Bones, Skeletal System, and Articulations: Study Guide for ANP Students

Chapter 6 – Bones and Bone Tissue

Functions of the Skeletal System

• Support: Provides structural framework for the body.

• Protection: Shields vital organs (e.g., skull protects brain, ribs protect heart and lungs).

• Movement: Serves as levers for muscles to act upon.

• Mineral Storage: Reservoir for calcium and phosphate.

• Blood Cell Production: Hematopoiesis occurs in red bone marrow.

• Fat Storage: Yellow bone marrow stores triglycerides.

Types of Bone Tissue

• Compact Bone: Dense, strong outer layer; provides strength and support.

• Spongy Bone: Porous, lighter; contains trabeculae and spaces for marrow.

Classification of Bones by Shape

• Long Bones: Longer than wide (e.g., femur, humerus).

• Short Bones: Cube-shaped (e.g., carpals, tarsals).

• Flat Bones: Thin, often curved (e.g., sternum, skull bones).

• Irregular Bones: Complex shapes (e.g., vertebrae, pelvis).

• Sesamoid Bones: Embedded in tendons (e.g., patella).

Gross Structure of a Long Bone

• Diaphysis: Shaft of the bone; contains medullary cavity.

• Epiphysis: Ends of the bone; contains spongy bone and red marrow.

• Epiphyseal Plate: Growth plate; site of lengthwise growth in children.

• Epiphyseal Line: Remnant of growth plate in adults.

• Articular Cartilage: Hyaline cartilage covering joint surfaces.

• Periosteum: Dense connective tissue covering bone; contains osteogenic cells.

• Endosteum: Thin membrane lining medullary cavity.

• Medullary Cavity: Central cavity containing yellow marrow in adults.

Blood Supply and Innervation of Bone

• Bones are highly vascularized; nutrient arteries enter through nutrient foramina.

• Nerves accompany blood vessels, providing sensation and regulation.

Bone Matrix Composition

• Inorganic Component: Hydroxyapatite (calcium phosphate crystals) provides hardness.

• Organic Component: Collagen fibers and ground substance provide flexibility and tensile strength.

Microscopic Structure of Bone

• Osteon (Haversian System): Structural unit of compact bone.

• Central Canal: Contains blood vessels and nerves.

• Concentric Lamellae: Rings of bone matrix around central canal.

• Lacunae: Small spaces housing osteocytes.

• Canaliculi: Tiny canals connecting lacunae for nutrient/waste exchange.

• Interstitial Lamellae: Fill spaces between osteons.

• Perforating (Volkmann's) Canals: Connect central canals transversely.

Spongy Bone Structure

• Trabeculae: Lattice-like network of bone tissue.

• Spaces: Filled with bone marrow.

• Diploe: Spongy bone in flat bones (e.g., cranial bones).

Bone Marrow

• Red Marrow: Site of hematopoiesis; found in spongy bone of children and some adult bones (e.g., pelvis, sternum).

• Yellow Marrow: Fat storage; replaces red marrow in long bones of adults.

Bone Cells

• Osteoprogenitor Cells: Stem cells that differentiate into osteoblasts.

• Osteoblasts: Bone-forming cells; secrete bone matrix.

• Osteocytes: Mature bone cells; maintain bone tissue.

• Osteoclasts: Bone-resorbing cells; break down bone matrix.

Primary vs. Secondary Bone

• Primary (Woven) Bone: First bone formed; irregular collagen arrangement.

• Secondary (Lamellar) Bone: Mature bone; organized collagen fibers.

Bone Formation (Ossification)

• Intramembranous Ossification: Bone develops from mesenchymal tissue (e.g., flat bones of skull).

• Endochondral Ossification: Bone forms by replacing hyaline cartilage (e.g., long bones, most bones of body).

Bone Growth

• Longitudinal Growth: Occurs at epiphyseal plates; increases length.

• Appositional Growth: Increases bone diameter by adding new bone to surface.

Bone Remodeling

• Continuous process of bone formation and resorption.

• Maintains bone strength and mineral homeostasis.

Hormonal Regulation of Bone

• Calcitonin: Lowers blood calcium by inhibiting osteoclasts.

• Parathyroid Hormone (PTH): Increases blood calcium by stimulating osteoclasts.

• Vitamin D (Calcitriol): Promotes calcium absorption in intestines.

• Growth Hormone: Stimulates bone growth.

• Thyroid Hormone: Regulates bone growth and development.

• Sex Hormones: Promote bone growth and epiphyseal plate closure.

Mechanical Stress and Bone

• Weight-bearing exercise stimulates bone formation and increases bone density.

Chapter 7 – The Skeletal System

Structural Divisions of the Skeleton

• Axial Skeleton: Skull, vertebral column, rib cage; supports and protects organs.

• Appendicular Skeleton: Limbs and girdles; enables movement.

Bone Markings

• Projections: Sites of muscle and ligament attachment (e.g., tuberosity, crest).

• Surfaces: Form joints (e.g., condyle, facet).

• Depressions/Openings: Passage for vessels/nerves (e.g., foramen, fossa).

Cartilage in the Skeleton

• Hyaline Cartilage: Most abundant; covers articular surfaces.

• Fibrocartilage: Intervertebral discs, pubic symphysis.

• Elastic Cartilage: External ear, epiglottis.

Major Bones of the Axial Skeleton

• Skull (cranial and facial bones)

• Vertebral column (cervical, thoracic, lumbar, sacrum, coccyx)

• Thoracic cage (ribs, sternum)

Major Bones of the Appendicular Skeleton

• Pectoral girdle (clavicle, scapula)

• Upper limbs (humerus, radius, ulna, carpals, metacarpals, phalanges)

• Pelvic girdle (hip bones)

• Lower limbs (femur, tibia, fibula, tarsals, metatarsals, phalanges)

Cranial and Facial Bones

• Cranial Bones: Enclose brain; include frontal, parietal, temporal, occipital, sphenoid, ethmoid.

• Facial Bones: Form face; include maxilla, mandible, zygomatic, nasal, lacrimal, palatine, inferior nasal concha, vomer.

• Hyoid Bone: Supports tongue; not attached to other bones.

Special Features

• Orbit: Eye socket formed by several bones.

• Nasal Cavity: Formed by ethmoid, vomer, and others.

• Paranasal Sinuses: Air-filled spaces in skull bones; lighten skull, resonate voice.

Vertebral Column

• Regions: Cervical (7), thoracic (12), lumbar (5), sacrum, coccyx.

• Curves: Cervical and lumbar (concave), thoracic and sacral (convex).

• Vertebral Foramen: Contains spinal cord.

• Intervertebral Foramina: Exit for spinal nerves.

• Intervertebral Discs: Annulus fibrosus (outer), nucleus pulposus (inner).

Joints of the Skull and Vertebral Column

• Atlanto-occipital Joint: Nodding "yes" (occipital condyles and atlas).

• Atlanto-axial Joint: Shaking "no" (atlas and axis).

Pelvic Girdle and Lower Limb

• Male vs. Female Pelvis: Female pelvis is wider, shallower for childbirth.

• Thigh, Leg, Ankle, Foot: Femur, tibia, fibula, tarsals, metatarsals, phalanges.

• Arches of the Foot: Medial, lateral, and transverse arches for weight distribution.

Chapter 8 – The Skeletal System: Articulations

Definition and Classification of Joints

• Joint (Articulation): Site where two or more bones meet.

• Structural Classification:

  • Fibrous Joints: Bones joined by dense connective tissue; immovable or slightly movable (e.g., sutures, syndesmoses, gomphoses).

  • Cartilaginous Joints: Bones joined by cartilage; no joint cavity (e.g., synchondroses, symphyses).

  • Synovial Joints: Bones separated by fluid-filled cavity; freely movable.

• Functional Classification:

  • Synarthrosis: Immovable joint.

  • Amphiarthrosis: Slightly movable joint.

  • Diarthrosis: Freely movable joint.

Synovial Joint Structure

• Articular Cartilage: Hyaline cartilage covering bone ends.

• Joint (Articular) Capsule: Encloses joint cavity; fibrous layer and synovial membrane.

• Synovial Fluid: Lubricates, nourishes cartilage, absorbs shock.

• Ligaments: Reinforce joint.

• Nerves and Blood Vessels: Supply joint.

Accessory Structures of Synovial Joints

• Bursae: Fluid-filled sacs reducing friction.

• Tendon Sheaths: Elongated bursae around tendons.

• Fat Pads: Cushion and protect joint.

Types of Synovial Joints and Movements

• Plane: Gliding movements (e.g., intercarpal joints).

• Hinge: Flexion/extension (e.g., elbow).

• Pivot: Rotation (e.g., proximal radioulnar joint).

• Condyloid: Flexion/extension, abduction/adduction (e.g., wrist).

• Saddle: Similar to condyloid but greater movement (e.g., thumb).

• Ball-and-Socket: All axes, most mobile (e.g., shoulder, hip).

Movements at Synovial Joints

• Flexion/Extension: Decrease/increase angle between bones.

• Abduction/Adduction: Movement away/toward midline.

• Circumduction: Circular movement.

• Pronation/Supination: Rotation of forearm.

• Depression/Elevation: Lowering/raising a body part.

• Dorsiflexion/Plantarflexion: Upward/downward movement of foot.

• Eversion/Inversion: Turning sole of foot outward/inward.

• Protraction/Retraction: Anterior/posterior movement in transverse plane.

• Opposition: Thumb movement to touch fingers.

Examples of Specific Joints

• Elbow Joint: Includes annular, medial collateral, ulnar collateral, and radial collateral ligaments.

• Shoulder (Glenohumeral) Joint: Highly mobile, less stable; susceptible to dislocation.

• Hip Joint: Acetabular labrum, articular capsule, ligament of head of femur, iliofemoral, ischiofemoral, and pubofemoral ligaments provide stability.

• Knee Joint: Patellar ligament, lateral and medial menisci, anterior and posterior cruciate ligaments (ACL, PCL).

• TMJ (Temporomandibular Joint): Allows opening/closing, protrusion/retraction, side-to-side movement.

Stability vs. Mobility

• Shoulder joint: More mobile, less stable.

• Hip joint: Less mobile, more stable.

Rotator Cuff Muscles

• Supraspinatus, infraspinatus, teres minor, subscapularis strengthen the shoulder joint.

Table: Comparison of Joint Types

Joint Type	Structural Features	Movement	Example
Fibrous	Dense connective tissue, no cavity	Immovable/slightly movable	Sutures of skull
Cartilaginous	Cartilage, no cavity	Slightly movable	Intervertebral discs
Synovial	Joint cavity, synovial fluid	Freely movable	Shoulder, knee

Key Equations

• Calcium Homeostasis:

$\text{PTH} \uparrow \Rightarrow \text{Osteoclast activity} \uparrow \Rightarrow [Ca^{2+}]_{blood} \uparrow$

$\text{Calcitonin} \uparrow \Rightarrow \text{Osteoclast activity} \downarrow \Rightarrow [Ca^{2+}]_{blood} \downarrow$

• Bone Remodeling:

$\text{Bone Mass} = \text{Bone Formation} - \text{Bone Resorption}$

Additional info: This guide expands on the learning objectives by providing definitions, examples, and context for each topic, suitable for exam preparation in Anatomy and Physiology courses.