Biology Chapter 6: Skeletal System Overview

Osteoblasts

• Osteoblasts synthesize and secrete the organic matrix of bone, primarily collagen, which provides the framework for mineral deposition.
• They play a key role in bone formation by initiating the process of bone mineralization through the deposition of calcium phosphate crystals onto the collagen matrix.

Intramembranous Ossification

• In intramembranous ossification, mesenchymal tissue directly transforms into bone without the formation of a cartilaginous intermediate.
• It is responsible for the formation of flat bones like the skull bones, clavicle, and some facial bones.

Spongy Bone vs. Compact Bone

• Spongy Bone: Contains a network of trabeculae (thin struts of bone), creating a porous structure, is lighter and weaker than compact bone, and is found at the ends of long bones and in the interior of flat bones.
• Compact Bone: Dense and solid, found on the outer surface of bones, provides strength and support, and contains Haversian canals that house blood vessels and nerves.

Synovial Joints

• Synovial Joints: Characterized by a joint cavity filled with synovial fluid, which reduces friction and lubricates the joint.
• Diarthroses (synovial joints) allow for the greatest range of motion, with examples including the shoulder, hip, and knee joints.

Blood Calcium Regulation

• Parathyroid Hormone (PTH) is the primary hormone responsible for increasing blood calcium levels.
• It stimulates osteoclasts to resorb bone, releasing calcium into the bloodstream, and also promotes resorption of calcium from the kidneys and intestines.

Vertebral Joints

• The joints between vertebrae are classified as symphyses, which are characterized by fibrocartilaginous discs connecting bony surfaces.
• These joints allow for limited movement and provide flexibility and support to the vertebral column.

Bone Growth

• Appositional Growth: Occurs when new bone tissue is deposited on the surface of existing bone, increasing its width. It involves the activity of osteoblasts laying down new bone matrix on the periosteum.
• Interstitial Growth: Occurs within the cartilage of growing bones, adding length to the bone. It relies on chondrocytes within the epiphyseal plates dividing and producing new cartilage matrix.

Sarcomere Proteins

• Actin: Thin filaments that form the sliding component of the muscle contraction mechanism.
• Myosin: Thick filaments that have "heads" that bind to actin filaments, initiating the sliding process.

Mandible

• The mandible (lower jawbone) is the only movable facial bone in the human skull.

Slow-Twitch Muscle Fibers

• Slow-Twitch Muscle Fibers: Primarily used for endurance activities, are fatigue-resistant, and rely heavily on oxidative metabolism to produce energy.

Floating Ribs

• Floating Ribs: The 11th and 12th ribs are classified as floating ribs because they do not attach directly to the sternum (breastbone) through costal cartilages.

ATP in Muscle Contraction

• ATP (adenosine triphosphate) powers the muscle contraction cycle.
• It is required for myosin to detach from actin, re-energize for the next binding, and maintain the resting state of the sarcomere.

Intervertebral Discs

• Intervertebral Discs: Act as shock absorbers between vertebrae, allow for limited movement, and contribute to the flexibility and support of the vertebral column.

Fulcrum

• Fulcrum: The fixed point around which a lever rotates, often the joint where a muscle is attached to a bone.

Pivot Joints

• Pivot Joints: Synovial joints that allow for rotational movement around a single axis.
• Examples include the joint between the atlas (C1) and axis (C2) vertebrae in the neck, allowing for head rotation, and the joint between the radius and ulna bones in the forearm, enabling the hand to pronate and supinate.

Antagonist Muscle

• Antagonist Muscle: The muscle that opposes the action of the agonist muscle in a pair.
• For example, in the biceps and triceps pair, the triceps is the antagonist to the biceps, relaxing as the biceps contracts to bend the elbow.

This quiz covers essential concepts from Chapter 6 regarding the skeletal system. It includes the functions of bones, types of bone cells, and the anatomy of long bones, along with the processes of ossification and bone growth. Prepare to test your knowledge of both compact and spongy bone structures and their roles in maintaining health.