Muscle Physiology. Outline I.Skeletal Muscle Structure II.Muscle Contraction: Cell Events III.Muscle...
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Transcript of Muscle Physiology. Outline I.Skeletal Muscle Structure II.Muscle Contraction: Cell Events III.Muscle...
![Page 1: Muscle Physiology. Outline I.Skeletal Muscle Structure II.Muscle Contraction: Cell Events III.Muscle Contraction: Mechanical Events IV.Muscle Metabolism.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d585503460f94a37699/html5/thumbnails/1.jpg)
Muscle Physiology
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Outline
I. Skeletal Muscle Structure
II. Muscle Contraction: Cell Events
III. Muscle Contraction: Mechanical Events
IV. Muscle Metabolism
V. Types of Skeletal Muscle Fibers
VI. Smooth and Cardiac Muscles
![Page 3: Muscle Physiology. Outline I.Skeletal Muscle Structure II.Muscle Contraction: Cell Events III.Muscle Contraction: Mechanical Events IV.Muscle Metabolism.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d585503460f94a37699/html5/thumbnails/3.jpg)
Outline
I. Skeletal Muscle Structure
II. Muscle Contraction: Cell Events
III. Muscle Contraction: Mechanical Events
IV. Muscle Metabolism
V. Types of Skeletal Muscle Fibers
VI. Smooth and Cardiac Muscles
![Page 4: Muscle Physiology. Outline I.Skeletal Muscle Structure II.Muscle Contraction: Cell Events III.Muscle Contraction: Mechanical Events IV.Muscle Metabolism.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d585503460f94a37699/html5/thumbnails/4.jpg)
1- Skeletal Muscle Structure
– Muscle = group of fascicles– Muscle fibers extend length of muscle from tendon to
tendon
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Motor units
• Motor unit: Composed of one motor neuron and all the muscle fibers that it innervates
• There are many motor units in a muscle
• The number of fibers innervated by a single motor neuron varies (from a few to thousand)
• The fewer the number of fibers per neuron the finer the movement (more brain power)
• Which body part will have the largest motor units? The smallest?
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Components of a muscle fiber
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Figure 12.2 (2 of 2)
Muscle fiber components
• Sarcolemma: muscle cell membrane
• Sarcoplasma: muscle cell cytoplasm
• Motor end plate: contact surface with axon terminal
• T tubule: cell membrane extension into the sarcoplasm (to reach the myofibrils)
• Cisternae: areas of the ER dedicated to Ca++ storage (located on each side of the T-tubules)
• Myofibrils: organized into sarcomeres
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The sarcomere
• The myofibrils are organized into a repetitive pattern, the sarcomere
• Myosin: thick filament• Actin: thin filament• Bands formed by pattern:
A and I and H bands• Z line: area of attachment
of the actin fibers• M line: Myosin fiber
centers
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Figure 12.5d
The sarcomere
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Myosin structure
• Many myosin molecules per filament, golf club shape
• Long tail topped by a thickening: the head forms crossbridges with the thin filament
• Presence of the enzyme, ATPase in the head release energy for contraction
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Figure 12.4
Actin structure• Formed by 3 different
proteins: - globular (G) actins: bind to
myosin heads - tropomyosin: long, fibrous
molecule, extending over actin, and preventing interaction between actin and myosin
- troponin: binds reversibly to calcium and able to move tropomyosin away from the actin active site
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Outline
I. Skeletal Muscle Structure
II. Muscle Contraction: Cell Events
III. Muscle Contraction: Mechanical Events
IV. Muscle Metabolism
V. Types of Skeletal Muscle Fibers
VI. Smooth and Cardiac Muscles
![Page 13: Muscle Physiology. Outline I.Skeletal Muscle Structure II.Muscle Contraction: Cell Events III.Muscle Contraction: Mechanical Events IV.Muscle Metabolism.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d585503460f94a37699/html5/thumbnails/13.jpg)
Figure 11.13
2- Muscle contraction: Cell events
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Synaptic events• The AP reaches the axonal
bulb• Voltage-gated calcium
channels open• The influx of calcium in the
bulb activates enzymes the vesicles containing the neurotransmitter molecule dock and release the neurotransmitter in the synapse
• The neurotransmitter for skeletal muscles is always acetylcholine
• The receptors on the muscle fiber are cholinergic receptors
• These receptors are nicotinic (fast) acting receptors
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2- The Mechanism of Force Generation in Muscle
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Figure 12.7
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Figure 12.6
• http://www.blackwellpublishing.com/matthews/myosin.html
• http://www.ebsa.org/npbsn41/intro_muscle.html
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Muscle relaxation• Ach is removed from the
receptors by acetylcholinesterase
• Ligand-gated Na+channels close
• Na/K pumps reestablish the RMP
• Ca++ ions leave troponin and are brought back into the cisternae (this process needs energy)
• Tropomyosin moves back over the actin active site
• The myosin heads release their binding to actin
• The filaments passively move back into resting position
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Applications• Myasthenia gravis: autoimmune disease where antibodies against
the Ach receptors are produced. Which consequences do you expect?
• Muscular dystrophy: some proteins forming the muscle fibers are abnormal. Which consequences do you expect?
• Curare binds to the Ach receptor without activating them. What are the effect of curare on the skeletal muscle?
• The botulism toxin prevents the release of the neurotransmitter into the synapse. What will be the consequence?
• Nerve gas inhibits acetylcholinerestase present in the synapse. What will be the consequence?
•
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• Rigor mortis: why does the body stiffen shortly after death?
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Outline
I. Skeletal Muscle Structure
II. Muscle Contraction: Cell Events
III. Muscle Contraction: Mechanical Events
IV. Muscle Metabolism
V. Types of Skeletal Muscle Fibers
VI. Smooth and Cardiac Muscles
![Page 22: Muscle Physiology. Outline I.Skeletal Muscle Structure II.Muscle Contraction: Cell Events III.Muscle Contraction: Mechanical Events IV.Muscle Metabolism.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d585503460f94a37699/html5/thumbnails/22.jpg)
3- Muscle contraction: Mechanical events
• 1 stimulation 1 twitch
• Muscle twitch: 3 phases:
- latent phase
- contraction phase
- relaxation phase
☻ do not confuse the AP and the twitch!!!
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Figure 12.16
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Events during the twitch
• Latent phase: Stimulus to beginning contraction: AP to myosin binding to actin active site
• Contraction phase: beginning to end of muscle tension myosin heads slide along the actin filaments
• Relaxation phase: peak tension to no tension Ca++ ions moved back into the cisternae, tropomyosin moves back over actin, myosin head release actin and the filaments move back into resting position
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Figure 12.18
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Isometric/isotonic contractions
• Isometric: muscle contraction without movement no muscle shortening
• Isotonic: muscle contraction with movement muscle shortens
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Figure 12.15
Effect of consecutive stimuli: Treppe
• Treppe: gradual increase in contraction intensity during sequential stimulation
• Might be due to calcium ions accumulating in the cytoplasm with each stimulation
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Figure 12.17
Summation and tetanus
• Summation: Rapid sequence of stimuli muscle twitches fuse into each other, each subsequent one being stronger that its precedent (due to Ca++?)
• Tetanus: very rapid sequence of stimuli: no relaxation
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Figure 12.19
Recruitment
• An increase in force is made possible by recruiting more motor units
• Muscles have various sizes of motor units allows them to adjust the size of the effort to be made
• Activating motor units alternatively allows the muscle to sustain contraction with minimal fatigue
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Outline
I. Skeletal Muscle Structure
II. Muscle Contraction: Cell Events
III. Muscle Contraction: Mechanical Events
IV. Muscle Metabolism
V. Types of Skeletal Muscle Fibers
VI. Smooth and Cardiac Muscles
![Page 31: Muscle Physiology. Outline I.Skeletal Muscle Structure II.Muscle Contraction: Cell Events III.Muscle Contraction: Mechanical Events IV.Muscle Metabolism.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d585503460f94a37699/html5/thumbnails/31.jpg)
IV- Muscle metabolism• Muscle fibers use ATP (only
first few seconds) for contraction
• ATP must then be generated by the muscle cell:
- from creatine phosphate, first - from glucose and glycogen - from fatty-acids
ATP formation from the above compound is possible if oxygen is present (oxidative phosphorylation: 36 ATP per glucose)
Oxygen is delivered to the muscle by myoglobin, a molecule with high affinity to oxygen and related to hemoglobin
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Figure 12.11
If the effort is strong and sustained, the muscle might not have enough oxygen delivered to it by myoglobin anaerobic glycolysis with only 2 ATP formed per glucose and synthesis of lactic acid
Consequence of anaerobic metabolism?
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Muscle fatigue• Muscle fatigue: a decline in the
ability of the muscle to sustain the strength of contraction
• Causes: - rapid build-up of lactic acid - decrease in oxygen supply - decrease in energy supply
(glucose, glycogen, fatty-acids)- Decreased neurotransmitter at
the synapse - psychological causes
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Effects of exercise on the muscle
• Aerobic exercises: long sustained exercises promote increased oxidative capacity of the muscle fiber increased blood vessel supply, increased mitochondria
• High intensity, short burst exercise: increased glycolytic activity increased synthesis of glycolytic enzymes, increased synthesis of myofibrils (increased muscle size)
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Outline
I. Skeletal Muscle Structure
II. Muscle Contraction: Cell Events
III. Muscle Contraction: Mechanical Events
IV. Muscle Metabolism
V. Types of Skeletal Muscle Fibers
VI. Smooth and Cardiac Muscles
![Page 36: Muscle Physiology. Outline I.Skeletal Muscle Structure II.Muscle Contraction: Cell Events III.Muscle Contraction: Mechanical Events IV.Muscle Metabolism.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d585503460f94a37699/html5/thumbnails/36.jpg)
Figure 12.23
V- Types of Muscle Fibers• Various muscles contract at different speed
composed of different types of muscle fibers
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Basis for classification
• Velocity of contraction: slow vs fast
• Energy source: oxidative vs glycolytic
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Oxydative Glycolytic
Primary energy through oxidative phosphorylation
– Many mitochondria– Myoglobin (red)– Small diameter– Resistant to fatigue
Primary energy through anaerobic glycolysis
– Fewer mitochondria– Many glycolytic
enzymes– High glycogen stores– Use little oxygen—
anaerobic– Large diameter– Quick to fatigue
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• Which types of meat are chicken breast and duck breast?
• Why the difference?
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Outline
I. Skeletal Muscle Structure
II. Muscle Contraction: Cell Events
III. Muscle Contraction: Mechanical Events
IV. Muscle Metabolism
V. Types of Skeletal Muscle Fibers
VI. Smooth and Cardiac Muscles
![Page 42: Muscle Physiology. Outline I.Skeletal Muscle Structure II.Muscle Contraction: Cell Events III.Muscle Contraction: Mechanical Events IV.Muscle Metabolism.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d585503460f94a37699/html5/thumbnails/42.jpg)
VI- Smooth and Cardiac Muscles
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Skeletal Cardiac Smooth
Appearance
Control voluntary unvoluntary Unvoluntary
Neural input somatic ANS ANS
Hormone 0 Epi Epi/others
Ca++ prot Troponin Troponin Calmodulin
Gap junctions No Yes Yes
Pacemaker No Yes No
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Readings
• Chp. 12, p. 323-359