BIOL 1030 Introduction to Biology: Organismal Biology. Fall 2009 Sections B & D. Steve Thompson:

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1 BIOL 1030 Introduction to Biology: Organismal Biology. Fall 2009 Sections B & D Steve Thompson: stthompson@valdosta.edu 1

2 Motion the skeleton and muscles The musculoskeletal system What holds us up against gravity, supports and protects our internal organs, makes a bunch of those organs work, and gives us the ability to move. Muscles provide motion, and the... Skeleton adds a firm supporting structure for muscles to pull against, and gives shape and protection to the body. 32

3 Skeletons come in many flavors. The simplest is a... Hydrostatic skeleton, which is merely... Fluid constrained within a flexible tissue. 3

4 An exoskeleton is the next simplest. It is the... Calcium-containing shells of mollusks or the jointed chitin exoskeletons of arthropods. But these critters have to molt to grow beyond a certain size! 4

5 Many animals use an endoskeleton. This is composed of... Internal plates, cartilage, or bone. For example, star fishes use and other echinoderms use calcium rich internal spines and plates; and... Sharks and rays have internal skeletons entirely composed of cartilage. 5

6 Vertebrate skeleton Most vertebrates have an internal skeleton made of bone and cartilage. Axial skeleton skull, vertebral column, ribs, and sternum; Appendicular skeleton appendages and the bones that support them; Pectoral girdle clavicles, scapulae, support the arms; Pelvic girdle hipbones, sacrum, support the legs. 6

7 Axial versus appendicular... the ankle bone s connected to the... 7

8 Dem Bones the Skeleton Dance 8

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11 Bones (not the TV show)... Support and protect the body. They are... Connected to muscles to provide movement. They also supply calcium and minerals when the body needs it (negative feedback loop). And are the site of much blood cell formation. There are many bone shapes but they are all lightweight and strong because they are porous. Plus there is a marrow cavity in long bones. 11

12 The majority of the vertebrate skeleton consists of bone and cartilage. Bone cells suspended in a matrix of collagen and minerals. Consist of: Osteoblasts bone-forming cells; Osteocyte former osteoblast embedded in matrix; Osteoclast bone-degrading cell; Osteon set of concentric rings of osteocytes; Compact bone has closely packed osteons. Spongy bone has large spaces. And it has... Red bone marrow where blood cells are produced. 12

13 Zoom in on a bone 13

14 What is cartilage? Chondrocytes secrete collagen and elastin, which make cartilage both... Firm and flexible. However, it... Lacks a blood supply, which makes it... Slow to heal. But it has a very... High water content that provides bathing nutrients and shock absorbancy. 14

15 Some cartilages in your body 15

16 Bone growth Most bones originate as cartilage models in the embryo. Osteoblasts enter and secrete bone causing the bone to calcify and become rigid. After birth, bone growth is concentrated near the growth plates at the ends of the long bones. Even after a person stops growing, bone is continually under reconstruction. 16

17 And it ll regrow after breaking, even without properly being set. 17

18 Bones are a reservoir for calcium. As we saw last time, hormones from the parathyroid and thyroid control the exchange in a negative feedback loop. 18

19 Osteoporosis bones lose more calcium than they add as a person ages, particularly women due to hormone effects after menopause (osteoporotic bone on right). 19

20 Bone remodeling and calcium loss Chapter31/osteoporosis_final.swf 20

21 Joint the area where two bones meet not the ones smoked. Synovial joints consist of movable bones joined by a fluid-filled capsule of fibrous connective tissue. Ligaments connective tissue attaching one bone to another. Tendon attach bone to muscle. Arthritis is a common disorder of joints. 21

22 What the type of joint we re talking about looks like 22

23 Rheumatoid arthritis is a debilitating autoimmune disease where the body attacks its own joints! 23

24 OK, what about the muscles of the muscuskeletal system? Skeletal muscles generate voluntary movements between pairs of bones. There are more than 600 skeletal muscles in humans. They can only pull, never push. Therefore,... Antagonistic pairs of muscles provide back-and-forth movements. 24

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27 Here s a few of them don t worry about memorizing their names, though you probably already know some of them. 27

28 Antagonistic action 28

29 Muscle tissue consists of muscle fibers. Muscle fibers are individual muscle cells combined into bundles. The fiber can be 30 cm long and has many nuclei. Most of the volume of a fiber made up of hundreds of thousands of myofibrils. Myofibril contractile bundle made of: Thin filaments actin, and... Thick filaments myosin. 29

30 Here s an overview video. 30

31 We ll look at each of the parts in more depth. 31

32 The sliding filament model Sarcomere repeated units of a myofibril. Muscle fiber contracts when the thin filaments slide between the thick filaments. This shortens the sarcomere. The myosin head forms cross bridges that contact actin molecules. ATP provides the energy. The whole thing ratchets with each ATP. 32

33 In more detail 33

34 And in real life... 34

35 Here s an overview animation. Chapter31/sarcomere_contraction.swf 35

36 And a zoom-in of the mechanism Chapter31/myofilament.swf 36

37 And in even more detail... Chapter31/BreakdwnDrngCntrctn.swf 37

38 A neuromuscular junction is the... Synapse between a neuron and the muscle cell. A motor neuron conveys a message from CNS to the muscle for that muscle to contract. This causes a... Neurotransmitter to cross the cleft of the synapse and bind to receptors on the muscle fiber s cell membrane. The cell membrane is highly folded here and extends deep into the interior of the muscle fiber cell. The... Impulse causes the endoplasmic reticulum to release calcium ions. These... Calcium ions bind to regulatory proteins on the actin molecules. This causes those regulatory... Proteins to move aside allowing the muscle freedom to contract. The filament sliding stops when calcium is no longer available. 38

39 Here s a diagram. 39

40 Energy requirements Skeletal muscle contraction requires huge amounts of ATP, so there s lots and lots of mitochondria. Remember, this is where... Much of aerobic respiration occurs. Creatine phosphate can rapidly replenish ATP by donating a high-energy phosphate to ADP. But fermentation takes over, if oxygen runs low. This causes lactic acid buildup, which makes your muscles burn. Oxygen debt means the body needs to replenish ATP and creatine stores as well as oxygen. 40

41 How do the nerves modulate muscle activity? Twitch the electrical stimulation of an isolated muscle produces a single rapid cycle of contraction and relaxation. However,... Jerky movement like this is not (usually) found in body. Two integrated mechanisms coordinate the action: 1. In individual muscle cells a high rate of action potentials produces tetanus (smooth, maximal contraction caused by continuous stimulation). 2. Motor units (one neuron and all the muscle fibers that it innervates) that control a few fibers produce finescale movements while those controlling large numbers of fibers produce large, coarser movements. 41

42 From twitch to tetanus 42

43 Fast versus slow twitch, huh? Skeletal muscle fibers fall into two categories dependent on how quickly they contract and tire. Slow twitch muscle fibers ( dark meat ) are fatigue resistant and contract slowly because they have more mitochondria and myoglobin and their myosin heads split ATP more slowly than... Fast twitch muscle fibers ( white meat ), which fatigue quickly, but can provide large busts of power because they split ATP very quickly. They run out of steam quickly because they have to rely on anaerobic pathways to generate ATP. 43

44 Enough! We ll cover how the body gets oxygen in and around the body, and gets rid of carbon dioxide next time. 44