Bone Structure and Histology

Key Terms and Definitions

• Articular Cartilage: Smooth, white tissue covering the ends of bones in joints, reducing friction and absorbing shock.

• Epiphysis: The rounded end of a long bone, involved in joint articulation and growth.

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

• Epiphyseal Line: Remnant of the epiphyseal plate (growth plate) in adult bones, marking where bone growth occurred.

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

• Compact Bone: Dense bone tissue forming the outer layer of bones, providing strength and protection.

• Medullary Cavity: Central cavity within the diaphysis of long bones, containing bone marrow.

• Yellow Bone Marrow: Fatty tissue found in the medullary cavity of adult long bones, primarily for fat storage.

• Red Bone Marrow: Hematopoietic tissue found in spongy bone, responsible for blood cell production.

Histology of Bone

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

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

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

• Lacunae: Small spaces between lamellae housing osteocytes.

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

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

• Perforating (Volkmann's) Canals: Canals running perpendicular to the central canals, connecting blood and nerve supply of the periosteum to those in the central canal.

Axial Skeleton

Bones of the Skull: Cranial and Facial

The skull is composed of cranial and facial bones, each with distinct features and functions.

Cranial Bones (8)

• Frontal Bone (1):

  • Supraorbital foramen (or notch)

  • Glabella

  • Frontal sinuses

• Parietal Bones (2)

• Temporal Bones (2):

  • Squamous portion

  • Petrous portion

  • Zygomatic process (forms zygomatic arch)

  • Mandibular fossa

  • External acoustic/auditory meatus

  • Styloid process

• Occipital Bone (1):

  • Foramen magnum*

  • Occipital condyles

• Sphenoid Bone (1):

  • Sella turcica

  • Optic canal (foramen)*

  • Chiasmatic groove

  • Pterygoid processes

  • Superior orbital fissure

  • Foramen rotundum

  • Foramen ovale

  • Foramen spinosum

• Ethmoid Bone (1):

  • Crista galli

  • Cribriform plate (with olfactory foramina)

  • Perpendicular plate

  • Olfactory foramina*

Facial Bones (14)

• Mandible (1):

  • Mandibular condyle

  • Coronoid process of the mandible

  • Mandibular foramen

  • Mental foramen

  • Alveolar margin

• Maxillae (2):

  • Alveolar margin

  • Palatine process

  • Infraorbital foramen (or fossa)

  • Incisive foramen (fossa)

• Palatine (2)

• Zygomatic Bone (2):

  • Temporal process (forms zygomatic arch)

• Lacrimal Bone (2):

  • Lacrimal groove (fossa)

Other Bones Related to the Skull

• Hyoid Bone (1): A U-shaped bone in the neck that supports the tongue and is not directly attached to other bones.

• Ear Ossicles (located within the Petrous portion of the temporal bone):

  • Malleus (2)

  • Incus (2)

  • Stapes (2)

Sutures

• Coronal suture

• Sagittal suture

• Squamous suture

• Lambdoidal suture

Fetal Skull

• Fontanels: anterior and posterior

• Suture: Frontal (only on fetal skull)

Vertebral Column

The vertebral column supports the body and protects the spinal cord. It is divided into regions with distinct vertebrae.

• Intervertebral discs: fibrocartilaginous pads between vertebrae for shock absorption.

• Intervertebral foramen: openings between vertebrae for spinal nerves.

Features of All Vertebrae

• Centrum (body)

• Vertebral foramen*

• Transverse process

• Spinous process

• Pedicle

• Lamina

• Vertebral arch

• Superior articular process and facet*

• Inferior articular process and facet*

Cervical Vertebrae (7)

• All cervical vertebrae:

  • Transverse foramen*

Thoracic Vertebrae (12)

• Transverse costal facet*

• Superior costal facet

• Inferior costal facet

Lumbar Vertebrae (5)

• Medial sacral crest

• Sacral foramen

• Sacral canal

Sacrum (5 fused)

• Medial sacral crest

• Sacral foramen

• Sacral canal

Coccyx (3-5 fused)

Thoracic Cage

The thoracic cage protects vital organs and supports the upper body.

Sternum (1)

• Manubrium

• Body

• Xiphoid process

Ribs (left/right)

• True ribs (14)

• False ribs (6)

• Floating ribs (4)

• Head of rib

• Shaft

• Tubercle of rib*

• Sternal end

• Vertebral end

• Costal groove

Key Functions of Marked Structures (*)

Additional Info

• The axial skeleton includes the skull, vertebral column, and thoracic cage, providing central support and protection for the brain, spinal cord, and thoracic organs.

• Bone histology is essential for understanding bone growth, repair, and function.

• Knowing the location and function of key foramina and processes is crucial for understanding neurovascular pathways and joint mechanics.