Skeletal System: Bone Tissue, Bones, and Joints – Study Notes

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Skeletal System: Bone Tissue, Bones, and Joints

Introduction to the Skeletal System

The skeletal system provides the structural framework for the human body, protects vital organs, facilitates movement, stores minerals, and houses bone marrow for blood cell production. This unit covers the structure and function of bone tissue, the anatomy of bones, and the classification and function of joints.

Bone Tissue

Structure and Function of Bone Tissue

Bone tissue is a specialized connective tissue composed of cells, fibers, and ground substance.
It provides support, protection, and enables movement by serving as points of attachment for muscles.
Bone tissue is dynamic, constantly being remodeled through the actions of osteoblasts (bone-forming cells) and osteoclasts (bone-resorbing cells).
There are two main types of bone tissue: compact bone (dense and strong) and spongy bone (porous and lightweight).

Structure of bone tissue, showing compact and spongy bone

Axial Skeleton

Skull Anatomy

The skull is a complex structure composed of cranial and facial bones. It protects the brain and forms the structure of the face.

Cranial bones include the frontal, parietal, temporal, occipital, sphenoid, and ethmoid bones.
Facial bones include the maxilla, mandible, zygomatic, nasal, lacrimal, palatine, inferior nasal concha, and vomer.
Sutures are immovable joints that connect the bones of the skull.

Labeled diagram of the skull, anterior view

Infant Skull and Fontanelles

Infant skulls have soft spots called fontanelles that allow for growth of the brain and skull during development.
Fontanelles ossify and become sutures as the child grows.

Infant skull showing fontanelles

Vertebral Column

The vertebral column, or spine, supports the head and trunk, protects the spinal cord, and provides attachment points for ribs and muscles.

It consists of 33 vertebrae in five regions: cervical (7), thoracic (12), lumbar (5), sacral (5 fused), and coccygeal (4 fused).
Intervertebral discs act as shock absorbers between vertebrae.

Labeled diagram of the vertebral column

Appendicular Skeleton

Pectoral Girdle and Upper Limb

The pectoral girdle consists of the clavicle and scapula, connecting the upper limb to the axial skeleton.
The upper limb includes the humerus, radius, ulna, carpals, metacarpals, and phalanges.

Labeled diagram of the pectoral girdle and upper limb Labeled diagram of the humerus Labeled diagram of the radius and ulna Labeled diagram of the bones of the hand

Pelvic Girdle and Lower Limb

The pelvic girdle consists of two hip bones (coxal bones), which articulate with the sacrum and femur.
The lower limb includes the femur, patella, tibia, fibula, tarsals, metatarsals, and phalanges.

Labeled diagram of the pelvic girdle Labeled diagram of the femur

Thoracic Cage

The thoracic cage is formed by the sternum, ribs, and thoracic vertebrae.
It protects the heart and lungs and supports the shoulder girdles and upper limbs.
There are 12 pairs of ribs: true ribs (1–7), false ribs (8–12), and floating ribs (11–12).

Labeled diagram of the thoracic cage

Joints (Articulations)

Classification of Joints

Fibrous joints: Immovable joints held together by fibrous tissue (e.g., sutures of the skull).
Cartilaginous joints: Slightly movable joints connected by cartilage (e.g., intervertebral discs).
Synovial joints: Freely movable joints with a synovial cavity (e.g., shoulder, knee, elbow).

Structure of Synovial Joints

Synovial joints have articular cartilage, a joint (synovial) cavity, an articular capsule, synovial fluid, reinforcing ligaments, and nerves and blood vessels.
Types of synovial joints include hinge, pivot, ball-and-socket, saddle, condyloid, and plane joints.

Labeled diagram of a synovial joint

Movements at Synovial Joints

Movements include flexion, extension, abduction, adduction, rotation, circumduction, pronation, and supination.

Illustrations of joint movements

Summary Table: Major Bones of the Human Skeleton

Region	Major Bones
Skull	Frontal, Parietal, Temporal, Occipital, Sphenoid, Ethmoid, Maxilla, Mandible, Zygomatic
Vertebral Column	Cervical, Thoracic, Lumbar, Sacrum, Coccyx
Thoracic Cage	Sternum, Ribs
Pectoral Girdle	Clavicle, Scapula
Upper Limb	Humerus, Radius, Ulna, Carpals, Metacarpals, Phalanges
Pelvic Girdle	Hip bones (Ilium, Ischium, Pubis)
Lower Limb	Femur, Patella, Tibia, Fibula, Tarsals, Metatarsals, Phalanges

Additional info:

Bone is a reservoir for minerals, especially calcium and phosphate.
Red bone marrow is the site of hematopoiesis (blood cell formation).
Osteoporosis is a common disorder characterized by decreased bone mass and increased fracture risk.