Physiology of a Muscle Unit 4 Part 2 Notes. What functional properties allow a muscle to perform its...
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Transcript of Physiology of a Muscle Unit 4 Part 2 Notes. What functional properties allow a muscle to perform its...
![Page 1: Physiology of a Muscle Unit 4 Part 2 Notes. What functional properties allow a muscle to perform its duties? Irritability – Ability to receive and respond.](https://reader030.fdocuments.in/reader030/viewer/2022032702/56649ce65503460f949b3ab9/html5/thumbnails/1.jpg)
Physiology of a Muscle
Unit 4Part 2 Notes
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What functional properties allow a muscle to perform its duties?
• Irritability–Ability to receive and respond to a
stimulus• Contractility
–Ability to shorten when adequate stimulus is received
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What functional properties allow a muscle to perform its duties?
• Conductivity–Ability for impulse to travel along
plasma membrane of muscle cell• Elasticity
–Ability to recoil and resume original length
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What role does the nervous system play in muscle movement?
• Motor Unit – one neuron and all the skeletal muscle cells it stimulates
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Within a motor unit…
• Muscle Fibers
• Axons
• Axon Terminals (neuromuscular junctions)
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Nerve endings and muscle fibers don’t physically touch…
• Neuromuscular juction – where axon terminals match up with muscle fibers
• Snyaptic cleft – space between nerve endings and muscle fibers; chemical impulses travel here between nerve endings and muscle
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Two Major Steps Of Muscle Contractions(Not in your packet-o-notes)
1st Stimulation of Muscle by Nerve• The brain sending a
message through a neuron to the muscles to simply tell that muscle to MOVE!
Video #1: http://
tinyurl.com/NerveImpulse
2nd Muscle Contraction
• Once the muscle has the message from the brain to move, the muscle will move its fibers and contract.
Video #2http://tinyurl.com/aqspwh
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What steps occur to stimulate muscle movement?
• 1. Nerve impulse reaches axon terminals
• 2. Chemical Neurotransmitter (ACh – acetylcholine) released
• 3. ACh diffuses across synaptic cleft and attaches to receptors
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What steps occur to stimulate muscle movement?
• 4. ACh causes the sarcolemma to become temporarily permeable to Na+
• 5. Na+ rush into the muscle cell
• 6. Excess of positive ions creates electric current (action potential)
• 7. Muscle contracts (another whole set of steps!)
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http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__action_potentials_and_muscle_contraction.html
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__myofilament_contraction.html
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__sarcomere_contraction.html
More animations which may help you understand how a muscle contracts!
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• So, we know how muscle contraction is stimulated… but now we need to know the steps that help muscle contraction to happen!
• Called the Sliding Filament Theory
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The Sliding Filament Theory
• Muscle fibers activated by nervous system due to action potential
• Calcium ions (Ca+2) happen to be released– Do you remember which structure releases those
calcium ions???
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The Sliding Filament Theory
• Muscle fibers activated by nervous system due to action potential
• Calcium ions (Ca+2) happen to be released– Do you remember which structure releases those
calcium ions???– THE SARCOPLASMIC RETICULUM
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The Sliding Filament TheoryNote: this part is worded a little differently than your packet-o-notes
• Release of Ca+2 binds to troponin which then moved tropomyosin out of the way and stops it from blocking binding sites on the thin filament (actin).
• Once Actin is unblocked, the cross-bridges on the thick filaments(Myosin) attach to the binding sites on the Actin
• Let the sliding begin!
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The Sliding Filament Theory
• Energized by energy from ATP, cross-bridges attach and detach from thin filaments
• Works like an oar to keep moving thin filaments closer and closer together (Attach, pull, detach!)
Check this video to see how it works! http://tinyurl.com/aqspwh
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The Sliding Filament Theory
• As this process is happening in every sarcomere throughout the muscle, the muscle itself is contracting!
• The whole series of events (beginning with the nervous system signal) takes just a few thousandths of a second!!!
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ADP
Pi
Net entry of Na+ Initiatesan action potential whichis propagated along thesarcolemma and downthe T tubules.
T tubuleSarcolemma
SR tubules (cut)
SynapticcleftSynaptic
vesicle
Axon terminal
ACh ACh ACh
Neurotransmitter released diffusesacross the synaptic cleft and attachesto ACh receptors on the sarcolemma.
Action potential inT tubule activatesvoltage-sensitive receptors,which in turn trigger Ca2+
release from terminalcisternae of SRinto cytosol.
Calcium ions bind to troponin;troponin changes shape, removingthe blocking action of tropomyosin;actin active sites exposed.
Contraction; myosin heads alternately attach toactin and detach, pulling the actin filaments towardthe center of the sarcomere; release of energy byATP hydrolysis powers the cycling process.
Removal of Ca2+ by active transportinto the SR after the actionpotential ends.
SR
Tropomyosin blockage restored,blocking myosin binding sites onactin; contraction ends andmuscle fiber relaxes.
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
1
2
3
4
5
6
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The Sliding Filament Theory• Notice in the contracted
muscle, the H zone has disappeared
• The I band has shortened significantly (all that’s left is the Z disc)
• The A band (the dark striations!) have stayed the same thickness
• Check out this animation to see what happens to the sarcomere!! http://tinyurl.com/5u8q25b
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Where’s all this energy coming from?
• As a reminder, energy comes from ATP because of breaking a phosphate bond
• Breaking a bond releases energy• When this energy is used by your body,
it releases heat• Because ATP is the only energy source
that can be used to move the cross-bridges back and forth (which contract the muscle), ATP must be regenerated continuously
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ATP Regeneration – 3 Sources
• Direct phosphorylation of ADP by creatine phosphate– When ATP used, changes to ADP– Creatine phosphate adds that missing phosphorous
back on!– PROBLEM: only makes 1 ATP at a time… so not very
much. And, only supplies energy for 15-20 seconds of activity!
– Your body will always do this, but it’s not very effective. Therefore, we have to have other ways of supplying energy…..
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ATP Regeneration – 3 Sources• Aerobic respiration
– Occurs in the mitochondria– Glucose broken down to pyruvic acid (releasing 2
ATP), and then into carbon dioxide and water (releasing 34 ATP)
– 36 ATP made for 1 glucose! A lot of energy! And, can supply energy for hours at a time!
– PROBLEM: NEEDS OXYGEN
– But what if you’re out of oxygen??? Then your muscles will begin……..
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ATP Regeneration – 3 Sources
• Anaerobic glycolysis and lactic acid formation– Glucose broken down to pyruvic acid, releasing 2
ATP– If oxygen present, process continues to the rest of
aerobic respiration…– BUT… if oxygen is inadequate, or muscle activity is
intense, pyruvic acid is instead changed to lactic acid
– PROBLEM: Buildup of lactic acid is not good… promotes muscle fatigue and soreness. And, only supplies energy for 30 seconds of activity!
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ATP Regeneration
• 95% of ATP produced through aerobic respiration
• C6H12O6 (aq) + 6O2 (g) → 6CO2 (g) + 6H2O + ATP
• If you don’t have proper blood circulation or breathing, muscles can’t get oxygen needed for aerobic respiration
• If they can’t get oxygen, they can’t produce enough ATP, which means muscles can’t contract!
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Muscle Fatigue• A muscle is fatigued when it is unable to contract
even though it is being stimulated – means you don’t have ATP to move the cross-bridges!
• Lack of oxygen can cause…– Lactic acid buildup (anaerobic glycolysis)– ATP supply low (production can’t keep up with
usage)– Muscle will contract less and less effectively,
eventually stopping contraction completely
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Muscle Fatigue
• FYI: When you breathe heavy after physical activity, your muscles are trying to get enough oxygen for aerobic respiration to replace all of the ATP you used!
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Muscle Contraction
• Isotonic contractions–Myofilaments slide, shortening the
muscle–Movement occurs – bending knee,
rotating arms, smiling
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Muscle Contraction
• Isometric contractions–Myofilaments trying to slide, but
can’t – just building up tension (crossbridges are “rowing”, but actin is not moving together)
–Movement doesn’t occur – object too heavy to lift, push against wall
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Muscle Tone
• Muscle tone – sustained partial contraction of a muscle; muscle stays firm, healthy, and ready for action
• Muscle inactivity can lead to muscle weakness and wasting (this is why Range of Motion exercises on bedridden people is important!)
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Effect of Exercise on Muscles
• Aerobic exercises include…–Running–Jogging–Biking–Elliptical
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Effect of Exercise on Muscles
• Increase endurance of muscles because muscle cells will form more mitochondria and store more oxygen (meaning more energy for the muscles)
• Also – improves body metabolism, improve digestion, enhance coordination, strengthens skeleton, heart & lungs more efficient
• Muscles do NOT increase in size!
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Effect of Exercise on Muscles• Resistance exercises include…
– Pushing against wall– Contracting muscles (likes gluteus maximus)– Lifting weights
• Does increase muscle size!– Due to enlargement of individual muscle cells (makes
more myofilaments)– You don’t add more muscle cells – you just bulk up
the ones you already have!!!–
• NEED BOTH TYPES OF EXERCISES IN ANY TRAINING PROGRAM!