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).

Cranial Features

• Calvaria: Dome-like upper portion (skullcap).

• Cranial Floor: Contains foramina (openings for nerves and blood vessels) and fossae (depressions for brain regions).

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

Key Cranial Bones and Landmarks

• Frontal Bone: Forehead region.

• Parietal Bones: Sides and roof of the cranium.

• Temporal Bones: Four regions: squamous (thin, easily fractured), petrous (houses inner/middle ear), tympanic (external ear), mastoid (mastoid process, site of mastoiditis).

• Occipital Bone: Contains foramen magnum (brain-spinal cord continuity), occipital condyles (articulate with atlas).

• Sphenoid Bone: "Keystone" of the cranium; contains sella turcica (pituitary gland), optic foramina, superior orbital fissure.

• Ethmoid Bone: Crista galli, cribriform plate (olfactory foramina), perpendicular plate (nasal septum), superior/middle nasal conchae.

Facial Bones and Landmarks

• Mandible: Only movable skull bone; features body, ramus, mandibular condyle (TMJ), alveoli (tooth sockets), mandibular symphysis.

• Maxillae: "Keystone" of the face; forms upper jaw, alveoli, palatine processes (hard palate).

• Other Facial Bones: Palatine, zygomatic, lacrimal, nasal, vomer (nasal septum), inferior nasal conchae.

• Hyoid Bone: Not part of the skull; only bone that does not articulate with another bone.

Orbit and Sinuses

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

• Paranasal Sinuses: Found in frontal, sphenoid, ethmoid, and maxillary 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: Cervical (7), thoracic (12), lumbar (5).

• 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/inferior articular processes, intervertebral foramina (for spinal nerves).

Regional Differences

• Cervical: Transverse foramina, bifid spinous processes (except C7), atlas (C1, no body/spinous process), axis (C2, dens/odontoid process), C7 (vertebra prominens).

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

• Lumbar: Massive body, short/hatchet-shaped spinous process.

Spinal Curvatures

• Primary Curvatures: Thoracic and sacral (present at birth).

• Secondary Curvatures: Cervical and lumbar (develop after birth).

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).

Sacrum and Coccyx

• Sacrum: Median sacral crest, sacral foramina, sacral canal, sacral hiatus (site for saddle-block anesthesia), sacral promontory (obstetric landmark).

• Coccyx: Remnant of tail, 3-5 fused vertebrae.

Bony Thorax (Thoracic Cage)

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

• Ribs: 12 pairs; structure includes head, neck, shaft, angle, tubercle, costal groove (houses nerves/vessels).

• Types of Ribs:

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

  • False (vertebrochondral): 8-10, attach via cartilage.

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

Appendicular Skeleton

Pectoral (Shoulder) Girdle

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

• Scapula: Borders (axillary, vertebral), inferior angle, spine, infraspinous/supraspinous/subscapular fossae, coracoid process, acromion process, glenoid cavity.

Upper Limb

• Arm (Humerus): Head, greater/lesser tubercles, trochlea, capitulum, medial/lateral epicondyles, olecranon fossa.

• Forearm:

  • 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 (two rows of four).

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

Pelvic (Hip) Girdle and Bony Pelvis

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

• Bony Pelvis: Two coxal bones + sacrum + coccyx.

• Landmarks: Iliac crest, anterior superior iliac spine, arcuate lines, ischial tuberosity, ischial spine, obturator foramen, acetabulum, greater/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, bounded by coccyx, ischial tuberosities/spines, pubic arches.

• Comparison of Male and Female Pelves: Female pelvis is wider, shallower, and has a larger pelvic inlet/outlet for childbirth.

Lower Limb

• Thigh (Femur): Head, fovea capitis, neck, greater/lesser trochanters, lateral/medial epicondyles, patellar surface, intercondylar fossa.

• Leg:

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

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

• Foot: 7 tarsals (calcaneus, talus largest), 5 metatarsals, 14 phalanges, medial/lateral longitudinal arches, transverse arch.

The Fetal Skeleton

Fetal Skull

• Fontanels: Soft spots (anterior, posterior, sphenoidal, mastoid) allowing skull flexibility during birth and brain growth.

• 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, sacral) present at birth; secondary (cervical, lumbar) develop after birth (cervical at ~3 months, lumbar at ~12 months).

• Bone Development: Many bones (vertebrae, sternum, patellae, coxal bones, carpals, tarsals, rib cage) are not fully ossified or fused in the fetus compared to the adult.

Bone Markings of the Appendicular Skeleton

• Palpable landmarks: scapular spine, acromion process, olecranon process, medial epicondyle, styloid process of ulna, tibial tuberosity, medial/lateral malleolus, iliac crest, anterior superior iliac spine, ischial tuberosity.

• Common terms (e.g., "wrist bone", "ankle bone") may not accurately reflect anatomical structure; use anatomical terms for precision.

Extremities: Miscellaneous Questions

• Palm: Metacarpals

• Hand: Metacarpals and phalanges

• Wrist: Carpals

• Ankle: Tarsals

• Heel: Calcaneus

• "Wrist bone": Styloid process of radius/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; during pronation, radius crosses over ulna.

• Leg bones: Tibia articulates with femur; fibula provides lateral stability.

• Knee joint: Formed by femoral and tibial condyles; anatomical name: tibiofemoral joint.

Articulations (Joints) and Body Movements

Joints (articulations) are classified by structure and function. Movements depend on joint type and participating bones.

Joint Type	Specific Joint	Range of Movement at Joint	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
Additional info: ...	Other synovial, cartilaginous, and fibrous joints can be added as needed.

Structural Features of Synovial Joints

• Articular cartilage

• Joint (articular) capsule

• Synovial membrane

• Synovial fluid

• Ligaments

Knee Joint: The 3 "C's"

• Cartilage: Articular cartilage and menisci (fibrocartilage discs)

• Collateral ligaments: Medial (tibial) and lateral (fibular)

• Cruciate ligaments: Anterior and posterior

Review of Long Bone Structure

• Diaphysis: Shaft

• Epiphyses: Ends

• Compact bone: Dense outer layer

• Spongy bone: Internal network of trabeculae

• Epiphyseal line: Remnant of growth plate (epiphyseal plate)

• Red marrow: Hematopoietic tissue

• Yellow marrow: Fat storage

• Periosteum: Dense irregular connective tissue covering bone

• Endosteum: Lines internal bone surfaces

Clinical Significance

• Mastoid process: Site of infection (mastoiditis) if middle ear infection spreads.

• Squamous portion of temporal bone: Thin, easily fractured in trauma.

• Sacral promontory and ischial spine: Obstetric landmarks for pelvic measurements.

• Ligamentum teres (hip): Carries blood supply to femoral head; damage can lead to avascular necrosis.

Additional info:

• Foramina in the cranial floor allow passage of cranial nerves and blood vessels.

• Spinal taps are performed below the termination of the spinal cord to avoid injury (L4-L5 in adults).

• Pelvic orientation is important for anatomical and clinical reference.