Module 7.1 Overview of the Skeletal System

Structure of the Skeletal System and Skeletal Cartilages

The skeletal system consists of about 206 bones and their associated cartilages, which work together to protect and support the body. The skeleton is divided into two main groups: the axial skeleton and the appendicular skeleton.

• Axial skeleton: Forms the body's longitudinal axis and encloses body cavities that protect underlying organs. It includes:

  • The skull

  • The vertebral column

  • The thoracic cage

• Appendicular skeleton: Consists of the bones of the pectoral girdle, upper limb, pelvic girdle, and lower limb. This group is primarily suited for movement, support, and muscle attachment.

  • The pectoral girdle

  • The upper limb

  • The pelvic girdle

  • The lower limb

Bone Markings

Bones have a number of surface features, including depressions, openings, and projections:

• Depressions: Pathways for blood vessels and nerves or sites for articulations.

• Openings: Enclose delicate structures and allow them to travel through bones.

• Projections: Sites where bones articulate or where ligaments and tendons attach.

Module 7.2 The Skull

Overview of Skull Structure

The skull is composed of 22 bones, divided into two groups: cranial bones and facial bones.

• Cranial bones (8):

  • Frontal (1)

  • Occipital (1)

  • Ethmoid (1)

  • Sphenoid (1)

  • Temporal (2)

  • Parietal (2)

• Facial bones (14):

  • Maxillary (2)

  • Zygomatic (2)

  • Nasal (2)

  • Lacrimal (2)

  • Palatine (2)

  • Inferior nasal conchal bones (2)

  • Mandible (1)

  • Vomer (1)

All bones of the skull (except the mandible) are fused at immovable joints called sutures.

Many skull bones contain air-filled, membrane-lined spaces called sinuses. Four bones surrounding the nasal cavity contain large sinuses called paranasal sinuses.

The superior portion of the cranial cavity is called the cranial vault or calvaria.

Cavities within the Skull

• Orbits: Cavities that encase the eyeball, lacrimal gland, and associated structures.

• Nasal cavity: Formed by several bones and lined with mucous membranes. Includes:

  • Posterior wall: Sphenoid body and pterygoid processes.

  • Lateral wall: Ethmoid and perpendicular plate of palatine, inferior nasal conchae, and maxilla.

  • Floor: Palatine and maxilla.

  • Nasal septum: Perpendicular plate of ethmoid and vomer, dividing the cavity into two nasal fossae.

• Paranasal sinuses: Frontal, sphenoid, ethmoid, and maxillary bones. Functions:

  • Communicate with nasal cavity through small openings.

  • Warm, humidify inspired air.

  • Reduce weight of skull and enhance voice resonance.

• Oral cavity: Contains the tongue, teeth, and most salivary glands; first part of the digestive tract.

Fetal Skull Bones

• Fetal skull bones are not fused; soft spots called fontanels are present until cranial bones complete development at 18–24 months.

• Fontanels and unfused sutures allow flexibility for birth.

Module 7.3 The Vertebral Column and Thoracic Cage

Overview of the Vertebral Column

The vertebral column, or spine, is composed of an average of 33 bones called vertebrae. Vertebrae are classified by location and structure:

• 7 cervical vertebrae (neck)

• 12 thoracic vertebrae (articulate with ribs)

• 5 lumbar vertebrae (lower back)

• 5 sacral vertebrae (fused to form sacrum)

• 3–5 coccygeal vertebrae (fused to form coccyx)

Spinal Curvatures

• Cervical curvature: Concave, develops as infant lifts head.

• Thoracic curvature: Convex, present at birth.

• Lumbar curvature: Concave, develops as child begins to walk.

• Sacral curvature: Convex, present at birth.

Abnormal curvatures include:

• Scoliosis: Abnormal lateral curvature.

• Lordosis: Exaggerated cervical/lumbar curvature.

• Kyphosis: Exaggerated thoracic curvature (hunchback).

Structure of Vertebrae

• Body (centrum): Primary weight-bearing surface.

• Vertebral foramen: Large opening for spinal cord.

• Vertebral arch: Formed by pedicles and laminae.

• Transverse processes: Lateral projections for muscle attachment.

• Spinous process: Posterior projection for muscle attachment.

The seven cervical vertebrae are the smallest and have unique features:

• C1: The atlas

• C2: The axis

Thoracic and Lumbar Vertebrae

• Thoracic vertebrae: Articulate with ribs, have costal facets.

• Lumbar vertebrae: Largest, support most weight.

• Sacrum: Five fused vertebrae, forms posterior pelvic boundary.

• Coccyx: Three to five fused vertebrae, final segment.

Intervertebral Discs

There are 23 intervertebral discs, which are fibrocartilage pads between vertebrae that absorb shock and bind the column together.

• Nucleus pulposus: Soft inner jelly-like substance, shock absorber.

• Anulus fibrosus: Outer ring of fibrocartilage, contains nucleus pulposus.

Thoracic Cage

The thoracic cage consists of the sternum, 12 pairs of ribs, and thoracic vertebrae. It protects vital organs and supports breathing.

• Sternum (breastbone):

  • Manubrium

  • Body

  • Xiphoid process

• Ribs: 12 pairs, curved into a C-shape. Each attaches to a thoracic vertebra.

• Intercostal spaces: Spaces between ribs, important for breathing.

• Costal margin: Formed by costal cartilage of ribs 7–10.

• Rib structure (ribs 2–9):

  • Head

  • Tubercle

  • Shaft (body)

Module 7.4 Bones of the Pectoral Girdle and Upper Limb

Pectoral Girdle

The pectoral girdle consists of the clavicle and scapula, supporting the 30 bones of the upper limb.

• Clavicle (collarbone):

  • Sternal end

  • Acromial end

  • Conoid tubercle

• Scapula (shoulder blade):

  • Coracoid process

  • Subscapular fossa

  • Glenoid cavity

  • Spine

  • Acromion at acromioclavicular joint (AC)

Upper Limb Bones

• Humerus: Largest bone of the upper limb, articulates with scapula and forearm.

  • Greater tubercle

  • Lesser tubercle

  • Surgical neck

  • Deltoid tubercle

  • Radial groove

  • Medial and lateral epicondyles

  • Capitulum

  • Trochlea

  • Radial fossa

  • Coronoid fossa

  • Olecranon fossa

• Forearm bones:

  • Radius (lateral):

    • Radial head

    • Radial tuberosity

    • Ulnar notch

    • Radial styloid process

  • Ulna (medial):

    • Trochlear notch

    • Radial notch

    • Styloid process

• Wrist (carpus): Eight short bones arranged in two rows.

  • Proximal row: Scaphoid, lunate, triquetrum, pisiform

  • Distal row: Trapezium, trapezoid, capitate, hamate

• Hand and fingers:

  • Metacarpals: Five long bones (numbered I–V)

  • Phalanges: 14 bones (proximal, middle, distal for each finger; thumb has only proximal and distal)

Module 7.5 Bones of the Pelvic Girdle and Lower Limb

Pelvic Girdle

The pelvic girdle and bones of the lower limb complete the appendicular skeleton. The hipbones (coxal bones) make up the pelvic girdle, which articulates with the sacrum.

• Bowl-shaped pelvis: Composed of sacrum and two coxal bones.

*Additional info: The notes above have been expanded for clarity and completeness, including definitions and examples of anatomical features, as well as logical grouping of fragmented points.*