The Skeletal System
Divisions of the Skeletal System
 The human skeletal system is divided into two major
divisions
 Axial
Skeleton
 Appendicular skeleton
Axial Skeleton
 The
axial skeleton contains the bones of the
head, neck, and torso (80 bones total)
appendicular skeleton
 The
appendicular skeleton contains the bones
of the upper and lower extremities (126 bones
total)
Human Skeleton
 The
all
human skeleton has a total of 206 bones in
Bones
 Functions:
 Support
 Protection
 Movement
 Storage
 Blood cell formation
Bones
 Function- Support
 Form the internal framework that supports and anchors all soft
organs
Bones
 Function- Protection
 Bones protect soft body organs

Ex. Skull protects brain
Bones
 Function- Movement
 Skeletal Muscles attach to bones by tendons
 Bones are used as levers to move body
Bones
 Functions-storage
 Fat is stored in internal cavities of bones
Bones
 Functions-storage
 Store minerals

Most important—Calcium and phosphorus
Bones
 Functions-storage
 Calcium in its ion form (Ca 2+ ) must always be present in
blood
for nervous system to transmit messages
 For muscles to contract
 For blood to clot


Bones are a storage place for Calcium
Bones
 Functions-storage
 Blood cell formation

Hematopoiesis (formation of blood cells) occurs in the cavities of
bone marrow
Bones
 Classification of bones
 2 basic types of bone types
Compact Bone
 Spongy Bone

Bones
 Compact Bone
 Dense
 Looks smooth
Bones
 Spongy Bone
 Small needle-like pieces of bone
 Lots of open space
Shapes of Bones
 Long Bones
 Short Bones
 Irregular Bones
Bones
 Long Bones
 Longer than they are wide
 Usually have a shaft with heads at both ends
 Mostly compact bones
 most bones of limbs
Bones
 Short Bones
 Generally cube-shaped
 Mostly spongy bone

Ex. Patella (knee cap) , bones of wrist and ankle
Flat Bones
 Thin, flattened, usually curved
 Two thick layers of compact bone sandwiching a
layer of spongy bone
 Bones of skull, ribs, sternum
Irregular Bones
 Don’t fit other categories
 Ex. Vertebrate, hip bone
Structure of a long bone
 Diaphysis Shaft
 Makes up most of the bone’s length
 Composed of compact bone
 Covered and protected by periosteum
Structure of a long bone
 Cavity of shaft
 In infants- this area forms blood cells


Red marrow
In adults primarily filled with yellow marrow (adipose)
Called yellow marrow cavity or medullary cavity
 Red marrow is confined to spongy bone

Structure of a long bone
 Epiphyses- the ends of the long bone
 Epiphyseal line

Thin line spanning the epiphysis
Structure of a long bone
 Epiphyseal plate
 Plate of hyaline cartilage
 Causes the lengthwise growth of a long bone
 By end of puberty the plate is completely replaced by bone
Structure of Long Bone
 Surfaces of bones aren’t smooth
 Bumps, holes, and ridges
 Bone markings
 Reveal where muscles, tendons, and ligaments were attached
 Reveal where blood vessels and nerves passed
Structure of Long Bone
 Bone markings
 Projections or processes

Grow out from the bone surface
Depressions or cavities

Indentations in the bone
Structure of a long
 Microscopic anatomy
 Compact bone:
To the naked eye looks very dense
 With microscope we see a much different picture!

Structure of a long
 Microscopic anatomy
 Compact bone
Passageways carrying nerves and blood vessels
 Provides living bone with nutrients and route for waste disposal

Structure of Long Bone
 Osteocytes
 The mature bone cells
 Found in cavities of the bone matrix called lacunae ( a very
tough matrix)
Structure of Long Bone
 Osteocytes
 Lacunae arranged in concentric circles called lamellae
 Lacunae arranged around central (Haversian) canals
Structure of Long Bone
 Perforating (Volkmann’s) canals
 Run into the compact bone at right angles to the shaft
 Let the inside of bone communicate with outside
Bone Formation, Growth, and Remodeling
 Embryo’s skeleton
 Primarily hyaline cartilage
 Young child
 Most of cartilage has been replaced by bone
 Remains in isolated areas
Bridge of nose
 Parts of ribs
 joints

Bone Formation, Growth, and Remodeling
 Most bones develop using hyaline cartilage
structures as their “models”
 Ossification- the formation of bone
Bone Formation, Growth, and Remodeling
 Ossification
 2 major stages

1. hylane cartilage model is completely covered with bone by bone
forming cells called osteoblasts
Bone Formation, Growth, and Remodeling
 Ossification
 Step Two:
Hyaline cartilage model is digested away
 Opens up a medullary cavity within newly formed bone

Bone Formation, Growth, and Remodeling
 By birth
 Most hyaline cartilage models have been converted to bone
 Excepts two reasons
Articular cartilages –cover bone ends
 Epiphyseal plates

Bone Formation, Growth, and Remodeling
 Articular cartilages
 Persist for life
 Reduce friction at the joint surfaces
Bone Formation, Growth, and Remodeling
 How is the articular cartilage injured?
 Trauma- twisting, sport injury
 Certain diseases
 Gradually over time
Bone Formation, Growth, and Remodeling
 When there is significant loss of the articular
cartilage, the knee is considered to have “arthritis”.
Bone Formation, Growth, and Remodeling
 Epiphyseal plates
 Provide for longitudinal growth of long bones during
childhood
 New cartilage is formed on external surface
 Old cartilage is broken down and replaced by bony matrix
Bone Formation, Growth, and Remodeling
 Epiphyseal plates
 Growth controlled by hormones
 Ends during adolescence, when the epiphyseal plates are
completely converted to bone
Bone Formation, Growth, and Remodeling
 How do bones widen? –called Appositional Growth
 Osteoblasts in the periosteum add bone to the external face
 Osteoclasts in the endosteum remove bone from inner wall
 What happens when long bone growth ends?
Bone Formation, Growth, and Remodeling
 Bone Remodeling
 Bones continually remodeled in response to 2 factors:
1. calcium levels in the blood
 2. the pull of gravity and muscles on the skeleton

Bone Formation, Growth, and Remodeling
 Bone Remodeling
 When blood calcium levels are low
Parathyroid hormone (PTH) is released into blood
 PTH activates osteoclasts (bone destroying cells) to break down
bone matrix and release calcium

Bone Formation, Growth, and Remodeling
 Bone Remodeling
 When blood calcium levels are too high (hypercalcemia)

Calcium is deposited in bone matrix as hard calcium salts
Bone Formation, Growth, and Remodeling
 Bone Remodeling
 Essential for bones to:
retain normal proportions
 Strengthen as body increases size and weight

Bone Formation, Growth, and Remodeling
 Bone Remodeling
 Bedridden or physically inactive people tend to lose bone mass
and atrophy
 Because they aren’t subjected to stress
Bone Formation, Growth, and Remodeling
 Rickets
 Disease of children in which bones fail to calcify

Bones soften and definite bowing of weight-bearing bones of legs
occurs
Bone Formation, Growth, and Remodeling
 Rickets—
 Called osteomalacia in adults
 Causes
Usually due to lack of calcium in diet
 Or lack of vitamin D
 Is needed to absorb calcium

Divisions of the Skeletal System
 Axial
Bones of the Axial Skeleton
 Bones of the axial skeleton are divided into four
major groups
1)
2)
3)
4)
Bones of the Skull
Hyoid Bone
Bones of the Spinal Column
Sternum and Ribs
Bones of the Axial Skeleton
 Bones of the Skull (28 total)
 Cranial Bones (8 total) form the
cranium which surrounds
the brain
Bones of the Axial Skeleton
 Bones of the Skull (28 total)

Cranial Bones

1) Frontal Bone (1 bone)
• Anterior Portion of Cranium (Forehead)
• Forms Anterior Cranial Floor
• Forms the Roofs of Orbits (Eye Sockets)
Bones of the Axial Skeleton
 Bones of the Skull (28 total)

Cranial Bones

2) Parietal Bone (2 bones)
• Forms Superior Portion of Cranium
Bones of the Axial Skeleton
 Bones of the Skull (28 total)

Cranial Bones

3) Temporal Bone (2 bones)
• Forms Lateral Portion of Cranium & Lateral Cranial Floor
Bones of the Axial Skeleton
 Bones of the Skull (28 total)

Cranial Bones

4) Occipital Bone (1 bone)
• Forms Posterior Portion of Cranium & Posterior Cranial Floor
•
Bones of the Axial Skeleton
 Bones of the Skull (28 total)

Cranial Bones
 5) Sphenoid Bone (1 bone)
• Forms central portion of
cranial floor
• Known as the “keystone of
the cranium” because
the sphenoid bone
anchors all the other
cranial bones
Bones of the Axial Skeleton
 Bones of the Skull (28 total)

Cranial Bones
 6) Ethmoid Bone (1 bone)
• Complex, irregularly shaped bone found between the nasal and the
sphenoid bones
•
•
Bones of the Axial Skeleton
 Bones of the Skull (28 total)

Facial Bones
 1) Nasal Bone (2 bones)
• Forms the bridge of the nose
•
•
Bones of the Axial Skeleton
 Bones of the Skull (28 total)

Facial Bones
 2) Maxillary bone (2 Bones)
• Upper jawbone that forms the central portion of the face
• Forms the floor of the orbits and the anterior portion of
the hard palate
•
•
Bones of the Axial Skeleton
 Bones of the Skull (28 total)

Facial Bones
 3) Zygomatic Bone (2 Bones)
• Forms the cheekbones and
the lateral walls of the
orbits
•
•
Bones of the Axial Skeleton
 Bones of the Skull (28 total)

Facial Bones
 4) Mandible Bone (1 Bone)
• Lower jawbone
• Largest and strongest bone of the face
•
•
Bones of the Axial Skeleton
 Bones of the Skull (28 total)

Facial Bones
 5) Lacrimal Bone (2 Bones)
• Forms the medial walls
of the orbits
• Bones are paper thin
•
•
Bones of the Axial Skeleton
 Bones of the Skull (28 total)

Facial Bones
 6) Palatine Bone (2 Bones)
• Forms posterior portion of the hard palate and forms the
lateral and posterior walls of the nasal cavity
•
•
Bones of the Axial Skeleton
 Bones of the Skull (28 total)

Facial Bones
 8)
Vomer Bone (1 Bone)
• Forms the lower portion of the nasal septum
•
Bones of the Axial Skeleton
 Bones of the Skull (28 total)

Bones of the Ear
 Three
tiny bones located in the middle ear
• 1) Malleus (2 Bones)
• 2) Incus (2 Bones)
• 3) Stapes (2 Bones)
•
Bones of the Axial Skeleton
 Bones of the Skull (28 total)
 Bones
of the Ear
Smallest
bones in the body
Carry sound vibrations to inner ear
Amplifies sound about 7x
Bones of the Axial Skeleton
 Hyoid Bone (1 total)
The hyoid bone is a U shaped bone found in the neck
between the mandible and the larynx
 It is the only bone in the body which does not form a joint
with another bone (held in place by ligaments and
muscles)

Bones of the Axial Skeleton
 Hyoid Bone (1 total)
 Function:
 Supports
the base of the tongue
Bones of the Axial Skeleton
 Vertebral Column –Spine
 26 irregular bones connected by ligaments
 Flexible, curved structure
Bones of the Axial Skeleton
 Vertebral Column –Spine
 Running through the central cavity of vertebral column is the
delicate spinal cord
 Spine preserves and protects spinal cord
Bones of the Axial Skeleton
 Vertebral Column –Spine
 Single vertebrae are separated by pads of flexible fibrocartilage
called intervertebral discs

They cushion the vertebrae and absorb shock
Bones of the Axial Skeleton
 Vertebral Column –Spine
 Young Person
Discs have high water content ( 90%)
 Discs are spongy and compressible

Bones of the Axial Skeleton
 Vertebral Column –Spine
 Aging
The water content of disc decreases
 Drying of discs and weakening of ligaments predisposes older
people to herniated discs (slipped disc)
if slipped disc presses on spinal cord- major pain

Bones of the Axial Skeleton
 Vertebral Column –Spine
 The spine has 2 curvatures
1. Primary Curvature
 2. Secondary Curvature

Bones of the Axial Skeleton
 Vertebral Column –Spine
 Primary Curvaturecurvature in the thoracic and sacral regions
 Called primary because it is there when we are born

Bones of the Axial Skeleton
 Vertebral Column –Spine
 Secondary CurvatureCervical curvature- develops when baby begins to lifts its head
 Lumbar curvature- develops when baby begins to walk

Bones of the Axial Skeleton
 Several types of abnormal spinal curvature
1. Scoliosis-
Bones of the Axial Skeleton
 Several types of abnormal spinal curvature
2. lordosis-
Bones of the Axial Skeleton
 Several types of abnormal spinal curvature
2. lordosis-
 Several types of abnormal spinal curvature
3. kyphosis-
 Bones of the vertebral column (backbone)
Bones of the Axial Skeleton
 Bones of the Spinal Column (26 total)
 1) Cervical Vertebrae (7 Bones)
• Top seven vertebrae of the spinal column
• The atlas (to bear )is the first cervical vertebrae
• The axis is the second cervical vertebrae
Bones of the Axial Skeleton
 Bones of the Spinal Column (26 total)
 1) Cervical Vertebrae (7 Bones)
Bones of the Axial Skeleton
 Bones of the Spinal Column (26 total)
 2) Thoracic Vertebrae (12 Bones)
• Middle 12 vertebrae of the spinal column
Bones of the Axial Skeleton
 Bones of the Spinal Column (26 total)
 3) Lumbar Vertebrae (5 Bones)
• Bottom five vertebrae of the spinal column
Bones of the Axial Skeleton
 Bones of the Spinal Column (26 total)
 4) Sacrum (5 Bones Fused Into 1 Bone)
• Five separate vertebrae that fuse into 1 bone after the
bones mature
Bones of the Axial Skeleton
 Bones of the Spinal Column (26 total)
 5) Coccyx (4 or 5 Bones Fused Into 1 Bone)
• Tailbone; consists of separate vertebrae that have fused
together
Bones of the Axial Skeleton
 Sternum and Ribs (25 total)

Sternum (1 Bone)

“Breastbone”
Bones of the Axial Skeleton
 Ribs
 You have two types of ribs
1.
2.
True Ribs
False Ribs
Bones of the Axial Skeleton
 Sternum and Ribs (25 total)

Ribs (12 pairs = 24 Ribs)

True Ribs (First 7 pairs)
• Ribs attach directly to the sternum by costal cartilage
Bones of the Axial Skeleton
 Ribs
False
Ribs (Bottom 5 pairs)
• Rib pairs 8, 9, & 10 attach indirectly to the sternum
by the costal cartilage of rib pair #7
• Rib pairs 11 & 12 are called floating ribs because
they do not attach to the sternum at all
Bones of the Axial Skeleton
All
ribs attach to a thoracic vertebrae
posteriorly
Bones of the Axial Skeleton
 Bones of the Upper Extremities

The sternum, ribs, and vertebral column create the thorax
Bones of the Appendicular Skeleton
 Bones of the Upper Extremities
 Clavicle (2 Bones)

Collarbone
Bones of the Appendicular Skeleton
 Bones of the Upper Extremities
 Scapula (2 Bones)

Shoulder Blade
Bones of the Appendicular Skeleton
 Bones of the Upper Extremities
 The scapula and clavicle together make up the shoulder girdle
Bones of the Appendicular Skeleton
 Bones of the Upper Extremities
 Humerus (2 Bones)

Long bone of the upper arm
Bones of the Appendicular Skeleton
 Bones of the Upper Extremities
 Radius (2 Bones)
 Ulna (2 Bones)
The radius and ulna are
bones of the forearm
 The radius is on the thumb
side and the ulna is on the
little finger side

Bones of the Appendicular Skeleton
 Bones of the Upper Extremities
 Carpals (16 Bones; 8 in Each Hand)

Bones of the wrist
Bones of the Appendicular Skeleton
 Bones of the Upper Extremities
 Metacarpals (10 Bones, 5 in Each Hand)

Bones in the palm of the hand
Bones of the Appendicular Skeleton
 Bones of the Upper Extremities
 Phalanges (28 Bones, 14 in Each Hand)

Bones of the fingers (3 in each finger and 2 in the thumb)
Bones of the Appendicular Skeleton
 Bones of the Lower Extremities (Label bones in your
notes !)
Skeletal Differences in Men & Women
Male
Female
Skeletal Differences in Men & Women
Bones of the Appendicular Skeleton
 Bones of the Lower Extremities
 Femur Bone
Thigh bone

Longest, largest, and strongest
bone in the body
Bones of the Appendicular Skeleton
 Bones of the Lower Extremities
 Patella (2 Bones)

Kneecap
Bones of the Appendicular Skeleton
 Bones of the Lower Extremities
 Tibia
 Fibula
The tibia and fibula are the
bones of the lower leg
 Tibia “shin bone” is larger,
medial, and more superficial
than the fibula

Bones of the Appendicular Skeleton
 Bones of the Lower Extremities
 Tarsal Bones (14 Bones, 7 in Each Foot)

Bones that form the heel and the posterior portion of the foot
Bones of the Appendicular Skeleton
 Bones of the Lower Extremities
 Metatarsals (10 Bones, 5 in each foot)

Bones that form the long portion of the foot
Bones of the Appendicular Skeleton
 Bones of the Lower Extremities
 Phalanges (28 Bones, 14 in each foot)

Bones of the toes (3 in each toe except big toe; big toe has 2 bones)