Study Guide: The Human Skeleton and Articulations

The Axial Skeleton

Overview

The axial skeleton forms the central axis of the body and consists of the skull, vertebral column, and bony thorax. It provides support, protection for the central nervous system and thoracic organs, and serves as an attachment point for muscles.

• Skull: Protects the brain and forms the structure of the face.

• Vertebral column: Supports the body and protects the spinal cord.

• Bony thorax: Protects the heart and lungs.

Skull

• Cranium: 8 flat bones (frontal, 2 parietal, 2 temporal, occipital, sphenoid, ethmoid) that enclose and protect the brain.

• Calvaria: The dome-like upper portion of the skull.

• 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).

• Facial bones: 14 bones (mandible, 2 maxillae, 2 palatine, 2 zygomatic, 2 lacrimal, 2 nasal, vomer, 2 inferior nasal conchae) that form the face and provide muscle attachment.

• Hyoid bone: A unique bone in the neck that does not articulate with other bones; supports the tongue and larynx.

Key Features and Clinical Notes:

• Foramina: Allow passage of cranial nerves and blood vessels.

• Mastoid process: Prone to infection (mastoiditis) if middle ear infections are untreated.

• Squamous region of temporal bone: Thin and easily fractured.

• Mandibular condyle: Forms the temporomandibular joint (TMJ), the only movable joint in the skull.

• Maxillae: Called the "keystone" bones of the face because they articulate with all other facial bones except the mandible.

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

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

Nasal Septum: Formed by the vomer and perpendicular plate of the ethmoid.

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

Vertebral Column

• Structure: 24 vertebrae + sacrum + coccyx.

• Typical vertebra: Consists of a body, vertebral arch, spinous and transverse processes, lamina, pedicle, vertebral foramen, and articular processes.

• Intervertebral foramina: Openings for spinal nerves, formed by notches in adjacent vertebrae.

Regional Differences:

• Cervical (7): Transverse foramina, bifid spinous processes (except C7), atlas (C1) lacks body/spinous process, axis (C2) has dens.

• Thoracic (12): Heart-shaped body, long inferiorly pointing spinous process, facets for rib articulation.

• Lumbar (5): Large, massive body, short and thick spinous processes.

Spinal Curvatures:

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

• Secondary: 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).

Termination of Spinal Cord: Adult: L1-L2; Infant: L3-L4. Spinal taps are performed below these levels to avoid injury.

Sacrum and Coccyx

• Sacrum: 5 fused vertebrae; features include median sacral crest, sacral foramina, sacral canal, sacral hiatus (site for saddle-block anesthesia), and sacral promontory (obstetric landmark).

• Coccyx: 3-5 fused vertebrae; forms the tailbone.

Bony Thorax (Thoracic Cage)

• Sternum: Fusion of manubrium, body, and xiphoid process. Landmarks: jugular notch, sternal angle, xiphisternal joint.

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

• Types of Ribs:

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

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

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

The Appendicular Skeleton

Overview

The appendicular skeleton includes the bones of the limbs and the girdles that attach them to the axial skeleton. It is essential for movement and manipulation of the environment.

Pectoral (Shoulder) Girdle

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

• Scapula: Flat, triangular bone with axillary and vertebral borders, inferior angle, spine, infraspinous/supraspinous/subscapular fossae, coracoid and acromion processes, and glenoid cavity (articulates with humerus).

Upper Limb

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

• Forearm:

  • Radius: Head, neck, radial tuberosity, lateral styloid process.

  • Ulna: Olecranon process, trochlear notch, medial styloid process.

• Wrist: 8 carpal bones in two rows.

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

Pelvic (Hip) Girdle and Bony Pelvis

• Pelvic Girdle: Two coxal 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/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 (see lab manual for details).

Lower Limb

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

• Leg:

  • Tibia: Medial/lateral condyles, tibial tuberosity, medial malleolus.

  • Fibula: Head, lateral malleolus.

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

The Fetal Skeleton

Fetal Skull

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

• Ossification centers: Sites where bone formation begins.

• Frontal and mandibular bones: Paired in fetus, single in adult.

Fetal Skeleton Features

• Spinal Curvatures: Only primary (thoracic and sacral) present at birth; secondary (cervical and lumbar) develop after birth (cervical at ~3 months, lumbar at ~12 months).

• Bone Development: Many bones (vertebrae, sternum, patellae, coxal bones, carpals, tarsals) are not fully ossified at birth; rib cage is more cartilaginous and flexible.

Bone Markings of the Appendicular Skeleton

Palpable Landmarks

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

Note: Anatomical terms are preferred over common terms (e.g., "ankle bone" refers to the malleolus).

Extremities: Miscellaneous Questions

• Palm: Formed by metacarpals.

• Hand: Metacarpals and phalanges.

• Wrist: Carpals.

• Ankle: Tarsals (mainly talus).

• 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 the first metatarsal.

• Lateral forearm bone: Radius (in anatomical position).

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

• Radius articulation: 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 femur (condyles) and tibia (condyles); anatomical name is tibia femoral joint.

Articulations (Joints) and Body Movements

Joint Classification

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

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

Joint Models and Specimens

• Shoulder joint: Humerus, scapula (spine, acromion, coracoid, fossae), clavicle, tendons (biceps, rotator cuff), ligaments.

• Knee joint: Femur, tibia, fibula, articular cartilage (hyaline), menisci (fibrocartilage), cruciate and collateral ligaments, patella, patellar ligament, tibial tuberosity.

• Hip joint: Coxal bone, femur (epiphysis, diaphysis), articular capsule, ligamentum teres, acetabular labrum (fibrocartilage).

Five Structural Features of Synovial Joints:

• Articular cartilage

• Joint (articular) cavity

• Articular capsule

• Synovial fluid

• Reinforcing ligaments

Three "C's" of the Knee Joint: Collateral ligaments, Cruciate ligaments, Cartilages (menisci).

Long Bone Structure Review

• Diaphysis: Shaft of the bone.

• Epiphyses: Ends of the bone.

• Compact bone: Dense outer layer.

• Spongy bone: Internal network of trabeculae.

• Epiphyseal line: Remnant of epiphyseal plate (growth plate) in adults.

• Red marrow: Site of blood cell formation.

• Yellow marrow: Fat storage.

• Periosteum: Dense irregular connective tissue covering bone surface.

• Endosteum: Lines internal bone surfaces.

Difference between Epiphyseal Line and Plate: Plate is cartilage (site of growth in children); line is bone (after growth ends).