Introduction to the Skeletal System and Axial Skeleton: Laboratory Study Guide

Introduction to the Skeletal System and Axial Skeleton

This study guide covers the essential laboratory objectives and terminology for understanding the structure and function of the skeletal system, with a focus on the axial skeleton. It includes identification of bone and cartilage types, microscopic anatomy, and the major bones and features of the axial skeleton.

Overview of the Skeletal System

• Skeletal System: The framework of bones and cartilage that supports and protects the body, enables movement, and houses bone marrow for blood cell production.

• Axial Skeleton: The central part of the skeleton, including the skull, vertebral column, and rib cage.

Cartilage Types and Locations

Cartilage is a flexible connective tissue found in various parts of the body. There are three main types, each with distinct locations and functions.

• Fibrocartilage: Tough, dense cartilage that resists compression and tension.

  • Locations: Pubic symphysis, intervertebral discs, meniscus of the knee.

• Hyaline Cartilage: Most common type; provides smooth surfaces for movement at joints, flexibility, and support.

  • Locations: Costal cartilage (ribs), synovial articulating surfaces, growth plates (epiphyseal plates).

• Elastic Cartilage: Contains elastic fibers, allowing flexibility.

  • Locations: Pinna of ear, epiglottis.

Anatomy of a Long Bone

Long bones are characterized by a central shaft and two ends. Understanding their structure is essential for identifying bone features and functions.

• Diaphysis: The shaft or central part of a long bone.

• Epiphysis: The ends of a long bone; can be proximal (closer to the body) or distal (farther from the body).

• Articular Cartilage: Hyaline cartilage covering the joint surfaces of epiphyses, reducing friction.

• Epiphyseal Line: Remnant of the epiphyseal plate in adults; marks where bone growth occurred.

• Epiphyseal Plate: Growth plate made of cartilage in children and adolescents; site of bone lengthening.

• Medullary Cavity: Central cavity within the diaphysis, containing yellow bone marrow in adults.

• Periosteum: Dense connective tissue membrane covering the outer surface of bone (except at joints).

• Endosteum: Thin membrane lining the medullary cavity.

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

• Spongy Bone: Porous bone tissue found inside bones, especially at the epiphyses; contains red bone marrow.

Microscopic Anatomy of the Osteon

The osteon (Haversian system) is the fundamental structural unit of compact bone, providing strength and support.

• Osteon: Cylindrical structure consisting of concentric layers (lamellae) of bone matrix.

• Central (Haversian) Canal: Channel in the center of each osteon containing blood vessels and nerves.

• Osteocyte: Mature bone cell residing in a lacuna, maintaining bone tissue.

• Lacuna: Small cavity within bone matrix housing an osteocyte.

• Canaliculus (plural: Canaliculi): Tiny channels connecting lacunae, allowing communication and nutrient exchange between osteocytes.

• Lamellae: Concentric rings of bone matrix within an osteon.

• Perforating (Volkman’s) Canal: Canals running perpendicular to central canals, connecting blood and nerve supply between osteons.

Cells of Cartilage and Bone

• Chondrocytes: Mature cartilage cells found in lacunae within cartilage matrix.

• Osteoblasts: Bone-forming cells responsible for synthesizing bone matrix.

• Osteocytes: Mature bone cells derived from osteoblasts, maintaining bone tissue.

• Osteoclasts: Large, multinucleated cells that break down bone matrix (bone resorption).

Axial Skeleton: Major Bones and Markings

The axial skeleton consists of the skull, vertebral column, rib cage, and associated structures. Below are the key bones and features to identify.

Skull

• Frontal Bone

• Parietal Bone

• Temporal Bone

  • Zygomatic process

  • Styloid process

  • Mastoid process

  • External acoustic meatus

• Occipital Bone

  • Occipital condyle

  • Foramen magnum

• Ethmoid Bone

• Sphenoid Bone

• Mandible Bone

  • Mandibular ramus

  • Mental foramen

• Maxillae Bone

• Palatine Bone

• Zygomatic Bone

• Lacrimal Bone

• Vomer Bone

• Nasal Bone

• Sutures

  • Coronal suture

  • Sagittal suture

  • Squamous suture

  • Lambdoid suture

• Fontanel (on fetal skull)

  • Anterior fontanel

  • Posterior fontanel

General Features of a Vertebra

• Body

• Spinous process

• Transverse process

• Intervertebral foramen (exit point for spinal nerves)

• Vertebral foramen

• Vertebral arch

• Articular process and facet (superior and inferior)

• Pedicle

• Lamina

Vertebrae Types and Features

• Cervical Vertebrae (C1-C7): Smallest vertebrae; C1 (Atlas) and C2 (Axis) are specialized for head movement.

  • Transverse foramen (unique to cervical vertebrae)

  • C1 Atlas: Anterior arch

  • C2 Axis: Dens (odontoid process)

• Thoracic Vertebrae (T1-T12): Articulate with ribs; have costal facets.

• Lumbar Vertebrae (L1-L5): Largest vertebrae; support most body weight.

• Sacrum: Fused vertebrae; contains sacral foramen.

• Coccyx: Tailbone; small, fused vertebrae.

Rib Cage

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

• Ribs:

  • Head

  • Shaft

  • Tubercle

  • Junction with costal cartilage

• True Ribs (1-7): Attach directly to the sternum via costal cartilage.

• False Ribs (8-12): Attach indirectly or not at all to the sternum.

• Floating Ribs (11-12): Do not attach to the sternum.

Hyoid Bone

• U-shaped bone in the neck that supports the tongue and is not directly attached to other bones.

Summary Table: Types of Cartilage and Locations

Type of Cartilage	Main Features	Locations
Fibrocartilage	Strong, resists compression	Pubic symphysis, intervertebral discs, meniscus
Hyaline cartilage	Flexible, smooth surfaces	Costal cartilage, synovial surfaces, growth plates
Elastic cartilage	Flexible, elastic fibers	Pinna of ear, epiglottis

Example: Identifying a Long Bone

• When examining a femur (thigh bone), you can identify the diaphysis (shaft), epiphyses (ends), articular cartilage at the joint surfaces, and the medullary cavity inside the shaft.

Additional info:

• Bone markings such as foramina (holes), processes (projections), and condyles (rounded articular surfaces) are important for muscle attachment and articulation with other bones.

• Fontanels in the fetal skull allow for flexibility during birth and brain growth in infancy.