Skeletal
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the skeletal system is strong, light, adapted
for protection, and adapted for motion
◦ axial – longitudinal axis
◦ appendicular – limbs and girdles
◦ also includes joints, cartilages, and ligaments
functions
support – internal framework,
supports/anchors all soft organs
 protection – protect by surrounding softer
body organs
 movement – skeletal muscle attach to bones
via tendons and are used as levers to move
 storage – fat is found in internal cavities, Ca
and P in bone tissue
 blood cell formation (hematopoiesis) – in
marrow of some bones
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types
 compact bone – dense and smooth
 spongy bone – small needle-like pieces
with open spaces
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classification
 the shape of each bone determines its function
 long bones –
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longer than they are wide
shaft with a head at each end
mostly compact
all limb bones except metacarpals and metatarsals
short bones –
◦ generally cube shaped
◦ mostly spongy
◦ metacarpals and metatarsals
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flat bones –
◦ thin, flat, and curved
◦ 2 thin layers of compact bone with a layer of
spongy bone in between
◦ skull, ribs, sternum
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irregular bones –
◦ do not fit any other category
◦ vertebrae and hips
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bone markings are where
muscles/tendons/ligaments attach and where
blood vessels/nerves pass
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structure of a long bone
diaphysis –
◦ the shaft
◦ mostly compact bone
◦ covered with periosteum
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epiphyses –
◦ the ends of the long bones
◦ thin layer of compact bone surrounding spongy bone
◦ covered with cartilage to decrease friction
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yellow marrow (medullary) cavity –
◦ storage area of fat tissue in adults
◦ contains red marrow in infants that make RBCs
microscopic anatomy
 mature bone cells (osteocytes) are found in cavities (lacunae)
and secrete a solid matrix
 lacunae are arranged in a circle (lamella) around a central
canals (osteonic canal)
 several lamella (lamellae) surrounding a single central canal is
an osteon
 canals run lengthwise thru the bone to carry blood vessels
and nerves from end to end
 tiny canals (canaliculi) run horizontally to connect all lacunae
 allows all osteocytes to be well supplied with nutrients even
though the matrix is solid
 larger canals (perforating) run horizontally between the
osteons
bone formation, growth, and
remodeling
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the skeleton is formed from bone and cartilage
◦ 2 of the strongest tissues in the body
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babies have cartilage that is gradually replaced by
bone (ossification)
◦ cartilage contains osteoblasts which secretes bone matrix
◦ bone matrix replaces cartilage matrix
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osteocytes replace chondrocytes
cartilage becomes bone
◦ process is continually repeated
◦ result is bone growth to lengthen long bones
◦ growth hormone starts the process and sex hormones
continue growth during puberty
◦ cartilage only remains in ears, nose, ends of ribs, and joints
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bones are continually remodeled
◦ to release Ca into the blood
 Ca levels drop below homeostatic levels
 parathyroid glands release hormone to activate bone-destroying
cells (osteoclasts)
 bone matrix is broken down to release Ca into the blood
◦ to remove Ca from the blood
 blood Ca levels that are too high cause hypercalcemia
 Ca is removed from the blood and deposited into bone matrix
◦ to retain normal proportions during growth
◦ bones become thicker with age
◦ bones form larger projections in response to bulkier
muscles
 osteoblasts lay down new matrix, become trapped, and become
osteocytes
Bone Fractures
in youth, most fractures/breaks occur from
trauma that twists or smashes bones
 in older adults, bones thin/weaken so fractures
are more common
 fractures are set by reduction and immobilization
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◦ closed reduction is by external manipulation
◦ open reduction is by surgery and requires bone to be
pinned/wired
◦ hematoma forms where the bone breaks
◦ cartilage callus is replaced by osteoblasts and
osteocytes to form a spongy bony callus
◦ bony callus continually remodeled and strengthened
into a permanent patch
Explain how this picture makes you feel and
describe it using vocabulary you have learned
about bones, tissues and integument.
Axial Skeleton
forms the longitudinal axis (skull, vertebral column, bony
thorax)
 skull
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cranium
encloses/protects brain
frontal bone – forehead/brows/superior orbit
parietal bones – superior and lateral cranium
temporal bones – inferior to parietal
external auditory meatus – ear canal
 styloid process – needle-like projection for neck muscle attachments
 zygomatic process – bridge that joins with zygomatic bone to form
cheekbones
◦ mastoid process – contains air cavities and provides attachment
site for neck muscles
 jugular foramen – allows for passage of jugular vein
 carotid canal – allows for passage of carotid arteries
◦ occipital bone – floor and back wall of skull
 foramen magnum – passage of spinal cord to the
brain
 occipital condyles – rests the skull on the first
vertebra
◦ sphenoid – part of the floor of cranial cavity,
part of the orbit
◦ ethmoid bone – irregular and anterior to
sphenoid, forms roof of nasal cavity and
medial orbit
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facial bones
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holds the eyes in position
attached to each other with sutures (except mandible)
maxillae – fuse to form upper jaw, carry teeth in alveolar margin
palatine process – hard palate
zygomatic bones – lateral orbits, connect with temporal bones
to form cheekbones
lacrimal bones – medial orbits, groove for tear ducts
nasal bones – bridge of the nose
vomer bone – median line in the nasal cavity that forms the
septum
inferior conchae – thin curved bone projecting into the nasal
cavity
mandible – strongest bone of the face, lower jaw
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hyoid bone
◦ not a part of the skull be closely related to the
mandible and temporal bone
◦ only bone not articulated with another bone
◦ suspended midneck above the larynx by attachments
to the styloid process
◦ serves as a movable base for the tongue and
attachment site for neck muscles
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fetal skull
◦ regions of skull are not yet ossified and are connected
by fibrous membranes (fontanels)
◦ fontanels allow fetal brain to grow during late
pregnancy and the skull to compress during birth
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vertebral column (spine)
◦ made of 26 irregular bones (reinforced by ligaments),
the sacrum, and coccyx
◦ separated and cushioned by flexible intervertebral
discs
◦ supports the skull and protects the spine
◦ all have 6 common features:
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body – weight-bearing part, anterior side
vertebral arch – formed from the joining of all extensions
vertebral foramen – spinal cord canal
transverse processes – 2 lateral projections
spinous process – posterior projection
superior articular processes – projections allowing vertebra
to articulate (join) together
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cervical vertebrae (C1-C7)
◦ 7 vertebrae in the neck region
◦ first is the atlas (supports the skull and allows
anterior/posterior movements)
◦ second is the axis (allows lateral movements)
◦ remaining 5 are smallest and lightest
◦ all have transverse foramen for vertebral
arteries travelling to the brain
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thoracic vertebrae(T1-T12)
◦ next 12 vertebrae
◦ from the most superior rib to the most
inferior rib
◦ designed to articulate with the head of the
ribs
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lumbar vertebrae (L1-L5)
◦ lower back
◦ massive bodies to withstand heavy stresses
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sacrum
◦ fusion of 5 vertebrae
◦ articulates with L5 (superior), the coccyx
(inferior), and the ilium (laterally)
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coccyx (tailbone)
◦ fusion of 3 to 5 small vertebrae
◦ remnant of mammalian tails
bony thorax (thoracic cage)
 thoracic vertebrae
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◦ 12 vertebrae that articulates with the ribs
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sternum (breastbone)
◦ fusion of 3 bones (manubrium, body, and
xiphoid process)
◦ contains hematopoietic tissue
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ribs
◦ 12 pairs that all articulate with the thoracic
vertebrae
◦ first 7 pairs are true ribs – articulate with the
sternum by costal cartilage
◦ next 5 pairs are false ribs – articulate
indirectly to sternum or not at all
 (last 2 pair lack articulation and are floating ribs)
appendicular skeleton
composed of 126 bones of the limbs
 the pectoral and pelvic girdles (attach the
limbs to the axial skeleton)
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pectoral girdle consists of two bones
(clavicle, scapula)
◦ very light and allows upper limb to have
exceptionally free movement
◦ attaches to the axial skeleton at only one
point (sternoclavicular joint)
◦ clavicle is a slender, doubly curved bone
 attaches to the manubrium of the sternum medially
and to the scapula laterally
 acts as a brace to hold the thorax
 helps prevent shoulder dislocation
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scapula is triangular
 not directly attached to the axial skeleton
 loosely held in place by trunk muscles
 glenoid cavity is a shallow socket that receives the
head of the arm bone
 (poorly reinforced by ligaments)
 loose attachment of the scapula allows it to slide
back and forth against the thorax
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bones of the upper limbs
◦ arm is formed by a single bone (humerus)
◦ forearm is formed by two bones (radius and
the ulna)
◦ (in anatomical position, the radius is lateral
and the ulna is medial)
◦ hand consists of the carpals, the metacarpals,
and the phalanges
◦ (carpals form the wrist, metacarpals form the
palm, phalanges forms the fingers)
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pelvic girdle is formed by two coxal bones
(hip bones)
◦ hip bones, sacrum, and coccyx form the bony
pelvis
◦ each hip bone is formed by the fusion of three
bones (ilium, ischium, and pubis)
 ilium - large, flaring bone, forms most of the hip bone
 ischium - the most inferior part, receives body weight
when sitting
 pubis - the most anterior part
 all fuse at a deep socket (acetabulum) that receives the
head of the femur
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bones of the lower limbs
◦ carry total body weight when standing
◦ bones are much thicker and stronger than the comparable
bones of the upper limb
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femur
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only bone in the thigh
heaviest/strongest bone in the body
head articulates with the acetabulum
neck is a common fracture site
slants medially as it turns downward (bring knees in line with the
body's center of gravity)
tibia is larger, medial, and the proximal end articulates
with the distal femur to form the knee
 fibula lies alongside the tibia, is thin, sticklike, and has
no part in forming the knee
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foot is composed of tarsals, metatarsals, and
phalanges
◦ tarsus (ankle) supports body weight – especially
the calcaneus (heel) and talus
◦ serves as a lever that propels the body forward
when walking/running
◦ bones are arranged to form three strong arches
◦ two longitudinal (medial and lateral) and one
transverse
◦ ligaments/tendons hold bones firmly in the
arched position but allow movement
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joints (articulations)
◦ with one exception (hyoid) every bone forms
a joint with at least one other bone
◦ two functions - hold the bones together
securely / give the rigid skeleton mobility
◦ classified in two ways - functionally and
structurally
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functional - focuses on the amount of
movement
◦ freely movable joints (limbs)
◦ immovable / slightly movable joints (axial
skeleton)
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structural - fibrous, cartilaginous, and
synovial joints
◦ fibrous
 immovable
◦ cartilaginous
 bone ends connected by cartilage
 slightly movable (intevertebral joints)
◦ synovial
 surfaces enclosed by a capsule of tissue and ligaments
 are freely movable
 more flexibility than other joint types (flexibility varies
slightly)
inflammatory disorders of joints
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bursitis - inflammation of bursae or synovial membrane
◦ sprain - ligaments / tendons are damaged by excessive stretching
or torn away from the bone
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arthritis - over 100 different inflammatory or degenerative
diseases that damage the joints
◦ acute forms of arthritis
◦ usually result from bacterial invasion (treated with antibiotics)
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chronic forms of arthritis
◦ osteoarthritis - usually slow / irreversible, rarely crippling
◦ rheumatoid arthritis - autoimmune disease, cartilage is
destroyed, scar tissue forms, bone ends connect, scar tissue
ossifies, bone ends become fused
◦ gouty arthritis - uric acid accumulates in blood, may be
deposited as crystals in the soft tissues of a single joint