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Muscles & Motor Locomotion Why Do We Need All That ATP?

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Presentation on theme: "Muscles & Motor Locomotion Why Do We Need All That ATP?"— Presentation transcript:

1 Muscles & Motor Locomotion Why Do We Need All That ATP?

2 Muscle involuntary, striated auto-rhythmic voluntary, striated heart
All cells have a fine network of actin and myosin fibers that contribute to cellular movement. But only muscle cells have them in such great abundance and far more organized for contraction. SMOOTH MUSCLE Smooth muscle was the first to evolve. Lining of blood vessels, wall of the gut, iris of the eye. Some contract only when stimulated by nerve impulse. Others generate electrical impulses spontaneously and then are regulated by nervous system. CARDIAC MUSCLE Small interconnected cell with only one nucleus. Interconnected through gap junctions. Single functioning unit that contract in unison via this intercellular communication. Mostly generate electrical impulses spontaneously. Regulated rather than initial stimulation by nervous system. SKELETAL MUSCLE Fusion of many cells so multi-nucleated. Attached by tendon to bone. Long thin cells called muscle fibers. moves bone multi-nucleated involuntary, non-striated digestive system arteries, veins evolved first

3 Organization of Skeletal muscle
plasma membrane nuclei tendon muscle fiber (cell) myofibrils myofilaments

4 Muscles movement Muscles do work by contracting
skeletal muscles come in antagonistic pairs flexor vs. extensor contracting = shortening move skeletal parts tendons connect bone to muscle ligaments connect bone to bone

5

6 Structure of striated skeletal muscle
Muscle Fiber muscle cell divided into sections = sarcomeres Sarcomere functional unit of muscle contraction alternating bands of thin (actin) & thick (myosin) protein filaments

7 Muscle filaments & Sarcomere
Interacting proteins thin filaments braided strands actin tropomyosin troponin thick filaments myosin

8 Thin filaments: actin Complex of proteins
braid of actin molecules & tropomyosin fibers tropomyosin fibers secured with troponin molecules

9 Thick filaments: myosin
Single protein myosin molecule long protein with globular head bundle of myosin proteins: globular heads aligned

10 Thick & thin filaments Myosin tails aligned together & heads pointed away from center of sarcomere

11 Interaction of thick & thin filaments
Cross bridges connections formed between myosin heads (thick filaments) & actin (thin filaments) cause the muscle to shorten (contract) sarcomere sarcomere

12 thick filament (myosin) So that’s where those 10,000,000 ATPs go!
Where is ATP needed? binding site thin filament (actin) myosin head ADP thick filament (myosin) 1 2 ATP So that’s where those 10,000,000 ATPs go! Well, not all of it! form cross bridge release cross bridge 1 1 1 3 shorten sarcomere Cleaving ATP  ADP allows myosin head to bind to actin filament 1 4

13 Closer look at muscle cell
Sarcoplasmic reticulum Transverse tubules (T-tubules) Mitochondrion multi-nucleated

14 Muscle cell organelles
Ca2+ ATPase of SR Muscle cell organelles Sarcoplasm muscle cell cytoplasm contains many mitochondria Sarcoplasmic reticulum (SR) organelle similar to ER network of tubes stores Ca2+ Ca2+ released from SR through channels Ca2+ restored to SR by Ca2+ pumps pump Ca2+ from cytosol pumps use ATP There’s the rest of the ATPs! But what does the Ca2+ do? ATP

15 Muscle at rest Interacting proteins
at rest, troponin molecules hold tropomyosin fibers so that they cover the myosin-binding sites on actin troponin has Ca2+ binding sites

16 The Trigger: motor neurons
Motor neuron triggers muscle contraction release acetylcholine (Ach) neurotransmitter

17 Nerve trigger of muscle action
Nerve signal travels down T-tubule stimulates sarcoplasmic reticulum (SR) of muscle cell to release stored Ca2+ flooding muscle fibers with Ca2+

18 Ca2+ triggers muscle action
At rest, tropomyosin blocks myosin-binding sites on actin secured by troponin Ca2+ binds to troponin shape change causes movement of troponin releasing tropomyosin exposes myosin- binding sites on actin

19 How Ca2+ controls muscle
Sliding filament model exposed actin binds to myosin fibers slide past each other ratchet system shorten muscle cell muscle contraction muscle doesn’t relax until Ca2+ is pumped back into SR requires ATP ATP ATP

20 Put it all together… 1 2 3 ATP 7 4 6 ATP 5

21 How it all works… Action potential causes Ca2+ release from SR
Ca2+ binds to troponin Troponin moves tropomyosin uncovering myosin binding site on actin Myosin binds actin uses ATP to "ratchet" each time releases, "unratchets" & binds to next actin Myosin pulls actin chain along Sarcomere shortens Z discs move closer together Whole fiber shortens  contraction! Ca2+ pumps restore Ca2+ to SR  relaxation! pumps use ATP ATP ATP

22 Fast twitch & slow twitch muscles
Slow twitch muscle fibers contract slowly, but keep going for a long time more mitochondria for aerobic respiration less SR  Ca2+ remains in cytosol longer long distance runner “dark” meat = more blood vessels Fast twitch muscle fibers contract quickly, but get tired rapidly store more glycogen for anaerobic respiration sprinter “white” meat

23 Muscle limits Muscle fatigue Muscle cramps lack of sugar low O2
lack of ATP to restore Ca2+ gradient low O2 lactic acid drops pH which interferes with protein function synaptic fatigue loss of acetylcholine Muscle cramps build up of lactic acid ATP depletion ion imbalance massage or stretching increases circulation

24 Diseases of Muscle tissue
ALS amyotrophic lateral sclerosis Lou Gehrig’s disease motor neurons degenerate Myasthenia gravis auto-immune antibodies to acetylcholine receptors Stephen Hawking

25 Botox Bacteria Clostridium botulinum toxin
blocks release of acetylcholine botulism can be fatal muscle

26 Rigor mortis So why are dead people “stiffs”? no life, no breathing
no breathing, no O2 no O2, no aerobic respiration no aerobic respiration, no ATP no ATP, no Ca2+ pumps Ca2+ stays in muscle cytoplasm muscle fibers continually contract tetany or rigor mortis eventually tissues breakdown & relax measure of time of death

27 So don’t be a stiff! Ask Questions!!

28 Ghosts of Lectures Past (storage)

29 Shortening sarcomere Myosin pulls actin chain along toward center of sarcomere Sarcomere shortens (Z lines move closer together) Muscle contracts energy from: ATP glycogen Z Z Z Z

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