The Skeletal System

206 Bones in t he Human Skeleton

2

Bones are Organs Each bone is a complex living organ made up of

many cells, protein fibers, and minerals.

They come in many sizes and shapes.

The largest bone is the femur and the smallest is

the stapes.

The humerus is pictured here.

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The Skeletal System Also Includes

Joints

Cartilages

Ligaments

4

Anatomy of the

Skeletal System

5

Two Divisions of the Skeleton

Axial Skeleton &

Appendicular Skeleton6

Axial Skeleton

Bones that form the longitudinal axis of the body make up the axial skeleton

Vertebral Column Vertebrae Sacrum Coccyx

Bony Thorax Ribs Sternum

Skull Cranium Facial Bones

7

Axial Skeleton

Vertebral

Column

Bony Thorax or

Rib Cage

Skull

8

Vertebral Column

Composed of 33 bones

before birth; some later fuse

to form 26 separate bones

7 cervical vertebrae (red)

12 thoracic vertebrae (blue)

5 lumbar vertebrae (yellow)

Sacrum – 5 fused (green)

Coccyx – 4 fused (purple)

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Structure of a Vertebrae

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Cervical Vertebrae

7 vertebrae

located in the

neck

Smallest and

lightest

vertebrae

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Atlas & AxisThe first vertebra is

called the atlas, C1.

The second vertebra

is called the axis, C2.

12

Thoracic Vertebrae

12 thoracic

vertebrae

Articulate with ribs

Larger than

cervical vertebrae

Long spinous

process that hooks

sharply downward

13

Lumbar Vertebrae

5 lumbar

vertebrae

Much larger

than other

vertebrae to

support the

weight of the

upper body 14

Bony Thorax or Rib Cage 12 pairs of ribs articulate with

the 12 thoracic vertebrae

posteriorly

True ribs, pairs 1-7 (red),

articulate anteriorly directly to

the sternum by cartilage

False ribs, pairs 8-12 (green &

blue), articulate indirectly or not

at all

The last 2 pair do not connect at

all and are called floating ribs

(blue). 15

Sternum

Manubrium

Body

Xiphoid

Process16

The Skull� The skull is

for med by t wo

set s of bones:

� Cranium

� Facial bones

� All are j oined by

immovable j oint s

except for t he

mandible

(j awbone)

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Lateral View of Skull

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Hyoid Bone No direct articulation

to another bone

Provides attachment

for these muscles:

Floor of mouth

Tongue

Larynx

Epiglottis

Pharynx

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Auditory Ossicles

The smallest

bones in the

body are

located in the

middle ear:

Malleus

Incus

Stapes

20

Appendicular Skeleton

Includes the

limbs and the

girdles which

attach the

limbs to the

axial skeleton

Pectoral (Shoulder) Girdle

Collar bones

Shoulder blades

Upper Limbs

Arms

Hands

Pelvic (Hip) Girdle

Coxal Bones

Lower Limbs

Legs

Feet

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Appendicular Skeleton

Pectoral Girdle: clavicle, scapula

Upper Limbs: humerus, ulna, radius, carpals, metacarpals, phalanges

Pelvic Girdle: ilium ischium, and pubis

Lower Limbs: femur, patella, tibia, fibula, tarsals, metatarsals, phalanges

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Pectoral Girdle

The clavicle is

commonly

called the collar

bone.

The scapula is

commonly

called the

shoulder blade.

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Arm Bones

• Humerus: Upper Arm

Bone

• Radius: elbow to thumb

side of the wrist

• Ulna: elbow to pinkie side

of the wrist

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Bones of the Hand

Carpals

Metacarpals

Phalanges

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Pelvic Girdle The pelvic girdle

consists of two

coxal or hip bones.

Each hip bone is

formed from the

fusion of 3 bones:

Ilium

Ischium

Pubis

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The Coxal Bones

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Leg Bones Femur – thigh bone

Patella – knee cap

Tibia – large bone in

lower leg;

sometimes called

the shin bone

Fibula – smaller

bone in lower leg;

forms the lateral

ankle

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Bones of the Foot

Tarsals

Metatarsals

Phalanges

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Shape

s of

Bones• Long

• Short

• Flat

• Irregular

• Sesamoid

Flat Irregular

Long

Short

Sesamoid

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Two Basic Types of Bone Compact Bone is dense

and looks smooth and

homogeneous.

Spongy Bone is composed

of small pieces of bone

and lots of open space.

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Compact

Bone• In long bones,

surrounds

spongy bone at

ends

• Along shaft

surrounding

medullary cavity Spongy Bone

• At ends of long

bones32

Microscopic Anatomy of Spongy Bone

The open spaces keep

bones light

Found in the ends of long

bones

Also fills short bones, flat

bones and some parts of

irregular bones

Contains red marrow

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Microscopic Anatomy of Compact Bone

Composed of a matrix

of hard mineral salts

reinforced with tough

collagen fibers

Bone cells are called

osteocytes

Osteocytes are found in

tiny cavities within the

matrix called lacunae

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bone cell35

Gross Anatomy of a Long Bone

Diaphysis

Shaft

Composed of

compact bone

Epiphysis

Ends of the bone

Composed

mostly of spongy

bone

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Other Features of

Long Bones

• Articular Cartilages:

cover epiphyses for

smooth movement

• Epiphyseal Line:

marking left from

growth at epiphyseal

plate

• Periosteum: fibrous,

connective tissue

that covers the

diaphysis 37

Bone Marrow

Red Marrow – in

cavities of spongy

bone in flat bones

and epiphyses of long

bones, site of

hematopoiesis

Yellow Marrow – fat

storage in medullary

cavity

Red Marrow

Medullary Cavity

Yellow Marrow

Compact Bone

Periosteum

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Bone Markings Bumps, holes, and ridges

where muscles, tendons,

and ligaments are

attached and where blood

vessels and nerves pass

through

Two categories:

projections or

processes

depressions or cavities

Projections:

Tuberosity

Trochanter

Tubercle

Process

Condyle

Depressions or

Openings:

Meatus

Fossa

Foramen 39

Examples of Bone Markings

Styloid

Process

Olecranon Process

Olecranon Fossa

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Bone Markings on the Femur

Proximal Posterior

Distal Anterior

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Joints

Also called articulations

Where two bones meet

Hold bones together, but also give mobility

Three Types:

1. Fibrous – no

movement, ex: skull

2. Cartilaginous – slightly

moveable, ex: pubic

symphysis, vertebrae

3. Synovial – bones

separated by cavity

filled with synovial

fluid, allow the most

movement42

Synovial Joints

Articular

cartilage

Fibrous

articular

capsule

Joint cavity –

contains fluid

Reinforced by

ligaments

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Types of

Synovial

Joints

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Ball and Socket Joints

The most

moveable

type of joint

Found in the

shoulder and

hip

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Physiology of the

Skeletal System

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Function Overview

Support

Protection

Movement

Hematopoiesis

Storage47

Support

Internal

framework that

supports and

anchors all

soft organs.

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Protection

Protects soft

body organs

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Movement

Skeletal muscles

attach to bones by

tendons

Tendons use the

bones as levers to

move body parts

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Storage

Fat storage in

yellow marrow

The minerals

calcium and

phosphorous are

stored in bone

tissue

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HematopoiesisBlood cell

formation occurs

in red marrow.

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Developmental

Aspects

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Fontanels Spaces between

bones of the skull

in an infant

Commonly called

soft spots

Fully ossified by 2

years

Allows for growth

of the brain and

skull54

Ossification Ossification is the

formation of bone

from cartilage

At birth, bones are

part cartilage and

part bone

The skeleton is fully

ossified by age 2

except for epiphyseal

(growth) plates

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Longitudinal Growth X-ray of 12 year

old showing

epiphyseal

(growth) plates at

the distal ends of

the tibia & fibula

Epiphyseal plates

are fully ossified by

the end of

adolescence 56

Bone Formation & Growth

Key Terms:

Ossification – bone formation

Epiphyseal plates – provide for

longitudinal growth; increase in length

Appositional growth – increase in

diameter

Osteoblasts – bone-building cells

Osteoclasts – bone-destroying cells

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Bone Remodeling Breaking down & reforming of bone that occurs

throughout life to maintain proportion & strength as well as healthy calcium levels

58

Osteoporosis• Weakening of the

bone that occurs

with aging

• One in two

women and one

in four men over

age 50 will have

an osteoporosis-

related fracture.

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Hip Fracture

A hip fracture is

actually a femoral

fracture that occurs

in the proximal end of

the femur near the

hip

The 1-year mortality

rate after a hip

fracture is 20% X-ray following

hip replacement60

Diseases and

Conditions

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Types of Fractures

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Arthritis

Osteoarthritis usually

part of aging

Rheumatoid Arthritis

autoimmune disease

Arthritis is an inflammation of the joints.63

Rickets

Lack of vitamin D,

calcium, or

phosphorous

Bones fail to

calcify; stay soft

Usually in children

ages 3-36 months

Rare in developed

countries

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Herniated Disc Protruding discs of

cartilage between

the vertebrae

Can irritate nearby

nerves and result

in pain, numbness

or weakness in an

arm or leg

65

Scoliosis

Abnormal

curvature of the

spine

May be congenital

or result from

disease or trauma

66

The Skeletal System

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