Skeletal System: Bones, Cartilage, and Key Structures

Study Guide - Smart Notes

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Skeletal System Overview

Introduction

The skeletal system provides the framework for the human body, supporting movement, protecting organs, and housing bone marrow for blood cell production. It consists of bones, cartilage, joints, and associated structures.

Bone Structure and Types

Compact Bone vs. Spongy Bone

Bones are classified based on their density and structure:

Compact bone: Dense, forms the outer layer of bones, composed of osteons (Haversian systems).
Spongy (cancellous) bone: Less dense, found at the ends of long bones and inside flat bones, contains trabeculae.

Long Bone Anatomy

Diaphysis: Shaft of a long bone.
Epiphysis: Ends of a long bone; proximal (closer to body center) and distal (farther from body center).

Microscopic Structure of Bone and Cartilage

Compact Bone (Osteon Model)

Compact bone is organized into cylindrical units called osteons:

Osteon: Functional unit of compact bone.
Lamella: Concentric rings of bone matrix within an osteon.
Osteocyte: Mature bone cell residing in a lacuna.
Lacuna: Small cavity housing an osteocyte.
Canaliculi: Tiny channels connecting lacunae, allowing nutrient and waste exchange.
Central canal: Center of osteon, contains blood vessels and nerves.

Hyaline Cartilage

Hyaline cartilage is a flexible connective tissue found in joints and respiratory structures:

Chondrocyte: Cartilage cell residing in a lacuna.
Lacuna: Space containing a chondrocyte.
Matrix: Gel-like substance surrounding chondrocytes, rich in collagen fibers.

Bone Composition Experiments

Effects of Acid and Baking on Bone

Bones contain both organic (collagen) and inorganic (minerals) components. Experiments can demonstrate the roles of these components:

	Component Removed	Component Remaining	Characteristics
Bones in Acid	Minerals (inorganic)	Collagen (organic)	Flexible, rubbery
Baked Bones	Collagen (organic)	Minerals (inorganic)	Brittle, easily broken

Major Bones and Landmarks of the Axial Skeleton

Skull Bones and Features

Frontal bone: Forehead region; contains supraorbital foramen and frontal sinus.
Parietal bone: Sides and roof of the skull.
Temporal bone: Contains zygomatic process, mandibular fossa, styloid process, mastoid process, petrous ridge, and external acoustic meatus.
Occipital bone: Contains foramen magnum, occipital condyle, and external occipital protuberance.
Ethmoid bone: Perpendicular plate, middle nasal conchae, cribriform plate, crista galli.
Zygomatic bone: Cheekbone; forms zygomatic arch with temporal bone.
Maxillary bone: Upper jaw; contains infraorbital foramen and palatine process.
Sphenoid bone: Lesser and greater wings, optic foramen, sella turcica, sphenoid sinus.
Mandible: Lower jaw; mental foramen, condyle, coronoid process, ramus.
Palatine, nasal, vomer, lacrimal bones: Contribute to nasal cavity and orbit.

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 Features

Fontanels: Soft spots in infant skulls (anterior, posterior, sphenoidal, mastoid) allowing for growth and birth.

Vertebral Column

Typical Vertebra Structure

Body: Main weight-bearing portion.
Vertebral foramen: Canal for spinal cord.
Transverse process: Lateral projections for muscle attachment.
Spinous process: Posterior projection.
Superior/inferior articular surfaces: Articulate with adjacent vertebrae.
Lamina and pedicle: Form vertebral arch.

Cervical Vertebrae

C1 (Atlas): Supports skull, no body.
C2 (Axis): Contains dens (odontoid process) for rotation.

Thoracic Vertebrae

Costal facets: Articulate with ribs.
Transverse costal facet: For tubercle of rib.
Superior costal facet: For head of rib.

Lumbar Vertebrae

Superior/inferior articular surfaces: For articulation.

Sacrum and Coccyx

Sacrum: Five fused vertebrae; sacral promontory, sacral foramina.
Coccyx: Tailbone, fused vertebrae.

Thoracic Cage

Ribs and Sternum

True ribs: Attach directly to sternum (vertebrosternal).
False ribs: Attach indirectly or not at all (vertebrochondral and floating).
Floating ribs: No anterior attachment.
Sternum: Manubrium, body, xiphoid process.

Appendicular Skeleton

Pectoral Girdle and Upper Limb

Scapula: Acromion, coracoid process, glenoid cavity, margins, fossae, spine, angles.
Humerus: Greater/lesser tubercle, head, necks, deltoid tuberosity, capitulum, trochlea, fossae.
Radius: Head, neck, tuberosity, styloid process.
Ulna: Coronoid/olecranon process, trochlear notch, radial notch, styloid process.

Pelvic Girdle and Lower Limb

Coxal bones (os coxae): Ilium (crest, ASIS), ischium (tuberosity, spine), pubis (symphysis), acetabulum, obturator foramen, greater sciatic notch.
Femur: Head, neck, trochanters, tuberosity, condyles.
Patella: Kneecap.
Tibia: Condyles, tuberosity, medial malleolus.
Fibula: Head, lateral malleolus.
Foot: Tarsals (talus, calcaneus), metatarsals, phalanges.

Joints

Major Joints

Shoulder
Elbow
Hip
Knee

Key Bone Landmarks and Functions

Selected Landmarks

Acromion: Shoulder bone landmark.
Atlas: First cervical vertebra, supports skull.
Cribriform plate: Ethmoid bone, passage for olfactory nerves.
Crista galli: Ethmoid bone, attachment for meninges.
Deltoid tuberosity: Humerus, attachment for deltoid muscle.
Fontanels: Soft spots in infant skulls.
Foramen magnum: Occipital bone, passage for spinal cord.
Radial tuberosity: Radius, attachment for biceps.
Sacral promontory: Sacrum, obstetric landmark.
Sella turcica: Sphenoid bone, houses pituitary gland.
Tibial tuberosity: Tibia, attachment for quadriceps.
Transverse foramina: Cervical vertebrae, passage for vertebral arteries.
Zygomatic arch: Cheekbone, formed by zygomatic and temporal bones.

Orbit of the Eye

Bones Forming the Orbit

Frontal
Lacrimal
Ethmoid
Zygomatic
Maxillary
Sphenoid
Palatine (Additional info: palatine forms a small part of the orbit)

Summary Table: Bone Composition Experiments

	Component Removed	Component Remaining	Characteristics
Bones in Acid	Minerals (inorganic)	Collagen (organic)	Flexible, rubbery
Baked Bones	Collagen (organic)	Minerals (inorganic)	Brittle, easily broken

Key Terms and Definitions

Osteon: Cylindrical structure in compact bone.
Lamella: Layer of bone matrix in osteon.
Osteocyte: Mature bone cell.
Lacuna: Small cavity for osteocyte or chondrocyte.
Canaliculi: Channels for cell communication in bone.
Chondrocyte: Cartilage cell.
Matrix: Extracellular substance in bone or cartilage.

Formulas and Equations

Bones are composed of organic and inorganic components:

Organic (collagen): Provides flexibility.
Inorganic (hydroxyapatite): Provides strength and rigidity.

Hydroxyapatite formula:

Additional info:

Some bones and features (e.g., palatine in orbit) are inferred for completeness.
Fontanels allow for skull deformation during birth and rapid brain growth in infancy.
Bone composition experiments illustrate the importance of both collagen and minerals for bone function.