Skeletal System Notes
Osteology- study of bones
Skeletal system = bones, cartilage, ligaments & other connective tissue that stabilizes/connects bone
ANATOMY
Adult human skeleton has 206 individual bones arranged into a supporting but flexible framework
Number of bones varies person to person due to age & genetic factors
Birth- 270 bones
Number increases during infancy as ossification occurs
Number decreases during adolescence as bones fuse together
Some adults have sutural bones within skull joints & sesamoid bones form in tendons in response to repeated stress on a joint
Skeleton divided into axial & appendicular
Axial- 80 bones; more rigid structure; includes cranial, facial & vertebral bones as well as thorax
Appendicular- 126 bones; consists of pectoral & pelvic girdles & bones of the appendages
Bone shapes can help indicate function
Long bones- longer than they are wide; provide body support & function as levers during body movement; ex. Humerus, femur, ulna, radius, tibia, fibula, phalanges
Short bones- cube shaped; transfer forces of movement; ex. Carpals, tarsals, sesamoid bones
Flat bones- have broad surfaces for muscle attachment or protection of underlying organs ex. Ribs, cranial bones, sternum, scapula
Irregular bones- varied shapes & many surface features for muscle attachment; ex. Vertebrae, hip bones, some cranial/facial bones
Structure of long bone
Compact bone- hard & dense; protective exterior of all bone
Spongy bone- deep inside compact bone; porous
Diaphysis- bone shaft or cylinder of compact bone around central medullary cavity; provides leverage & major weight support
Medullary cavity- inside diaphysis; lined with connective tissue layer (endosteum which covers internal surfaces & is used for bone growth/repair); contains yellow bone marrow in adults
Epiphysis- ends of shaft containing spongy bone surrounded by layer of compact bone; red bone marrow found here; enlarge to strengthen joint & provide surface area for tendon & ligament attachment
Articular cartilage- thin layer of hyaline cartilage capping each epiphysis; reduces friction & absorbs shock in joint
Nutrient foramina- small openings into bone along diaphysis where blood vessels can enter bone
Epiphyseal plate- cartilage region between epiphysis & diaphysis where linear bone growth occurs as well as ossification; called metaphysis in mature bone
Periosteum- dense irregular connective tissue covering bone surface; lots of blood vessels; where tendons/ligaments attach; where bone growth in width occurs; held to bone by perforating fibers
Bone tissue- many bone cell types embedded in matrix of calcium/phosphorous salts as well as collagenous fibers
Types of bone cells
Osteogenic (osteoprogenitor) cells- found next to endosteum & periosteum; stem cells that will give rise to osetoblasts & osteoclasts

Osteoblasts- bone forming cells that make/secrete matrix substance; found in periosteum & medullary cavity; as they become entrapped in matrix they become osteocytes
Osteocytes- mature bone cells made of osteoblasts that have secreted bone tissue around themselves; found in compact bone; help keep bone healthy by secreting enzymes & influencing bone mineral content; regulates release of calcium ions by bone into blood; maintain matrix & detect mechanical stress
Osteoclasts- large multi-nucleated cells that break down bone tissue during building/remodeling
Bone lining cells- made of osteoblasts along surface of bones; regulate movement of calcium & phosphorous in/out of bone
Compact bone- cylindrical osteons or haversian systems run parallel to long axis of bone; central
haversian canal surrounded by concentric rings or lamellae; inside central canal & haversian canals are blood vessels & nerves that run through the bone; lacunae (osteocytes) arranged between lamellae & connect together by canaliculi or tiny channels; nutrients, wastes, minerals,
& gases travel through canaliculi; perforating canals run at right angles to central canals & have blood vessels & nerves
Spongy bone- has lattice appearance due to spikes of bone tissue called trabeculae; lots of blood, gives bone strength without adding weight; no osteons present; osteocytes found between parallel lamellae
In most bones, a cartilage structure is replaced by bone tissue through endochrondral bone formation
Bone continues to change shape- prominences develop as stress is applied to periosteum & new bone tissue forms; ex. Greater trochanter of femur enlarges as adult if physically active
Inactivity causes bones to lose tissue
Absence of gravity (such as during space flight) results in bone mineral loss if no exercising is done
Human skull has 8 cranial bones & 14 facial bones
Cranial bones fit together to enclose & protect brain & sense organs
Facial bones form framework of face & support teeth; do not come into contact with brain; most are paired
Cavities of skull
Cranial cavity- largest; holds brain
Nasal cavity- divided into 2 nasal fossae by nasal septum
Paranasal sinuses- 4 sets of cavities within bones around nasal area
Middle & inner ear cavities- below cranial cavity; houses sense organs & balance organs
Orbits- around eyes; formed by both facial/cranial bones
Buccal cavity- mouth; formed partially by bone
Babies are born with soft spots (fontanels) in scalp; these are connective tissue membranes that cover gaps between developing bone; ossification of these is complete by 2 years of age
Fontanels permit rapid brain growth in infant as well as molding of head during birthing process
Sutures of cranium connect the fontanels & will form future joints between bones
Cranial bones
Frontal- anterior roof of cranium, forehead, roof of nasal cavity & superior arch of orbits; contains frontal sinuses to lessen weight of skull & act as resonance chambers for voice
Parietal- upper sides & roof of cranium
Temporal- lower sides of cranium; contains ear canal
Occipital- posterior & base of skull; foramen magnum is large hole through which spinal cord passes; occipital condyles are structures that articulate with first vertebrae
Sphenoid- anterior base of cranium; contains several foramen such as optical canal through which nerves & vessels pass

Ethmoid- anterior portion of floor of cranium; forms the roof of nasal cavity & separates it into
Facial bones
2 chambers
Maxilla- two join to form upper jaw; supports upper teeth; contains large maxillary sinus
Palatine- L shaped bones that form posterior third of hard palate & part of nasal cavity
Zygomatic- cheek bones & lateral margin of orbits
Lacrimal- thin bones that form anterior part of medial wall of orbit; smallest of facial bones; allows tears to drain into nasal cavity
Nasal- small rectangular bones forming part of nasal septum
Vomer- thin flat bone forming lower part of nasal septum
Mandible- largest strongest facial bone; only movable bone of skull
Hyoid bone- single bone; not attached directly to any other bone; supports tongue & provides attachment for muscles; frequently fractured during strangulation
Auditory ossicles- small bones in middle ear cavity; malleus, incus, stapes
Vertebral column- made of vertebrae separated by fibrocartilaginous intervertebral discs; enclose & protect spinal cord; support skull, articulate with rib cage & provides attachment for trunk muscles; typically 33 individual vertebrae; between vertebrae are intervertebral foramina where spinal nerves pass
4 curves of vertebral column- cervical, thoracic, lumbar, pelvic
Curves needed for increasing strength & maintaining balance of upper body as well as making possible bipedal stance
Develop at about 3 months of age
Parts of vertebrae
Body- anterior drum shaped region in contact with intervertebral discs
Arch- posterior surface that helps form the vertebral formen where the spinal cord is
Processes- several bumps etc on vertebrae where muscles attach & vertebrae interlock
Types of vertebrae
Cervical- 7; form neck & support head; bone tissue densest here; atlas is first cervical vertebrae
& it lacks a body; joint here allows for nodding of head; 2 nd is called axis & it allows for rotation of head
Thoracic- 12; articulate with ribs to form the posterior anchor of rib cage; larger than cervical &
T12 is larger than T1
Lumbar- 5; heavy bodies & thick processes for attaching powerful back muscles
Sacrum- wedge shaped & provides foundation for pelvic girdle; 4-5 vertebrae that are fused by age 26
Coccyx- triangular tailbone made of 3-5 fused coccyeal vertebrae; start to fuse at puberty
Rib cage- made of thoracic vertebrae, 12 paired ribs, costal cartilages & sternum; its job is to enclose & protect the heart & lungs as well as supporting the pectoral girdle & playing a role in breathing
Sternum- elongated flat bony breastplate; 3 parts- manubrium, body & xiphoid process; ribs attach to sides of manubrium & body while abdominal muscles attach to xiphoid process
Ribs- 12 pairs that each attaches to a different thoracic vertebrae
True ribs- first 7 pairs anchored to a different thoracic vertebrae
False ribs- pairs 8-10; anchored to sternum indirectly by common cartilage
Floating ribs- pairs 11 & 12; don’t attach to sternum at all
Pectoral girdle- made of 2 scapulae & 2 clavicles; only attaches to anterior part of axial skeleton; primary function is to provide attachment for muscles that move shoulder & elbow

Clavicle- slender collarbone; connects arm to axial skeleton & holds shoulder joint away from body
Scapula- large triangular shoulder blade on back of rib cage; spine is bony ridge on posterior surface that strengthens scapula so its won’t bend; shoulder joint formed by glenoid cavity; 15 muscles attach here
Brachium- arm; extends from shoulder to elbow
Humerus- longest bone of upper extremity whose head fits in glenoid cavity; distal end articulates with bones of forearm; large medial epicondyle protects the ulnar nerve, hitting this nerve is called “hitting your funny bone”
Antebrachium- forearm; extends from elbow to wrist
Ulna- on medial side; more firmly connected to humerus; longer of the 2 bones of forearm; articulates at both ends with radius
Radius- on lateral or thumb side; articulates with wrist bones at distal end
Manus- hand; contains 27 bones
Carpus- wrist; made of 8 carpal bones arranged in 2 rows
Metacarpals- palm of hand containing 5 metacarpal bones; heads form your knuckles when you clench your fist
Phalanges- 14 bones of your digits; thumb has 2 & all other fingers have 3
Pelvic girdle- made of 2 ossa coxae (hip bones) united anteriorly at the symphysis pubis; attaches to sacrum of vertebral column; supports the weight of body from the vertebral column and supports/protects your lower viscera
Pelvis- deep bowl-like structure of ossa coxae, sacrum & coccyx
Greater (false) pelvis- expanded part of pelvis above pelvic rim
Lesser (true) pelvis- below pelvic brim to pelvic outlet
Hipbone- 3 parts: ilium, ischium & pubis; fused together in adult, large circular depression
(acetabulum) is where leg attaches
Ilium- uppermost & largest; has crest & 4 spines; your hip is the iliac crest sticking out
Ischium- posterionferior bone of os coxae; ischial tuberosity supports weight of body when you sit
Pubis- anterior bone; forms the symphysis pubis joint of the pelvis
Male pelvis & female pelvis are different due to pregnancy & birth requirements
Male- more massive, heart shaped outlet, narrower outlet, iliac spines closer together, acetabulum faces to sides, symphysis pubis deeper & longer
Female- more delicate, round or oval outlet, wider outlet, wider between iliac spines, acetabulum faces more anteriorly, shallower shorter symphysis pubis, pubic arch wider
Femur- thighbone; longest heaviest strongest bone of body; head fits into acetabulum; slightly curved so knee joint is in line with body’s plane of gravity & female’s curves more since her pelvis is wider
Patella- kneecap; large sesamoid bone on anterior side of distal femur; develops due to strain in tendon of quadriceps femoris muscle; functions to protect knee joint & to strengthen tendon
Leg- lower portion of lower limb between knee & foot
Tibia- articulates with femur & ankle at ends and on the sides of fibula; larger bone of lower leg since it bears the weight
Fibula- long slender bone; used mostly for muscle attachment
Pes- foot; contains 26 bones that support weight of body & provide leverage/mobility during walking

Tarsus- 7 tarsal bones in ankle; talus connects to tibia & fibula; calcaneous is largest & forms the heel
Metatarsus- 5 metatarsal bones; with first being the largest & it is attached to the big toe; ball of foot is formed by heads of first metatarsal bones
Phalanges- 14; big toe (hallus) has only 2 but other toes have 3
Arches of foot- formed by structure/arrangement of bones & held in place by ligaments/tendons
Longitudinal arch- goes from talus in ankle to distal ends of metatarsals
Transverse arch- extends across width of foot
Flat feet or fallen arches due to weakening of ligaments/tendons in feet
Arthrology- study of joints; looks at structure, classification & function of joints
Kinesiology- study of the mechanics of human motion as it relates to bones, muscles & joints
Ligaments- tough bands of connective tissue that hold bones together at a joint
Joint- junction of two or more bones; articulation
Types or Classes of Joints
Fibrous or synarthroses- firmly bind bones together with dense regular fibrous connective tissue
Cartilaginous or amphiarthroses- firmly unites bones with cartilage
Synovial or diarthroses- freely movable joints; enclosed by joint capsules that contain fluid
Structure of joint determines the direction & range of movement it allows; more mobile it is the less stable the joint is
Fibrous joints- tightly bound by fibrous connective tissue; some stay rigid & others are slightly movable
Types of fibrous joints
Suture- found only in the skull; have thin layer of dense irregular connective tissue; immovable or slightly mobile; form at 18 months of age to replace fontanels
Serrated- interlocking saw-like joint; ex. Between parietal bones
Squamous- edge of one bone overlaps articulating bone; ex. Between temporal
& parietal
Plane- edges are smooth & do not overlap; ex. Between maxillary & palatine bones to make hard palate
Syndesmoses- held together by collagenous fibers & interosseous ligaments; slight movement is allowed here; ex. Joint between ear drum & middle ear bones, between ulna & radius as well as between tibia & fibula
Gomphoses- fibrous joints between teeth & jaw bones
Cartilaginous joints- allow limited movement in response to twisting & compression
Types of cartilaginous joints
Symphyses- adjoining bones covered by hyaline cartilage; pad of fibrocartilage cushions joint; ex. Symphysis pubis & intervertebral discs
Synchondroses- hyaline cartilage between articulating bones; some form between diaphysis & epiphyses of long bones in children & then become ossified; others don’t ossify like between sphenoid, occipital, temporal & ethmoid bones
Synovial joints- freely movable; enclosed by joint capsules containing synovial fluid; provide wide range of precise, smooth movements; range of movement is determined by structure of bones involved, strength of joint capsule & strength of associated ligaments/tendons, size, arrangement & action of muscles spanning joint
Structure of synovial joint
Joint capsule- fibroelastic encasing that is filled with lubricating synovial fluid

Synovial fluid- secreted by synovial membrane lining capsule; rich in hyaluronic acid & albumin; contains phagocytic cells to clean up debris caused by wear; lubricating material found between articular cartilages; egg white-like consistency
Articular cartilage- hyaline cartilage that caps the bone ends; no blood vessels so must be nourished by synovial fluid movement; provide smooth surface at ends of bones in joints
Ligaments- flexible connective tissue cords that connect bone to bone; found inside/outside of joint capsule
Meniscus- only in knee joint; tough fibrous cartilaginous pads that cushion bones
Bursa- flattened pouch-like sacs filled with synovial fluid; found between muscles or where tendons pass over bones; needed to cushion
Types of synovial joints
Plane (gliding)- side to side & back/forth movements; surfaces are nearly flat; ex. Intercarpal & intertarsal
Hinge- permit movement in only one plane; one bone surface always concave & the other is convex; most common type; ex. Knee (considered most complex joint), elbow
Pivot- rotates around a central axis; conical bone fits into a depression; ex. Axis & atlas
Condyloid (angular, ellipsoid)- oval convex surface fits in concave depression; allows movement up/down as well as side to side; ex. Wrist, ankle, knuckles
Saddle- modified condyloid; only found at thumb & hand joint and between incus & malleus
Ball & Socket- rounded covex surface fits in a cuplike cavity; has greatest range of movements; free circular movement; ex. Hip & shoulder
In skeletal system the bones work as levers & joints as fulcrums while muscle action supplies the force
Joint actions
Angular movements- increase or decrease joint angle
Flexion- joint bends; closes angle; moving arm or leg from its normal position straight in front of body; bones are brought closer together
Plantar flexion- pressing foot downward as to rise on toes
Extension- joint unbends or straightens; opens angle; move arm or leg from its normal position toward the rear; articulating bones move farther apart; returning body part to its anatomical position
Hyperextension- body part is extended beyond the anatomical position
Abduction- moving arm or leg away from the midline of the body in a lateral direction
Adduction- opposite of abduction; moving arm or leg toward midline of body
Circular movements
Rotation- movement of body part around its own axis
Supination- rotating forearm so palm faces forward
Pronation- rotating forearm so palm faces downward
Circumduction- movement of body part so a cone-shaped airspace is traced
Other movements
Inversion- movement of foot sole inward
Eversion- movement of foot sole outward
Protraction- movement of body part forward on plane parallel to ground
Retraction- returning protracted body part on plane parallel to ground
Elevation- raises body part
Depression- lowers body part

PHYSIOLOGY
Functions
Storage- stores mineral salts such as calcium/phosphorous for use in body; also lipids are stored in the yellow bone marrow
Support/Protection- many bones protect internal organs; ex. Cranium, rib cage, vertebrae, pelvis
Movement- works with muscular system to move body
Hemopoiesis- blood formation in red bone marrow
Bone is both light & strong
Made of very hard, tiny crystals formed from minerals
Mineral crystals held together by collagen
If you remove the collagen from bone, the crystals don’t stick together & bones can easily crumble
If you remove the crystals of minerals, the bones become rubbery & flexible
Near distal end of each bone is epiphyseal plate where cartilage cells divide & lengthen a bone
Growth continues until full length is reached & then cartilage is completely replaced & no further growth occurs
Ossification (calcification)
Process of bone formation
Mainly occurs by converting cartilage to bone
Types of ossification: endochondral & intramembranous
Intramembranous ossification
Some bones form from embryonic membranous connective tissue without a cartilage phase
Flat bones, facial bones, mandible, clavicle
Membranes eventually ossify & form flat bones
Endochondral ossification
Begins in 2 nd month of fetal development
Cartilage cells in center of shaft (diaphysis) become filled with minerals by calcification
Some cells around cartilage change into osteoblasts that secrete osteoid (hardened organic part of bone)
Cartilage becomes surrounded by compact bone (periosteal bone collar) which in turn is surrounded by periosteum (connective tissue cover)
Periosteal bud moves from periosteum to center of cartilage & a primary ossification center is established; bud consists of osteoblasts & blood vessels
Secondary ossification centers form where spongy bone develops & eventually bone completely replaces cartilage
Some Disorders of the Skeletal System
Sprain- tearing or straining of tendons/ligments around a joint
RICE
Rest- if activity of joint causes pain; begin rehab exercises ASAP to increase flexibility/strength and to reduce the chance of repeat injury; keep moving since it will draw fluids away & reduce swelling
Ice- 20 min every 2 hours after injury to limit swelling/inflammation
Compression- wrap with ACE bandage to limit swelling
Elevate- reduces swelling
Reducing swelling ASAP shortens recovery time by several days

Torn ligaments- ex. ACL in knee
Popping sound followed by swelling, pain, inflammation, weakness & stiffness
Non-operative treatment includes physical therapy to improve strength/endurance of muscles that cross the joint & use of a knee brace
Reconstructive surgery involves replacing the ligament with a section of the patellar tendon, follow surgery with physical therapy
Fracture- bone crack; begins to repair itself immediately because bones have so many blood vessels; still may take 2-3 months to repair
Dislocation- when bone is forced out of its proper joint position; should only be realigned by doctor; shoulder joint is most susceptible to dislocation due to less ligament reinforcement; symptoms include tenderness & swelling
Hyperextension- extension of a joint beyond the anatomical position so joint angle is greater than 180
Bursitis- inflammation, pain & stiffness in bursa sac near a joint caused by stress to joint
Arthritis- affects 90% of adults over age 40 (1 in 6 US residents); exercise can help reduce joint pain & stiffness; increases flexibility, muscle strength, cardiac fitness & endurance
Osteoarthritis (degenerative arthritis, degenerative joint disease)- occurs as a result of aging; bones begin to rub together & become painful; irritation of joints or wear/abrasion of joints; joints become stiff/knobby; formation of bony spurs in joint cavities; may lead to joint replacement; leading cause of disability in US
Rheumatoid- joints become swollen/painful due to inflammation of synovial membrane; autoimmune disorder where immune system begins to destroy joint tissue; cartilage in joint is destroyed & replaced by calcium; affects 3x more women than men with an onset between the ages of 20 & 45
Damaged joints can be replaced by artificial joints which can be inserted/cemented into place; but
Rickets bone must bind tightly to the artificial surface so joint must be coated with ceramic substance to encourage bone cells to grow close to surface of artificial joint; “total hip replacement” involves removing the damaged portion of the femur & an artificial head & neck are attached by a spike that extends into marrow cavity of shaft; prosthetic joints are weaker & generally implanted into elderly who are less likely to subject them to stress; implants can deteriorate so may have to be replaced in 15 years
Vitamin D deficiency in children whose cartilage continues to form rather than being replaced by bone
Vitamin D enables bloodstream to absorb calcium which is then stored in bones
Bones remain soft & become bent or distorted
Symptoms include muscular weakness, disturbances in growth, cramps, muscle twitches,
Osteoporosis irritability
Condition that makes bones fragile & easily broken (especially hip, wrist or backbone)
Bone matrix & calcium is lost in spongy bone
More bone is destroyed than replaced
Symptoms: loss of bone mass, deterioration of bone quality leading to reduced bone strength
& increased risk of fractures
Risk factors: female (1 in 2 women, 1 in 8 men), advanced age, family history, Asian or
Caucasian, estrogen deficiency, low calcium intake, inactivity, ingestion of certain medications, smoking, drinking alcohol, underweight, short small boned body type, caffeine, soft drinks/processed foods, early menopause

Treatments: estrogen replacement therapy, calcitonin works to prevent further bone loss, some meds suppress osteoclast activity, weight bearing exercises 3-4 times a week for prevention (walking, jogging, tennis, dancing, etc), 1000-1500 mg calcium supplements (but never more than 2000 mg) & 400-800 units of vitamin D daily
Acromegaly- too much growth hormone is released after puberty when epiphyseal plates have closed; cartilage & small bones react to hormone resulting in abnormal growth of hands, feet, lower jaw, skull & clavicle; President Lincoln believed to have this
Paget’s Disease = osteitis deformans
May be caused by inherited weakness of immune system or viral infection or both
Osteoclast activity accelerates producing acute osteoporosis; skeleton becomes deformed because new bone is poorly formed; quickens pace of bone breakdown/reformation so that new layers of bone are structurally disorganized, misshapen & considerably larger than original ones
Occurs in pelvis, skull, vertebrae, femur, tibia
Affects slightly more men than women, occurs after age 40
Diagnosis relies on Xrays or blood tests (looking for increased levels of alkaline phosphatase)
Treated by drugs (calcitonin) that slows or blocks rate of bone breakdown/formation
Sinusitis- inflammation/congestion of sinuses in the facial bones caused by increased nasal mucus which slows drainage & pressure builds up
TMJ syndrome = myofascial pain syndrome
Mandible is pulled out of alignment; person experiences facial pain & the inability to open mouth fully
Linked to grinding teeth during sleep & emotional stress
Treatment includes application of heat to joint & use of anti-inflammatory drugs
Kyphosis- hunchback appearance due to exaggerated curvature of thoracic area of spine; caused by osteoporosis, compression fractures to anterior portions of vertebrae, heavy weightlifting during adolescence, chronic contractions of muscles that insert on vertebrae or abnormal vertebral growth
Lordosis- swayback; abdomen/buttocks protrude because of exaggeration of lumbar curvature; may be due to excess abdominal weight (pregnancy or obesity)
Scoliosis- abnormal lateral curvature of spine; most often in thoracic region; may result from developmental problems; treatment consists of exercises, braces & surgical procedures
Slipped disc- supporting posterior ligaments of spine are weakened & the disc is forced partially into the vertebral canal; often occurs due to advancing age but can also occur due to whiplash
Herniated disc- disc again protrudes into vertebral canal but now sensory nerves are distorted/compressed; results in severe backache, abnormal posture, or sensory function; most common in cervical or lumbar regions