Post on 06-Apr-2017
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Physiology of Skeletal Muscle
Dr. Fanny Casado fanny.casado@pucp.edu.pe
ING338: Human Physiol. for Engineers. 2017-1
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Learning objectives Explain the relationship between muscle
power with load and muscle type to explain how striated muscle converts action potential into mechanical movement.
Use the Hill’s muscle model to explore length-tension energetics and force-velocity relationships.
ING338: Human Physiol. for Engineers. 2017-1
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ING338: Human Physiol. for Engineers. 2017-1
Movement and heat
Organ pressure
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Type of contraction
Distance change Function Work
Concentric Shortening (+ D) Acceleration + Isometric No change (0 D) Fixation 0 Eccentric Lenghthening (- D) Deceleration -
Power = Energy / time Energy = Work = Force x(distance) Power = (Force x distance)/time
Muscle power varies with the load and muscle type
ING338: Human Physiol. for Engineers. 2017-1
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Experimental set-up for measuring isometric force in an isolated muscle
ING338: Human Physiol. for Engineers. 2017-1
Muscle contraction or Twitch
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The motor unit consists of all of the muscle fibers innervated by a single motor neuron
ING338: Human Physiol. for Engineers. 2017-1
Cerebrum’s motor cortex or Sensory input
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Increase in the muscle twitch with increased recruitment of motor fibers by increasing the strength of the external stimulus
ING338: Human Physiol. for Engineers. 2017-1
Despite increased voltage, force plateaus
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External electrode stimulation of a nerve
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The muscle force summates with repetitive stimulation
ING338: Human Physiol. for Engineers. 2017-1
Despite increased frequency, force plateaus
Tetany has been reached
Tetanus/twitch varies with muscle type
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Elastic properties: The length-tension relationship in muscle
ING338: Human Physiol. for Engineers. 2017-1
Relaxed muscles exert no force. When stretched passively, passive force is produced
To reach tetanus
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The basis of strength training in exercise physiology Muscle force can vary by:
Recruitment of muscle fibers Variation of the frequency of activation Variation of the muscle length
Skeletal muscle length is hardest to modify because muscles in physiologically state are arranged near the top of their length.
ING338: Human Physiol. for Engineers. 2017-1
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Measuring the force and velocity of isotonic muscle contractions
ING338: Human Physiol. for Engineers. 2017-1
1. Isometric contraction 2. Muscle length changes after
enough afterload force has been produced
3. Afterload is lifted at constant velocity: Isotonic contraction
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The speed of muscle contraction depends on the load that must be moved
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Type of contraction
Distance change Function Work
Concentric Shortening (+ D) Acceleration + Isometric No change (0 D) Fixation 0 Eccentric Lengthening (- D) Deceleration -
Power = energy / time Energy = Work =Force * Distance Power = (Force * Distance)/time
Power = Force * Velocity
Muscle power varies with the load and muscle type
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Power is about two to three times greater in fast-twitch muscle
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Slow- vs. fast-twitch muscles
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Slow-twitch Fast-twitch It is aerobic It is anaerobic It needs steady power (lots of mitochondria)
It needs explosive power
It has endurance It fatigues easily Runners use it Weight-lifters use it
Concentric and eccentric contractions
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Arrangement of muscle fibers within a muscle
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Activity Muscle cells are long, multinucleated cells that are shaped something like cylinders that taper near the ends. Consider a 10 cm length of a muscle cell that is 50 mm in diameter. Assume that the cell is a right circular cylinder and that the capacitance of the muscle cell membrane is 1 mf cm-2. Neglect the ends of the cylinder and edge effects where the membrane bends at the edges. A. How many charges have to move across the
membrane in order to produce a potential of -80 mV, negative inside?
B. The total concentration of anions (negatively charged ions) in the cytosol is about 150 x 10-3 M, and the total concentration of cations (positively charged ions) is about the same. About how many cation charges are there in the cytosol of the muscle cell of 10 cm length and 50 mm diameter?
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