Human Skeleton Anatomy

• The adult human skeleton consists of 206 bones.

Axial Skeleton

• Contains 80 bones.
• The skull is composed of 22 bones, divided into 8 cranial bones and 14 facial bones.
• The hyoid bone is located in the neck and does not articulate with other bones.
• The vertebral column includes 26 bones: 7 cervical, 12 thoracic, 5 lumbar, 1 sacrum (fused from 5), and 1 coccyx (fused from 4).
• The thoracic cage contains 25 bones: 1 sternum and 24 ribs.

Facial Bones

• There are 14 facial bones in total.
• The paired facial bones include the maxillae, zygomatic, nasal, lacrimal, palatine, and inferior nasal conchae.
• The unpaired facial bones are the mandible and vomer.

Cranial Bones

• There are 8 cranial bones.
• The paired cranial bones are the parietal and temporal bones.
• The unpaired cranial bones include the frontal, occipital, sphenoid, and ethmoid bones.

Vertebral Column

• The cervical region has 7 vertebrae, located in the neck.
• The thoracic region has 12 vertebrae, located in the upper/mid-back, articulating with the ribs.
• The lumbar region has 5 vertebrae, located in the lower back and are the largest.
• The sacral region has 1 bone, fused from 5 vertebrae, forming the back of the pelvis.
• The coccygeal region has 1 bone, fused from 4 vertebrae, forming the tailbone.

Sternum

• The manubrium is the upper portion, articulating with the clavicles and first two ribs.
• The body is the main portion, articulating with ribs 3-7.
• The xiphoid process is a small, lower projection that is cartilaginous in youth and ossifies in adulthood.

Ribs

• There are 24 ribs in humans, arranged in 12 pairs.
• True ribs (1-7) directly attach to the sternum via costal cartilage.
• False ribs (8-12) indirectly attach to the sternum or not at all.
• Floating ribs (11-12) do not attach to the sternum.

Hand and Feet Bones

• There are 8 carpal bones per hand.
• There are 5 metacarpal bones per hand.
• There are 14 phalanges per foot.
• Each toe has 3 phalanges (proximal, middle, distal), except the big toe (hallux), which has 2 (proximal and distal).
• There are 5 metatarsal bones per foot.

Differences Between Male and Female Pelvis

• The male pelvis is narrower and heavier.
• The male pelvis is deeper and more funnel-shaped.
• The male pelvic inlet is smaller and heart-shaped.
• The male pubic arch angle is smaller (90 degrees).
• The male sacrum is shorter and less curved.

Other Important Bone Concepts

• Hematopoiesis is the process of blood cell formation, which takes place in bone marrow.
• Bones store minerals, with calcium being the most abundant.
• The three types of cartilage are hyaline, elastic, and fibrocartilage, each serving different purposes.
• Bone and cartilage are connective tissues.
• Yellow bone marrow is found in the medullary cavity of long bones and primarily stores fat, increasing with age.
• Red bone marrow is found in the spongy bone and is responsible for hematopoiesis.

Bone Fractures

• Open fractures involve the bone protruding through the skin.
• Closed fractures do not involve a break in the skin.
• Greenstick fractures are incomplete fractures, common in children.
• Comminuted fractures involve the bone breaking into multiple fragments.
• Impacted fractures occur when one fragment of bone is driven into another.

Bone Terminology

• Articulation is the point where two bones meet.
• An osteon is the basic structural unit of compact bone.
• Trabeculae are the irregular latticework of thin bony struts in spongy bone.
• Compact bone is dense and solid.
• Spongy bone is porous and contains trabeculae.
• The epiphyseal plate is the growth plate in long bones.

Bone Classifications and Cells

• The five bone classifications are long, short, flat, irregular, and sesamoid. Examples include the femur (long), carpal (short), skull (flat), vertebra (irregular), and patella (sesamoid).
• Chondroblasts produce cartilage matrix.
• Chondrocytes maintain cartilage matrix.
• Osteogenic cells are stem cells that differentiate into osteoblasts.
• Osteoblasts form new bone matrix.
• Osteocytes maintain bone matrix.
• Osteoclasts break down bone.

Long Bone Anatomy

• The epiphysis is the end of a long bone.
• The diaphysis is the shaft of a long bone.
• The metaphysis is the region between the diaphysis and epiphysis.
• The medullary cavity is the hollow space within the diaphysis, containing bone marrow.
• Articular cartilage covers the joint surfaces of the epiphysis.
• The periosteum is the outer covering of bone.
• The endosteum lines the inner surfaces of bone.

Axial Skeleton Definitions (Chapter 8)

• The axial skeleton includes the bones of the skull, vertebral column, and rib cage.
• Paranasal sinuses are air-filled spaces within the skull bones around the nasal cavity.
• Fontanelles are soft spots in the infant skull.
• Cleft lip is a congenital split in the upper lip.
• Cleft palate is a congenital split in the roof of the mouth.
• Kyphosis is an excessive curvature of the thoracic spine (hunchback).
• Lordosis is an excessive curvature of the lumbar spine (swayback).
• Scoliosis is an abnormal lateral curvature of the spine.
• The atlas is the first cervical vertebra (C1).
• The axis is the second cervical vertebra (C2).