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Three properties of a muscle that is concerning us in this chapter
Excitability- respond to chemicals released from nerve cells
Conductivity- ability to propagate electrical signals over membrane
Contractility - ability to shorten and generate force
Describe the five stages of muscle contractions
Nerve impulses reaches an axon terminal & synaptic vesicles release acetylcholine
ACh diffuses to receptors on the sarcolemma and Na+ channels open and Na+ rushes to cell
A muscle action potential spreads over sarcolemma and down transverse tubules
SR releases Ca+2 into sarcoplasm
Ca+2 binds to troponin and causes troponin- tropomyosin complex to move and reveal myosin binding sites an actin the contraction cycle begins
Describe what happens to filaments of muscle
Myosin cross bridges pull on thin filaments
Thin filaments slide inward
Z Discs come toward each other
Sarcomeres shorten the muscle fiber shorten the muscle shortens
Force of muscle contraction depends on the length of the sarcomere
Too stretched =
Too contracted =
Too stretched = less over lap less cross bridges
Too contracted = good overlap but Z-discs crumpled myosin heads z discs block this process - wrist flexors making a fist
If the force generated by the muscle is greater than the external force =
Concentric
If the force generated by the muscle is equal to the external force =
Isometric
If the force generated by the muscle is less that the external force =
Eccentric
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