Essentials of Human AnatomyEssentials of Human Anatomy

The Skeletal System 1

Bone

• Bones are organs• Bones are composed of all tissue types. • Their primary component is osseous

connective tissue. • The matrix is sturdy and rigid due to

calcification (also called mineralization).

Function of Bones

• Support:Support: form the framework that supports the body and cradles soft organs

• Protection:Protection: provide a protective case for the brain, spinal cord, and vital organs

• Movement:Movement: provide levers for muscles• Mineral storage:Mineral storage: reservoir for minerals, especially

calcium and phosphorus• Blood cell formation:Blood cell formation: hematopoiesis occurs within the

marrow cavities of bones• Energy storageEnergy storage (fat in yellow marrow)

Support and Protection

• Bones provide structural support and serve as a framework for the entire body.

• Bones protect many delicate tissues and organs from injury and trauma.

Movement

• Muscles attach to the bones of the skeleton–Contract and pull on bone–Functions as a series of levers.

Storage of Mineral and Energy Reserves

• More than 90% of the body’s reserves of the minerals calcium and phosphate are stored and released by bone.

HematopoiesisBlood Cell Formation

• Blood cell production in red bone marrow– located in some spongy bone.

• Red bone marrow contains stem cells– form all of the blood cell types.

Changes in the Human SkeletonChanges in the Human Skeleton

• In embryos, the skeleton is primarily hyaline cartilage

• During development, much of this cartilage is replaced by bone

• Cartilage remains in isolated areas

Bridge of the nose

Parts of ribs

Joints

Classification of Bones on the Basis of Classification of Bones on the Basis of ShapeShape

Classification of BonesClassification of Bones Long bones

• Generally longer than wide.

• Have a shaft with heads at both ends.

• Contain mostly compact bone

• Examples: Femur, humerus

Classification of BonesClassification of Bones

Short bones

• Generally cube-shape

• Contain more spongy bone than compact

• Examples: Carpals, tarsals

Classification of BonesClassification of Bones Flat bones

• Thin and flattened like pancackes.

• Usually curved

• They have two thin layers of compact bone sandwiching a layer of spongy bone

• Examples: Skull, ribs, sternum

Classification of BonesClassification of Bones

Irregular bones

• Do not fit into other bone classification categories

• Irregular shape

• Example: Vertebrae

The Histologic Types:

• Compact bone ( cortical)

• Spongy bone ( cancellous)

Compact Bone:

• Haversian systemHaversian system, or osteon – the structural unit of compact bone– Lamella – weight-bearing, column-like matrix tubes

composed mainly of collagen– Haversian, or central canal – central channel

containing blood vessels and nerves– Volkmann’s canals – channels lying at right angles to

the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal

Compact Bone

• Osteocytes – mature bone cells• Lacunae – small cavities in bone that contain

osteocytes• Canaliculi – hairlike canals that connect

lacunae to each other and the central canal

Compact Bone:

Spongy (cancellous) Bone

• Does not contain osteons. • trabeculae surrounding red marrow spaces

Cell Types of Bone

• Osteoblasts: Osteoblasts: – Form matrix & collagen fibers but can’t divide

• Osteocytes: Osteocytes: – Mature cells that no longer secrete matrix

• Osteoclasts: Osteoclasts: – Huge cells from fused monocytes (WBC)– Function in bone resorption at surfaces such as

endosteum

3 types of cells in bone tissue3 types of cells in bone tissue

SKLETAL SYSTEM

• It is divided into two parts :Axial

Appendicular

Bone Structure - External Cartilage protection for joints

Bone Structure - External

Epiphyse

Epiphyses

Expanded ends of long bones

Exterior is compact bone, and the interior is spongy bone

Joint surface is covered with articular (hyaline) cartilagelocation of red bone marrow

Epiphyseal line separates the diaphysis from the epiphyses

Bone Structure - ExternalDiaphysis

Tubular shaft that forms the axis of long bones

Composed of compact bone that surrounds the medullary cavity

Yellow bone marrow (fat) is contained in the medullary cavity

Diaphysis

Bone Membranes

• PeriosteumPeriosteum – double-layered protective membrane– Outer fibrous layer

• dense regular connective tissue– Inner osteogenic layer

• composed of osteoblasts and osteoclasts• Richly supplied with nerve fibers, blood, and lymphatic

vessels, which enter the bone via nutrient foramina• Secured to underlying bone by Sharpey’s fibers

• Endosteum Endosteum – delicate membrane covering internal surfaces of bone

Blood and Nerve Supply of Bone

• Periosteal arteries– Supply periosteum

• Nutrient arteries– Enter through nutrient foramen– Supplies compact bone of diaphysis &

red marrow

• Metaphyseal & epiphyseal aa– Supply red marrow & bone tissue of

epiphyses

Skeletal system includesSkeletal system includes

Axial division– Skull and associated bones

Auditory ossiclesHyoid bones

– Vertebral column– Thorax (Thoracic cage )– Ribs sternum

Appendicular division- Pectoral girdle- Pelvic girdle

skull is formed of two sets of bones:-

cranium is encloses and protects the fragile brain tissues. = 8 bones: frontal, occipital, 2 temporals, 2 parietals, sphenoid and ethmoid

facial bones holed the eyes in an anterior position and allow the facial muscles to show our feelings. = 14 bones: nasals, maxillae, zygomatics, mandible, lacrimals, palatines, inferior nasal conchae, vomer.

The Adult Skull

Bones of the Cranium

Frontal View

Frontal

Frontal View

Parietal

Frontal View

Temporal

Frontal View

Nasal

Frontal View

Vomer

Frontal View

Zygoma

Frontal View

Maxilla

Frontal View

Mandible

Frontal View

FrontalParietal

Temporal

Zygoma

Nasal

VomerMaxilla

Mandible

Frontal View

Lateral View

Frontal

Lateral View

Parietal

Lateral View

Temporal

Lateral View

Nasal

Lateral View

Zygoma

Lateral View

Maxilla

Lateral View

Mandible

Lateral View

Sphenoid

Lateral View

Occipital

Lateral View

Mastoid Process

Lateral View

External Auditory Meatus

Lateral View

Frontal

NasalZygomaMaxilla

Mandible

Parietal

SphenoidTemporal

Occipital

External Auditory Meatus

Mastoid Process

Lateral View

Fetal skull• The skull of a newborn differs from an adult one:

– The infant’s face is very tiny compared to the cranium.– The whole skull is large compared to infant’s body length– The adult skull represents only 1/8th of the total body

length, whereas that of new born infant is 1/4th as long as its entire body.

– The fetal skull has fibrous cartilage area between the cranial bones.

– These membranous area are called fontanels, which allow the fetal skull to be compressed during birth and allow the infant’s brain to be grow.

– The fontanels usually closes by age 20-22 months.

Fetal skull

Adult Vertebral Column

Formed from 33 bones in the adult

Divided into five major regions Cervical vertebrae

7 vertebrae of the neck region Thoracic vertebrae

12 vertebrae of the thoracic region Lumbar vertebrae

5 vertebrae of the lower back Sacrum

Inferior to lumbar vertebraeArticulates with coxal bones

CoccyxMost inferior region of the vertebral column

Intervertebral disks

The single vertebrae are separated by pads of elastic cartilage intervertebral disks Cushion vertebrae and absorb

shocks. Have a high water content (about

90%) and are compressible.

General Structure of Vertebrae

Cervical Vertebrae

• Atlas – 1st; supports head• Axis – 2nd; dens pivots to turn head• transverse foramina• bifid spinous processes• vertebral prominens – useful landmark

Thoracic Vertebraelong spinous processesRib facets

Lumbar Vertebrae

large bodies thick, short spinous processes

Sacrum

five fused vertebrae median sacral crest posterior sacral foramina posterior wall of pelvic cavity sacral promontory

Coccyx

TailboneFour fused vertebrae

Thorax

Often called the thoracic cage.Components of the thorax

Sternum– anteriorly Ribs – laterally Thoracic vertebrae – posteriorly

Protects thoracic organs (heart, lungs, and major blood vessels).

The Thorax

Sternum

Breast bone is typical flat bone and the result of fusion of three bones. Manubrium – superior section Body – bulk of sternum Xiphoid process – inferior end of sternum

Attached to the 1st seven pairs of ribs.

Ribs

The 12 pairs of ribs form the wall of the thoracic cage.

All ribs attach to vertebral column posteriorly True ribs - superior seven pairs of ribs Attach

directly to sternum by costal cartilageFalse ribs – inferior five pairs of ribsHave cartilages attachment to the sternum that

are indirect or are not attached at all. Ribs 11–12 are known as floating ribs

The Thoracic cage

Ribs

RibsRibs

APPENDICULAR SKELETON

• It is formed of :Pectoral girdlePelvic girdleBones of the upper and lower limbs.

PECTORAL GIRDLE

• It is formed of :• CLAVICLE which holds

the arm away from the thorax.

• SCAPULA (WING).

Clavical

Scapula

UPPER LIMB

• ARM :Humerus• FORE ARM: Radius &

Ulna.• Long bones They are

formed of Epiphysis on each end. Diaphysis a tubular shaft. It is covered externally by the periosteum.

HAND

• WRIST : Carpal bones.• PALM : Metacarpal

bones.• FINGERS : Phalanges.• They are examples of

short bones.

PELVIC GIRDLE• Formed of the two HIP

bones.• Each hip bone is formed

of three parts : ILium. Ischium. Pubis.

• The hip bones and the sacrum form the bony pelvis.

LOWER LIMB

• THIGH : Femur.• LEG : Tibia & Fibula.• Also Patella bone

FOOT

• TARSUS : Tarsal bones.• Metatarsals. • Phalanges.