Study Guide: The Human Skeleton – Axial and Appendicular Components

Axial and Appendicular 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.

• Axial Skeleton: Skull, vertebral column, and thoracic cage (ribs and sternum).

• Appendicular Skeleton: Pectoral girdle, pelvic girdle, and the bones of the upper and lower limbs.

The Skull

The skull is composed of cranial bones (protecting the brain) and facial bones (forming the structure of the face).

Cranial Bones

• Frontal Bone: Forms the forehead and the upper part of the eye sockets. Contains the supraorbital foramen (passage for nerves and vessels) and frontal sinuses.

• Parietal Bones: Form the sides and roof of the cranial cavity.

• Temporal Bones: Contain the zygomatic processes, zygomatic arch, external acoustic meatus (ear canal), mastoid process, styloid process, and carotid canal.

• Occipital Bone: Contains the occipital condyles (articulate with the first cervical vertebra), external occipital protuberance, and ligamentum nuchae (ligament attachment).

• Sphenoid Bone: Features the sella turcica (houses the pituitary gland), greater and lesser wings, pterygoid process, and optic canals.

• Ethmoid Bone: Contains the cribriform plate (olfactory nerve passage), crista galli (ridge for membrane attachment), and perpendicular plate (part of nasal septum).

Sutures

Sutures are immovable joints connecting the bones of the skull.

• Lambdoid Suture: Between parietal and occipital bones.

• Coronal Suture: Between frontal and parietal bones.

• Sagittal Suture: Between the two parietal bones.

• Squamous Suture: Between parietal and temporal bones.

Facial Bones

• Mandible: Lower jaw; features include the body (chin), rami, condylar process (articulates with temporal bone), coronoid process (muscle attachment), and mandibular notch.

• Maxillary Bones: Upper jaw; includes zygomatic process, palatine process (forms part of hard palate), and infraorbital foramen.

• Zygomatic Bones: Cheekbones.

• Nasal Bones: Bridge of the nose.

• Lacrimal Bones: Medial wall of orbit; contains lacrimal fossa.

• Palatine Bones: Posterior part of hard palate.

• Vomer: Forms part of the nasal septum.

• Hyoid Bone: U-shaped bone in the neck; does not articulate with other bones.

• Paranasal Sinuses: Air-filled spaces in cranial and facial bones, lined with mucosa.

The Vertebral Column

The vertebral column supports the body, protects the spinal cord, and provides attachment points for ribs and muscles. It consists of 33 vertebrae in five regions.

• Cervical (7): Neck region.

• Thoracic (12): Upper back, articulates with ribs.

• Lumbar (5): Lower back.

• Sacrum (5 fused): Forms posterior wall of pelvis.

• Coccyx (4 fused): Tailbone.

Ligaments of the Vertebral Column

• Anterior Longitudinal Ligament: Runs along the anterior surface of vertebral bodies; prevents hyperextension.

• Posterior Longitudinal Ligament: Runs along the posterior surface; limits flexion.

Intervertebral Disc

Located between vertebrae, these discs absorb shock and allow movement.

• Nucleus Pulposus: Gel-like center providing elasticity and compressibility.

• Anulus Fibrosus: Outer ring of fibrocartilage (not listed but important for context).

Structure of a Typical Vertebra

• Body: Weight-bearing portion.

• Pedicle and Lamina: Form the vertebral arch.

• Vertebral Foramen: Canal for spinal cord.

• Intervertebral Foramen: Passage for spinal nerves.

• Spinous Process: Posterior projection for muscle/ligament attachment.

• Transverse Process: Lateral projections.

• Superior and Inferior Articular Processes: Form joints with adjacent vertebrae.

Special Vertebrae

• Atlas (C1): Supports the skull; allows nodding motion.

• Axis (C2): Has the dens (odontoid process) for rotation.

Sacrum and Coccyx

• Sacral Promontory: Anterior border of the sacrum.

• Auricular Process: Articulates with ilium of pelvis.

• Ala (Wing): Lateral part of sacrum.

• Sacral Canal: Continuation of vertebral canal.

• Coccyx: Small, triangular bone at the base of the vertebral column.

Thoracic Cage

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

• Sternum: Consists of manubrium, body, and xiphoid process.

• Ribs: 12 pairs:

  • True Ribs (1-7): Attach directly to sternum.

  • False Ribs (8-10): Attach indirectly via cartilage.

  • Floating Ribs (11-12): No anterior attachment.

Pectoral Girdle and Upper Limb

The pectoral girdle attaches the upper limb to the trunk and consists of the clavicle and scapula.

Clavicle

• Sternal End: Articulates with sternum.

• Acromial End: Articulates with scapula.

Scapula

• Medial and Lateral Borders

• Glenoid Cavity: Articulates with humerus.

• Inferior Angle

• Spine: Prominent ridge on posterior surface.

• Acromion: Lateral end of spine; articulates with clavicle.

• Coracoid Process: Attachment for muscles.

• Suprascapular Notch

• Supraspinous and Infraspinous Fossae: Muscle attachment sites.

Humerus

• Head: Fits into glenoid cavity.

• Anatomical and Surgical Necks

• Greater and Lesser Tubercles

• Intertubercular Sulcus

• Deltoid Tuberosity

• Trochlea and Capitulum: Distal articular surfaces.

• Medial and Lateral Epicondyles

• Olecranon Fossa

Ulna and Radius

• Ulna: Olecranon (elbow), ulnar styloid process.

• Radius: Radial head, radial tuberosity, radial styloid process, Colle's fracture (distal radius fracture).

• Interosseous Membrane: Connects radius and ulna.

Carpals, Metacarpals, and Phalanges

• Carpals: 8 wrist bones in two rows:

  • Proximal Row (lateral to medial): Scaphoid, Lunate, Triquetrum, Pisiform

  • Distal Row (lateral to medial): Trapezium, Trapezoid, Capitate, Hamate

• Metacarpals: 5 bones (thumb is 1st digit)

• Phalanges: 14 bones in the fingers (proximal, middle, distal for each except thumb)

Carpal Tunnel Syndrome

A condition caused by compression of the median nerve as it passes through the carpal tunnel in the wrist, leading to pain and numbness in the hand.

Pelvic Girdle and Lower Limb

The pelvic girdle attaches the lower limbs to the axial skeleton and supports the weight of the upper body.

Coxal Bones (Hip Bones)

• Ilium: Iliac crest, anterior superior iliac spine, greater sciatic notch

• Ischium: Ischial spine, lesser sciatic notch, ischial tuberosity

• Pubis: Pubic tubercle, pubic symphysis, obturator foramen

• Pelvic Inlet and Outlet: Openings defined by the pelvic bones; important in childbirth.

Femur

• Fovea Capitis: Small pit in the head for ligament attachment.

• Head and Neck of Femur

• Greater and Lesser Trochanters: Muscle attachment sites.

• Linea Aspera: Ridge on posterior shaft.

• Medial and Lateral Condyles and Epicondyles

• Intercondylar Fossa

Tibia and Fibula

• Tibia: Medial and lateral condyles, intercondylar eminence, tibial tuberosity, Osgood Schlatter's disease (inflammation at tibial tuberosity), tibial plateau, medial malleolus

• Fibula: Head, lateral malleolus

Tarsals, Metatarsals, and Phalanges

• Tarsals: 7 ankle bones: calcaneus (heel), talus (articulates with tibia), navicular, cuboid, and three cuneiforms

• Metatarsals: 5 bones of the foot

• Phalanges: 14 bones in the toes (proximal, middle, distal for each except big toe)

Additional info:

• The appendicular skeleton is essential for movement and manipulation of the environment.

• Understanding the landmarks and features of bones is crucial for identifying sites of muscle attachment, articulation, and clinical relevance (e.g., fractures, nerve entrapment).