skeletal system anatomy & physiology. the skeletal system your skeleton comprises ~ 20% of your...
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Skeletal System
Anatomy & Physiology
The Skeletal System
Your skeleton comprises ~ 20% of your total body mass
There are 206 bones in your body, separated into 2 divisions:– 1. Axial skeleton: head, vertebrae and rib
cage– 2. Appendicular Skeleton: pelvis,
scapulae and limbs
Axial: pink Appendicular: green
5 Functions of Bones
1. Support: legs support the weight of body, ribs support thoracic cavity
2. Protections: protects all soft tissue organs3. Movement: muscles use bones as levers,
allowing for movement4. Storage: fat stored in internal cavities of
bones; calcium and phosphorus also stored5. Blood Cell Formation: hematopoesis; the
production of blood cells within marrow cavities
Bone Types
There are two types of bones:– 1. Compact bone: dense bone which is
smooth and solid; surrounds all bone; appears dense
– 2. Spongy bone: internal portion of bone; consists of small needle-like projections of bone called trabeculae with many open spaces filled with marrow
Bone Types
Bone Classification
Bones come in many shapes and sizes and are classified into 4 distinct groups:
1. Long Boneso Longer than wideo Built to absorb stresso Consists of a shaft and 2 heads at each endo Mostly compact but some spongy bone internallyo Examples: all bones of limbs except patella, carpals
and tarsals
Long Bone: the femur
Bone Classification
2. Short Boneso Roughly cube-likeo Contains mostly spongy boneo Thin layer of compact bone on surfaceo Examples: carpals and tarsalso Sesamoid bone: a bone embedded in a
tendon; varies in size and numbers/each individual; act to alter the pull of a tendon; i.e. patella
Short Bones: carpals of the wrist
Bone Classification
3. Flat Boneso Thin, flattened and usually curvedo 2 parallel compact surfaces with a spongy
layer betweeno examples: sternum, ribs and skull bones
Bone Classification
4. Irregular Boneso Do not fit any other classificationo Complicated shapeso Mostly spongy with thin compact layero Examples: vertebrae and hip bones
Anatomical Structure of a Long Bone Diaphysis: shaft of long bone; walls
made of compact bone Periosteum: fibrous sheath that covers
long bones– Highly vascularized– Functions in bone nourishment and
attachment sites
Anatomical Structure of a Long Bone Sharpey’s Fibers: connective tissue
fibers that secures the periosteum to underlying bone
Epiphyses: ends of long bones– Enlarged for muscle attachment – Predominately spongy bone
Anatomical Structure of a Long Bone Articular Cartilage: covers ends of
epiphyses and provides a slippery surface that decrease friction at joint surfaces
Medullary Cavity: holds marrow in center of diaphysis– Yellow marrow: fat storage in adults, found in
medullary cavity– Red marrow: found in diaphysis of infants, in flat
bones & epiphyses of adults; makes red blood cells
Anatomical Structure of a Long Bone
Endosteum: sheath covering medullary cavity
Bone Composition
Bone contains inorganic & organic components– Inorganic calcium carbonate & calcium
phosphate; provides hardness– Organic collagen: to further reinforce the
matrix
Osteoporosis: brittle bones
Normal Spongy Bone Osteoporotic Spongy Bone
Bone Cells: 3 Types
Osteoblasts: arise from embryonic cells and found on outer surfaces of adult bones; aid in matrix production
Osteocytes: mature bone cells; trapped in lacunae
Osteoclasts: secretes substances that dissolve mineral salt crystals
Bone – cell types
“Ruffled” Border
Note locations of
Osteoclasts & osteoblasts
Microscopic Anatomy of Bone
Lacunae: cavities in bones where osteocytes are found
Lamellae: a circular layer of bone
Microscopic Anatomy of Bone
Haversion Canals: a system of interconnecting canals in adults compact one; runs lengthwise through bone, carrying blood vessels and nerves to all areas of bones
Canaliculi: tiny canals that connect all the bone cells to the nutrient supply; radiate outward from Haversion Canals
Microscopic Anatomy of Bone
Volkmann’s Canals: communication system from exterior of bone to interior; runs at right angle to diaphysis
Osteon/Haversion Systems: each haversian canal with lamellae, osteocytes and caniliculi
Haversion Systems
Bone Development
Embryonic Skeleton: predominately hyaline cartilage
Fontanels: in skull at birth– Allows for growth of brain
Bone Development
Young child to late adolescence: cartilage replaced by bone– Epiphyseal Growth Plates: allows for
interstitial growth (lengthwise)– Cartilage near the epiphyses regenerates– Cartilage near the diaphysis hardens to
bone eventually they’ll meet, halting lengthwise growth
Epiphyseal Growth Plate
Epiphyseal Growth Plates
Bone Development & Growth
Ossification
The replacement of cartilage by bone Cartilage is covered by osteoblasts Cartilage is “eaten” away, leaving the
medullary cavity open within the bone
Appositional Growth
Outward growth of bone during adulthood– Bones change based on calcium levels & muscles
acting on the skeleton– Decreased blood calcium leads to bone
breakdown– Increased demand by muscles on bones causes
bone to thicken– Weight gain also increase bone diameter– Adult bone constantly remodels (breakdown &
growth) to help maintain homeostasis of blood mineral levels
Skeletal System
Axial Skeleton
Axial Skeleton
Includes 80 bones of the skull, vertebral column and bony thorax
Functions:– Supports head, neck & trunk– Protects brain, spinal cord and thoracic
organs
Skull
Composed of flat bones Function:
– Used for attachment of head muscles & protects the brain
Sutures of the Skull
Sutures: interlocking joints that unite skull bones– Coronal: where parietal bones meet frontal– Sagittal: where 2parietal bones meet
superiorly– Squamos: where parietal and temporal
bones meet on lateral aspects of skull– Lambdoidal: where parietal bones meet
occipital bones meet posteriorly
Vertebral Column aka the Spine
Location: runs from the base of the skull to the coccyx (tailbone)
Function: – Surrounds and protects the spinal cord– Provides attachment sites for ribs and back
muscles
Vertebral Column
Characteristics– 26 interconnected
irregular bones– Provides a flexible,
curved structure– Serves as axial
support of the trunk
Vertebral Column
Curvatures of the Spine:– S-shaped to prevent shock to head in motion– Allows for trunk flexibility– Increases resiliency & flexibility of the spine– Functions like a spring, not a rod
Cervical & Lumbar Curves: concave posteriorly
Thoracic & Sacral Curves: convex posteriorly
Curvatures of the Spine
Abnormal Curvatures of the Vertebral Column
Lordosis: aka sway back– An accentuated
lumbar curve
Kyphosis: aka hunchback– An exaggerated
thoracic curve
Scoliosis: the twisted disease– An abnormal lateral
curvature in the thoracic region
– Typical in girls in late childhood
Lordosis & Kyphosis
Scoliosis
Cervical Vertebrae
7 total extending from base of skull to ~ shoulder line
Numbered C1-C7 Smallest & lightest vertebrae Unique vertebrae
– Atlas or C1: no body; holds the occipital bone, allows nodding motion (“yes”)
– Axis or C2: acts as a pivot for rotation; shake head (“no”)
Thoracic Vertebrae
12 total; runs through mid-back Numbered T1-T12 Larger than cervical Longer, palpable spinous processes Ribs attach here posteriorly
Lumbar Vertebrae
5 total Numbered L1-L5 Huge bodies and
short spinous processes
Holds most of body weight & stress; very sturdy
Sacrum & Coccyx
Sacrum– Formed from 5 fused
vertebrae– Numbered S1-S5– Makes up posterior
wall of pelvis– Strengthens &
stabilizes pelvis Coccyx
– 4 fused vertebrae
Ligaments of the Spine
There are several; only 2 you need to know– Anterior Longitudinal Ligament: resists
back hyperextension– Posterior Longitudinal Ligament: resists
back flexion
Intervertebral Discs
Cushion-like pads between vertebrae Asts as shock absorbers during motion Makes up ~25% of length of column Flattens during the day
Intervertebral Discs
Ribs
Flat bones 12 total pairs Attach posteriorly to thoracic spine Function:
– Protect thoracic organs True Ribs: the superior 7 pairs
– Attach directly to sternum by costal cartilage False Ribs: the inferior 5
– 8-10: join each other by cartilage and indirectly attach to sternum
– 11& 12: the floating ribs, no anaterior attachment
Rib Cage
Pelvis
Has 2 regions: true and false pelvises False pelvis superior to true pelvis True pelvis dimensions are a concern
to child-bearing women Pelvic structure differs between men
and women
Gender Difference of Pelvis
Men– Narrow outlet– Heavier & thicker bone
structure– Ilia less flared, more
vertical– Sacrum long and curved– Ischia close together– Less rounded pubic arch
Women– Inlet circular & large– Pelvis shallow, lighter &
thinner– Ilia flare laterally– Sacrum shorter & less
curved– Ischia farther apart &
shorter– Pubic arch is more
rounded