The Axial Skeleton: Structure, Function, and Classification

스터디 가이드 - 스마트 노트

자료에 맞춘 맞춤형 노트, 핵심 정의, 예시, 맥락을 확장해 제공합니다.

The Axial Skeleton and Homeostasis

Role of the Axial Skeleton in Homeostasis

The axial skeleton plays a crucial role in maintaining homeostasis by providing protection and support for vital organs and contributing to mineral storage.

Protection of Organs: The cranium surrounds the brain, the vertebrae protect the spinal cord, and the ribs encase the heart and lungs.
Calcium Storage: Bones act as reservoirs for calcium, an essential ion for physiological processes.

Divisions of the Skeleton

Axial vs. Appendicular Skeleton

The human skeleton is divided into two main divisions, each with distinct components and functions.

Axial Skeleton (80 bones): Includes the skull, auditory ossicles, hyoid bone, ribs, sternum, vertebrae, and sacrum. It forms the central axis of the body.
Appendicular Skeleton (126 bones): Comprises the bones of the upper and lower limbs and the girdles (pectoral and pelvic) that attach the limbs to the axial skeleton.

Division	Structure	Number of Bones
Axial Skeleton	Skull (Cranium, Face), Hyoid bone, Auditory ossicles, Vertebral column, Thorax (Sternum, Ribs)	80
Appendicular Skeleton	Pectoral girdles (Clavicle, Scapula), Upper limbs (Humerus, Ulna, Radius, Carpals, Metacarpals, Phalanges), Pelvic girdle (Hip bones), Lower limbs (Femur, Patella, Fibula, Tibia, Tarsals, Metatarsals, Phalanges)	126

Types of Bones

Classification by Shape

Bones are classified into five main types based on their shape, each serving specific structural and functional roles.

Long Bones: Greater length than width (e.g., humerus, femur). Adapted for movement and support.
Short Bones: Cube-shaped (e.g., wrist bones, tarsals). Provide stability and some movement.
Flat Bones: Thin layers of parallel plates (e.g., sternum, cranial bones). Offer protection and broad surfaces for muscle attachment.
Irregular Bones: Complex shapes (e.g., vertebrae, some facial bones). Specialized for protection and support.
Sesamoid Bones: Shaped like a sesame seed (e.g., patella). Develop in tendons to protect them from stress and wear.

Example: The femur is a long bone, the carpal bones are short bones, the sternum is a flat bone, the vertebrae are irregular bones, and the patella is a sesamoid bone.

Classification by Location

Sutural Bones: Small, extra bone plates located within the sutures of cranial bones. Sutures are immovable joints found only in the skull.

Bone Surface Markings

Types and Functions of Surface Markings

Bones have characteristic surface markings that serve as sites for attachment, passage of soft tissues, and formation of joints. These markings are divided into two main categories:

Depressions and Openings: Allow passage of soft tissues (nerves, blood vessels, ligaments, tendons) or form joints.
Processes: Projections or outgrowths that form joints or serve as attachment points for connective tissues.

Major Depressions and Openings

Term	Description	Example
Fissure	Narrow slit between adjacent parts of bones for passage of blood vessels or nerves	Superior orbital fissure of sphenoid bone
Foramen	Opening through which blood vessels, nerves, or ligaments pass	Optic foramen of sphenoid bone
Fossa	Shallow depression	Coronoid fossa of humerus
Sulcus	Furrow along bone surface that accommodates blood vessel, nerve, or tendon	Intertubercular sulcus of humerus
Meatus	Tubelike opening	External auditory meatus of temporal bone

Major Processes

Term	Description	Example
Condyle	Large, round protuberance with a smooth articular surface at end of bone	Lateral condyle of femur
Facet	Smooth, flat, slightly concave or convex articular surface	Superior articular facet of vertebra
Head	Usually rounded articular projection supported on neck of bone	Head of femur
Crest	Prominent ridge or elongated projection	Iliac crest of hip bone
Epicondyle	Typically roughened projection above condyle	Medial epicondyle of femur
Line	Long, narrow ridge or border (less prominent than crest)	Linea aspera of femur
Spinous process	Sharp, slender projection	Spinous process of vertebra
Trochanter	Very large projection	Greater trochanter of femur
Tubercle	Variably sized rounded projection	Greater tubercle of humerus
Tuberosity	Variably sized projection with rough, bumpy surface	Ischial tuberosity of hip bone

Additional info: Surface markings are essential for the attachment of muscles, ligaments, and tendons, and for the passage of neurovascular structures.