Chapter 42 – The Animal Body and How It Moves
1. Organization of the Animal Body (read pages 856-866)
a. Review these diagrams on your own
i. Page 857 fig 42.4 – Levels of Organization Within the Body
ii. Page 856 fig. 42.3 – Four Vertebrate Tissue Types
2. Striated Muscle Tissue Structure – see page 867
a. One of three types of muscle tissue
b. Muscle fibers (muscle cells) – see page 868 and 876 and 877
i. Sarcolemma
1. Cell membrane
2. Propagate impulse (action potential)
ii. Sarcoplasm (cytoplasm)
iii. Bundles of myofibrils
1. Push nuclei against sarcolemma
2. Consist of myofilaments
iv. Myofilaments
1. Overlap, give striated appearance
2. Two types of proteins
a. Actin
i. Thinner, chain of globular proteins
b. Myoxin
i. Thicker, two polypeptide chains with globular head
3. Arrangement of myofilaments – see page 877
a. Z line = protein disk to which actin attaches
b. Sarcomere – contractile unit. Z line to Z line
c. Sliding Filament Mechanism
i. A band = length of myosin
ii. I band = actin + Z band
iii. H band = myosin only
iv. During contraction…
1. A band stays same length, I band and H
bands decrease
2. Sarcomere decreases (Z line gets closer)
v. Sarcoplasmic Reticulum (smooth ER) – see page 878
1. Stores calcium ions
vi. T-system (transverse system)
1. Invagination of sarcolemma surrounding SR
2. Propogates (sends) impulse to SR
3. Regulation of Muscle Contraction
a. Initiated by voluntary impulse
b. Neuromuscular junction – see page 948
i. Where motor neurons synapse with one or more muscle fibers
ii. Acetylcholine (neurotransmitter) binds to sarcolemma receptor
iii. Impulse (depolarization of membrane) is initiated along sarcolemma
iv. http://highered.mcgraw-hill.com/olc/dl/120107/bio_c.swf
c. Impulse (Action potential) travels to T-system to Sarcoplasmic Reticulum
i. Voltage gated Ca+2 channels open
ii. Ca+2 released into sarcoplasm from the SR
4. Role of Two Regulatory Proteins – see page 878
a. Both are attached to actin
b. Troponin
i. Has binding site for Ca+2
c. Tropomyosin
i. Attached to troponin
ii. Covers binding sites for myosin heads on actin
d. Ca+2 in sarcoplasm attaches to troponin
i. Troponin changes shape
ii. Tropomyosin moves away from binding sites
iii. Myosin binding sites exposed
iv. Ca+2 activate ATPase in myosin head, energy released
v. Myosin head changes shape and binds to actin (cross-bridge)
vi. Contraction begins
5. Cross Bridge Cycle
a. At rest
i. Myosin head NOT attached to actin
ii. ATP intact
iii. ATPase inactive (part of head)
b. Impulse releases Ca+2 into sarcoplasm
i. Activates ATPase
ii. ATP hydrolyzed into ADP + Pi
iii. Myosin head changes shape towards actin
iv. Binding causes myosin head to change shape again
1. Actin pulled across myosin (Power stroke)
2. ADP and Pi released
v. New ATP attaches
1. Myosin head resumes original configuration (shape)
2. Actin is released
vi. As impulses continue releasing Ca+2 power strokes (cross bridge cycle)
continue
vii. Sliding Filament Mechanism
1. Myosin pulls/slides actin across with each cross-bridge cycle
2. Sarcomere decreases (Z-bands closer together)
3. H band decreases (actin slides over myosin)
4. I band decreases (Z bands pulled by actin)
5. A band remains same (length of myosin)
viii. When impulse stops…
1. Ca+2 pumped back into SR
2. Ca+2 removed from tropinin
3. Tropomyosin slides back over binding sites
4. Myosin heads detach
5. Actin filament slides back to resting state
6. ATP attaches to myosin head
ix. In death, no ATP…
1. Myosin heads stay attached to actin = rigor mortis