Comprehensive Study Guide: The Human Skeleton and Articulations

The Human Skeleton: Axial and Appendicular Divisions

Overview of the Skeleton

The human skeleton is divided into two main parts: the axial skeleton and the appendicular skeleton. The axial skeleton forms the central axis of the body, while the appendicular skeleton consists of the limbs and girdles that attach them to the axial skeleton.

• Axial Skeleton: Skull, vertebral column, and bony thorax (rib cage)

• Appendicular Skeleton: Pectoral girdle, upper limbs, pelvic girdle, and lower limbs

Axial Skeleton

Skull

The skull protects the brain and forms the structure of the face. It consists of the cranium and facial bones.

• Cranium: 8 flat bones (frontal, 2 parietal, 2 temporal, occipital, sphenoid, ethmoid)

• Facial Bones: 14 bones (mandible, 2 maxillae, 2 palatine, 2 zygomatic, 2 lacrimal, 2 nasal, vomer, 2 inferior nasal conchae)

Key Features:

• Calvaria: Dome-like upper portion of the skull

• Cranial Floor: Contains foramina for nerves and blood vessels; divided into anterior, middle, and posterior fossae

• Sutures: Immovable joints between skull bones (coronal, sagittal, lambdoidal, squamous, occipitomastoid)

• Foramina: Openings for passage of cranial nerves and vessels (e.g., foramen magnum, optic foramina)

• Processes and Regions: Zygomatic process, mastoid process, styloid process, mandibular fossa, etc.

Clinical Notes:

• Mastoid process: Can become infected (mastoiditis) after untreated middle ear infection

• Squamous region of temporal bone: Thin and easily fractured

Special Bones:

• Hyoid bone: Only bone that does not articulate with another bone; supports the tongue

Orbit of the Eye: Formed by 7 bones: frontal, sphenoid, zygomatic, maxilla, palatine, lacrimal, ethmoid

Paranasal Sinuses: Found in frontal, sphenoid, ethmoid, and maxilla bones

Nasal Septum: Formed by vomer and perpendicular plate of ethmoid

Hard Palate: Formed by palatine processes of maxillae and palatine bones

Vertebral Column

The vertebral column supports the body and protects the spinal cord. It consists of 24 vertebrae, the sacrum, and the coccyx.

• Vertebrae: 7 cervical, 12 thoracic, 5 lumbar

• Sacrum: 5 fused vertebrae

• Coccyx: 3-5 fused vertebrae (tailbone)

Structure of a Typical Vertebra:

• Body, vertebral arch, vertebral foramen, spinous process, transverse processes, pedicle, lamina, superior and inferior articular processes, intervertebral foramina

Distinguishing Features:

• Cervical: Transverse foramina, bifid spinous processes (except C7), atlas (C1) and axis (C2) specialized for head movement

• Thoracic: Heart-shaped body, long inferiorly pointing spinous process, facets for rib articulation

• Lumbar: Large, massive body, short and thick spinous process

Spinal Curvatures:

• Primary (present at birth): Thoracic and sacral

• Secondary (develop after birth): Cervical (when infant lifts head), lumbar (when infant begins to walk)

Intervertebral Discs:

• Annulus fibrosus: Outer fibrocartilage

• Nucleus pulposus: Inner gelatinous core

• Herniated disc: Nucleus pulposus protrudes through annulus fibrosus (also called slipped or ruptured disc)

Clinical Note: Spinal taps are performed below L1-L2 in adults to avoid spinal cord injury.

Bony Thorax (Thoracic Cage)

The bony thorax protects the heart and lungs and supports the shoulder girdles and upper limbs.

• Sternum: Manubrium, body, xiphoid process; landmarks include jugular notch, sternal angle, xiphisternal joint

• Ribs: 12 pairs

  • True ribs (vertebrosternal): 1-7, attach directly to sternum

  • False ribs: 8-12, attach indirectly or not at all

    • Vertebrochondral: 8-10, attach to cartilage of rib 7

    • Floating (vertebral): 11-12, no anterior attachment

• Thoracic vertebrae: Articulate with ribs

Rib Structure: Head, neck, shaft, angle, tubercle, costal groove (contains intercostal vessels and nerves)

Appendicular Skeleton

Pectoral (Shoulder) Girdle

The pectoral girdle attaches the upper limbs to the trunk and allows for a wide range of motion.

• Clavicle: S-shaped bone; lateral (acromial) and medial (sternal) ends

• Scapula: Flat, triangular bone with key features:

  • Spine, acromion process, coracoid process, glenoid cavity, supraspinous fossa, infraspinous fossa, subscapular fossa, axillary and vertebral borders, inferior angle

Upper Limb

• Arm (Brachium): Humerus

  • Head, greater and lesser tubercles, trochlea, capitulum, medial and lateral epicondyles, olecranon fossa

• Forearm (Antebrachium): Radius and ulna

  • Radius: Head, neck, radial tuberosity, styloid process (lateral wrist bone)

  • Ulna: Olecranon process (elbow), trochlear notch, styloid process (medial wrist bone)

• Wrist: 8 carpal bones in two rows

• Hand: 5 metacarpals, 14 phalanges (3 per finger, 2 per thumb)

Pelvic (Hip) Girdle and Bony Pelvis

The pelvic girdle supports the weight of the upper body and protects pelvic organs.

• Pelvic Girdle: Two coxal (hip) bones, each formed by fusion of ilium, ischium, and pubis

• Bony Pelvis: Two coxal bones + sacrum + coccyx

• Key Landmarks: Iliac crest, anterior superior iliac spine, ischial tuberosity, ischial spine, obturator foramen, acetabulum, greater and lesser sciatic notches, pubic symphysis

• Pelvic Divisions:

  • False pelvis: Above iliopectineal line; part of abdomen

  • True pelvis: Below iliopectineal line; forms birth canal

  • Pelvic inlet (brim): Superior margin of true pelvis

  • Pelvic outlet: Inferior margin of true pelvis

• Sex Differences: Female pelvis is wider and shallower for childbirth

Lower Limb

• Thigh: Femur

  • Head, fovea capitis, neck, greater and lesser trochanters, lateral and medial epicondyles, patellar surface, intercondylar fossa

• Leg: Tibia and fibula

  • Tibia: Medial and lateral condyles, tibial tuberosity, medial malleolus (inner ankle bone)

  • Fibula: Head, lateral malleolus (outer ankle bone)

• Foot: 7 tarsals (calcaneus, talus are largest), 5 metatarsals, 14 phalanges

• Arches: Medial and lateral longitudinal, transverse

The Fetal Skeleton

Fetal Skull

• Fontanels: Soft spots (anterior, posterior, sphenoidal, mastoid) that allow for brain growth and passage through birth canal

• Ossification Centers: Sites where bone formation begins

• Frontal and Mandibular Bones: Paired in fetus, fuse to become single bones in adult

Fetal Skeleton Features

• Spinal Curvatures: Only primary (thoracic and sacral) present at birth; secondary (cervical and lumbar) develop after birth

• Bone Development: Many bones (e.g., vertebrae, sternum, patellae, coxal bones, carpals, tarsals) are not fully ossified at birth

• Rib Cage: More flexible in fetus

Bone Markings of the Appendicular Skeleton

Palpable Bone Markings

• Scapular spine, acromion process, olecranon process, medial epicondyle of humerus, styloid process of ulna, tibial tuberosity, medial and lateral malleolus, iliac crest, anterior superior iliac spine, ischial tuberosity

Note: Anatomical terms are preferred over common terms (e.g., 'medial malleolus' instead of 'inner ankle bone').

Miscellaneous Questions on Extremities

• Palm: Formed by metacarpals

• Hand: Metacarpals and phalanges

• Wrist: Carpals

• Ankle: Tarsals

• Heel: Calcaneus

• "Wrist bone": Styloid process of radius or ulna

• "Elbow bone": Olecranon process of ulna

• "Funny bone": Medial epicondyle of humerus

• "Ankle bone, inside": Medial malleolus of tibia

• "Ankle bone, outside": Lateral malleolus of fibula

• "Shoulder blades": Scapulae

• "Ball" of the foot: Head of first metatarsal

• Lateral forearm bone: Radius

• Elbow joint: Formed by ulna and humerus (trochlear notch of ulna with trochlea of humerus); anatomical name: humeroulnar joint

• Radius articulates proximally with: Humerus and ulna

• Pronation: Radius crosses over ulna

• Leg bones articulating with femur: Tibia

• Function of fibula: Muscle attachment, stabilizes ankle

• Knee joint: Femur (condyles) with tibia (condyles); anatomical name: tibiofemoral joint

Articulations (Joints) and Body Movements

Classification of Joints

Joints (articulations) are classified by structure and function. The main types are synovial, cartilaginous, and fibrous joints.

Joint Type	Specific Joint	Range of Movement	Specific Movement
Synovial, pivot	Atlanto-axial (C1, C2)	Uniaxial	Rotation
Synovial, hinge	Elbow (humeroulnar)	Uniaxial	Flexion/Extension
Synovial, ball-and-socket	Shoulder (glenohumeral)	Multiaxial	Flexion/Extension, Abduction/Adduction, Rotation
Cartilaginous, symphysis	Pubic symphysis	Amphiarthrotic	Slight movement
Fibrous, suture	Cranial sutures	Synarthrotic	No movement
Fibrous, syndesmosis	Distal tibiofibular joint	Amphiarthrotic	Slight movement
Additional info: ...	Additional info: ...	Additional info: ...	Additional info: ...

Features of Synovial Joints

• Articular cartilage (hyaline cartilage)

• Joint (articular) cavity

• Articular capsule

• Synovial fluid

• Reinforcing ligaments

Special Structures: Menisci (articular discs, fibrocartilage), bursae (fluid-filled sacs)

Joint Models and Specimens

• Shoulder Joint: Humerus, scapula (spine, acromion, coracoid, fossae), clavicle, tendons, ligaments

• Knee Joint: Femur, tibia, fibula, articular cartilage, menisci, cruciate and collateral ligaments, patella, quadriceps tendon, patellar ligament

• Hip Joint: Coxal bone, femur (head, ligamentum teres), acetabular labrum, synovial bursa

Three "C's" of the Knee Joint: Cruciate ligaments, collateral ligaments, cartilage (menisci)

Long Bone Structure Review: Diaphysis, epiphyses, compact and spongy bone, epiphyseal line (remnant of growth plate), red and yellow marrow, trabeculae, periosteum (dense irregular connective tissue), endosteum

Key Definitions and Concepts

• Foramen: Opening in bone for nerves/vessels

• Process: Projection for muscle/ligament attachment

• Condyle: Rounded articular projection

• Epicondyle: Raised area above a condyle

• Fossa: Shallow depression

• Trochanter: Large, blunt projection (femur)

• Tuberosity: Large, rounded projection

• Articulation: Joint between bones

• Synovial Joint: Freely movable joint with synovial cavity

• Cartilaginous Joint: Bones joined by cartilage

• Fibrous Joint: Bones joined by fibrous tissue

Additional info:

• Some content (e.g., fetal skeleton, clinical notes) was expanded for clarity and completeness.

• Table entries for joint types were inferred and expanded for academic context.

• Definitions and examples were added to ensure the guide is self-contained and exam-ready.