Skeletal System: Bones, Cartilage, and Key Structures

Study Guide - Smart Notes

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Skeletal System Overview

Introduction

The skeletal system provides the structural framework for the human body, protects vital organs, facilitates movement, and serves as a reservoir for minerals. It is composed of bones, cartilage, and associated connective tissues.

Bone Structure and Types

Compact Bone vs. Spongy Bone

Bones are classified based on their density and structure into compact bone and spongy (cancellous) bone.

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

Bone Anatomy

Diaphysis: Shaft of a long bone.
Epiphysis: Ends of a long bone; subdivided into proximal and distal epiphyses.

Microscopic Structure of Bone and Cartilage

Compact Bone (Ground Bone)

Compact bone is organized into cylindrical structures called osteons or Haversian systems.

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

Hyaline Cartilage

Hyaline cartilage is a flexible connective tissue found in joints, respiratory tract, and fetal skeleton.

Chondrocyte: Cartilage cell residing in a lacuna.
Lacuna: Small cavity containing a chondrocyte.
Matrix: Gel-like ground substance rich in collagen fibers.

Comparison Table: Bone and Cartilage Slides

Feature	Compact Bone	Hyaline Cartilage
Cell Type	Osteocyte	Chondrocyte
Location	Lacuna	Lacuna
Matrix	Calcified, organized in lamellae	Gel-like, rich in collagen
Special Structures	Osteon, canaliculi, central canal	None

Effects of Chemical Treatments on Bone

Bones can be treated with acid or heat to study their composition and properties.

	Component Removed	Component Remaining	Characteristics
Bones in Acid	Mineral (inorganic) component	Organic matrix (collagen)	Flexible, rubbery
Baked Bones	Organic component (collagen)	Mineral (inorganic) component	Brittle, easily broken

Major Bones and Landmarks of the Axial Skeleton

Skull Bones

The skull consists of several bones with distinct landmarks important for protection and muscle attachment.

Frontal Bone: Forehead region; includes supraorbital foramen and frontal sinus.
Parietal Bone: Forms the sides and roof of the cranium.
Temporal Bone: Contains zygomatic process, mandibular fossa, styloid process, mastoid process, and petrous ridge.
Occipital Bone: Contains foramen magnum, occipital condyle, and external occipital protuberance.
Ethmoid Bone: Perpendicular plate, cribriform plate, crista galli, middle nasal conchae.
Sphenoid Bone: Lesser and greater wings, optic foramen, sella turcica, sphenoid sinus.
Lacrimal Bone: Contains lacrimal fossa.
Zygomatic Bone: Cheekbone, forms zygomatic arch with temporal bone.
Maxillary Bone: Infraorbital foramen, palatine process.
Mandible: Mental foramen, mandibular condyle, coronoid process, ramus.
Palatine, Nasal, Vomer Bones: Form parts of the nasal cavity and palate.

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 the two parietal bones.

Fetal Skull Features

Fontanels: Soft spots in the fetal skull that allow for growth and passage during birth.
Anterior, Posterior, Anterolateral (sphenoidal), and Posterolateral (mastoid) fontanels.

Vertebral Column

Typical Vertebrae

Body: Main weight-bearing region.
Vertebral (spinal) foramen: Passage for spinal cord.
Transverse Process: Lateral projections for muscle attachment.
Spinous Process: Posterior projection for muscle attachment.
Superior/Inferior Articular Surfaces: Articulate with adjacent vertebrae.
Lamina and Pedicle: Form vertebral arch.

Cervical Vertebrae

C1 (Atlas): Supports the skull, allows nodding motion.
C2 (Axis): Contains the dens (odontoid process), allows rotation.
Transverse Foramen: Passage for vertebral arteries.

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: Articulate with adjacent vertebrae.

Sacrum and Coccyx

Sacrum: Formed by fusion of five vertebrae; contains sacral promontory and sacral foramina.
Coccyx: Tailbone, formed by fusion of small vertebrae.

Ribs and Sternum

True Ribs: Attach directly to sternum (vertebrosternal).
False Ribs: Attach indirectly or not at all (vertebrochondral and floating).
Floating Ribs: Do not attach to sternum.
Sternum: Consists of manubrium, body, and 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, radial tuberosity, styloid process.
Ulna: Coronoid process, 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, patellar surface.
Patella: Kneecap.
Fibula: Head, lateral malleolus.
Tibia: Condyles, tuberosity, medial malleolus.
Foot: Tarsals (talus, calcaneus), metatarsals, phalanges.

Joints

Shoulder, Elbow, Hip, Knee: Major synovial joints allowing movement.

Key Bone Landmarks and Functions

Selected Landmarks and Their Functions

Acromion: Palpable shoulder bone.
Atlas: First cervical vertebra, supports the skull.
Fontanels: Soft spots in infant skull for growth and birth.
Foramen Magnum: Passage for spinal cord.
Deltoid Tuberosity: Attachment for deltoid muscle.
Ischial Tuberosity: Supports body when sitting.
Radial Tuberosity: Attachment for biceps muscle.
Sacral Promontory: Landmark for obstetrics.
Sella Turcica: Houses pituitary gland.
Spina Bifida: Congenital defect of vertebral arch closure.
Tibial Tuberosity: Attachment for quadriceps femoris muscle.
Transverse Foramina: Passage for vertebral arteries in cervical vertebrae.
Zygomatic Arch: Formed by zygomatic and temporal bones.

Sample Study Questions

Practice Questions

What is the only movable joint in the skull? Answer: Temporomandibular joint (TMJ).
Which bones form the only movable joint in the skull? Answer: Mandible and temporal bone.
Which bone contains the foramen magnum? Answer: Occipital bone.
What structure passes through the foramen magnum? Answer: Spinal cord.
Name the six bones that form the orbit of the eye. Answer: Frontal, lacrimal, ethmoid, zygomatic, maxillary, sphenoid.
What is the function of foramina? Answer: Passage for nerves and blood vessels.
Olfactory nerves pass through what structure? Answer: Cribriform plate of ethmoid bone.
Which ribs are called "true ribs"? Answer: Ribs 1-7.
Which ribs are called "false ribs"? Answer: Ribs 8-12.
Which ribs are called "floating ribs" and why? Answer: Ribs 11-12; they do not attach to the sternum.
What part of the scapula articulates with the head of the humerus? Answer: Glenoid cavity.
What part of the humerus is a common site of fractures? Answer: Surgical neck.
The projection of the wrist, along the thumb side of the arm, is what structure? Answer: Styloid process of radius.
Name the part of the os coxa which provides attachment for back, thigh, and abdominal wall muscles; as well as serves as a landmark for intramuscular injections. Answer: Iliac crest.
The lateral projection of the ankle is formed by which structure? Answer: Lateral malleolus of fibula.
The "shin" is the common name for which bone? Answer: Tibia.

Additional info:

Fontanels allow for cranial expansion and passage through the birth canal.
Spina bifida is a neural tube defect resulting from incomplete closure of vertebral arches.
Foramina are critical for neurovascular communication between regions.