15. - each muscle fiber is connected to a motor neuron - nerve fiber meets at the motor end plate
16. - end of motor neurons contains synaptic vesicles that have neurotransmitters in them - one motor neuron can control many muscle fibers motor unit
18. Skeletal Muscle Contraction a specific sequence of events needs to occur in order for a muscle fiber to contract - it starts with a nerve impulse traveling down a motor neuron axon - the nerve impulse causes the synaptic vesicles to release the neurotransmitter ACh - the ACh attaches to ACh receptors on sarcolemma then is broken down by acetylcholinesterase Neurotransmitter release
19. - the nerve impulse travels through the muscle fiber which causes the sarcoplasmic reticulum to release Ca 2+ ions - the calcium attaches to the troponin protein which will then move the tropomyosin proteins to uncover the active site on the actin
20. - the myosin heads attach to the active site on the actin filament - ATP is used, and the myosin pulls on the actin by the myosin cross-bridges - the muscle shortens as a contraction occurs Muscle contraction - the muscle will stay contracted until the Ca 2+ is reabsorbed by the SR - the active site will be covered up - actin slides back into its original position Muscle contraction 1
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22. Energy Sources for Contraction - ATP supplies the energy - ADP needs to be regenerated into ATP - can borrow a phosphate from creatine phosphate - regenerate through the process of cell respiration
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24. - myoglobin - can store O 2 in muscles for cell respiration - if O 2 levels are low and oxygen debt occurs glucose pyruvic acid lactic acid cramps
25. - can lead to muscle fatigue muscle loses ability to contract
26. Muscular Response Threshold Stimulus - minimal strength needed to start a contraction All - or - None Response - a muscle fiber will contract or it will not - no partial contractions Recruitment - the greater the stimulus, the more motor units will be activated, more muscle fibers will contract
27. The myogram latent period contraction period relaxation period recovery period
28. latent period - time between stimulus and contraction contraction period - time for the muscle to contract relaxation period - actin slides back into place recovery period - O 2 resupplied to muscles
29. Muscular hypertrophy - muscles get larger due to increased use Muscular atrophy - muscles get smaller due to less use
30. Smooth Muscle - thin - contains actin and myosin - are randomly arranged no striations 2 Types a) Multiunit - found in eye and blood vessels - contracts only after receives a nerve impulse
31. b) Visceral - found in internal organs - displays rhythmic patterns - muscles able to stimulate each other - no continuous stimulus needed - Contraction is almost the same as in skeletal muscles - besides ACh, can be stimulated by norepinephrin - contraction occurs more slowly - muscles are able to stretch
32. Cardiac Muscles - only found in the heart - has actin and myosin - contains many mitochondria
33. Muscular Dystrophy caused by a defective gene the muscle fibers are unusually susceptible to damage muscles become weaker and may be replaced by fat and connective tissue there are over 40 types of MD there is no cure
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35. Anabolic Steroids Anabolic steroids change muscle mass and strength by three processes. 1. Increases the production of proteins 2. Blocks the hormone cortisol , which decreases muscle breakdown 3. Leads cells to differentiate into muscle more readily than fat
