Lesson 12: How do animals move? (copy)
1. Compare and contrast hydrostatic skeleton, exoskeleton, and endoskeleton.
Animals possess three types of skeletons:
Hydrostatic skeleton: Found in organisms like earthworms, this structure consists of a fluid-filled cavity surrounded by muscles. The muscles exert force against the fluid, facilitating movement. Earthworms use two sets of muscles: circular muscles, which pressurize the fluid, and longitudinal muscles, which cause bristle-like chaetae to protrude and grip the ground, enabling movement.
Exoskeleton: Arthropods such as insects and crustaceans possess an external, rigid skeleton composed of chitin. This structure provides protection and serves as a site for muscle attachment. However, growth is restricted, necessitating periodic molting, during which the animal is vulnerable to predators.
Endoskeleton: Found in vertebrates and echinoderms, an endoskeleton is composed of rigid internal elements that provide structural support and muscle attachment points. Vertebrate skeletons are primarily composed of bone and cartilage, whereas echinoderms, like sea urchins and starfish, have endoskeletons made of calcium carbonate (calcite).
2. Describe the structure and function of cartilage and bone.
Cartilage: A specialized connective tissue designed to withstand compression and tension. It is tough yet flexible and found in many joints.
Cartilage consists of chondroblasts, which secrete extracellular matrix and become trapped within lacunae, maturing into chondrocytes.
The matrix is composed of glycoproteins and collagen fibers.
Oxygen and nutrients reach cartilage cells via diffusion from surrounding blood vessels, as cartilage is avascular, meaning it lacks blood vessels.
Due to its avascular nature, cartilage heals slowly when damaged.
Bone: Another specialized connective tissue that is stronger but less flexible than cartilage.
Bone consists of organic components (collagen fibers, polysaccharides) for flexibility and inorganic hydroxyapatite (calcium phosphate minerals) for hardness.
Osteoblasts secrete an enzyme that promotes hydroxyapatite formation, giving bone its rigidity.
Some osteoblasts become trapped in the matrix, transforming into osteocytes, which reside in lacunae and connect via tiny canals called canaliculi for intercellular communication.
3. Describe how growth occurs in epiphyses.
Bones develop through two processes:
Intramembranous ossification (occurs in flat bones like the skull).
Endochondral ossification (occurs in long bones like vertebrae, ribs, and limbs).
Growth occurs at the epiphyses (widened ends of bones) in growth plates made of cartilage.
Young cartilage cells undergo mitosis, thicken, age, and die, contributing to bone lengthening.
Simultaneously, calcification occurs from the shaft side, replacing cartilage with bone.
Growth in length stops in late adolescence, but width growth continues throughout life.
4. Explain how bone remodeling occurs.
Bone is constantly changing through the coordinated actions of:
Osteoblasts, which deposit new bone.
Osteoclasts, which resorb existing bone (derived from white blood cells, not mesenchyme).
Bone remodeling is stimulated by mechanical stress and hormones.
Increased mechanical stress (e.g., weightlifting) signals osteoblasts to produce more bone matrix, strengthening the bone.
Osteoporosis occurs when bone resorption outpaces bone deposition, leading to fragile bones. Treatments include a high-calcium diet, vitamin D, and weight-bearing exercise to stimulate bone growth.
5. Summarize how muscles produce movement at joints.
Muscles contract to generate movement at joints.
Muscles attach to bones either directly or via tendons.
Origin: Fixed attachment point of a muscle.
Insertion: Movable attachment point.
Antagonistic muscles: One muscle produces a movement that is reversed by another (e.g., quadriceps extend the leg while hamstrings flex it).
power movement at join through contraction
Types of joints and their movement:
Ball-and-socket joints (hip, shoulder) allow a wide range of motion.
Hinge joints (knee, elbow) permit movement in one direction.
Gliding joints (vertebrae, wrist) allow sliding motions.
Combination joints (jaw) allow rotation and side-to-side movement.
Tendons that connect
6. Describe the structure of human skeletal muscle.
Skeletal muscle consists of bundles of long multinucleated muscle fibers.
Each muscle fiber contains myofibrils, composed of:
Thick filaments (myosin).
Thin filaments (actin).
The structural unit of contraction is the sarcomere, spanning from Z-line to Z-line.
A bands (dark regions) contain stacked thick filaments.
I bands (light regions) contain only thin filaments.
H zone (within A band) has only thick filaments.
**Label muscle structure
7. Describe the sliding filament mechanism of muscle contraction.
During contraction:
Actin and myosin filaments slide past each other, shortening the sarcomere.
Myosin heads bind to actin, forming cross-bridges.
ATP hydrolysis moves the myosin head into an energized state.
Power stroke: Myosin pulls actin toward the sarcomere’s center.
New ATP binds, breaking the cross-bridge, and the cycle repeats.
Regulation by calcium:
At rest, tropomyosin blocks actin-binding sites.
Calcium ions (Ca²⁺) bind to troponin, shifting tropomyosin to expose actin-binding sites.
Ca²⁺ is released from the sarcoplasmic reticulum when stimulated by a motor neuron at the neuromuscular junction.
8. Differentiate between slow-twitch and fast-twitch muscle fibers.
Slow-twitch fibers:
Rely on aerobic respiration.
High capillary density, mitochondria, and myoglobin (appear dark).
Fatigue-resistant, ideal for endurance activities (e.g., marathon running).
Fast-twitch fibers:
Generate rapid power, fatigue quickly.
Some respire anaerobically, relying on glycogen stores.
Fewer capillaries, mitochondria, and myoglobin (appear white).
Suited for short bursts of activity (e.g., sprinting).
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Conclusion
This lesson covered the structure and function of the skeletal and muscular systems, emphasizing how bones grow, remodel, and contribute to movement. We explored muscle contraction, including the sliding filament theory, and differentiated between slow-twitch and fast-twitch fibers. Understanding these principles helps explain adaptations in different organisms and human movement efficiency.