Bones, Skeleton, and Joints: Study Guide for Chapters 6–9

Chapter 6: Bones and Skeletal Tissues

Types of Cartilage

Cartilage is a resilient and flexible connective tissue found throughout the body. It serves as a precursor to bone and provides support in various structures.

• Hyaline Cartilage: Most abundant; provides support with flexibility. Found in articular surfaces, costal cartilages, nose, trachea, and larynx.

• Elastic Cartilage: Contains more elastic fibers; maintains shape and flexibility. Found in external ear and epiglottis.

• Fibrocartilage: Highly compressible; resists tension. Found in intervertebral discs, pubic symphysis, and menisci.

• Example: The meniscus in the knee is fibrocartilage, providing shock absorption.

Growth of Cartilage

Cartilage grows by two mechanisms:

• Appositional Growth: New layers added to the surface by chondroblasts.

• Interstitial Growth: Chondrocytes divide and secrete new matrix within the cartilage.

Cells Related to Bone Maintenance

Bones are maintained by specialized cells:

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

• Osteocytes: Mature bone cells; maintain bone tissue.

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

Components of a Generic Bone

Bones have several structural components:

• Diaphysis: Shaft of a long bone.

• Epiphysis: Ends of a long bone.

• Metaphysis: Region between diaphysis and epiphysis.

• Medullary Cavity: Central cavity containing bone marrow.

• Periosteum: Outer fibrous covering.

• Endosteum: Inner lining of the medullary cavity.

Bone Markings

Bone markings are anatomical features that serve as attachment points or passageways.

Type	Description	Example
Process	Projection for muscle attachment	Spinous process of vertebra
Foramen	Opening for blood vessels/nerves	Foramen magnum in skull
Fossa	Shallow depression	Olecranon fossa of humerus
Condyle	Rounded articular surface	Femoral condyles
Tuberosity	Large, rough projection	Tibial tuberosity

Microscopic Structure of Compact Bone

Compact bone is organized into structural units called osteons (Haversian systems).

• Osteon: Cylindrical unit with concentric lamellae.

• Central Canal: Contains blood vessels and nerves.

• Lacunae: Spaces housing osteocytes.

• Canaliculi: Tiny channels connecting lacunae.

Bone Formation (Ossification)

Bone develops by two processes:

• Intramembranous Ossification: Direct formation from mesenchyme; forms flat bones.

• Endochondral Ossification: Bone replaces hyaline cartilage; forms most bones.

Epiphyseal Plate Anatomy

The epiphyseal plate is a region of growing cartilage in long bones, responsible for lengthwise growth.

• Zones: Resting, proliferation, hypertrophy, calcification, ossification.

• Example: Growth in height during adolescence is due to activity at the epiphyseal plate.

Chapter 7: Bones, Part 1: The Axial Skeleton

Axial vs. Appendicular Skeleton

The skeleton is divided into two main regions:

• Axial Skeleton: Skull, vertebral column, thoracic cage.

• Appendicular Skeleton: Limbs and girdles.

Skull: Cranium and Facial Bones

The skull protects the brain and forms the structure of the face.

• Cranial Bones: Enclose the brain (e.g., frontal, parietal, temporal, occipital).

• Facial Bones: Form the face (e.g., maxilla, mandible, zygomatic).

• Sutures: Immovable joints between skull bones (e.g., coronal, sagittal, lambdoid).

Bone	Type	Location
Frontal	Cranial	Forehead
Maxilla	Facial	Upper jaw
Mandible	Facial	Lower jaw
Parietal	Cranial	Top/sides of skull

Vertebral Column: Components and Curvatures

The vertebral column supports the body and protects the spinal cord.

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

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

• Example: The lumbar curvature helps absorb shock during walking.

Ligaments of the Spine

Ligaments stabilize the vertebral column.

• Anterior Longitudinal Ligament: Prevents hyperextension.

• Posterior Longitudinal Ligament: Prevents hyperflexion.

• Ligamentum Flavum: Connects adjacent vertebrae.

Structure of a Typical Vertebra

Vertebrae share common features:

• Body: Weight-bearing portion.

• Vertebral Arch: Forms vertebral foramen.

• Processes: Spinous, transverse, articular.

Regional Vertebral Differences

Vertebrae differ by region:

• Cervical: Small body, transverse foramina.

• Thoracic: Larger body, facets for ribs.

• Lumbar: Largest body, short spinous process.

Thoracic Cage

The thoracic cage protects vital organs and supports respiration.

• Sternum: Manubrium, body, xiphoid process.

• Ribs: 12 pairs; true (1–7), false (8–12), floating (11–12).

Abnormal Spinal Curvatures

Spinal curvatures can become abnormal:

• Scoliosis: Lateral curvature.

• Kyphosis: Excessive thoracic curvature.

• Lordosis: Excessive lumbar curvature.

Chapter 8: Bones, Part 2: The Appendicular Skeleton

Girdles: Pectoral and Pelvic

Girdles attach limbs to the axial skeleton.

• Pectoral Girdle: Clavicle and scapula; attaches upper limb.

• Pelvic Girdle: Ilium, ischium, pubis; attaches lower limb.

Upper Limb Bones and Landmarks

The upper limb consists of the arm, forearm, and hand.

• Arm: Humerus; landmarks include head, greater/lesser tubercle.

• Forearm: Radius and ulna; landmarks include olecranon, styloid process.

• Hand: Carpals (8), metacarpals (5), phalanges (14).

Lower Limb Bones and Landmarks

The lower limb consists of the thigh, leg, and foot.

• Thigh: Femur; landmarks include head, neck, greater/lesser trochanter.

• Leg: Tibia and fibula; landmarks include medial/lateral malleolus.

• Foot: Tarsals (7), metatarsals (5), phalanges (14).

Arches of the Foot

The foot has longitudinal and transverse arches for weight distribution and shock absorption.

• Medial Longitudinal Arch: Highest arch; supports most weight.

• Lateral Longitudinal Arch: Lower arch; balances the foot.

• Transverse Arch: Runs across the foot.

Chapter 9: Joints

Definition and Classification of Joints

Joints (articulations) are sites where two or more bones meet. They are classified by structure and function.

Structural Type	Description	Example
Fibrous	Connected by fibrous tissue; no cavity	Sutures in skull
Cartilaginous	Connected by cartilage	Intervertebral discs
Synovial	Joint cavity with synovial fluid	Shoulder, knee

Anatomical Terminology of Joint Movements

Movements at joints are described by specific terms:

• Flexion: Decreases angle between bones.

• Extension: Increases angle between bones.

• Abduction: Moves limb away from midline.

• Adduction: Moves limb toward midline.

• Rotation: Bone turns around its axis.

Ligaments and Tendons in Major Joints

Ligaments and tendons stabilize and support joints.

• Ligaments: Connect bone to bone; provide stability.

• Tendons: Connect muscle to bone; facilitate movement.

• Example: The anterior cruciate ligament (ACL) stabilizes the knee.

Synovial Joints: Structure and Types

Synovial joints are freely movable and have a joint cavity.

• General Structure: Articular cartilage, joint cavity, synovial membrane, ligaments.

• Types: Plane, hinge, pivot, condyloid, saddle, ball-and-socket.

Type	Movement	Example
Hinge	Flexion/extension	Elbow
Ball-and-socket	Multiaxial	Shoulder, hip
Pivot	Rotation	Atlas/axis
Saddle	Thumb movement	Carpometacarpal joint

Factors Influencing Stability of Synovial Joints

Joint stability depends on:

• Shape of articular surfaces

• Ligament number and location

• Muscle tone

Major Joints: Shoulder, Elbow, Hip, Knee, Ankle

Each major joint has unique features:

• Shoulder: Ball-and-socket; greatest range of motion.

• Elbow: Hinge; stable due to ligaments.

• Hip: Ball-and-socket; deep socket for stability.

• Knee: Largest joint; complex with menisci and ligaments.

• Ankle: Hinge; stabilized by ligaments.

Clinical Application: Herniated Disc

A herniated disc occurs when the nucleus pulposus protrudes through the annulus fibrosus, compressing spinal nerves.

• Symptoms: Pain, numbness, weakness.

• Treatment: Physical therapy, surgery.