Essentials 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: form the framework that supports the body and cradles soft organs Protection: provide a protective case for the brain, spinal cord, and vital organs Movement: provide levers for muscles Mineral storage: reservoir for minerals, especially calcium and phosphorus Blood cell formation: hematopoiesis occurs within the marrow cavities of bones Energy 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.

Hematopoiesis Blood 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 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 Shape

Classification 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 Bones Short bones Generally cube-shape Contain more spongy bone than compact Examples: Carpals, tarsals

Classification 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 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 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 3 types of cells in bone tissue Osteoblasts: Form matrix & collagen fibers but can’t divide Osteocytes: Mature cells that no longer secrete matrix Osteoclasts: Huge cells from fused monocytes (WBC) Function in bone resorption at surfaces such as endosteum

SKLETAL SYSTEM It is divided into two parts : Axial Appendicular

Bone Structure - External Cartilage protection for joints

Bone Structure - External Epiphyses Expanded ends of long bones Exterior is compact bone, and the interior is spongy bone Joint surface is covered with articular (hyaline) cartilage location of red bone marrow Epiphyseal line separates the diaphysis from the epiphyses Epiphyse

Bone Structure - External Diaphysis 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 Periosteum – 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 – 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 includes Axial division Skull and associated bones Auditory ossicles Hyoid bones Vertebral column Thorax (Thoracic cage ) Ribs sternum Appendicular division - Pectoral girdle - Pelvic girdle

The Adult Skull 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.

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

Frontal View Frontal Parietal Temporal Nasal Vomer Zygoma Maxilla 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

Lateral View Parietal Frontal Sphenoid Nasal Temporal Zygoma Occipital Maxilla Mastoid Process Mandible External Auditory Meatus 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 vertebrae Articulates with coxal bones Coccyx Most 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 Vertebrae long spinous processes Rib 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 Tailbone Four 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 cartilage False ribs – inferior five pairs of ribs Have 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

Ribs

APPENDICULAR SKELETON It is formed of : Pectoral girdle Pelvic girdle Bones 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.