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 human skeleton has a total of 206 bones in all

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 BonesShort BonesIrregular 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 curvedTwo thick layers of compact bone

sandwiching a layer of spongy boneBones of skull, ribs, sternum

Irregular Bones

Don’t fit other categoriesEx. 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) Bones of the Skull2) Hyoid Bone3) Bones of the Spinal Column4) 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

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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

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Bones of the Axial Skeleton

Bones of the Skull (28 total) Facial Bones

1) Nasal Bone (2 bones)• Forms the bridge of the nose

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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

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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

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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

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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

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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

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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

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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)

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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 Curvature-

curvature 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 Curvature-

Cervical 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 curvature1. Scoliosis-

Bones of the Axial Skeleton

Several types of abnormal spinal curvature2. lordosis-

Bones of the Axial Skeleton

Several types of abnormal spinal curvature2. lordosis-

Several types of abnormal spinal curvature3. 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. True Ribs2. 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)