Skeletal System Overview

The skeletal system provides structural support, protection for internal organs, and facilitates movement. This study guide covers the structure of bone tissue, the anatomy of the skull, and the vertebral column, as well as key features of ribs and intervertebral discs.

Bone Tissue Structure

Bone Specimen Types

• Compact Bone: Dense, strong bone tissue forming the outer layer of bones.

• Spongy (Cancellous) Bone: Porous, lighter bone tissue found at the ends of long bones and inside flat bones.

Histology of Bone

Compact Bone (Microscopic Structure)

• Osteon (Haversian System): The fundamental structural unit of compact bone, consisting of concentric lamellae around a central canal.

• Osteonic (Haversian) Canal: Central channel containing blood vessels and nerves.

• Lamella: Layers of bone matrix within the osteon.

• Blood Vessel (Arteriole): Supplies nutrients and removes waste from bone cells.

• Perforating (Volkmann) Canal: Channels that connect adjacent osteons and carry blood vessels.

• Lacuna: Small spaces housing osteocytes (bone cells).

• Canaliculi: Tiny canals connecting lacunae, allowing communication between osteocytes.

• Interstitial Lamellae: Layers of bone matrix found between osteons.

• Collagen Fibers: Provide tensile strength and flexibility to bone.

Spongy Bone (Microscopic Structure)

• Trabeculae: Lattice-like network of bone tissue providing structural support.

• Bone Marrow: Soft tissue within bone spaces; red marrow produces blood cells, yellow marrow stores fat.

• Lacunae: Spaces containing osteocytes, similar to compact bone.

• Canaliculi: Channels for nutrient and waste exchange between osteocytes.

• Lamella: Concentric layers of bone matrix within trabeculae.

Skull Anatomy

Colored Skull Identification

• Frontal (Tan): Forehead region.

• Parietal (Green): Sides and roof of the cranium.

• Temporal (Brown): Lower sides of the skull, houses ear structures.

• Occipital (Blue): Back and base of the skull.

• Maxilla (Purple): Upper jaw.

• Mandible (Large White): Lower jaw.

• Nasal (Small White): Bridge of the nose.

• Sphenoid (Red): Base of the skull, behind the eyes.

• Ethmoid (Yellow): Forms part of the nasal cavity and eye orbits.

• Lacrimal (Dark Orange): Small bone forming part of the eye socket.

• Zygomatic (Light Orange): Cheekbone.

White Whole and Half Skulls

• Frontal Bone

• Parietal Bone

• Temporal Bone

  • Mastoid Process: Bony projection behind the ear, attachment for neck muscles.

• Occipital Bone

  • Occipital Condyle: Articulates with the first cervical vertebra (atlas).

  • Foramen Magnum: Large opening for the spinal cord.

  • Jugular Foramen: Passage for jugular vein and cranial nerves.

• Maxilla

• Mandible

• Lacrimal Bone

• Zygomatic Bone

• Nasal Bone

• Vomer

• Ethmoid Bone

  • Perpendicular Plate: Forms part of the nasal septum.

  • Cribriform Plate: Contains olfactory foramina for smell.

• Sphenoid Bone

  • Sella Turcica: Depression housing the pituitary gland.

  • Hypophyseal Fossa: Part of the sella turcica.

• Palatine Bone

Cranial Fossae

• Posterior Cranial Fossa: Houses the cerebellum.

• Middle Cranial Fossa: Supports the temporal lobes.

• Anterior Cranial Fossa: Supports the frontal lobes.

Cranial Sutures

• Coronal Suture: Between frontal and parietal bones.

• Sagittal Suture: Between the two parietal bones.

• Lambdoid Suture: Between parietal and occipital bones.

• Squamous Suture: Between parietal and temporal bones.

Maxillary and Ethmoid Bones (External and Internal View)

• Maxillary (Yellow): Upper jaw and part of the orbit.

• Sphenoid (Purple): Base of the skull.

• Frontal (Green): Forehead region.

• Ethmoid (Orange): Nasal cavity and orbit.

Vertebral Column

Regions and Curvatures

• Lordotic Curve: Inward curve (cervical and lumbar regions).

• Kyphotic Curve: Outward curve (thoracic and sacral regions).

Vertebrae Identification

• C6: Sixth cervical vertebra.

• T9: Ninth thoracic vertebra.

• L4: Fourth lumbar vertebra.

Vertebral Anatomy

• Body: Main weight-bearing portion.

• Superior/Inferior Articular Process and Facet: Articulate with adjacent vertebrae.

• Transverse Process: Lateral projections for muscle/ligament attachment.

• Pedicle: Connects body to arch.

• Lamina: Forms posterior part of vertebral arch.

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

• Vertebral Foramen: Canal for spinal cord.

• Intervertebral Foramen: Openings for spinal nerves.

Special Vertebrae

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

  • Anterior/Posterior Arch, Lateral Mass, Transverse Process, Transverse Foramen

• Axis (C2): Has the Dens (odontoid process) for rotation of the head.

Regional Vertebral Features

• Cervical Vertebrae: Small body, transverse foramen, bifid spinous process.

• Thoracic Vertebrae: Articulating surfaces for ribs, spinous process points down.

• Lumbar Vertebrae: Large body, superior articular facets face medially, spinous process points directly posterior.

Thoracic Cage

Sternum Anatomy

• Body: Main part of the sternum.

• Xiphoid Process: Inferior tip of the sternum.

• Manubrium: Superior part of the sternum.

Rib Classification

• True Ribs: Attach directly to the sternum (e.g., Rib #4).

• False Ribs: Attach indirectly or not at all to the sternum (e.g., Rib #8).

• Floating Ribs: Do not attach to the sternum (e.g., Rib #11).

Intervertebral Discs

• Annulus Fibrosis: Tough outer layer of the disc.

• Nucleus Pulposus: Gel-like center providing cushioning.

• Herniation: Nucleus pulposus protrudes through the annulus, potentially compressing nerves.

Key Terms and Definitions

• Osteocyte: Mature bone cell found in lacunae.

• Trabeculae: Supporting bundles in spongy bone.

• Suture: Immovable joint between skull bones.

• Foramen: Opening in bone for nerves and blood vessels.

Example: Herniated Disc

A herniated disc occurs when the nucleus pulposus pushes through a tear in the annulus fibrosis, often causing back pain or nerve compression.