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Foramen Magnum

Large opening in the skull for spinal cord.

Bifid Vertebrae

Cervical vertebrae with split spinous processes.

Total Bones in Adult Body

206 bones after fusion from childhood.

Ribs in Adult Body

24 ribs, 12 pairs in total.

Fontanels

Soft spots on a baby's skull for growth.

Ethmoid Bone

Single bone located between the eyes.

Atlas Vertebra

C1 vertebra, supports the skull.

Axial Vertebra

C2 vertebra, allows head rotation.

Tendons

Connect muscles to bones, facilitating movement.

Ligaments

Connect bones to other bones, providing stability.

Skeletal System

Parts of the skeletal system include bones, joints, cartilages, and ligaments.

Axial skeleton

One of the two subdivisions of the skeleton.

Appendicular skeleton

One of the two subdivisions of the skeleton.

Functions of the Bones

Support the body, protect soft organs, allow movement via attached muscles, store minerals and fats, and blood cell formation (hematopoiesis).

Protection of soft organs

The skull and vertebrae protect the brain and spinal cord, while the rib cage protects thoracic cavity organs.

Blood cell formation

Also known as hematopoiesis.

Adult skeleton

The adult skeleton has 206 bones.

Osseous tissue

There are two basic types: compact bone and spongy bone.

Compact bone

Dense, smooth, and homogeneous type of osseous tissue.

Spongy bone

Contains small needlelike pieces of bone and many open spaces.

Classification of Bones

Bones are classified on the basis of shape into four groups: long, flat, short, and irregular.

Long bones

Typically longer than they are wide, with a shaft and enlarged ends, containing mostly compact bone.

Examples of long bones

Femur and Humerus.

Flat bones

Thin, flattened, and usually curved, with two layers of compact bone sandwiching a layer of spongy bone.

Examples of flat bones

Most bones of the skull, ribs, and sternum.

Short bones

Generally cube-shaped, containing mostly spongy bone with an outer layer of compact bone.

Examples of short bones

Carpals (wrist bones) and tarsals (ankle bones).

Irregular bones

Have irregular shapes and do not fit into other bone classification categories.

Examples of irregular bones

Vertebrae and hip bones.

Long bone anatomy

Includes the diaphysis (shaft) and periosteum.

Diaphysis

Makes up most of the bone's length and is composed of compact bone.

Periosteum

The outside covering of the diaphysis, a fibrous connective tissue membrane.

Perforating (Sharpey's) fibers

Secure the periosteum to the underlying bone.

Epiphysis

Composed mostly of spongy bone enclosed by thin layer of compact bone.

Articular cartilage

Covers the external surface of the epiphyses, made of hyaline cartilage, and decreases friction at joint surfaces.

Epiphyseal line

Remnant of the epiphyseal plate seen in adult bones.

Epiphyseal plate

Flat plate of hyaline cartilage seen in young, growing bone that causes lengthwise growth of a long bone.

Endosteum

Lines the inner surface of the shaft and is made of connective tissue.

Medullary cavity

Cavity inside the shaft that contains yellow marrow (mostly fat) in adults and red marrow for blood cell formation until age 6 or 7.

Bone markings

Sites of attachments for muscles, tendons, and ligaments, and passages for nerves and blood vessels.

Projections or processes

Grow out from the bone surface, with all projections beginning with 'T'.

Depressions or cavities

Indentations, with all depressions beginning with 'F' (except facet).

Trabeculae

Small, needlelike pieces of bone that compose spongy bone.

Lacunae

Cavities in bone matrix that house osteocytes.

Lamellae

Concentric circles of lacunae situated around the central (Haversian) canal.

Central (Haversian) canal

Opening in the center of an osteon that runs lengthwise through bone and carries blood vessels and nerves.

Osteon (Haversian system)

A unit of bone containing central canal and matrix rings, serving as the structural and functional unit of compact bone.

Canaliculi

Tiny canals that radiate from the central canal to lacunae, forming a transport system connecting all bone cells to a nutrient supply.

Perforating (Volkmann's) canal

Canal perpendicular to the central canal that carries blood vessels and nerves.

Bone

Relatively lightweight and resists tension and other forces.

Organic parts of bone

Collagen fibers that make bone flexible and have great tensile strength (stretch without breaking).

Calcium salts in bone

Deposited in the bone to make it hard and resist compression.

Ossification

The process of bone formation.

Hyaline cartilage models

The structures on which ossification occurs.

Phases of long bone growth

Involves two major phases.

Osteoblasts

Bone-forming cells that cover the hyaline cartilage model with bone matrix in an embryo.

Medullary cavity

The space opened up when the enclosed cartilage is covered by bone and digested away.

Articular cartilages

One of the two regions in a long bone where cartilage is retained by birth.

Epiphyseal plates

The second region in a long bone where cartilage is retained by birth.

Appositional growth

The process by which bones grow in width.

Hormones controlling bone growth

Growth hormone and sex hormones.

Factors affecting bone remodeling

Calcium ion level in the blood and the pull of gravity and muscles on the skeleton.

Parathyroid hormone (PTH)

Released when calcium ion levels in blood are low, activating osteoclasts.

Hypercalcemia

High blood calcium levels that prompt calcium storage to bones by osteoblasts.

Fracture

A break in a bone.

Closed (simple) fracture

A break that does not penetrate the skin.

Open (compound) fracture

A broken bone that penetrates through the skin.

Reduction and immobilization

The treatment for bone fractures.

Closed reduction

Bones are manually coaxed into position by physician's hands.

Open reduction

Bones are secured with pins or wires during surgery.

Healing time for fractures

6-8 weeks.

Hematoma

Blood-filled swelling, or bruise, formed during the repair of bone fractures.

Fibrocartilage callus

A structure that forms during bone fracture repair, consisting of cartilage matrix, bony matrix, and collagen fibers that splint the broken bone.

Bony callus

Replaces the fibrocartilage callus during the repair of bone fractures, formed by the migration of osteoblasts and osteoclasts.

Bone remodeling

The process that occurs in response to mechanical stresses during the healing of a bone fracture.

Axial Skeleton

Forms the longitudinal axis of the body and is divided into three parts: skull, vertebral column, and bony thorax.

Cranium bones

Bones that enclose the brain.

Facial bones

Bones that hold the eyes in anterior position and allow facial muscles to express feelings.

Sutures

Immovable joints that join the bones of the skull.

Mandible

The only bone in the skull that is attached by a freely movable joint.

Frontal bone

One of the eight cranial bones that protect the brain.

Occipital bone

One of the eight cranial bones that protect the brain.

Ethmoid bone

One of the eight cranial bones that protect the brain.

Sphenoid bone

One of the eight cranial bones that protect the brain.

Parietal bones

A pair of cranial bones that protect the brain.

Temporal bones

A pair of cranial bones that protect the brain.

Maxillae

A pair of facial bones.

Palatine bones

A pair of facial bones.

Lacrimal bones

A pair of facial bones.

Zygomatic bones

A pair of facial bones.

Nasal bones

A pair of facial bones.

Vomer bone

A single facial bone.

Inferior nasal conchae

A pair of facial bones.

Paranasal sinuses

Hollow portions of bones surrounding the nasal cavity that lighten the skull and amplify sounds made as we speak.

Hyoid bone

The only bone that does not articulate with another bone, serving as a movable base for the tongue and aiding in swallowing and speech.

Vertebral column

Provides axial support, extending from the skull to the pelvis, consisting of 26 vertebral bones separated by intervertebral discs.

Cervical vertebrae

Seven vertebrae located in the neck.

Thoracic vertebrae

Twelve vertebrae located in the chest region.

Lumbar vertebrae

Five vertebrae associated with the lower back.

Sacrum

Formed by the fusion of five vertebrae.