Skeletal System Review Flashcards

Educational Objectives & System Overview

• Identify and describe the fundamental functions and anatomical structures of the human skeletal system.

• Differentiate between the structural and functional divisions of the skeletal system: the axial skeleton ($80\,\text{bones}$) and the appendicular skeleton ($126\,\text{bones}$).

• Classify and describe the three primary functional types of joints, including specific subclassifications of freely movable joints.

• Examine bone histogenesis, tissue types, cellular mechanisms, and the bone remodeling process.

• Identify major anatomical bone markings, including projections, processes, depressions, and openings.

• Analyze common skeletal disorders, traumatic injuries, structural deformities, and neoplasms, evaluating their pathophysiology, clinical presentation, and diagnostic features.

• Master medical terminology, root words, combining forms, and anatomical directional terminology pertinent to the skeletal system.

Medical Terminology

• Bones (oss/e, oste/o): Primary structural framework of the body; provides mechanical protection for internal organs, facilitates movement, and acts as a primary storage reservoir for the mineral calcium.

• Bone Marrow (myel/o): Soft connective tissue found within bone cavities.

  • Red Bone Marrow: Site of hematopoiesis/hemopoiesis (blood cell production).

  • Yellow Bone Marrow: Composed primarily of adipose tissue (lipocytes) for energy and fat storage.

• Cartilage (chondr/o): Smooth, resilient, non-vascular connective tissue that covers articular surface ends of bones to reduce friction and absorb shock during joint motion.

• Joints (arthr/o): Articulations between two or more bones that work in coordination with skeletal muscles to enable mobility.

• Ligaments: Tough, fibrous bands of connective tissue that connect bone to bone, serving to reinforce, direct, or restrict joint movement.

• Tendons: Highly tensile bands of dense fibrous connective tissue that attach skeletal muscle to bone, translating muscular contraction into skeletal leverage.

• Synovial Membranes: Specialized tissue lining the inner surface of joint capsules in synovial joints; secretes lubricating fluid.

• Synovial Fluid: Viscous, clear fluid secreted by synovial membranes that reduces friction between articular cartilages during joint movement.

• Bursa (burs/o): Fluid-filled sac lined with synovial membrane that cushions friction-prone areas where tendons, muscles, or skin slide over bony prominences.

Primary Functions of the Skeletal System

• Protection: Encases vital internal organs within rigid bony structures (e.g., the cranium protects the brain; the vertebral column shields the spinal cord; the thoracic cage encloses the heart and lungs).

• Support & Framework: Provides a rigid, structural framework that supports soft tissues, anchoring skeletal muscles, fat, and skin.

• Movement & Leverage: Bones act as mechanical levers that, when pulled upon by contracting muscles across joints, produce body movements.

• Blood Cell Formation (Hemopoiesis / Hematopoiesis): Red bone marrow residing within specific bone cavities produces red blood cells (erythrocytes), white blood cells (leukocytes), and blood platelets (thrombocytes).

• Mineral & Fat Storage: Serves as the primary metabolic reservoir for essential minerals—storing over $90\%$ of the body's calcium and phosphorus supply—while yellow bone marrow stores triglycerides (adipose energy reserves).

Bone Tissue Classification & Cellular Composition

• System Scale: The adult human skeleton consists of $206\,\text{bones}$, whereas an infant skeleton contains approximately $300\text{--}350\,\text{bones}$ at birth, which subsequently fuse during growth and development.

• Osseous Tissue Types:

  • Compact Bone (Cortical Bone): Dense, hard, highly structured, and homogeneous outer layer of bone. Composed of tightly packed osteons (Haversian systems) designed for mechanical strength and structural load-bearing.

  • Spongy Bone (Cancellous Bone): Lightweight, porous, network-like inner architecture composed of needle-like bony struts called trabeculae. Contains numerous open spaces filled with red or yellow bone marrow.

• Types of Bone Cells:

  • Osteocytes: Mature, fully differentiated bone cells embedded within lacunae that maintain daily cellular metabolism and matrix integrity.

  • Osteoblasts: Immature, bone-forming cells responsible for synthesizing and secreting organic matrix components, specifically collagen (the fundamental structural protein required for building bone tissue and providing tensile strength), which subsequently mineralizes.

  • Osteoclasts: Large, multinucleated, bone-destroying cells derived from monocytes; responsible for bone resorption by breaking down the mineralized bone matrix to release calcium and phosphate into the bloodstream.

• Bone Remodeling Process:

  • Remodeling is an ongoing dynamic metabolic process balanced by the coordinated actions of osteoblasts (bone formation) and osteoclasts (bone resorption).

  • Essential for structural adaptation to mechanical stress, repairing microscopic micro-fractures, and maintaining systemic calcium homeostasis.

  • Through continuous cellular remodeling, the human body completely renews the equivalent of an entirely new skeleton approximately every $7\,\text{years}$.

Classification of Bones by Shape

• Long Bones: Characterized by a length substantially greater than their width; consist of a central shaft with articular ends. Examples include the humerus, radius, ulna, femur, tibia, and fibula.

• Short Bones: Roughly cube-shaped or square in appearance, having equal vertical and horizontal dimensions; consist mostly of spongy bone surrounded by a thin layer of compact bone. Examples include carpal bones of the wrist and tarsal bones of the ankle.

• Flat Bones: Thin, flattened, and usually gentle curved structures consisting of two parallel plates of compact bone enclosing an inner layer of spongy bone. Examples include cranial bones of the skull and the sternum.

• Irregular Bones: Complex, highly specialized shapes that do not fit into any other category. Examples include the vertebrae and the pelvic os coxae.

• Sesamoid Bones: Small, rounded bones embedded within tendons adjacent to joint surfaces to reduce friction and alter muscle pulling angles. The patella (kneecap) is the primary example.

Anatomical Structure of a Long Bone

• Diaphysis: The elongated tubular main shaft of the long bone, composed of thick, heavy compact bone surrounding an inner cavity.

• Epiphysis: Expanded proximal and distal ends of the bone that articulate with adjacent bones; composed internally of spongy bone covered externally by a thin shell of compact bone.

• Epiphyseal Disk / Epiphyseal Plate: A layer of hyaline cartilage located at the junction of the diaphysis and epiphysis in growing children; responsible for longitudinal bone elongation.

• Articular Cartilage: A thin layer of smooth hyaline cartilage covering the outer joint surfaces of the epiphyses; buffers impacts and reduces friction during movement.

• Medullary Canal / Cavity: Hollow central chamber running longitudinally down the center of the diaphysis; contains bone marrow tissue.

• Red Bone Marrow: Hematopoietic tissue located primarily within spongy bone spaces (e.g., proximal epiphyses of the femur and humerus) that manufactures erythrocytes, leukocytes, and thrombocytes.

• Yellow Bone Marrow: Fat-rich tissue residing mainly in the adult medullary cavity; composed largely of adipocytes (lipocytes) for triglyceride storage.

• Endosteum: Vascular connective tissue membrane lining the internal surfaces of the medullary canal and trabeculae; contains bone-remodeling osteoblasts and osteoclasts.

• Periosteum: Tough, dense, double-layered fibrous membrane covering the outer surface of the bone (except at articular cartilage surfaces). Richly supplied with blood vessels, lymphatic vessels, and osteoblasts essential for bone growth, repair, and nutrition.

Bone Markings: Projections and Depressions

• Processes & Projections (Outgrowths that form joints or attachment points):

  • Head: A prominent, expanded rounded articular end of a long bone, typically supported by a constricted neck (e.g., head of femur, head of humerus).

  • Condyle: A large, rounded smooth articular prominence located at the end of a bone (e.g., medial and lateral femoral condyles).

  • Epicondyle: A prominent projection situated directly superior or proximal to a condyle for ligament and muscle attachment (e.g., medial and lateral femoral epicondyles).

  • Trochanter: An exceptionally large, blunt, irregularly shaped process found exclusively on the femur for major muscle attachment (e.g., greater trochanter).

  • Tubercle: A small, rounded process or nodule serving as an attachment point for tendons or muscles (e.g., Lister's tubercle on the distal radius).

  • Tuberosity: A large, rough, elevated process or bump designed for strong tendon and muscle attachment (e.g., greater tuberosity of humerus).

• Depressions & Openings (Conduits for blood vessels/nerves or joint surfaces):

  • Sinus: An air-filled hollow cavity or space enclosed within a cranial or facial bone.

  • Foramen: A smooth, defined hole or opening extending through bone allowing passage for nerves, blood vessels, or the spinal cord.

  • Fossa: A shallow, flattened, or concave depression on or within a bone, often forming a joint surface or housing soft tissue structures (e.g., glenoid fossa of the scapula).

  • Fissure: A narrow, slit-like groove, crack, or deep cleft through which blood vessels or nerves pass.

Divisions of the Human Skeleton

• Axial Skeleton ($80\,\text{bones}$): Forms the central vertical longitudinal axis of the human body. Composed of:

  • Skull ($29\,\text{bones}$): Includes Cranium ($8$), Facial bones ($14$), Auditory Ossicles ($6$), and Hyoid bone ($1$).

  • Spinal Column ($26\,\text{bones}$): $24$ individual vertebrae plus the fused Sacrum ($1$) and Coccyx ($1$).

  • Thorax / Rib Cage ($25\,\text{bones}$): Sternum ($1$) plus $24$ individual ribs ($12\,\text{pairs}$).

• Appendicular Skeleton ($126\,\text{bones}$): Comprises the upper and lower limbs and the bony girdles that attach them to the axial skeleton. Composed of:

  • Pectoral Girdles ($4\,\text{bones}$): Clavicles ($2$) and Scapulae ($2$).

  • Upper Limbs ($60\,\text{bones}$): Humerus ($2$), Radius ($2$), Ulna ($2$), Carpals ($16$), Metacarpals ($10$), Phalanges ($28$).

  • Pelvic Girdle ($2\,\text{bones}$): Hip bones / Os Coxae ($2$).

  • Lower Limbs ($60\,\text{bones}$): Femur ($2$), Patella ($2$), Tibia ($2$), Fibula ($2$), Tarsals ($14$), Metatarsals ($10$), Phalanges ($28$).

The Axial Skeleton: Skull & Associated Structures

• Cranium ($8\,\text{bones}$): Spherical bony vault surrounding and protecting the brain.

  • Frontal Bone ($1$): Forms the forehead, superior roof of the orbits, and anterior cranial floor.

  • Parietal Bones ($2$): Form the upper sides and smooth roof of the cranium.

  • Temporal Bones ($2$): Form the lower lateral sides and base of the cranium. Houses the external auditory meatus, mastoid process, styloid process, and zygomatic process of temporal bone.

  • Occipital Bone ($1$): Forms the posterior back wall and inferior base of the skull. Features the Foramen Magnum, a large central opening allowing passage of the spinal cord to connect with the brainstem.

  • Ethmoid Bone ($1$): Complex bone forming part of the anterior cranial floor, medial orbit walls, superior nasal septum, and nasal roof.

  • Sphenoid Bone ($1$): Key bat-shaped or butterfly-shaped central bone articulating with all other cranial bones; forms the base of the cranium and posterior walls of the orbits.

• Facial Bones ($14\,\text{bones}$): Structural framework for face, sensory organs, and jaw alignment.

  • Mandible ($1$): Lower jawbone; the only freely movable bone in the skull (articulating at the temporomandibular joint). Features the mandibular condyle, ramus, body, and mental foramen.

  • Maxillae ($2$): Upper jawbones fused at the midline; form the central face, anterior hard palate, and upper tooth sockets.

  • Zygomatic Bones ($2$): Cheekbones; articulate with the temporal bones to form the prominent zygomatic arches.

  • Nasal Bones ($2$): Small rectangular bones forming the structural bridge of the nose.

  • Lacrimal Bones ($2$): Delicate fingernail-sized bones located at the anterior medial aspect of each eye orbit; house lacrimal sacs for tear drainage.

  • Palatine Bones ($2$): Form the posterior portion of the hard palate (roof of the mouth) and floor of the nasal cavity.

  • Inferior Nasal Conchae ($2$): Curved scroll-like bones projecting from lateral nasal walls to swirl inhaled air.

  • Vomer ($1$): Thin, flat plow-shaped bone forming the inferior posterior portion of the nasal septum.

• Cranial Sutures: Immovable fibrous joint lines uniting adjacent skull bones.

  • Coronal Suture: Unites the frontal bone anteriorly with the parietal bones posteriorly.

  • Sagittal Suture: Midline suture uniting the left and right parietal bones superiorly.

  • Lambdoid / Lambdoidal Suture: Unites the parietal and temporal bones with the occipital bone posteriorly.

  • Squamosal Suture: Unites the temporal bone with the parietal bone laterally.

• Sinuses: Mucous membrane-lined, air-filled cavities within skull bones (frontal, ethmoidal, sphenoidal, maxillary) that lighten skull weight and serve as resonating chambers for voice production.

• Fontanels: Temporary areas of fibrous connective tissue between the cranial bones of an infant's skull; commonly called the "soft spots". They allow flexibility of the skull during birth and accommodate rapid brain growth during infancy.

• Hyoid Bone: U-shaped bone located in the anterior neck that supports the tongue and helps elevate the larynx during speaking and swallowing. It is unique because it does not articulate directly with any other bone.

Axial Skeleton

• Axial Skeleton: The central framework of the body. It includes the skull, vertebral column, and thoracic cage and provides support and protection for the brain, spinal cord, heart, and lungs.

Vertebral Column

• Vertebral Column: The central supporting structure of the trunk. It protects the spinal cord and provides support for the head and torso.

• Cervical Vertebrae: Seven vertebrae in the neck.

  • C1, Atlas: Supports the skull.

  • C2, Axis: Allows rotation of the head.

• Thoracic Vertebrae: Twelve vertebrae in the chest region that are associated with the ribs.

• Lumbar Vertebrae: Five vertebrae in the lower back that support much of the body's weight.

• Sacrum: Located at the back of the pelvic girdle and formed from fused vertebrae.

• Coccyx: The tailbone, formed from fused vertebrae.

• Intervertebral Discs: Pads of cartilage between the vertebrae that separate adjacent vertebrae, absorb shock, and allow the vertebral column to bend and twist.

• Basic Vertebral Structures:

  • Body: Main weight-bearing portion of a vertebra.

  • Spinous Process: Posterior projection of a vertebra.

  • Transverse Processes: Lateral projections of a vertebra.

  • Vertebral Foramen: Opening through which the spinal cord passes.

Thoracic Cage

• Thoracic Cage: Bony framework surrounding the thoracic cavity that protects the heart and lungs.

• Sternum: Breastbone located at the front of the chest.

  • Manubrium: Upper portion of the sternum.

  • Body: Large middle portion of the sternum.

  • Xiphoid Process: Small lower portion of the sternum.

• Ribs: Attach to the thoracic vertebrae in the back.

  • True Ribs: Ribs 1–7 that attach directly to the sternum.

  • False Ribs: Ribs 8–12.

  • Floating Ribs: Ribs 11–12 and have no attachment at the front of the body.

• Costal Cartilage: Cartilage that connects the ribs to the sternum and helps form the thoracic cage.

Pathology of the Axial Skeleton

• Temporomandibular Joint Disorders: Disorders affecting the joint associated with movement of the jaw.

• Kyphosis: Abnormal increase in the curvature of the thoracic spine, producing a hunchback or humpback appearance.

• Lordosis: Abnormal increase in the curvature of the lumbar spine, commonly called swayback.

• Scoliosis: Abnormal sideways curvature of the spine.

• Herniated Disc: Herniation of an intervertebral disc.

• Spinal Stenosis: Narrowing of the spinal canal that can put pressure on the spinal cord and nerves.

• Whiplash: Injury to the cervical spine caused by sudden forward-and-backward movement of the head and neck.

Appendicular Skeleton

• Appendicular Skeleton: Includes the limbs and the bony girdles that attach the limbs to the axial skeleton.

• Pectoral Girdle: Connects the upper limbs to the axial skeleton.

  • Scapulae: Shoulder blades.

  • Clavicles: Collarbones.

• Pelvic Girdle: Connects the lower limbs to the axial skeleton.

• Upper Limbs: Include the bones of the arms and hands.

• Lower Limbs: Include the bones of the legs and feet.

Pectoral Girdle and Upper Extremity

• Scapula: Shoulder blade.

  • Spine: Posterior projection of the scapula.

  • Coracoid Process: Projection of the scapula.

  • Acromion: Projection that forms part of the shoulder.

  • Glenoid Fossa: Socket that articulates with the humerus.

• Clavicle: Collarbone that forms part of the pectoral girdle.

• Humerus: Bone of the upper arm.

• Radius: One of the two bones of the forearm.

• Ulna: One of the two bones of the forearm.

  • Olecranon Process: Projection of the ulna that forms the point of the elbow.

• Carpals: Bones of the wrist.

• Metacarpals: Bones of the hand and palm.

• Phalanges: Bones of the fingers.

Carpal Bones

• Scaphoid

• Lunate

• Triquetrum

• Pisiform

• Trapezium

• Trapezoid

• Capitate

• Hamate

Pelvic Girdle and Lower Extremity

• Hip Bones: The two bones that form the pelvic girdle. Each hip bone contains:

  • Ilium: Large upper portion.

  • Ischium: Back and lower portion.

  • Pubis: Front portion.

• Anterior Superior Iliac Spine: Prominent projection on the front portion of the ilium.

• Iliac Crest: Upper border of the ilium.

• Pubic Symphysis: Joint connecting the right and left pubic bones at the front of the pelvis.

• Obturator Foramen: Large opening in the hip bone.

• Sacroiliac Joint: Joint between the sacrum and pelvic girdle.

• Ischial Tuberosity: Large projection of the ischium.

• Acetabulum: Cup-shaped socket that receives the head of the femur.

• Femur: Thigh bone and major bone of the upper leg.

  • Head: Rounded upper end that articulates with the acetabulum.

  • Neck: Narrow region connecting the head to the shaft.

  • Greater Trochanter: Large projection that provides a place for muscle attachment.

• Patella: Kneecap and a sesamoid bone.

• Tibia: Major inner bone of the lower leg.

  • Medial Malleolus: Projection at the ankle.

• Fibula: Outer bone of the lower leg.

  • Lateral Malleolus: Projection at the ankle.

• Tarsals: Bones of the ankle and foot.

• Metatarsals: Bones of the foot.

• Phalanges: Bones of the toes.

• Popliteal Fossa: Depression or space located behind the knee.

Tarsal Bones

• Calcaneus

• Talus

• Navicular

• Medial Cuneiform

• Intermediate Cuneiform

• Lateral Cuneiform

• Cuboid

Joints

• Joint: Location where two or more bones meet.

• Joints can be classified based on the amount of movement they permit.

• Fibrous Joints: Immovable joints.

• Cartilaginous Joints: Slightly movable joints.

• Synovial Joints: Freely movable joints.

Types of Synovial Joints

• Hinge Joint: Allows movement primarily in one direction.

  • Examples: Elbow and knee.

• Ball-and-Socket Joint: Allows movement in many directions.

  • Examples: Hip and shoulder.

• Gliding Joint: Allows bones to slide past one another.

  • Examples: Mid-carpal joints of the hand and mid-tarsal joints of the foot.

• Saddle Joint: Allows movement of the bones in multiple directions and is associated with the thumb.

• Pivot Joint: Allows rotational movement around a central axis.

  • Examples: Forearm and neck.

• Ellipsoidal Joint: Allows movement in multiple directions around two axes.

  • Example: Wrist.

Fractures

• Fracture: A break in a bone.

• Reduction: Returning a broken bone to its proper alignment.

• Immobilization: Preventing movement of an injured bone while it heals.

• Closed Fracture: The broken bone does not penetrate the skin.

• Compound (Open) Fracture: The broken bone penetrates the skin.

• Complete Fracture: The bone is completely broken through.

• Incomplete Fracture: The fracture does not extend through the entire bone.

• Colles' Fracture: Fracture of the wrist.

• Comminuted Fracture: Bone is shattered or crushed into many pieces.

• Greenstick Fracture: One side of the bone breaks while the other side bends. Common in children.

• Spiral Fracture: Fracture with an S-shaped pattern, usually caused by twisting.

• Transverse Fracture: Complete fracture that runs straight across the bone.

Connective Tissues and Joint Injuries

• Cartilage: Tough, flexible connective tissue that absorbs shock and provides smooth surfaces for movement at joints.

• Bursae: Fluid-filled sacs that protect areas from friction during movement.

• Ligaments: Tough connective tissue that connects bone to bone and helps support and limit joint movement.

• Sprain: Injury to a ligament.

• Strain: Injury to a muscle or tendon.

Joint Disorders

• Arthritis: Inflammation of the joints.

• Osteoarthritis: Noninflammatory arthritis involving degeneration of the bones and joints. It particularly affects weight-bearing joints.

• Rheumatoid Arthritis: Chronic inflammatory disorder affecting the joints. It can cause inflammation, swelling, stiffness, pain, and possible deformities caused by changes in cartilage.

• Bursitis: Inflammation of a bursa that can cause pain and impaired movement around the affected joint.

• Carpal Tunnel Syndrome: Pain caused by compression of a nerve as it passes between the bones and tendons of the wrist.

• Gout: Inflammation of the joints caused by excessive uric acid. Excess uric acid can form crystals in the joint, producing inflammation.

Bone Disorders

• Rickets: Condition associated with calcium and vitamin D deficiency during early childhood. It causes abnormal bone development and deformities, including bowed legs.

• Osteomyelitis: Infection and inflammation of the bone and bone marrow. It can be difficult to treat.

• Osteoporosis: Decrease in bone mass that causes bones to become thin and weak and increases the risk of fractures. The spine and pelvis are areas where fractures can occur.

• Talipes: Congenital deformity of the foot, commonly called clubfoot.

• Supernumerary Bone: Extra bone that may occur as an extra finger or toe bone and can be found in newborns.

Bone Tumors and Neoplasms

• Neoplasm: Abnormal growth of tissue that can be benign or malignant.

• Ganglion: Benign cyst located at the end of a long bone. It commonly occurs in the wrist.

• Ewing Sarcoma: Rare and aggressive cancer that forms in bone or the soft tissues surrounding bone. It primarily affects children and young adults, especially between about 10 and 25 years of age. It often occurs in the middle portion of a bone and can affect the hips, ribs, upper arms, and thighs.

• Osteosarcoma: Most common type of primary bone cancer. It mainly affects children and young adults, especially between about 10 and 25 years of age. It often begins at the ends of bones and is particularly associated with the area around the knee.

• Myeloma: Malignant cancer that originates in plasma cells in the bone.