Skeletal System

Introduction

• The framework of bones and cartilage that protects our organs and allows us to move is called the skeletal system.

• The branch of medicine that deals with the preservation and restoration of the skeletal system, articulations (joints), and associated structures is called orthopaedics.

The skeletal system performs the following functions:

• Support• Protection (for internal organs)• Movement• Mineral storage• Storage of blood cell-producing cells• Storage of energy

• Bone is very strong for its relatively light weight

• The major components of bone are:– Calcium carbonate– Calcium phosphate– Collagen– Water

Bone Composition

Cortical Bone

Spongy Bone

Medullary (marrow) cavity

Bone Composition Cont’d

• Calcium carbonate and calcium phosphate:– Make up 60-70% of bone weight– Provide much of the bone’s stiffness and resistance to pressing or

squeezing forces

• Collagen (a protein):– Gives bone its characteristic flexibility and contributes to its

ability to resist pulling and stretching forces – With aging, collagen is lost progressively and bone becomes more

brittle.

• Water– Bone consists of much smaller proportion of water than other

body parts

Bone Classification

• According to the degree of porosity, bone can be classified into two general categories:– Cortical bone (low porosity)– Spongy or cancellous bone (high porosity)

Cancellous bone Compact Bone

•Porosity •High (Low mineral content and high collagen)

•Low (High mineral content and low collagen)

•Structure •Honey comb • Compact

•Characteristic •Provides more flexibility but is not as stress resistant

•Stiffer and can resist greater stress but less flexible

•Function •Shock absorption due to its better ability to change shape are important

•Withstanding stress in body areas that are subject to higher impact loads

•Location •e.g. vertebrae •Long bones (e.g. bones of the arms and legs)

Effect of Fitness on Bone

• When bones are subjected to regular physical activity and habitual loads, they tend to become denser and more mineralized– e.g. Right forearm of the right-handed tennis player is

more dense than her left one from using it more frequently

• Inactivity works in the opposite direction, leading to a decrease in weight and strength. – e.g. Loss of bone mass has been noted in bed-ridden

patients, inactive senior citizens, and astronauts

Types of Bones

• There are five principal types of bones • All bones are classified based on shape

1. Long bones (e.g. thighs, legs, toes, arms, forearms,

and fingers)

• greater length than width• consist of a shaft and extremities (ends)• slightly curved for strength• consist mostly of compact bone (dense bone

with few spaces) but also contain considerable amounts of spongy bone (bone with large spaces)

2. Short bones (e.g. wrist, ankle bones)

• Somewhat cube-shaped and nearly equal in length and width

• Spongy except at the surface where there is a thin layer of compact bone

3. Flat bones(e.g. cranial bones, sternum, ribs,

scapulas)

• Generally thin and composed of two more or less parallel plates of compact bone enclosing a layer of spongy bone

• Flat bones afford considerable protection and provide extensive areas for muscle attachment

4. Irregular bones (e.g. vertebrae, and certain facial

bones)

• Have complex shapes and cannot be grouped into any of the other three categories

• They vary in the amount of spongy and compact bone

5. Sesamoid bones

• Are small bones in tendons where considerable pressure develops, for instance, the wrist

• Their number varies greatly from person to person

• All people have at least two sesamoid bones: the patella (kneecap)

Divisions of the Skeletal System• The adult human skeleton consists of 206 bones grouped

as the axial skeleton and the appendicular skeleton. • The axial division consists of the bones of the skull,

auditory ossicles, hyoid bone, ribs, breastbone, and the backbone.

• The appendicular division consists of the bones of the upper and lower extremities (limbs), plus the bones called girdles, which connect the extremities to the axial skeleton.

• There are 80 bones in the axial division and 126 in the appendicular. Listed below are the divisions of the skeletal system.

Skull

Sternum

Ribs

Vertebral Column

Axial Skeleton

Skull

• Divided into two parts:

a) Calvaria

b) Face

a) Calvaria

Frontal BoneParietal Bone

Temporal Bone

Occipital Bone

Calvaria Cont.• May be fractured in blows to the

skull (e.g., in hockey, being checked and hitting the skull on the ice)

• Temporal bone:– more fragile of the calvaria bones – overlies one of the major blood

vessels – if fractured and displaced internally

= medical emergency (picture)

b) Facial Bones

Lacrimal Bone

Nasal Bone

Maxilla Bone

Mandible Bone

Zygomatic Bone

Vertebral Column

Sacrum (mid-line region of buttocks)

Coccyx (4 or 5 fused vertebrae of the tail bone)

7 Cervical Vertebrae (of the neck)

12 Thoracic Vertebrae (of the chest)

5 Lumbar Vertebrae (of the lower back)

Lumbar vertebra, lateral view

Lumbar vertebra, superior view

Vertebral Column

• Vertebrae are arranged in a cylindrical column interspersed with fibrocartilaginous (intervertebral) discs

• Function:– provides a strong and flexible support for the body

and the ability to keep the body erect– the point of attachment for the muscles of the back. – protect the spinal cord and nerves– absorbs shock through the intervertebral discs without

causing damage to other vertebrae

Ribs

• Twelve pairs • Made up of :

– bone– cartilage which strengthen the chest cage and

permit it to expand. Curved and slightly twisted making it

ideal to protect the chest area

Ribs Cont’d• All 12 pairs of ribs articulate with the twelve thoracic vertebrae

posteriorly• Classified into three groups based on anterior attachment:

(picture)– true ribs

• 1-7• attach to both the vertebrae and the sternum

– false ribs • 8-10 • attach only to the sternum indirectly, through 7th rib

– floating ribs• 11 and 12 • only attach to the vertebral column

The Ribs

Manubrium

Sternal Body

Xiphoid Process

Costal Cartilages

True Ribs (1-7)

False Ribs (8-10)

Floating Ribs (11-12)

Sternum

• Mid-line breast bone • The clavicles and ribs one to seven

articulate with the sternum

Sternum – comprised of the manubrium, sternal body and xiphoid process

Consists of:

1. The pectoral gridle (chest)

2. Pelvic girdle (hip)

3. The upper limbs

4. The lower limbs

Appendicular skeleton

1.Pectoral GirdleConsists of:

– Scapula (shoulder blade) – Clavicle (collar bone)

Allows the upper limb great mobility The sternoclavicular joint is the only point of

attachment between the axial skeleton and the pectoral girdle

Scapula

Clavicle

2. Pelvic Girdle• Formed by pair of os coxae (hip

bones) • supports the bladder and

abdominal contents• Attachment:

– Posteriorly – join with the sacrum – Anteriorly - join to each other

anteriorly– Laterally – join to the head of thigh

bone through a cup-shaped acetabulum

3. Upper Limb

• Humerus– The arm bone – shoulder to elbow

• Radius and Ulna– The forearm bones– elbow to wrist– the radius being located on the

thumb side of the hand– when you pronate the

forearm, the radius is actually crossing over the ulna - try it yourself

Humerus

Ulna

Radius

Upper Limb Cont.

Carpals

Phalanges

MetacarpalsProximal

Phalanx

Middle PhalanxDistal

Phalanx

4. Lower Limb

• Femur – thigh bone – from hip to knee

• Patella – knee cap– sesamoid bone in the

tendon of the quadriceps muscles (thigh)

Femur

Patella

Lower Limb Cont’d• Tibia and Fibula

– leg bones– From knee to ankle– Tibia is medial and fibula is

lateral

• Medial malleolus and Lateral malleolus– The distal ends of the tibia and

fibula, respectively– commonly referred to as the

"ankle bones"– can be easily palpated

Fibula

Tibia

Lat. malleolus

Med. malleolus

Lower Limb Cont’d• Tarsals

– ankle bones– calcaneus or the heel bone– talus

• Metatarsals – 5 bones of the foot – unite with the toes

• Phalanges– toe bones– three per toe except the big

toe - proximal, middle and distal

Calcaneus

Talus

Phalanges

Metatarsals

Tarsals

Skeletal Surface Markings

• The surfaces of bones have various structural features adapted to specific functions. These features are called surface markings. Long bones that bear a great deal of weight have large, rounded ends that can form sturdy joints, for example. Other bones have depressions that receive the rounded ends.

Depressions and Openings

Foramen an opening through which blood vessels, nerves, or ligaments pass

Example:

Meatus a tubelike passageway running within a bone

Example:

Paranasal sinus

an air-filled cavity within a bone connected to the nasal cavity

Fossa a depression in or on a bone Example:

Processes that form Joints

Condyle a large, rounded articular prominence

Example:

Head a rounded articular projection supported on the constricted portion (neck) of a bone

Example:

Facet a smooth, flat surface Example:

Processes to which tendons, ligaments and other connective tissues attach

Tuberosity a large, rounded, usually roughened process

Example:

Spinous process

a sharp, slender projection Example:

Trochanter a large, blunt projection found only on the femur

Example:

Crest a prominent border or ridge Example: