Skeletal System Overview

Introduction

The skeletal system provides the structural framework for the human body, protects vital organs, enables movement, and serves as a reservoir for minerals. It consists of bones, cartilage, and joints, each with distinct anatomical features and functions.

Bone Structure and Types

Compact Bone vs. Spongy Bone

• Compact Bone: Dense, strong bone tissue forming the outer layer of bones. Contains osteons (Haversian systems) for structural support.

• Spongy (Cancellous) Bone: Porous bone tissue found at the ends of long bones and inside flat bones. Contains trabeculae and red bone marrow.

Long Bone Anatomy

• Diaphysis: Shaft of a long bone, composed mainly of compact bone.

• Epiphysis: Ends of a long bone, typically filled with spongy bone and red marrow.

• Proximal Epiphysis: End of the bone closest to the body's center.

• Distal Epiphysis: End of the bone farthest from the body's center.

Microscopic Structure of Bone and Cartilage

Compact Bone (Ground Bone)

• Osteon (Haversian System): Cylindrical structure containing concentric lamellae around a central canal.

• Lamella: Layers of bone matrix within the osteon.

• Osteocyte: Mature bone cell residing in lacunae.

• Lacuna: Small cavity housing an osteocyte.

• Canaliculi: Tiny channels connecting lacunae, allowing nutrient and waste exchange.

• Central Canal: Contains blood vessels and nerves.

Hyaline Cartilage

• Chondrocyte: Cartilage cell residing in a lacuna.

• Lacuna: Small cavity containing a chondrocyte.

• Matrix: Gel-like substance surrounding chondrocytes, rich in collagen fibers.

Bone Composition Experiments

Effects of Acid and Heat on Bone

Bones are composed of organic (collagen) and inorganic (mineral) components. Experiments can demonstrate the roles of these components:

Major Bones of the Axial and Appendicular Skeleton

Skull Bones

• Frontal Bone: Forehead region; contains supraorbital foramen and frontal sinus.

• Parietal Bone: Forms sides and roof of the cranium.

• Temporal Bone: Contains zygomatic process, mandibular fossa, styloid process, mastoid process, petrous ridge, and auditory meatus.

• Occipital Bone: Contains foramen magnum, occipital condyle, and external occipital protuberance.

• Lacrimal Bone: Small bone forming part of the eye socket.

• Ethmoid Bone: Contains perpendicular plate, middle nasal conchae, cribriform plate, and crista galli.

• Zygomatic Bone: Cheekbone; forms zygomatic arch with temporal bone.

• Maxillary Bone: Upper jaw; contains infraorbital foramen and palatine process.

• Sphenoid Bone: Contains lesser and greater wings, optic foramen, sella turcica, and sphenoid sinus.

• Mandible: Lower jaw; contains mental foramen, condyle, coronoid process, and ramus.

• Palatine Bone: Forms part of the hard palate.

• Nasal Bone: Bridge of the nose.

• Vomer: Forms part of the nasal septum.

Sutures of the Skull

• Coronal Suture: Between frontal and parietal bones.

• Squamous Suture: Between parietal and temporal bones.

• Lambdoid Suture: Between parietal and occipital bones.

• Sagittal Suture: Between two parietal bones.

Fetal Skull Fontanels

• Anterior Fontanel

• Posterior Fontanel

• Anterolateral (Sphenoidal) Fontanel

• Posterolateral (Mastoid) Fontanel

Vertebral Column

Typical Vertebrae

• Body: Main weight-bearing region.

• Vertebral (Spinal) Foramen: Canal for spinal cord.

• Transverse Process: Lateral projections for muscle attachment.

• Spinous Process: Posterior projection for muscle attachment.

• Superior/Inferior Articular Surface: Articulation points between vertebrae.

• Lamina and Pedicle: Parts of vertebral arch.

Cervical Vertebrae

• C1 (Atlas): Supports the skull; no body.

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

• Transverse Foramen: Passage for vertebral arteries.

Thoracic Vertebrae

• Costal Facets: Articulation points for ribs.

• Transverse Costal Facet: For tubercle of rib.

• Superior Costal Facet: For head of rib.

Lumbar Vertebrae

• Superior/Inferior Articular Surface: For articulation with adjacent vertebrae.

Sacrum and Coccyx

• Sacrum: Formed by fusion of five vertebrae; contains sacral promontory and foramina.

• Coccyx: Tailbone; formed by fusion of small vertebrae.

Thoracic Cage

Ribs and Sternum

• True Ribs: First seven pairs; attach directly to sternum.

• False Ribs: Ribs 8-12; do not attach directly to sternum.

• Floating Ribs: Ribs 11-12; do not attach to sternum at all.

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

Appendicular Skeleton

Pectoral Girdle and Upper Limb

• Scapula: Contains acromion, coracoid process, glenoid cavity, and various margins and fossae.

• Humerus: Contains greater/lesser tubercle, head, neck, deltoid tuberosity, capitulum, trochlea, and fossae.

• Radius: Contains head, neck, radial tuberosity, and styloid process.

• Ulna: Contains coronoid process, olecranon process, trochlear notch, radial notch, and styloid process.

Pelvic Girdle and Lower Limb

• Coxal Bones (Os Coxae): Includes ilium (iliac crest, ASIS), ischium (ischial tuberosity), and pubis (symphysis pubis).

• Femur: Contains head, neck, greater/lesser trochanter, gluteal tuberosity, linea aspera, patellar surface, and condyles.

• Patella: Kneecap.

• Fibula: Contains head and lateral malleolus.

• Tibia: Contains lateral/medial condyle, tibial tuberosity, and medial malleolus.

• Foot: Tarsals (talus, calcaneus), metatarsals, phalanges.

Joints

Major Joints

• Shoulder

• Elbow

• Hip

• Knee

Key Anatomical Landmarks and Functions

Selected Terms and Their Functions

• Acromion: Shoulder bone landmark.

• Atlas: First cervical vertebra; supports the skull.

• Fontanels: Soft spots in fetal skull for birth and brain growth.

• Foramen Magnum: Opening for spinal cord in occipital bone.

• Odontoid Process (Dens): Allows rotation of atlas and head.

• Olecranon Process: Tip of elbow.

• Radial Tuberosity: Attachment for biceps muscle.

• Sacral Promontory: Landmark in obstetrics.

• Sella Turcica: Houses pituitary gland.

• Tibial Tuberosity: Attachment for quadriceps femoris muscle.

• Transverse Foramina: Passage for vertebral arteries in cervical vertebrae.

• Zygomatic Arch: Cheekbone structure.

Example: Bone Composition Experiment

When a bone is soaked in acid, the mineral component (hydroxyapatite) is removed, leaving the organic collagen matrix. The bone becomes flexible and can bend without breaking. When a bone is baked, the organic collagen is destroyed, leaving only the mineral component, making the bone brittle and easy to break.

Summary Table: Bone Composition Experiment

Key Formulas and Equations

• Bone Strength Equation:

Additional info:

• Some anatomical terms and relationships were inferred from standard anatomy knowledge to provide context and completeness.

• Fontanels allow for skull deformation during birth and rapid brain growth in infancy.

• True, false, and floating ribs are classified based on their attachment to the sternum.