and scapula - acts as a brace holding arm away from thorax - shoulder blade - loosely held in place by muscles - glenoid cavity - shallow socket that receives head of arm bone upper limbs 30 bones form each upper limb (arm, forearm, and hand) arm humerus - heads fits into glenoid cavity forearm radius - lateral to ulna (on thumb side) in anatomical position - connected to ulna by interosseous membrane ulna - medial to radius in anatomical position hand carpals - 8 of them (2 rows of 4) - form the wrist metacarpals - 5 of them - form palm of hand - heads form knuckles phalanges - 14 of them - form fingers - 3 in each finger (proximal, medial, and distal) - 2 in the thumb (proximal and distal) pelvic girdle formed by 2 coxal bones (hip bones) bears the weight of upper body each hip bone consists of: ilium - connects to sacrum posteriorly - large, flaring bone ischium - inferior part of hip bone (“sit-down bone”) pubis - pubic bone - most anterior part of hip bone acetabulum - deep socket formed at site where the 3 hip bones join - head of femur fits here lower limbs 30 bones form each lower limb thigh femur - thigh bone - heaviest, strongest bone in body - head fits into acetabulum of hip bone - neck of femur - frequently fractured in elderly patella - kneecap leg tibia - shinbone - larger and more medial than fibula - forms inner bulge of ankle - connected to fibula by interosseous membrane fibula - thin bone - forms outer bulge of ankle foot tarsals metatarsals phalanges - 7 of them - form back of foot (tarsus) calcaneous - heelbone - 5 of them - form sole of feet - 14 of them - form toes (3 in each toe, except great toe which has 2) joints joints - AKA articulations - hold bones together - give skeleton mobility types of joints (based on function) synarthroses - immovable joints amphiarthoses - slightly immovable joints diarthroses - freely movable joints types of joints (based on structure) fibrous joints - fibrous tissue separates bones - immovable - example: sutures of the skull - CT fibers bind bones tightly cartilaginous joints - cartilage separates bones - most are slightly immovable (some immovable) - examples: pubic symphysis - joins pubic bones together intervertebral joints - fibrocartilage discs join vertebrae together epiphyseal plates - hyaline cartilage joints between ribs and sternum synovial joints - bones separated by a cavity filled with synovial fluid - freely movable synovial joints - all have 4 features: articular cartilage fibrous articular capsule joint cavity - hyaline cartilage covering bone ends - sleeve of fibrous CT enclosing joint surfaces - lined with a synovial membrane - enclosed by the capsule ligaments bursae - contains synovial fluid for lubrication - reinforce joint - flattened sacs lines with a synovial membrane & filled with synovial fluid - often part of synovial joints tendon sheaths - long bursa that wraps around a tendon subject to friction types of synovial joints plane joint - short gliding movements - example: intercarpal joints of the wrist hinge joint - angular movement in 1 plane (back-and-forth) - examples: elbow joint ankle joint joints between phalanges of the fingers pivot joint - rounded end of 1 bone fits into a sleeve or ring of bone - example: atlas and dens of the axis condyloid joint - moving bone moves from side to side and back and forth - example: knuckle joints (metacarpophalangeal) saddle joint - moving bone moves from side to side and back and forth - example: thumb joint ( carpometacarpal) ball-and-socket joint - spherical head of 1 bone fits into a socket of another bone - allow movement in many directions - most freely moving joints - examples: shoulder hip dislocation reduction - bones is forced out of its normal position - process of returning the bone to its proper position - should only be done by a physician bursitis - inflammation of bursae or synovial membrane sprain - ligaments or tendons reinforcing a joint are stretched & damaged - extremely painful - heal slowly (poor blood supply) arthritis - 1 out of 7 Americans suffer from it - over 100 inflammatory or degenerative diseases that damage the joints - joints are painful, stiff, and swollen osteoarthritis - most common form of arthritis - affects the aged - joint cartilage softens and breaks down over the years - exposed bone can thicken to form bone spurs which restrict movement - progresses slowly and is irreversible - rarely crippling rheumatoid arthritis gout - chronic inflammatory disease - autoimmune disease - many joints affected (especially fingers, wrists, ankles, & feet) - bones ends can become fused and/or deformed - may be severely crippling - uric acid accumulates in blood and is deposited as needle-like crystals in the joints - agonizingly painful - often affects the great toe osteoporosis - bone-thinning disease - bones become fragile - vertebrae often collapse resulting in a hunched-over posture