The Skeletal System and Joints

Hematopoiesis

The formation of blood cells (red, white, and platelets) taking place in red bone marrow.

Ligament

A band of dense connective tissue that attaches bone to bone and stabilizes the joint.

Tendon

A band of dense connective tissue that attaches muscle to bone to create movement.

Joint (articulation)

The meeting place between bones that gives the skeleton mobility while holding it together.

Osteon

The basic structural unit of compact bone, made of long cylinders acting as weight-bearing pillars.

Lamellae

Concentric rings of hard matrix that make up an osteon and resist twisting stress.

Central canal

Canal running through the middle of each osteon containing blood vessels and nerves.

Trabeculae

Tiny bone struts of spongy bone that resist stress and hold bone marrow in their spaces.

Lacunae

Small spaces between lamellae that house osteocytes.

Canaliculi

Tiny channels connecting lacunae to each other and the central canal for nutrient/waste transport.

Osteocyte

A mature bone cell that maintains bone tissue and monitors its health.

Osteoblast

A bone-forming cell that builds new bone matrix and repairs damage.

Osteoclast

A large, multinucleated cell that breaks down old or damaged bone for remodeling.

Ossification

The process of bone tissue formation.

Fracture

A break in a bone.

Why is bone a living organ?

It contains all 4 tissue types, has blood/nerves, constantly remodels, and carries out vital life functions.

6 Functions of the skeletal system

Support, protection, movement, storage (minerals/fat), blood cell formation, and hormone production.

Long bone example & function

Femur; acts as a lever to aid movement.

Short bone example & function

Carpals; provide support and stability with gliding movement.

Flat bone example & function

Sternum, scapula, ribs, and cranial bones; protect organs and provide large surface area for muscle attachment.

Irregular bone example & function

Vertebrae and hip bones; specialized shapes for protecting the spinal cord and bearing weight.

Sesamoid bone example & function

Patella; shaped like a sesame seed and embedded in a tendon to protect it.

Spongy Bone Structure

A type of bone tissue that has a porous structure, consisting of trabecular plates and spaces, providing strength and reducing weight while housing bone marrow.

Compact Bone Strucutre

Dense and smooth with a strong framework of osteons and lamellae, providing strength and support.

Compact Bone Location

dense outer layer (diaphysis)

Spongy Bone Location

porous inner tissue (epiphyses).

Intramembranous Ossification

Develops from a fibrous membrane (faster)

Endochondral Ossification

is the process by which cartilage is transformed into bone, primarily in long bones of the body. (Slower)

4 steps of bone remodeling

1. Osteocytes signal damage, 2. Osteoclasts resorb bone, 3. Macrophages clean debris, 4. Osteoblasts build new bone.

Pectoral girdle

Clavicle and scapula; attaches upper limbs to the axial skeleton with a high range of motion.

Pelvic girdle

Two hip bones; attaches lower limbs to the axial skeleton with high stability.

Closed Fracture

Breaks bone with skin intact.

Open Fracture

Breaks bone and tears through the skin.

Transverse Fracture

Breaks straight across the bone axis

Spiral Fracture

Breaks via a twisting motion

Comminuted Fracture

Breaks into many small pieces

Impacted Fracture

Break drives one bone fragment into another.

Greenstick Fracture

Partial bone fracture frequent in kids

Oblique Fracture

Bone breaks at a non-90-degree angle.

Female Pelvis

Wider, shallower, and has a larger opening and wider pubic arch for childbirth.

Male Pelvis

Less wide, smaller opening, deeper

True ribs

Pairs 1 to 7; attach directly to the sternum through their own costal cartilage.

False ribs

Pairs 8 to 12; do not attach directly to the sternum (8-10 join cartilage of rib 7).

Floating ribs

Pairs 11 and 12; lowest false ribs with no attachment at the front.

5 regions of the vertebral column

Cervical, thoracic, lumbar, sacral, and coccygeal.

Synarthrosis

A non-moving joint providing maximum stability (e.g., skull sutures).

Amphiarthrosis

A slightly moving joint that balances movement/stability and absorbs shock (e.g., pubic symphysis).

Diarthrosis

A freely moving joint with a wide range of motion but less stability (e.g., knee and elbow).

Suture

A fibrous joint that holds the bones of the skull together.

Syndesmosis

A fibrous joint where bones are held together only by ligaments (e.g., tibia and fibula).

Gomphosis

A fibrous joint holding a tooth in its socket by the periodontal ligament.

Synchondrosis

A cartilaginous joint made of hyaline cartilage (e.g., sternum and first rib).

Symphysis

A slightly movable cartilaginous joint made of fibrocartilage (e.g., intervertebral discs).

Gliding joint movement

Flat bone surfaces slipping back and forth or side to side (e.g., wrist and ankle).

Flexion Movement

Decreases joint angle

Extension Movement

Increases joint angle

Hyperextension

Extension that goes beyond the anatomical position.

Rotation

The turning of a bone around its own long axis.

Supination

Turns palm up

Pronation

Turns palm down

Abduction

Moves limb away from median plane

Adduction

Moves limb back to median plane

Opposition

Movement of the thumb across the palm to touch fingertips, made possible by a saddle joint.

Circumduction

Moving a limb in a circle.

Dorsiflexion

Lifts the foot upward

Plantar Flexion

Points the foot downward

Bursae

Fluid-filled sacs that prevent friction between structures in a joint.

Functional Joint Classification

Identifying based on movement amount

Structural Joint Classification

Identifying based on binding material and joint cavity presence

Movement vs. stability in joints

Inverse relationship: the more movable a joint is, the less stable it is.

Fibrous joints

Connected by collagen fibers with no joint cavity; mostly immovable.

Cartilaginous joints

Connected by cartilage with no joint cavity; slightly movable or rigid.

Synovial joints

Connected by dense connective tissue with a fluid-filled joint cavity; freely movable.

Hinge joint example & movement

Elbow and fingers; moves in one direction like a door hinge (flexion/extension).

Pivot joint example & movement

C1/C2 vertebrae and proximal radius/ulna; allows rotation, supination, and pronation.

Ball-and-socket joint

Shoulder and hip; most complex joints allowing multi-directional movement and rotation.