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.
2.
3.
4.
5.
Support: legs support the weight of body, ribs support thoracic cavity
Protections: protects all soft tissue organs
Movement: muscles use bones as levers, allowing for movement
Storage: fat stored in internal cavities of bones; calcium and phosphorus also stored
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 Bones o Longer than wide o Built to absorb stress o Consists of a shaft and 2 heads at each end o Mostly compact but some spongy bone internally o Examples: all bones of limbs except patella, carpals and tarsals

Long Bone: the femur

Bone Classification
2. Short Bones o Roughly cube-like o Contains mostly spongy bone o Thin layer of compact bone on surface o Examples: carpals and tarsals o 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 Bones o Thin, flattened and usually curved o 2 parallel compact surfaces with a spongy layer between o examples: sternum, ribs and skull bones

Bone Classification
4. Irregular Bones o Do not fit any other classification o Complicated shapes o Mostly spongy with thin compact layer o 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

Note locations of
Osteoclasts & osteoblasts
“Ruffled” Border

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

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

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
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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