Animal Locomotory Systems

1. Animal Locomotory Systems Biology 2: Form and Function

2. Types of skeleton • Hydraulic or hydrostatic skeletons use a fixed volume, non-compressible fluid contained within a sack, against which muscular contractions are applied • Exoskeleton surround the body, and are rigid, and often impermeable. As it is non-living, growth of an exoskeleton is problematic • Endoskeleton are rigid internal skeleton made of living connective tissue capable of growth and self-repair

3. Hydrostatic skeletons

4. Exo- and endoskeletons

5. The human skeletal system • Axial skeleton • Skull • Ribs • Spine • Appendicular skeleton • Pelvis • Limbs • Hands • Feet

6. The structure of bone • Bone consists of brittle but rigid Calcium Phosphate, interweaved with flexible but weak collagen • New bone is made in osteoblasts, intitially as cartilage (non-calcified bone) • New bone cells, osteocytes, are encase within lacunae, and may eventually be reconstituted by osteoclasts • Bone is laid down in layers (lamellae) located around Haversian canals • Ends and interior bone contains a more open lattice (spongy bone) which contains bone marrow

7. Bone structure 1

8. Bone structure 2

9. Types of joint • Fixed joint (immovable). e.g, sutures in skull • Slightly movable joints. e.g., spine • Movable (synovial joints) - full range of motion • Ball and socket (pelvis-femur, humerous-scapula) • Hinge (elbow) • Rotating (axis-atlas)

10. Immovable joints

11. Slightly movable joints

12. Freely movable joints

13. Muscles move bones • Muscle may act together (synergistic) or against each other (antagonistic) • Muscles contract by electrical stimulation from nervous system • Electrical stimulation can be replicated artificially to demonstrate a graded response • Single contraction-stimulation = twitch • Multiple contraction stimulations with slight recovery = summation • Multiple contraction stimulations with no recovery = tetanus • Isotonic contractions are those that result in muscle shortening • If muscle does not shorten because load is too great, then contraction is isometric

14. Muscle stimulation patterns

15. Flexor and Extensor muscles

16. The muscles of the human leg

17. Muscle composition • Muscles contain muscle fibres • A group of muscle fibers served by the same neuron is termed a motor unit • Muscle fibres (= cell) contains a bundle of myofibrils • Myofibrils are striated by dark and light bands • Dark bands consist of thick myofibrils • Light bands consist of thin myofibrils • At rest, light bands barely overlap with dark bands

18. Motor units

19. Muscle fibres

20. The three types of muscle

21. Skeletal muscle structure

22. Fine structure of the myofibril • At rest, thin myofilaments and thick myofilaments barely overlap • Light, or I-bands, are separated in their middle by z-lines • Thick, or A-bands, have a lighter center (referred to as an H-band) • Whole unit, from I-band to I-band (including one A-band, is termed a sarcomere, and is the functional contracting unit • On contraction, thin myofilaments slide along, and into the thick myofilaments, shortening the H-and z-lines; termed the sliding filament mechanism of contraction

23. Skeletal muscle structure at the myofibril level

24. Sliding filament mechanism of contraction

25. Contraction at the molecular level • Thick myofilaments consist of myosin fibres • Each myosin fibre has a head that can attach to a thin fibre as a cross-bridge • Thin myofilaments consist of actin fibres that can bind to the myosin heads of a thick myofilament • In the act of muscle contraction, Myosin converts ATP to ADP. This reconfigures the myosin head to bind to a actin fibre. As the myosin fibre contracts, the thin myofilament is dragged with it • At the end of this power stroke, the myosin head binds with further ATP - this releases the cross bridge, allowing the myosin to rebind at a site further up the thin myofilament

26. Thick filaments

27. Thin filaments

28. Interaction of thick and thin filaments

29. Cross-bridge cycle in muscle contraction

30. The control of contraction • Motor neurons release a neurotransmitter, Acetylcholine (ACh), which prompts the muscle fibre membrane to poduce an electrochemical impulse • Impulses travel along cellular invaginations known as transverse, or t-tubules • t-tubules carry impulse to the sarcoplasmic reticulum, as repository of Ca2+ • Ca2+ binds to troponin, a protein that in combination with tropomysosin, isolates the actin molecules of the thin myofilaments. During contraction, the binding of Ca2+ exposes the thin myofilament to crossbridge formation • Muscle relaxation is prompted by the cessation of nervous stimulation, which inhibits the supply of Ca2+ ions to troponin. The troponin-tropomyosin complex thus returns to its protective role, preventing crossbridge formation

31. Role of calcium in muscle contraction

32. Structures involved with Calcium and contraction

33. Types of muscle fibres • Slow-twitch (Type I, SlowOxidative, or red) fibres are deep red in color due to high levels of myoglobin, and have a high capacity for aerobic respiration and resist fatigue • Fast-twitch (Type II, Glycolitic, or white) fibres contain less myoglobin, are adapted to anaerobic respiration, and are capable of rapid, non-sustainable generation of power (can be strengthened through exercise) • Intermediate fast-twitch (FastOxidative) fibres are also resistant to fatigue. Performance may be improved by endurance exercises

34. Fast-twitch an slow-twitch fibres

35. Other notable modes of locomotion

36. Movements of swimming fishes

37. Locomotion in air