Anatomy & Physiology Study Notes: Axial and Appendicular Skeleton, and Joints

Axial Skeleton

I. Bones, Part I: The Axial Skeleton

The human skeleton is divided into the axial and appendicular skeletons. The axial skeleton forms the central axis of the body and includes the skull, vertebral column, and thoracic cage.

• Axial Skeleton: Composed of the skull, vertebral column, and thoracic cage.

• Appendicular Skeleton: Includes the limbs and girdles.

• Total Bones: 206 bones in the adult human body.

II. The Skull

The skull is the most complex bony structure, protecting the brain and supporting facial structures.

• Cranial Bones: Form the cranial cavity and protect the brain.

• Facial Bones: Form the framework of the face, anchor muscles, and house sensory organs.

Overview of Skull Geography

• Cranial Vault: Superior, lateral, and posterior aspects of the skull.

• Cranial Base: Inferior aspect with three fossae (anterior, middle, posterior).

Cranial Bones

• Eight cranial bones: frontal, parietal (2), temporal (2), occipital, sphenoid, ethmoid.

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

Facial Bones

• Fourteen facial bones: mandible, maxillae (2), zygomatic (2), nasal (2), lacrimal (2), palatine (2), vomer, inferior nasal conchae (2).

Special Parts of the Skull

• Paranasal Sinuses: Air-filled spaces that lighten the skull and enhance voice resonance.

• Orbits: Eye sockets.

• Hyoid Bone: U-shaped bone in the neck, not directly attached to other bones.

III. The Vertebral Column

The vertebral column (spine) supports the trunk, protects the spinal cord, and provides attachment points for ribs and muscles.

Regions and Normal Curvatures

• Five major regions: cervical (7), thoracic (12), lumbar (5), sacral (5 fused), coccygeal (4 fused).

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

Ligaments of the Spine

• Ligamentum flavum connects adjacent vertebrae.

• Anterior and posterior longitudinal ligaments run along the spine.

Intervertebral Discs

• Composed of nucleus pulposus (inner) and annulus fibrosus (outer).

• Act as shock absorbers and allow flexibility.

General Structure of Vertebrae

• Common features: body, vertebral arch, vertebral foramen, spinous process, transverse processes, articular processes.

Regional Vertebral Characteristics

• Cervical: Smallest, have transverse foramina, C1 (atlas) and C2 (axis) are specialized.

• Thoracic: Articulate with ribs, long spinous processes.

• Lumbar: Largest, bear most weight, short thick processes.

• Sacrum: Five fused vertebrae, forms posterior wall of pelvis.

• Coccyx: Four fused vertebrae, forms the tailbone.

IV. The Thoracic Cage

The thoracic cage protects vital organs and supports the shoulder girdles and upper limbs.

• Sternum: Manubrium, body, xiphoid process.

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

V. Disorders of the Axial Skeleton

• Cleft Palate: Failure of the palatine bones to fuse medially.

• Stenosis of the Lumbar Spine: Narrowing of the vertebral canal.

• Abnormal Spinal Curvatures: Scoliosis (lateral), kyphosis (thoracic), lordosis (lumbar).

Appendicular Skeleton

I. The Appendicular Skeleton

The appendicular skeleton consists of the pectoral and pelvic girdles and the bones of the upper and lower limbs.

II. The Pectoral Girdle

• Clavicle: Collarbone; articulates with sternum and scapula.

• Scapula: Shoulder blade; articulates with clavicle and humerus.

III. The Upper Limb

• Arm: Humerus (single bone of the upper arm).

• Forearm: Radius and ulna.

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

IV. The Pelvic Girdle

• Formed by two hip bones (coxal bones) and sacrum.

• Each hip bone: ilium, ischium, pubis.

• Pelvic differences: Female pelvis is wider for childbirth.

V. The Lower Limb

• Thigh: Femur (longest bone in the body).

• Leg: Tibia (medial, weight-bearing) and fibula (lateral, non-weight-bearing).

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

VI. Disorders of the Appendicular Skeleton

• Common disorders: fractures, hip dysplasia, clubfoot.

VII. The Appendicular Skeleton Throughout Life

• At birth, bones are not fully ossified; growth continues through childhood.

• Osteoporosis and limb fractures become more common with age.

Joints

I. Classification of Joints

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

• Structural Classification: Fibrous, cartilaginous, synovial.

• Functional Classification: Synarthroses (immovable), amphiarthroses (slightly movable), diarthroses (freely movable).

II. Fibrous Joints

• Sutures: Immovable joints between skull bones.

• Syndesmoses: Bones connected by ligaments (e.g., distal tibiofibular joint).

• Gomphoses: Peg-in-socket joints (e.g., teeth in alveolar sockets).

III. Cartilaginous Joints

• Synchondroses: Bones united by hyaline cartilage (e.g., epiphyseal plates).

• Symphyses: Bones united by fibrocartilage (e.g., pubic symphysis, intervertebral discs).

IV. Synovial Joints

• Most joints of the body; freely movable.

• Features: articular cartilage, joint cavity, synovial fluid, articular capsule, reinforcing ligaments, nerves, and blood vessels.

• Types: plane, hinge, pivot, condylar, saddle, ball-and-socket.

Movements at Synovial Joints

• Gliding: Flat bone surfaces slide past each other.

• Angular: Flexion, extension, abduction, adduction, circumduction.

• Rotation: Bone turns around its own long axis.

• Special Movements: Supination/pronation, dorsiflexion/plantar flexion, inversion/eversion, protraction/retraction, elevation/depression, opposition.

Factors Influencing Stability of Synovial Joints

• Articular surface shape, ligament number and location, muscle tone.

Selected Synovial Joints

• Knee Joint: Largest and most complex; primarily a hinge joint.

V. Disorders of Joints

• Joint Injuries: Sprains, dislocations, torn cartilage.

• Inflammatory and Degenerative Conditions: Bursitis, tendonitis, arthritis (osteoarthritis, rheumatoid arthritis, gout), Lyme disease.

Table: Major Types of Joints

Structural Type	Functional Type	Examples
Fibrous	Synarthrosis/Amphiarthrosis	Sutures, syndesmoses, gomphoses
Cartilaginous	Synarthrosis/Amphiarthrosis	Synchondroses, symphyses
Synovial	Diarthrosis	Knee, shoulder, hip, elbow

Additional info: These notes are based on standard textbook content for Anatomy & Physiology, with logical groupings and expanded explanations for clarity and completeness.