Anatomy Chapter 5: Bone Classification, Markings, and Joints

Long Bones

Longer than they are wide; absorb the stress of the body's weight. Example: all bones of the limbs except patella, wrist and ankle bones.

Short Bones

Cube-shaped or round; about as broad as they are long. Example: bones of wrist and ankle; sesamoid bones are specialized short bones that form in tendons (patella).

Irregular Bones

Has a shape that does not fit into any other category. Example: vertebrae and facial bones.

Flat Bones

Thin, flattened, and usually curved; provide protection & provide area for muscle attachment.

Projections

Grow out of bone surface.

Depressions

Indentations of bone.

Tuberosity

A large bump of bone used for muscle attachment.

Condyle

Round bump of bone that helps form a joint.

Foramen

A hole in the bone for blood vessels and nerves to pass through.

Hiatus

A hole in a membrane for blood vessels and nerves to pass through.

Skeletal System

Includes bones (osseous tissue), ligaments, tendons, and cartilage.

Support

Bones form internal framework that supports the body.

Protection

Bones protect soft bodied organs.

Movement

Skeletal muscles attached to bone via tendons use bones as levers to move the body and its parts (joints).

Storage

Fat is stored within internal cavities of bone (yellow marrow) & it is a storehouse for minerals like calcium and phosphorus.

Blood cell production (hematopoiesis)

Red marrow gives rise to red blood cells, white blood cells, and platelets.

Bones as Levers

Skeletal muscles attach to bones by tendons; they use the bones as levers to move the body and its parts.

Average number of bones in human body

The average human has approximately 206 bones in their body (born with 300).

Alive bones

Although bones appear to be dead, they are ALIVE!

Bones

Composed of active connective tissue that breaks down and regenerates itself constantly.

Bone hardness

Due to the crystalized salts that it contains.

Bone flexibility

Depends on its collagen fibers (protein) which give bones resistance to being stretched or torn apart.

Diaphysis

Shaft of the bone that makes up most of its length and is composed of compact bone.

Periosteum

Connective tissue membrane that protects the diaphysis.

Perforating fibers (Sharpey's fibers)

Secure periosteum to underlying bone.

Epiphyses

Proximal and distal ends of the bone, composed of a thin layer of compact bone filled with spongy bone.

Articular cartilage

Covers the outside of epiphyses to create a smooth surface that decreases friction at joint surfaces.

Epiphyseal (growth) plate

Hyaline cartilage located between the epiphysis and diaphysis that causes lengthwise growth of bone.

Medullary Cavity

Hollow, internal space of a diaphysis lined with connective tissue (endosteum) and filled with marrow.

Red marrow

Site of blood cell formation.

Yellow marrow

Contains adipose tissue (fat) and replaces red marrow in the skull and limbs as individuals age.

Axial Skeleton

Consists of the skull, cranium (8 bones), face (14 bones), hyoid (1 bone), auditory ossicles (6 bones), vertebral column (26 bones), thorax, sternum (1 bone), and ribs (24 bones), totaling 80 bones.

Appendicular Skeleton

Consists of the pectoral girdles (clavicle (2 bones), scapula (2 bones)), upper limbs (humerus (2 bones), ulna (2 bones), radius (2 bones), carpals (16 bones), metacarpals (10 bones), phalanges (28 bones)), pelvic girdle (hip, pelvic, or coxal bone (2 bones)), lower limbs (femur (2 bones), patella (2 bones), fibula (2 bones), tibia (2 bones), tarsals (14 bones), metatarsals (10 bones), phalanges (28 bones), totaling 126 bones.

Total in an adult skeleton

206 bones.

Compression fracture

Occurs in the vertebrae with collapse of the vertebrae, common in people with osteoporosis.

Depressed fracture

Usually occurs in the skull from blunt force trauma, where the bone is pushed inward and fractures at the point of impact.

Impacted fracture

Bone breaks into multiple fragments which are driven into each other, usually caused by a fall.

Spiral fracture

Caused by a twisting force, also known as a torsion fracture.

GREENSTICK FRACTURE

Extreme force causes a bone to bend, breaking partway through, much like a green twig when it is bent. Commonly seen in children. Some may heal in as little as 3 weeks.

COMMINUTED FRACTURE

Bone involved in the fracture is broken into several pieces. At least three separate pieces of bone must be present for a fracture to be classified as comminuted. Most common in elderly people or in people with conditions which weaken the bones, such as osteogenesis imperfecta (brittle bone disease) or cancer. Can also occur as the result of tremendous force, such as a car accident or a severe fall.

TRANSVERSE FRACTURE

Bone is completely broken in a manner that is perpendicular to the way the bone runs. Often results from a direct blow (imagine a karate chop directly across the arm), but it can also sometimes occur when people do things repetitively, like running (stress fracture).

OBLIQUE FRACTURE

Break which has a fracture line that runs diagonal to the bone shaft. Similar to a spiral fracture. Both breaks occur at a slant, but the oblique fracture tends to be a straight break while the spiral fracture has a pattern similar to a corkscrew.

AVULSION FRACTURE

A ligament or tendon pulls away from its attachment on the bone, and a fragment breaks off with it. Caused by muscle contraction or stretch that is stronger than the force that holds the tendon/ligament to the bone.

FISSURE OR HAIRLINE FRACTURE

An incomplete bone fracture. Multiple small lines that are visible, but DO NOT pass through the entire bone. Can be caused by any force that causes other fractures but not enough force to completely break the bone.

OPEN (COMPOUND) FRACTURE

Breaks through the skin. High risk of infection. More difficult to treat since *********** treating a skin injury in addition to a broken bone.

CLOSED FRACTURE

Does NOT break through the skin.

Microscopic Structure of Bone

Bone is one of the hardest materials in the body. Bone is light in weight but can resist tension. Bone is a living, vascular structure (blood supply) composed of organic tissue and minerals (Calcium phosphate). Bone is considered an organ because it is composed of different tissues.

Hardest Material in the Body

Enamel.

Compact Bone

Form walls of diaphysis & the thinner outer surface of other bones (flat bones of skull)

Lacunae

Arranged in concentric circles called lamellae around central (haversian) canals

Osteons

Functional units of compact bone consisting of central canal and matrix rings

Spongy (cancellous) Bone

Consists of interwoven beams of bone (trabeculae)

Trabeculae

Spaces among trabeculae filled with red or yellow marrow and blood vessels

Osseous (Bone) Tissue

Osteogenic cells - unspecialized stem cells that give rise to osteoblasts

Osteoblasts

Bone building cells (ossification) that become osteocytes as they secrete materials needed to make bone

Osteocytes

Mature bone cells that control the homeostasis of the bone and body by controlling the absorption of calcium and phosphates

Osteoclasts

Cells responsible for dissolving bone tissue to release minerals (resorption)

Ossification

Process where cartilage gets replaced by bone

Endochondral ossification

Bones develop using cartilage as a model, e.g., long bone formation in embryo, fetus, and young child

Epiphyseal (growth) plates

Responsible for lengthening bones

Appositional growth

Increases in thickness of bones due to osteoblasts building bone at the surface

Appositional Bone Growth

Bone remodeling process that increases the strength of bones in areas where bulk muscles are attached.

Bone Remodeling

The process by which bones constantly remodel in response to various factors.

Immovable Joints

Also known as synarthroses, these joints allow no movement.

Slightly Movable Joints

Also known as amphiarthroses, these joints allow a little movement.

Freely Movable Joints

Also known as diarthroses, these joints allow free movement.

Fibrous Joints

Joints that lie between bones that closely contact one another, allowing little to no movement.

Cartilaginous Joints

Joints where disks of fibrocartilage or hyaline cartilage connect the bones, allowing slight movement.

Synovial Joints

Joints that allow free movement and are more complex in structure than fibrous or cartilaginous joints.

Joint Capsule

A capsule of dense connective tissue that holds synovial joints together.

Synovial Fluid

Fluid secreted by the synovial membrane that lubricates the joint.

Menisci

Flattened, shock-absorbing pads of fibrocartilage found in some synovial joints.

Bursae

Fluid-filled sacs that may be present in some synovial joints.

Ball-and-Socket Joint

A joint where a ball-shaped head of one bone fits into a cup-shaped cavity of another bone, allowing the widest range of movement.

Condyloid Joint

A joint where an oval-shaped condyle of one bone fits into an elliptical cavity of another bone, allowing movement in different planes but not rotation.

Plane (Gliding) Joint

A joint where articulating surfaces are nearly flat or slightly curved, allowing sliding or twisting movement.

Hinge Joint

A joint where the convex surface of one bone fits into the concave surface of another, permitting movement in only one plane.

Pivot Joint

A joint where a cylindrical surface of one bone rotates within a ring formed of bone and ligament, allowing rotation around a central axis.

Saddle Joint

A joint that forms between bones whose articulating surfaces have both concave and convex regions, allowing a variety of movement.