Skeletal System: Structure and Components

• Components of the skeletal system include bones, cartilage, ligaments, tendons, and joints.
• The skeletal system provides structural support, attachment points, and protects internal organs.
• The axial skeleton is along the midline of the body, including the skull, spine, and ribcage
• The appendicular skeleton includes the bones in the limbs.
• Long bones include the femur and humerus
• Short bones include the carpals and tarsals
• Flat bones include skull bones and shoulder blades
• Irregular bones include facial bones and vertebrae of the spine
• Sesamoid bones include the kneecap.
• Flat bone macroscopic structure consists of two thin layers of compact bone with a middle layer of spongy bone.
• Common bone markings include the iliac crest (ridge on the pelvis), olecranon process (bony projection on elbow), glenoid (shallow depression), and condyle (raised area on the bone..
• Bone tissue cellular components include osteoprogenitor cells, osteoblasts, osteocytes, and osteoclasts
• Compact bone is dense, while spongy bone is less dense.
• Osteoblasts build new bones by producing bone matrix.
• Both intramembranous and endochondral bone formation work with the bone matrix.
• Endochondral formation forms with cartilage, while intramembranous formation forms with connective tissue.
• Osteoblasts form new bone and add growth to existing bone tissue
• Osteoclasts dissolve old and damaged bone tissue.
• Interstitial growth expands tissue from within by cell division, which is lengthwise growth.
• Appositional growth adds new material to the outer surface, increasing width or diameter.
• Fracture repair consists of inflammation (initial response), formation (holds bone together), and remodeling (regular bone replaces formation).
• Parathyroid hormone (PTH) increases plasma calcium levels by stimulating bone resorption, enhancing renal calcium reabsorption, and indirectly promoting intestinal calcium absorption through calcitriol activation.
• Calcitonin decreases plasma calcium levels by inhibiting bone resorption and promoting calcium excretion in the kidneys.

Axial & Appendicular Skeletons

• Frontal bone forms the forehead, located at the front of the skull
• Parietal bones are two bones forming the sides and top of the skull.
• Occipital bone is located at the back of the skull, forming the base.
• Temporal bones are situated on the sides of the skull, near the ears.
• The sphenoid bone is a complex bone deep within the skull, forming part of the eye sockets.
• The maxilla is the upper jaw bone
• The mandible is the lower jaw bone
• There are 7 Cervical Vertebrae which supports the head in the neck region
• There are 12 Thoracic Vertebrae connecting to the ribs in the mid-back
• There are 5 Lumbar Vertebrae which bears the most weight in the lower back
• Sacrum consists of fused vertebrae at the base of the spine
• Coccyx (Tailbone) is a small bone at the very end of the spine
• The rib cage is 12 pairs of curved bones surrounding the chest cavity, connecting to the sternum and thoracic vertebrae
• Sternum (Breastbone) is a flat bone in the center of the chest
• Clavicle (Collarbone): Connects the breastbone to the shoulder blade
• Scapula (Shoulder blade) is a flat bone on the back of the shoulder
• Humerus is the long bone in the upper arm
• Radius is the forearm bone on the thumb side
• Ulna is the forearm bone on the pinky finger side
• Ilium comprises the upper part of the hip bone
• Ischium comprises the lower part of the hip bone
• Pubis comprises the front part of the hip bone
• Femur (Thigh bone): Longest bone in the body, located in the upper leg
• Patella (Kneecap) is a small bone in front of the knee joint
• Tibia (Shinbone) is the main weight-bearing bone of the lower leg
• Fibula is a smaller bone alongside the tibia
• Tarsals are bones in the ankle
• Metatarsals are bones in the midfoot
• Phalanges are toe bones
• Condyle: Large prominence that supports cartilage
• Crest: A raised edge of a bone
• Epicondyle: A prominence above a condyle
• Head: A rounded extension that forms part of a joint
• Facet: A smooth, flat surface that forms a joint with another flat bone
• Epiphysis: The articulating segment at the ends of long bones
• Fissure: An open slit that usually contains nerves and blood vessels
• Foramen: A hole that contains nerves and blood vessels
• Groove: A furrow that contains blood vessels and nerves
• Fetal skulls differ significantly due to fontanelles where skull bones haven't fully fused; an adult skull has mostly fused sutures
• An adult male and female skeleton differs significantly due to the pelvis shape and size, where the female's is wider and shallower to accommodate childbirth and the males is narrower.
• Bed rest or immobilization can cause skeletal system changes like bone density loss, increasing fracture risk.
• Joints are classified structurally as fibrous (immovable), cartilaginous (slightly movable), and synovial (freely movable).
• Joints are classified functionally as synarthroses (immovable), amphiarthroses (slightly movable), and diarthroses (freely movable).
• A typical synovial joint includes articular cartilage, a joint capsule, a synovial membrane, and ligaments.
• The six structural types of synovial joints are plane (gliding), hinge, pivot, condyloid (ellipsoidal), saddle, and ball-and-socket joints.
• Synovial joints allow bones to slide or rotate, causing movements called abduction, adduction, extension, flexion, and rotation.

Overview of the skeletal system. Covering bones, cartilage, ligaments, tendons, joints, axial and appendicular skeleton. Also including the types of the bones, macroscopic structure and bone tissue cellular components.