Musculo-Skeletal System

1. Musculo-Skeletal System • Muscles + Bones = Locomotion

2. Muscles

3. Why muscles? • Muscle tissue is responsible for movement and locomotion in animals. • Muscles rely on contractile fibers to create motion. • In vertebrate animals and arthropods, muscles attach to a skeletal system to produce locomotion.

4. Locomotion • Locomotion is the result of muscles pulling on skeletal systems, which is why we often study these systems together.

5. Types of muscle tissue • These three types are found in vertebrates: • Skeletal: striated, voluntary control • Smooth: involuntary control • Cardiac: involuntary control

6. Smooth muscle • Have contractile fibers, but lack orderly striations of skeletal muscle. • Where would you expect smooth muscle (involuntary control) to be found?

7. Cardiac muscle • Influenced by nerves and hormones, but has “electrical” system of its own to initiate and coordinate contractions. • Where would you expect cardiac muscle to be found?

8. Skeletal muscle • Orderly striations are due to arrangement of contractile fibers. • Produces locomotion. • Where would you expect skeletal (voluntary control) muscle to be found?

9. Muscle fibers • A muscle cell is a “fiber.” • Fibers are multinucleated and contain myoglobin. (Similar to hemoglobin – what is its function?) • Myofibrils contain the contractile fibers.

10. Myofibril • The myofibril is composed of “thick” and “thin” filaments. • Each of these filaments is made up of strands of protein. • How might this arrangement of proteins create motion?

11. Thick and thin filaments • The thick filaments, made mostly of myosin, have small “heads” that move. • The thin filaments have points to which the myosin heads temporarily attach.

12. Muscle fiber action

13. All or nothing • Fibers are either “on” (contracted) or “off” (relaxed). • When lifting light weights, only a few fibers may be “on.” For heavy weights, many more may be “on,” and may take turns to prevent fatigue.

15. Slow Twitch, Fast Twitch • Slow-twitch fibers: lots of myoglobin and mitochondria. What activities would use these fibers?. • Fast-twitch: less myoglobin, but more able to use glycolysis to quickly produce ATP. What activities would use these fibers? • Different people have different ratios of these two fibers.

16. Fast-twitch fibers • Fast-twitch fibers are for bursts of strength and speed. • The tradeoff: Fast-twitch fibers fatigue sooner.

17. Slow-twitch fibers • Slow-twitch fibers are for endurance. • Trade-off: Slow-twitch fibers cannot supply a lot of power at once.

18. Working out • Exercise can build muscle mass. However, because muscle fibers (cells) are large, they rarely divide. • If muscle cells rarely divide, how do muscles get bigger from exercise?

19. Stretching • Stretching exercises add strength and flexibility by increasing muscle length. • Again, if muscle cells do not divide, how does a cell get longer from stretching? • Caution: stretching tendons can weaken joints.

20. Try this: • Hold your pen or pencil so that it casts a shadow on your paper. Line up the tip of the shadow with a point on your paper. • How still can you hold your hand? Does the point of the shadow move? Muscles generally contract by continuous “twitching” of muscle fibers. This makes it hard to hold your hand completely steady.

21. Skeletal Systems

22. Types of systems • Three basic types of skeletal systems in the animal kingdom: • Hydrostatic • Exoskeleton • Endoskeleton

23. Hydrostatic skeleton • Earthworms and sea anemones have a hydrostatic skeleton. • Circular muscles squeeze the body. Longitudinal muscles shorten the body. How do these actions produce motion in the earthworm?

24. Exoskeleton • Arthropods (insects, spiders, etc) have an external skeleton made of chitin (a carbohydrate). • Muscles attach to the exoskeleton, which is flexible at the joints. • What are some advantages and disadvantages of an exoskeleton?

25. Endoskeleton • Vertebrates have an endoskeleton made of cartilage or bone. • Bone and cartilage are living tissue (connective tissue). • What are some advantages and disadvantages of an endoskeleton?

26. Functions of the endoskeleton • Support and protection for the body. • Locomotion (in concert with muscles). • Produce blood cells in bone marrow. • Store calcium and phosphorous. • Store energy in yellow marrow.

27. Cartilage • Cartilage tissue consists of chondrocytes (cartilage cells) in a matrix of collagen protein. • Cartilage is tough, flexible material that pads joints and is found in the nose and ears.

28. Bone tissue • Bone is made up of bone cells in a matrix of collagen and minerals. • Three types of bone cells: osteocytes, osteoblasts, and osteoclasts. • Looking at this arrangement, can you see why bone and cartilage take a long time to heal?

29. Bones • Bones may made up of: • Compact bone tissue. • Spongy bone (location of red marrow) • Marrow cavity (location of yellow marrow)

30. Healing fractures

31. Osteoporosis • Osteoporosis is loss of bone mass, leading to brittle bones. • Age, lack of calcium and Vitamin D, sedentary lifestyle, multiple pregnancies, menopause, alcohol, and smoking contribute to osteoporosis.

32. Locomotion

33. Motion in Vertebrates • Motion and locomotion are produced by muscles pulling on bones. • Joints in the skeleton allow for parts of the body to flex and extend, allowing for motion. Ligaments attach bones to bones at the joints. • Muscles attach to bones by tendons. Origin is on a bone that remains stationary. Insertion is on a bone that moves.

34. Hinge joint • A hinge joint allows flexing and extending along one plane. • Pairs of muscles work opposite one another to create motion.

35. Ball and socket joint • A ball and socket arrangement allows rotational movement. • Multiple pairs of muscles allow movement in a range of directions.

36. Gliding joints • In gliding joints, bones slide past one another. • Gliding joints allow twisting motion.

37. Movement • Flexion: decreases angle of a joint. • Extension: increases angle of a joint. • Abduction: movement away from midline. • Adduction: movement toward midline. • Rotation: turning around an axis.

38. One last question: • In what ways do muscles and the skeletal system help maintain homeostasis? Discuss and list as many ways as you can think of.