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365 Cards in this Set

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how many muscle fibers are there in a typical muscle?
100's to 1000's
How many muscle fibers are in a single fascicle and what covers the fascicle?
10's to 100's\nperimysium
What's the diameter of a typical muscle fiber? How long are muscle fibers typically?
diameter = 100 micrometers or 0.1 mm\nlength = 1 cm to 10's of cm
How many myofibrils are there per muscle fiber?
~1000
What are the 2 contractile structures/units of muscle tissue?
myofibril and sarcomere
What's the diameter of a typical myofibril?
1 micrometer
What makes up a myofibril?
sarcomeres aligned in series
How long is a typical sarcomere?
2.5 micrometers
"With a muscle fiber that is 10 cm long, how many sarcomeres are aligned in series within each of the fiber's myofibrils?"
"10 cm / 2.5 micrometers = \n10 x 10^2- meters / 2.5 x 10^6- meters = \n4.0 x 10^4 = \n40,000 sarcomeres in a 10 cm long fiber"
What makes up myofilaments?
"Thin filaments made up of actin, troponin, and tropomyosin\nThick filaments made up of myosin only"
What components make up a myosin molecule and what chemical is used to determine the components?
"Heavy meromyosin (site of crossbridge and ATPase activity), subdivided into an S-1 segment (head of myosin) and an S-2 segment (neck of myosin)\nLight meromyosin (tail of myosin)\nPapain is used to cleave the myosin molecule"
How is a single myosin molecule more typically subdivided? What division determines the shortening velocity of a muscle fiber?
two myosin heavy chains (MHC)\nfour myosin light chains (MLC)\nMHC forms the backbone of the head and tail regions \nMLC are arranged on the head portion only\nThe type of MHC mostly determines shortening velocity
What are the two regulatory proteins involved in crossbridge cycling and what do they generally do? How are these two proteins differ in function during crossbridge cycling?
"troponin and tropomyosin\ninitiate and terminate contraction\ntropomyosin physically blocks the interaction between actin and myosin while the muscle is at rest\ntroponin has an affinity for calcium, and when calcium binds to troponin, troponin changes shape, pulls on tropomyosin, and causes the tropomyosin to expose the binding sites on actin"
How is muscle functionally organized (2 ways)?
Motor unit and sarcomere
What does a motor unit consist of?
"one alpha-motoneuron and all the muscle fibers it innervates, which usually all lie within one fascicle, but the fibers do not necessarily lie next to each other"
What's the range for the number of fibers in a motor unit?
10-15 up to the 1000's
Describe the parts of the sarcomere
extends from one Z-line to the next\nA-bands are the regions that contain thick filaments\nH-zone is the part of the A-band that only contains thick filaments (no thin)\nbisected by the M-line\nI-band contains only thin filaments and is bisected by the Z-lines\n
What happens to the bands/lines in a sarcomere during contraction?
Z-lines move closer together\nI-band and H-zone start to disappear
What are the four steps of the crossbridge cycle? Start from the beginning of muscle relaxation. Which step is the rate-limiting step?
"1. ATP binds to myosin, actin-myosin complex dissociates\n2. ATP is hydrolyzed by ATPase, energy released to cock"" the myosin head\n3. In presence of calcium, myosin binds with actin, energy stored in ""cocked"" crossbridge moves the thin filament past the thick filament\n4. Hydrolysis products of the ATPase reaction are released from myosin (rate-limiting step)"""
List the steps of generating an action potential in a muscle cell during excitation-contraction coupling.
"1. Action potential generated in alpha-motoneuron and travels down axon\n2. When the action potential reaches the axon terminal, vesicles in the axon terminal release Ach into the synaptic cleft\n3. ACh binds to receptors on the sarcolemma (muscle side of neuromuscular junction)\n4. Binding of ACh to the sarcolemma receptors causes sodium channels to open on the sarcolemma\n5. Sodium flows into the muscle cell, causing the depolarization of the muscle cell (from negative to positive)"
List the steps of excitation-contraction coupling, starting from the moment the muscle cell is depolarized to the removal of calcium from the cytosol of the cell. Do not list the steps of the crossbridge cycle.
1. Action potential travels along sarcolemma until enters a T-tubule, is sensed by a T-tubular voltage sensor, and causes a shape change of the sensor, in turn causing a shape change in the sarcoplasmic reticulum's Ca2+ channels

2. Ca2+ is released from the SR into the cell and binds to troponin, beginning the crossbridge cycle

3. Action potentials from the alpha-motoneuron end and release of Ca2+ from SR stops

4. Ca2+ ATPase pumps move calcium from the cytosol back into the SR
What are the 5 factors that affect force production in a muscle?
1. physiological cross-sectional area (PCSA)\n2. muscle length\n3. muscle shortening/lengthening velocity\n4. number of motor units recruited\n5. rate coding
What is the relationship between PCSA and force production in a muscle?
"direct relationship between PCSA and force production\nthe more sarcomeres in parallel, the higher the force produced"
What does muscle pennation angle do? Do pennated muscles produce less/more force than fusiform?
allows packing of a large number of fibers in to a small anatomical CSA\npennated muscles generally produce more force than fusiform
"If two muscles have an equal mass, but one has longer fibers than the other, which muscle will produce greater force? What are the tradeoffs for this muscle?"
the one with shorter fibers will produce greater force\nit will have a small range of motion and the fibers will be slower
What is the formula for PCSA? What assumptions can we make when calculating PCSA? How can we reduce the formula to one that makes it easy to quickly compare the PCSA's of two different muscles? What is the reduced relationship?
"PCSA = ((muscle mass in grams) x cos (angle of pennation))/((muscle density in grams per cubic centimeters) x (muscle fiber length))\nWe can assume that the cosine of the pennation angle ranges from 0.9-1.0, so we can consider it equal to 1 (drops out)\nMuscle density is the same for all muscles (1.056 g/cm3), so when comparing two muscles, we can drop out the density term, leaving us with the relationship:\nPCSA = (muscle mass in grams)/(muscle fiber length)\n"
What happens to force production when the sarcomere length is:\na. < 1.6 micrometers\nb. 1.6 - 2.0 micrometers\nc. 2.0 - 2.5 micrometers\nd. 2.5 - 3.6 micrometers\ne. > 3.6 micrometers?\nWhat is happening to the thick and thin filaments in each case?
a. force production greatly decreases; thick filaments bump into Z-lines\nb. decrease in force production; thin filaments attached to opposite Z-lines begin to interfere with each other\nc. no change in force production; no change in overlap of thick and thin filaments\nd. linear increase in force production; thick and thin filament overlap increases\ne. no force production; no overlap of thick and thin filaments\n
At what length range do most muscle fibers operate? What is this range called?
~2.0 - 2.3 micrometers\nplateau region
Describe the muscle-length tension curve.
"1. start with short sarcomere length and increase muscle length up to the muscle's optimal length: the tension developed is entirely active tension produced within the sarcomere by the degree of myofilament overlap\ntotal force = active force only\n2. increase muscle length beyond optimal length: the amount of overlap of myofilaments begins to decrease, causing active tension to decrease, but passive tension increases due to force on connective tissues\ntotal force increases, but not greatly\n"
What are the two types of forces at work that combine to get the total tension on a muscle? \n
"two forces: 1. passive, due to connective tissue architecture; 2. active/developed, due to amount of myofilament overlap"
What happens to the muscle beyond its optimal length? \n
"stretch sarcomeres to a point where myofilament overlap decreases, decreasing force production"
How would the length-tension curve differ between pennated and fusiform muscles?
"pennated muscles have more muscle fibers packed into a particular CSA while fusiform muscles have fewer muscle fibers and more connective tissue; therefore, the passive tension curve would be less steep than that for the pennated muscle, causing the total length-tension curve to plummit beyond the muscle's optimal length and climb sharply as tension on the connective tissue continues to increase with muscle length."
Why does muscle force production decrease with greater shortening/lengthening velocity?
"at a given time, the number of myosin crossbridges in contact with actin decreases as shortening/lengthening velocity increases"
What are the three types of muscle contractions? Describe each.
1. concentric: muscle shortens while it is activated\n2. isometric: muscle does not change length while activated\n3. eccentric: muscle lengthens while it is activated (pliometric contractions)
How would you get the greatest production of force during eccentric contractions? What is special about the state the muscle is in during eccentric contraction? What is the effect of velocity on force production during eccentric contractions?
"by using involuntary contractions (external electrical stimulation) rather than voluntary\ncompared to isometric and concentric contraction, eccentric contraction produces force with fewer motor units and fewer energetic costs (ATP and oxygen consumption): there is increased force produced per crossbridge and myosin is forcibly detached from actin, reducing the requirement of ATP for detachment"
In what order are alpha-motoneurons recruited to produce increasing force? What is the name of this rule of order?
"in increasing axon diameter; for low force contractions, motor units with small alpha-motoneurons are recruited, and for increasing force production, larger alpha-motoneurons are recruited.\nHenneman principle or Size principle"
What are the three types of motor units based on alpha-motoneuron size? What kind of muscle fibers does each unit type contain?
Slow (S) units: Type I or slow oxidative (SO) muscle fibers

Fast Fatigue-resistant (FR) units: Type IIa or fast oxidative glycolytic (FOG) fibers

Fast Fatigable (FF) units: Type IIb or fast glycolytic (FG) fibers
Contrast the number of muscle fibers and strength of each type of motor unit.
"S: small number of fibers, low force producing\nFR: intermediate number of fibers and intermediate strength\nFF: high number of fibers and high force producing"
Under what circumstances would the normal recruitment order of motor units not be followed? Is this a common circumstance? What drives motor unit recruitment?
"During novel, eccentric contractions and during sudden movements\nThe normal recruitment order is followed almost all the time -- a different order of recruitment is rare\nRecruitment is driven by demand for force and not by speed of movement"
What is rate coding?
discharge frequency for an alpha-motoneuron\nthe rate that action potentials are received at the synaptic terminal of an alpha-motoneuron branch
What is the relationship between force production and stimulation frequency?
force increases sigmoidally with stimulation frequency\n
To increase force production, but still remaining below 50% MVC, what does the body do? When increasing to a higher force level (> 50-80% MVC)?
< 50% MVC: increases motor unit recruitment and increases rate coding of motor units already active

50-80% MVC: force is increased by increasing rate coding only
What factors affect muscle shortening velocity?
load imposed on the muscle\nmuscle fiber length (not related to stretching a fiber)\nmotor units recruited
What is the relationship between load imposed on a muscle and its shortening velocity? What happens to the shortening velocity when no load is applied and when the load is at its maximum for a particular muscle?
"The greater the load, the lower the shortening velocity. When load is zero, the muscle can shorten at its maximal shortening velocity (Vmax). When load is so great that the muscle cannot shorten the contraction becomes isometric; the load at this point is called the maximal isometric force (Po)"
"What is the relationship between a muscle's fiber length (normal length, not stretching length) and its shortening velocity? What explains this relationship?"
"the longer the fiber length, the greater the shortening velocity\nthe number of sarcomeres in series is greater"
What is the relationship between the type of motor unit recruited and muscle shortening velocity? Why is this the case?
fast twitch fibers shorten faster (2x-4x) than slow twitch\nthis is due to the increased myosin ATPase activity and thus an increased crossbridge cycling rate in fast twitch fibers
Is there a great variation in fiber type composition between individuals? Between men and women? How does female fiber size compare to male fiber size?
"wide variation in fiber type between individuals, but not between men and women\nfemale fiber size (CSA) is 50-70% less than for males"
What is the difference in CSA between Type I and Type II fibers? The difference in force produced per CSA?
CSA and force per CSA are both the same for Type I and Type II fibers within the same species
What determines whether a person has more Type I than Type II muscle fibers? For which fiber type(s) is fiber type composition a decent predictor of performance?
"genetics, for the most part, and innervation: if you cross-innervate a fast muscle with a nerve from a slow muscle, the fast muscle takes on contractile characteristics of a slow muscle (and vice versa)\nalso, the types of activities a person does affects the % of fiber types, \n\nthe best correlation between fiber type compositoin and performance is for Type I and endurance time = 0.70\nthe correlation between Type II and torque and Type II and movement speed = 0.50"
"What are the effects of resistance training, decreased used, no use (as in spinal cord injury) and endurance training on PSA?"
Effect on PSA:\n1. resistance training: mass increases = PSA increases\n2. decreased use: mass decreases = PSA decreases\n3. no use: mass decreases = PSA decreases\n4. endurance training: no significant change
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how many muscle fibers are there in a typical muscle?
100's to 1000's
How many muscle fibers are in a single fascicle and what covers the fascicle?
10's to 100's\nperimysium
What's the diameter of a typical muscle fiber? How long are muscle fibers typically?
diameter = 100 micrometers or 0.1 mm\nlength = 1 cm to 10's of cm
How many myofibrils are there per muscle fiber?
~1000
What are the 2 contractile structures/units of muscle tissue?
myofibril and sarcomere
What's the diameter of a typical myofibril?
1 micrometer
What makes up a myofibril?
sarcomeres aligned in series
How long is a typical sarcomere?
2.5 micrometers
"With a muscle fiber that is 10 cm long, how many sarcomeres are aligned in series within each of the fiber's myofibrils?"
"10 cm / 2.5 micrometers = \n10 x 10^2- meters / 2.5 x 10^6- meters = \n4.0 x 10^4 = \n40,000 sarcomeres in a 10 cm long fiber"
What makes up myofilaments?
"Thin filaments made up of actin, troponin, and tropomyosin\nThick filaments made up of myosin only"
What components make up a myosin molecule and what chemical is used to determine the components?
"Heavy meromyosin (site of crossbridge and ATPase activity), subdivided into an S-1 segment (head of myosin) and an S-2 segment (neck of myosin)\nLight meromyosin (tail of myosin)\nPapain is used to cleave the myosin molecule"
How is a single myosin molecule more typically subdivided? What division determines the shortening velocity of a muscle fiber?
two myosin heavy chains (MHC)\nfour myosin light chains (MLC)\nMHC forms the backbone of the head and tail regions \nMLC are arranged on the head portion only\nThe type of MHC mostly determines shortening velocity
What are the two regulatory proteins involved in crossbridge cycling and what do they generally do? How are these two proteins differ in function during crossbridge cycling?
"troponin and tropomyosin\ninitiate and terminate contraction\ntropomyosin physically blocks the interaction between actin and myosin while the muscle is at rest\ntroponin has an affinity for calcium, and when calcium binds to troponin, troponin changes shape, pulls on tropomyosin, and causes the tropomyosin to expose the binding sites on actin"
How is muscle functionally organized (2 ways)?
Motor unit and sarcomere
What does a motor unit consist of?
"one alpha-motoneuron and all the muscle fibers it innervates, which usually all lie within one fascicle, but the fibers do not necessarily lie next to each other"
What's the range for the number of fibers in a motor unit?
10-15 up to the 1000's
Describe the parts of the sarcomere
extends from one Z-line to the next\nA-bands are the regions that contain thick filaments\nH-zone is the part of the A-band that only contains thick filaments (no thin)\nbisected by the M-line\nI-band contains only thin filaments and is bisected by the Z-lines\n
What happens to the bands/lines in a sarcomere during contraction?
Z-lines move closer together\nI-band and H-zone start to disappear
What are the four steps of the crossbridge cycle? Start from the beginning of muscle relaxation. Which step is the rate-limiting step?
"1. ATP binds to myosin, actin-myosin complex dissociates\n2. ATP is hydrolyzed by ATPase, energy released to ""cock"" the myosin head\n3. In presence of calcium, myosin binds with actin, energy stored in ""cocked"" crossbridge moves the thin filament past the thick filament\n4. Hydrolysis products of the ATPase reaction are released from myosin (rate-limiting step)"
List the steps of generating an action potential in a muscle cell during excitation-contraction coupling.
"1. Action potential generated in alpha-motoneuron and travels down axon\n2. When the action potential reaches the axon terminal, vesicles in the axon terminal release Ach into the synaptic cleft\n3. ACh binds to receptors on the sarcolemma (muscle side of neuromuscular junction)\n4. Binding of ACh to the sarcolemma receptors causes sodium channels to open on the sarcolemma\n5. Sodium flows into the muscle cell, causing the depolarization of the muscle cell (from negative to positive)"
"List the steps of excitation-contraction coupling, starting from the moment the muscle cell is depolarized to the removal of calcium from the cytosol of the cell. Do not list the steps of the crossbridge cycle."
"1. Action potential travels along sarcolemma until enters a T-tubule, is sensed by a T-tubular voltage sensor, and causes a shape change of the sensor, in turn causing a shape change in the sarcoplasmic reticulum's Ca2+ channels\n3. Ca2+ is released from the SR into the cell and binds to troponin, beginning the crossbridge cycle\n4. Action potentials from the alpha-motoneuron end and release of Ca2+ from SR stops\n5. Ca2+ ATPase pumps move calcium from the cytosol back into the SR\n"
What are the 5 factors that affect force production in a muscle?
1. physiological cross-sectional area (PCSA)\n2. muscle length\n3. muscle shortening/lengthening velocity\n4. number of motor units recruited\n5. rate coding
What is the relationship between PCSA and force production in a muscle?
"direct relationship between PCSA and force production\nthe more sarcomeres in parallel, the higher the force produced"
What does muscle pennation angle do? Do pennated muscles produce less/more force than fusiform?
allows packing of a large number of fibers in to a small anatomical CSA\npennated muscles generally produce more force than fusiform
"If two muscles have an equal mass, but one has longer fibers than the other, which muscle will produce greater force? What are the tradeoffs for this muscle?"
the one with shorter fibers will produce greater force\nit will have a small range of motion and the fibers will be slower
What is the formula for PCSA? What assumptions can we make when calculating PCSA? How can we reduce the formula to one that makes it easy to quickly compare the PCSA's of two different muscles? What is the reduced relationship?
"PCSA = ((muscle mass in grams) x cos (angle of pennation))/((muscle density in grams per cubic centimeters) x (muscle fiber length))\nWe can assume that the cosine of the pennation angle ranges from 0.9-1.0, so we can consider it equal to 1 (drops out)\nMuscle density is the same for all muscles (1.056 g/cm3), so when comparing two muscles, we can drop out the density term, leaving us with the relationship:\nPCSA = (muscle mass in grams)/(muscle fiber length)\n"
What happens to force production when the sarcomere length is:\na. < 1.6 micrometers\nb. 1.6 - 2.0 micrometers\nc. 2.0 - 2.5 micrometers\nd. 2.5 - 3.6 micrometers\ne. > 3.6 micrometers?\nWhat is happening to the thick and thin filaments in each case?
a. force production greatly decreases; thick filaments bump into Z-lines\nb. decrease in force production; thin filaments attached to opposite Z-lines begin to interfere with each other\nc. no change in force production; no change in overlap of thick and thin filaments\nd. linear increase in force production; thick and thin filament overlap increases\ne. no force production; no overlap of thick and thin filaments\n
At what length range do most muscle fibers operate? What is this range called?
~2.0 - 2.3 micrometers\nplateau region
Describe the muscle-length tension curve.
"1. start with short sarcomere length and increase muscle length up to the muscle's optimal length: the tension developed is entirely active tension produced within the sarcomere by the degree of myofilament overlap\ntotal force = active force only\n2. increase muscle length beyond optimal length: the amount of overlap of myofilaments begins to decrease, causing active tension to decrease, but passive tension increases due to force on connective tissues\ntotal force increases, but not greatly\n"
What are the two types of forces at work that combine to get the total tension on a muscle? \n
"two forces: 1. passive, due to connective tissue architecture; 2. active/developed, due to amount of myofilament overlap"
What happens to the muscle beyond its optimal length? \n
"stretch sarcomeres to a point where myofilament overlap decreases, decreasing force production"
How would the length-tension curve differ between pennated and fusiform muscles?
"pennated muscles have more muscle fibers packed into a particular CSA while fusiform muscles have fewer muscle fibers and more connective tissue; therefore, the passive tension curve would be less steep than that for the pennated muscle, causing the total length-tension curve to plummit beyond the muscle's optimal length and climb sharply as tension on the connective tissue continues to increase with muscle length."
Why does muscle force production decrease with greater shortening/lengthening velocity?
"at a given time, the number of myosin crossbridges in contact with actin decreases as shortening/lengthening velocity increases"
What are the three types of muscle contractions? Describe each.
1. concentric: muscle shortens while it is activated\n2. isometric: muscle does not change length while activated\n3. eccentric: muscle lengthens while it is activated (pliometric contractions)
How would you get the greatest production of force during eccentric contractions? What is special about the state the muscle is in during eccentric contraction? What is the effect of velocity on force production during eccentric contractions?
"by using involuntary contractions (external electrical stimulation) rather than voluntary\ncompared to isometric and concentric contraction, eccentric contraction produces force with fewer motor units and fewer energetic costs (ATP and oxygen consumption): there is increased force produced per crossbridge and myosin is forcibly detached from actin, reducing the requirement of ATP for detachment"
In what order are alpha-motoneurons recruited to produce increasing force? What is the name of this rule of order?
"in increasing axon diameter; for low force contractions, motor units with small alpha-motoneurons are recruited, and for increasing force production, larger alpha-motoneurons are recruited.\nHenneman principle or Size principle"
What are the three types of motor units based on alpha-motoneuron size? What kind of muscle fibers does each unit type contain?
Slow (S) units: Type I or slow oxidative (SO) muscle fibers\nFast Fatigue-resistant (FR) units: Type IIa or fast oxidative glycolytic (FOG) fibers\nFast Fatigable (FF) units: Type IIb or fast glycolytic (FG) fibers
Contrast the number of muscle fibers and strength of each type of motor unit.
"S: small number of fibers, low force producing\nFR: intermediate number of fibers and intermediate strength\nFF: high number of fibers and high force producing"
Under what circumstances would the normal recruitment order of motor units not be followed? Is this a common circumstance? What drives motor unit recruitment?
"During novel, eccentric contractions and during sudden movements\nThe normal recruitment order is followed almost all the time -- a different order of recruitment is rare\nRecruitment is driven by demand for force and not by speed of movement"
What is rate coding?
discharge frequency for an alpha-motoneuron\nthe rate that action potentials are received at the synaptic terminal of an alpha-motoneuron branch
What is the relationship between force production and stimulation frequency?
force increases sigmoidally with stimulation frequency\n
"To increase force production, but still remaining below 50% MVC, what does the body do? When increasing to a higher force level (> 50-80% MVC)?"
< 50% MVC: increases motor unit recruitment and increases rate coding of motor units already active\n50-80% MVC: force is increased by increasing rate coding only
What factors affect muscle shortening velocity?
load imposed on the muscle\nmuscle fiber length (not related to stretching a fiber)\nmotor units recruited
What is the relationship between load imposed on a muscle and its shortening velocity? What happens to the shortening velocity when no load is applied and when the load is at its maximum for a particular muscle?
"The greater the load, the lower the shortening velocity. When load is zero, the muscle can shorten at its maximal shortening velocity (Vmax). When load is so great that the muscle cannot shorten the contraction becomes isometric; the load at this point is called the maximal isometric force (Po)"
"What is the relationship between a muscle's fiber length (normal length, not stretching length) and its shortening velocity? What explains this relationship?"
"the longer the fiber length, the greater the shortening velocity\nthe number of sarcomeres in series is greater"
What is the relationship between the type of motor unit recruited and muscle shortening velocity? Why is this the case?
fast twitch fibers shorten faster (2x-4x) than slow twitch\nthis is due to the increased myosin ATPase activity and thus an increased crossbridge cycling rate in fast twitch fibers
Is there a great variation in fiber type composition between individuals? Between men and women? How does female fiber size compare to male fiber size?
"wide variation in fiber type between individuals, but not between men and women\nfemale fiber size (CSA) is 50-70% less than for males"
What is the difference in CSA between Type I and Type II fibers? The difference in force produced per CSA?
CSA and force per CSA are both the same for Type I and Type II fibers within the same species
What determines whether a person has more Type I than Type II muscle fibers? For which fiber type(s) is fiber type composition a decent predictor of performance?
"genetics, for the most part, and innervation: if you cross-innervate a fast muscle with a nerve from a slow muscle, the fast muscle takes on contractile characteristics of a slow muscle (and vice versa)\nalso, the types of activities a person does affects the % of fiber types, \n\nthe best correlation between fiber type compositoin and performance is for Type I and endurance time = 0.70\nthe correlation between Type II and torque and Type II and movement speed = 0.50"
"What are the effects of resistance training, decreased used, no use (as in spinal cord injury) and endurance training on PSA?"
Effect on PSA:\n1. resistance training: mass increases = PSA increases\n2. decreased use: mass decreases = PSA decreases\n3. no use: mass decreases = PSA decreases\n4. endurance training: no significant change
how many muscle fibers are there in a typical muscle?
100's to 1000's
How many muscle fibers are in a single fascicle and what covers the fascicle?
10's to 100's&#8perimysium
What's the diameter of a typical muscle fiber? How long are muscle fibers typically?
diameter = 100 micrometers or 0.1 mm&#8length = 1 cm to 10's of cm
How many myofibrils are there per muscle fiber?
~1000
What are the 2 contractile structures/units of muscle tissue?
myofibril and sarcomere
What's the diameter of a typical myofibril?
1 micrometer
What makes up a myofibril?
sarcomeres aligned in series
How long is a typical sarcomere?
2.5 micrometers
"With a muscle fiber that is 10 cm long, how many sarcomeres are aligned in series within each of the fiber's myofibrils?"
"10 cm / 2.5 micrometers = &#810 x 10^2- meters / 2.5 x 10^6- meters = &#84.0 x 10^4 = &#840,000 sarcomeres in a 10 cm long fiber"
What makes up myofilaments?
"Thin filaments made up of actin, troponin, and tropomyosin&#8Thick filaments made up of myosin only"
What components make up a myosin molecule and what chemical is used to determine the components?
"Heavy meromyosin (site of crossbridge and ATPase activity), subdivided into an S-1 segment (head of myosin) and an S-2 segment (neck of myosin)&#8Light meromyosin (tail of myosin)&#8Papain is used to cleave the myosin molecule"
How is a single myosin molecule more typically subdivided? What division determines the shortening velocity of a muscle fiber?
two myosin heavy chains (MHC)&#8four myosin light chains (MLC)&#8MHC forms the backbone of the head and tail regions &#8MLC are arranged on the head portion only&#8The type of MHC mostly determines shortening velocity
What are the two regulatory proteins involved in crossbridge cycling and what do they generally do? How are these two proteins differ in function during crossbridge cycling?
"troponin and tropomyosin&#8initiate and terminate contraction&#8tropomyosin physically blocks the interaction between actin and myosin while the muscle is at rest&#8troponin has an affinity for calcium, and when calcium binds to troponin, troponin changes shape, pulls on tropomyosin, and causes the tropomyosin to expose the binding sites on actin"
How is muscle functionally organized (2 ways)?
Motor unit and sarcomere
What does a motor unit consist of?
"one alpha-motoneuron and all the muscle fibers it innervates, which usually all lie within one fascicle, but the fibers do not necessarily lie next to each other"
What's the range for the number of fibers in a motor unit?
10-15 up to the 1000's
Describe the parts of the sarcomere
extends from one Z-line to the next&#8A-bands are the regions that contain thick filaments&#8H-zone is the part of the A-band that only contains thick filaments (no thin)&#8bisected by the M-line&#8I-band contains only thin filaments and is bisected by the Z-lines&#8
What happens to the bands/lines in a sarcomere during contraction?
Z-lines move closer together&#8I-band and H-zone start to disappear
What are the four steps of the crossbridge cycle? Start from the beginning of muscle relaxation. Which step is the rate-limiting step?
"1. ATP binds to myosin, actin-myosin complex dissociates&#82. ATP is hydrolyzed by ATPase, energy released to ""cock"" the myosin head&#83. In presence of calcium, myosin binds with actin, energy stored in ""cocked"" crossbridge moves the thin filament past the thick filament&#84. Hydrolysis products of the ATPase reaction are released from myosin (rate-limiting step)"
List the steps of generating an action potential in a muscle cell during excitation-contraction coupling.
"1. Action potential generated in alpha-motoneuron and travels down axon&#82. When the action potential reaches the axon terminal, vesicles in the axon terminal release Ach into the synaptic cleft&#83. ACh binds to receptors on the sarcolemma (muscle side of neuromuscular junction)&#84. Binding of ACh to the sarcolemma receptors causes sodium channels to open on the sarcolemma&#85. Sodium flows into the muscle cell, causing the depolarization of the muscle cell (from negative to positive)"
"List the steps of excitation-contraction coupling, starting from the moment the muscle cell is depolarized to the removal of calcium from the cytosol of the cell. Do not list the steps of the crossbridge cycle."
"1. Action potential travels along sarcolemma until enters a T-tubule, is sensed by a T-tubular voltage sensor, and causes a shape change of the sensor, in turn causing a shape change in the sarcoplasmic reticulum's Ca2+ channels&#83. Ca2+ is released from the SR into the cell and binds to troponin, beginning the crossbridge cycle&#84. Action potentials from the alpha-motoneuron end and release of Ca2+ from SR stops&#85. Ca2+ ATPase pumps move calcium from the cytosol back into the SR&#8"
What are the 5 factors that affect force production in a muscle?
1. physiological cross-sectional area (PCSA)&#82. muscle length&#83. muscle shortening/lengthening velocity&#84. number of motor units recruited&#85. rate coding
What is the relationship between PCSA and force production in a muscle?
"direct relationship between PCSA and force production&#8the more sarcomeres in parallel, the higher the force produced"
What does muscle pennation angle do? Do pennated muscles produce less/more force than fusiform?
allows packing of a large number of fibers in to a small anatomical CSA&#8pennated muscles generally produce more force than fusiform
"If two muscles have an equal mass, but one has longer fibers than the other, which muscle will produce greater force? What are the tradeoffs for this muscle?"
the one with shorter fibers will produce greater force&#8it will have a small range of motion and the fibers will be slower
What is the formula for PCSA? What assumptions can we make when calculating PCSA? How can we reduce the formula to one that makes it easy to quickly compare the PCSA's of two different muscles? What is the reduced relationship?
"PCSA = ((muscle mass in grams) x cos (angle of pennation))/((muscle density in grams per cubic centimeters) x (muscle fiber length))&#8We can assume that the cosine of the pennation angle ranges from 0.9-1.0, so we can consider it equal to 1 (drops out)&#8Muscle density is the same for all muscles (1.056 g/cm3), so when comparing two muscles, we can drop out the density term, leaving us with the relationship:&#8PCSA = (muscle mass in grams)/(muscle fiber length)&#8"
What happens to force production when the sarcomere length is:&#8a. < 1.6 micrometers&#8b. 1.6 - 2.0 micrometers&#8c. 2.0 - 2.5 micrometers&#8d. 2.5 - 3.6 micrometers&#8e. > 3.6 micrometers?&#8What is happening to the thick and thin filaments in each case?
a. force production greatly decreases; thick filaments bump into Z-lines&#8b. decrease in force production; thin filaments attached to opposite Z-lines begin to interfere with each other&#8c. no change in force production; no change in overlap of thick and thin filaments&#8d. linear increase in force production; thick and thin filament overlap increases&#8e. no force production; no overlap of thick and thin filaments&#8
At what length range do most muscle fibers operate? What is this range called?
~2.0 - 2.3 micrometers&#8plateau region
Describe the muscle-length tension curve.
"1. start with short sarcomere length and increase muscle length up to the muscle's optimal length: the tension developed is entirely active tension produced within the sarcomere by the degree of myofilament overlap&#8total force = active force only&#82. increase muscle length beyond optimal length: the amount of overlap of myofilaments begins to decrease, causing active tension to decrease, but passive tension increases due to force on connective tissues&#8total force increases, but not greatly&#8"
What are the two types of forces at work that combine to get the total tension on a muscle? &#8
"two forces: 1. passive, due to connective tissue architecture; 2. active/developed, due to amount of myofilament overlap"
What happens to the muscle beyond its optimal length? &#8
"stretch sarcomeres to a point where myofilament overlap decreases, decreasing force production"
How would the length-tension curve differ between pennated and fusiform muscles?
"pennated muscles have more muscle fibers packed into a particular CSA while fusiform muscles have fewer muscle fibers and more connective tissue; therefore, the passive tension curve would be less steep than that for the pennated muscle, causing the total length-tension curve to plummit beyond the muscle's optimal length and climb sharply as tension on the connective tissue continues to increase with muscle length."
Why does muscle force production decrease with greater shortening/lengthening velocity?
"at a given time, the number of myosin crossbridges in contact with actin decreases as shortening/lengthening velocity increases"
What are the three types of muscle contractions? Describe each.
1. concentric: muscle shortens while it is activated&#82. isometric: muscle does not change length while activated&#83. eccentric: muscle lengthens while it is activated (pliometric contractions)
How would you get the greatest production of force during eccentric contractions? What is special about the state the muscle is in during eccentric contraction? What is the effect of velocity on force production during eccentric contractions?
"by using involuntary contractions (external electrical stimulation) rather than voluntary&#8compared to isometric and concentric contraction, eccentric contraction produces force with fewer motor units and fewer energetic costs (ATP and oxygen consumption): there is increased force produced per crossbridge and myosin is forcibly detached from actin, reducing the requirement of ATP for detachment"
In what order are alpha-motoneurons recruited to produce increasing force? What is the name of this rule of order?
"in increasing axon diameter; for low force contractions, motor units with small alpha-motoneurons are recruited, and for increasing force production, larger alpha-motoneurons are recruited.&#8Henneman principle or Size principle"
What are the three types of motor units based on alpha-motoneuron size? What kind of muscle fibers does each unit type contain?
Slow (S) units: Type I or slow oxidative (SO) muscle fibers&#8Fast Fatigue-resistant (FR) units: Type IIa or fast oxidative glycolytic (FOG) fibers&#8Fast Fatigable (FF) units: Type IIb or fast glycolytic (FG) fibers
Contrast the number of muscle fibers and strength of each type of motor unit.
"S: small number of fibers, low force producing&#8FR: intermediate number of fibers and intermediate strength&#8FF: high number of fibers and high force producing"
Under what circumstances would the normal recruitment order of motor units not be followed? Is this a common circumstance? What drives motor unit recruitment?
"During novel, eccentric contractions and during sudden movements&#8The normal recruitment order is followed almost all the time -- a different order of recruitment is rare&#8Recruitment is driven by demand for force and not by speed of movement"
What is rate coding?
discharge frequency for an alpha-motoneuron&#8the rate that action potentials are received at the synaptic terminal of an alpha-motoneuron branch
What is the relationship between force production and stimulation frequency?
force increases sigmoidally with stimulation frequency&#8
"To increase force production, but still remaining below 50% MVC, what does the body do? When increasing to a higher force level (> 50-80% MVC)?"
< 50% MVC: increases motor unit recruitment and increases rate coding of motor units already active&#850-80% MVC: force is increased by increasing rate coding only
What factors affect muscle shortening velocity?
load imposed on the muscle&#8muscle fiber length (not related to stretching a fiber)&#8motor units recruited
What is the relationship between load imposed on a muscle and its shortening velocity? What happens to the shortening velocity when no load is applied and when the load is at its maximum for a particular muscle?
"The greater the load, the lower the shortening velocity. When load is zero, the muscle can shorten at its maximal shortening velocity (Vmax). When load is so great that the muscle cannot shorten the contraction becomes isometric; the load at this point is called the maximal isometric force (Po)"
"What is the relationship between a muscle's fiber length (normal length, not stretching length) and its shortening velocity? What explains this relationship?"
"the longer the fiber length, the greater the shortening velocity&#8the number of sarcomeres in series is greater"
What is the relationship between the type of motor unit recruited and muscle shortening velocity? Why is this the case?
fast twitch fibers shorten faster (2x-4x) than slow twitch&#8this is due to the increased myosin ATPase activity and thus an increased crossbridge cycling rate in fast twitch fibers
Is there a great variation in fiber type composition between individuals? Between men and women? How does female fiber size compare to male fiber size?
"wide variation in fiber type between individuals, but not between men and women&#8female fiber size (CSA) is 50-70% less than for males"
What is the difference in CSA between Type I and Type II fibers? The difference in force produced per CSA?
CSA and force per CSA are both the same for Type I and Type II fibers within the same species
What determines whether a person has more Type I than Type II muscle fibers? For which fiber type(s) is fiber type composition a decent predictor of performance?
"genetics, for the most part, and innervation: if you cross-innervate a fast muscle with a nerve from a slow muscle, the fast muscle takes on contractile characteristics of a slow muscle (and vice versa)&#8also, the types of activities a person does affects the % of fiber types, &#8&#8the best correlation between fiber type compositoin and performance is for Type I and endurance time = 0.70&#8the correlation between Type II and torque and Type II and movement speed = 0.50"
"What are the effects of resistance training, decreased used, no use (as in spinal cord injury) and endurance training on PSA?"
Effect on PSA:&#81. resistance training: mass increases = PSA increases&#82. decreased use: mass decreases = PSA decreases&#83. no use: mass decreases = PSA decreases&#84. endurance training: no significant change
how many muscle fibers are there in a typical muscle?
100's to 1000's
How many muscle fibers are in a single fascicle and what covers the fascicle?
10's to 100's
What's the diameter of a typical muscle fiber? How long are muscle fibers typically?
diameter = 100 micrometers or 0.1 mm
How many myofibrils are there per muscle fiber?
~1000
What are the 2 contractile structures/units of muscle tissue?
myofibril and sarcomere
What's the diameter of a typical myofibril?
1 micrometer
What makes up a myofibril?
sarcomeres aligned in series
How long is a typical sarcomere?
2.5 micrometers
With a muscle fiber that is 10 cm long, how many sarcomeres are aligned in series within each of the fiber's myofibrils?
10 cm / 2.5 micrometers =
What makes up myofilaments?
Thin filaments made up of actin, troponin, and tropomyosin
What components make up a myosin molecule and what chemical is used to determine the components?
Heavy meromyosin (site of crossbridge and ATPase activity), subdivided into an S-1 segment (head of myosin) and an S-2 segment (neck of myosin)
How is a single myosin molecule more typically subdivided? What division determines the shortening velocity of a muscle fiber?
two myosin heavy chains (MHC)
What are the two regulatory proteins involved in crossbridge cycling and what do they generally do? How are these two proteins differ in function during crossbridge cycling?
troponin and tropomyosin
How is muscle functionally organized (2 ways)?
Motor unit and sarcomere
What does a motor unit consist of?
one alpha-motoneuron and all the muscle fibers it innervates, which usually all lie within one fascicle, but the fibers do not necessarily lie next to each other
What's the range for the number of fibers in a motor unit?
10-15 up to the 1000's
Describe the parts of the sarcomere
extends from one Z-line to the next
\u000A
What happens to the bands/lines in a sarcomere during contraction?
Z-lines move closer together
\u000AI-band and H-zone start to disappear
What are the four steps of the crossbridge cycle? Start from the beginning of muscle relaxation. Which step is the rate-limiting step?
1. ATP binds to myosin, actin-myosin complex dissociates
\u000A4. Hydrolysis products of the ATPase reaction are released from myosin (rate-limiting step)
List the steps of generating an action potential in a muscle cell during excitation-contraction coupling.
1. Action potential generated in alpha-motoneuron and travels down axon
\u000A5. Sodium flows into the muscle cell, causing the depolarization of the muscle cell (from negative to positive)
List the steps of excitation-contraction coupling, starting from the moment the muscle cell is depolarized to the removal of calcium from the cytosol of the cell. Do not list the steps of the crossbridge cycle.
1. Action potential travels along sarcolemma until enters a T-tubule, is sensed by a T-tubular voltage sensor, and causes a shape change of the sensor, in turn causing a shape change in the sarcoplasmic reticulum's Ca2+ channels
\u000A
What are the 5 factors that affect force production in a muscle?
1. physiological cross-sectional area (PCSA)
\u000A5. rate coding
What is the relationship between PCSA and force production in a muscle?
direct relationship between PCSA and force production
\u000Athe more sarcomeres in parallel, the higher the force produced
What does muscle pennation angle do? Do pennated muscles produce less/more force than fusiform?
allows packing of a large number of fibers in to a small anatomical CSA
\u000Apennated muscles generally produce more force than fusiform
If two muscles have an equal mass, but one has longer fibers than the other, which muscle will produce greater force? What are the tradeoffs for this muscle?
the one with shorter fibers will produce greater force
\u000Ait will have a small range of motion and the fibers will be slower
What is the formula for PCSA? What assumptions can we make when calculating PCSA? How can we reduce the formula to one that makes it easy to quickly compare the PCSA's of two different muscles? What is the reduced relationship?
PCSA = ((muscle mass in grams) x cos (angle of pennation))/((muscle density in grams per cubic centimeters) x (muscle fiber length))
\u000A
\u000AWhat is happening to the thick and thin filaments in each case?
a. force production greatly decreases; thick filaments bump into Z-lines
\u000A
At what length range do most muscle fibers operate? What is this range called?
~2.0 - 2.3 micrometers
\u000Aplateau region
Describe the muscle-length tension curve.
1. start with short sarcomere length and increase muscle length up to the muscle's optimal length: the tension developed is entirely active tension produced within the sarcomere by the degree of myofilament overlap
\u000A
\u000A
two forces: 1. passive, due to connective tissue architecture; 2. active/developed, due to amount of myofilament overlap
\u000A
stretch sarcomeres to a point where myofilament overlap decreases, decreasing force production
How would the length-tension curve differ between pennated and fusiform muscles?
pennated muscles have more muscle fibers packed into a particular CSA while fusiform muscles have fewer muscle fibers and more connective tissue; therefore, the passive tension curve would be less steep than that for the pennated muscle, causing the total length-tension curve to plummit beyond the muscle's optimal length and climb sharply as tension on the connective tissue continues to increase with muscle length.
Why does muscle force production decrease with greater shortening/lengthening velocity?
at a given time, the number of myosin crossbridges in contact with actin decreases as shortening/lengthening velocity increases
What are the three types of muscle contractions? Describe each.
1. concentric: muscle shortens while it is activated
How would you get the greatest production of force during eccentric contractions? What is special about the state the muscle is in during eccentric contraction? What is the effect of velocity on force production during eccentric contractions?
by using involuntary contractions (external electrical stimulation) rather than voluntary
In what order are alpha-motoneurons recruited to produce increasing force? What is the name of this rule of order?
in increasing axon diameter; for low force contractions, motor units with small alpha-motoneurons are recruited, and for increasing force production, larger alpha-motoneurons are recruited.
What are the three types of motor units based on alpha-motoneuron size? What kind of muscle fibers does each unit type contain?
Slow (S) units: Type I or slow oxidative (SO) muscle fibers
Contrast the number of muscle fibers and strength of each type of motor unit.
S: small number of fibers, low force producing
Under what circumstances would the normal recruitment order of motor units not be followed? Is this a common circumstance? What drives motor unit recruitment?
During novel, eccentric contractions and during sudden movements
What is rate coding?
discharge frequency for an alpha-motoneuron
What is the relationship between force production and stimulation frequency?
force increases sigmoidally with stimulation frequency
To increase force production, but still remaining below 50% MVC, what does the body do? When increasing to a higher force level (> 50-80% MVC)?
< 50% MVC: increases motor unit recruitment and increases rate coding of motor units already active
What factors affect muscle shortening velocity?
load imposed on the muscle
What is the relationship between load imposed on a muscle and its shortening velocity? What happens to the shortening velocity when no load is applied and when the load is at its maximum for a particular muscle?
The greater the load, the lower the shortening velocity. When load is zero, the muscle can shorten at its maximal shortening velocity (Vmax). When load is so great that the muscle cannot shorten the contraction becomes isometric; the load at this point is called the maximal isometric force (Po)
What is the relationship between a muscle's fiber length (normal length, not stretching length) and its shortening velocity? What explains this relationship?
the longer the fiber length, the greater the shortening velocity
What is the relationship between the type of motor unit recruited and muscle shortening velocity? Why is this the case?
fast twitch fibers shorten faster (2x-4x) than slow twitch
Is there a great variation in fiber type composition between individuals? Between men and women? How does female fiber size compare to male fiber size?
wide variation in fiber type between individuals, but not between men and women
What is the difference in CSA between Type I and Type II fibers? The difference in force produced per CSA?
CSA and force per CSA are both the same for Type I and Type II fibers within the same species
What determines whether a person has more Type I than Type II muscle fibers? For which fiber type(s) is fiber type composition a decent predictor of performance?
genetics, for the most part, and innervation: if you cross-innervate a fast muscle with a nerve from a slow muscle, the fast muscle takes on contractile characteristics of a slow muscle (and vice versa)
What are the effects of resistance training, decreased used, no use (as in spinal cord injury) and endurance training on PSA?
Effect on PSA:
how many muscle fibers are there in a typical muscle?
100's to 1000's
How many muscle fibers are in a single fascicle and what covers the fascicle?
10's to 100's
What's the diameter of a typical muscle fiber? How long are muscle fibers typically?
diameter = 100 micrometers or 0.1 mm
How many myofibrils are there per muscle fiber?
~1000
What are the 2 contractile structures/units of muscle tissue?
myofibril and sarcomere
What's the diameter of a typical myofibril?
1 micrometer
What makes up a myofibril?
sarcomeres aligned in series
How long is a typical sarcomere?
2.5 micrometers
With a muscle fiber that is 10 cm long, how many sarcomeres are aligned in series within each of the fiber's myofibrils?
10 cm / 2.5 micrometers =\\u000A10 x 10^2- meters / 2.5 x 10^6- meters =\\u000A4.0 x 10^4 =\\u000A40,000 sarcomeres in a 10 cm long fiber
What makes up myofilaments?
Thin filaments made up of actin, troponin, and tropomyosin
What components make up a myosin molecule and what chemical is used to determine the components?
Heavy meromyosin (site of crossbridge and ATPase activity), subdivided into an S-1 segment (head of myosin) and an S-2 segment (neck of myosin)
How is a single myosin molecule more typically subdivided? What division determines the shortening velocity of a muscle fiber?
two myosin heavy chains (MHC)
What are the two regulatory proteins involved in crossbridge cycling and what do they generally do? How are these two proteins differ in function during crossbridge cycling?
troponin and tropomyosin
How is muscle functionally organized (2 ways)?
Motor unit and sarcomere
What does a motor unit consist of?
one alpha-motoneuron and all the muscle fibers it innervates, which usually all lie within one fascicle, but the fibers do not necessarily lie next to each other
What's the range for the number of fibers in a motor unit?
10-15 up to the 1000's
Describe the parts of the sarcomere
extends from one Z-line to the next
What happens to the bands/lines in a sarcomere during contraction?
Z-lines move closer together
\\u000AI-band and H-zone start to disappear
What are the four steps of the crossbridge cycle? Start from the beginning of muscle relaxation. Which step is the rate-limiting step?
1. ATP binds to myosin, actin-myosin complex dissociates
\\u000A4. Hydrolysis products of the ATPase reaction are released from myosin (rate-limiting step)
List the steps of generating an action potential in a muscle cell during excitation-contraction coupling.
1. Action potential generated in alpha-motoneuron and travels down axon
\\u000A5. Sodium flows into the muscle cell, causing the depolarization of the muscle cell (from negative to positive)
List the steps of excitation-contraction coupling, starting from the moment the muscle cell is depolarized to the removal of calcium from the cytosol of the cell. Do not list the steps of the crossbridge cycle.
1. Action potential travels along sarcolemma until enters a T-tubule, is sensed by a T-tubular voltage sensor, and causes a shape change of the sensor, in turn causing a shape change in the sarcoplasmic reticulum's Ca2+ channels
What are the 5 factors that affect force production in a muscle?
1. physiological cross-sectional area (PCSA)
\\u000A5. rate coding
What is the relationship between PCSA and force production in a muscle?
direct relationship between PCSA and force production
\\u000Athe more sarcomeres in parallel, the higher the force produced
What does muscle pennation angle do? Do pennated muscles produce less/more force than fusiform?
allows packing of a large number of fibers in to a small anatomical CSA
\\u000Apennated muscles generally produce more force than fusiform
If two muscles have an equal mass, but one has longer fibers than the other, which muscle will produce greater force? What are the tradeoffs for this muscle?
the one with shorter fibers will produce greater force
\\u000Ait will have a small range of motion and the fibers will be slower
What is the formula for PCSA? What assumptions can we make when calculating PCSA? How can we reduce the formula to one that makes it easy to quickly compare the PCSA's of two different muscles? What is the reduced relationship?
PCSA = ((muscle mass in grams) x cos (angle of pennation))/((muscle density in grams per cubic centimeters) x (muscle fiber length))
\\u000AWhat is happening to the thick and thin filaments in each case?
a. force production greatly decreases; thick filaments bump into Z-lines
\\u000A
At what length range do most muscle fibers operate? What is this range called?
~2.0 - 2.3 micrometers
\\u000Aplateau region
Describe the muscle-length tension curve.
1. start with short sarcomere length and increase muscle length up to the muscle's optimal length: the tension developed is entirely active tension produced within the sarcomere by the degree of myofilament overlap
What are the two types of forces at work that combine to get the total tension on a muscle?
two forces: 1. passive, due to connective tissue architecture; 2. active/developed, due to amount of myofilament overlap
What happens to the muscle beyond its optimal length?
stretch sarcomeres to a point where myofilament overlap decreases, decreasing force production
How would the length-tension curve differ between pennated and fusiform muscles?
pennated muscles have more muscle fibers packed into a particular CSA while fusiform muscles have fewer muscle fibers and more connective tissue; therefore, the passive tension curve would be less steep than that for the pennated muscle, causing the total length-tension curve to plummit beyond the muscle's optimal length and climb sharply as tension on the connective tissue continues to increase with muscle length.
Why does muscle force production decrease with greater shortening/lengthening velocity?
at a given time, the number of myosin crossbridges in contact with actin decreases as shortening/lengthening velocity increases
What are the three types of muscle contractions? Describe each.
1. concentric: muscle shortens while it is activated
How would you get the greatest production of force during eccentric contractions? What is special about the state the muscle is in during eccentric contraction? What is the effect of velocity on force production during eccentric contractions?
by using involuntary contractions (external electrical stimulation) rather than voluntary
In what order are alpha-motoneurons recruited to produce increasing force? What is the name of this rule of order?
in increasing axon diameter; for low force contractions, motor units with small alpha-motoneurons are recruited, and for increasing force production, larger alpha-motoneurons are recruited.
What are the three types of motor units based on alpha-motoneuron size? What kind of muscle fibers does each unit type contain?
Slow (S) units: Type I or slow oxidative (SO) muscle fibers
Contrast the number of muscle fibers and strength of each type of motor unit.
S: small number of fibers, low force producing
Under what circumstances would the normal recruitment order of motor units not be followed? Is this a common circumstance? What drives motor unit recruitment?
During novel, eccentric contractions and during sudden movements
What is rate coding?
discharge frequency for an alpha-motoneuron
What is the relationship between force production and stimulation frequency?
force increases sigmoidally with stimulation frequency
To increase force production, but still remaining below 50% MVC, what does the body do? When increasing to a higher force level (> 50-80% MVC)?
< 50% MVC: increases motor unit recruitment and increases rate coding of motor units already active
What factors affect muscle shortening velocity?
load imposed on the muscle
What is the relationship between load imposed on a muscle and its shortening velocity? What happens to the shortening velocity when no load is applied and when the load is at its maximum for a particular muscle?
The greater the load, the lower the shortening velocity. When load is zero, the muscle can shorten at its maximal shortening velocity (Vmax). When load is so great that the muscle cannot shorten the contraction becomes isometric; the load at this point is called the maximal isometric force (Po)
What is the relationship between a muscle's fiber length (normal length, not stretching length) and its shortening velocity? What explains this relationship?
the longer the fiber length, the greater the shortening velocity
What is the relationship between the type of motor unit recruited and muscle shortening velocity? Why is this the case?
fast twitch fibers shorten faster (2x-4x) than slow twitch
Is there a great variation in fiber type composition between individuals? Between men and women? How does female fiber size compare to male fiber size?
wide variation in fiber type between individuals, but not between men and women
What is the difference in CSA between Type I and Type II fibers? The difference in force produced per CSA?
CSA and force per CSA are both the same for Type I and Type II fibers within the same species
What determines whether a person has more Type I than Type II muscle fibers? For which fiber type(s) is fiber type composition a decent predictor of performance?
genetics, for the most part, and innervation: if you cross-innervate a fast muscle with a nerve from a slow muscle, the fast muscle takes on contractile characteristics of a slow muscle (and vice versa)
What are the effects of resistance training, decreased used, no use (as in spinal cord injury) and endurance training on PSA?
Effect on PSA:
how many muscle fibers are there in a typical muscle?
100's to 1000's
How many muscle fibers are in a single fascicle and what covers the fascicle?
10's to 100's
What's the diameter of a typical muscle fiber? How long are muscle fibers typically?
diameter = 100 micrometers or 0.1 mm
How many myofibrils are there per muscle fiber?
~1000
What are the 2 contractile structures/units of muscle tissue?
myofibril and sarcomere
What's the diameter of a typical myofibril?
1 micrometer
What makes up a myofibril?
sarcomeres aligned in series
How long is a typical sarcomere?
2.5 micrometers
With a muscle fiber that is 10 cm long, how many sarcomeres are aligned in series within each of the fiber's myofibrils?
10 cm / 2.5 micrometers =&#x000A;10 x 10^2- meters / 2.5 x 10^6- meters =&#x000A;4.0 x 10^4 =&#x000A;40,000 sarcomeres in a 10 cm long fiber
What makes up myofilaments?
Thin filaments made up of actin, troponin, and tropomyosin
What components make up a myosin molecule and what chemical is used to determine the components?
Heavy meromyosin (site of crossbridge and ATPase activity), subdivided into an S-1 segment (head of myosin) and an S-2 segment (neck of myosin)
How is a single myosin molecule more typically subdivided? What division determines the shortening velocity of a muscle fiber?
two myosin heavy chains (MHC)
What are the two regulatory proteins involved in crossbridge cycling and what do they generally do? How are these two proteins differ in function during crossbridge cycling?
troponin and tropomyosin
How is muscle functionally organized (2 ways)?
Motor unit and sarcomere
What does a motor unit consist of?
one alpha-motoneuron and all the muscle fibers it innervates, which usually all lie within one fascicle, but the fibers do not necessarily lie next to each other
What's the range for the number of fibers in a motor unit?
10-15 up to the 1000's
Describe the parts of the sarcomere
extends from one Z-line to the next
What happens to the bands/lines in a sarcomere during contraction?
Z-lines move closer together
&#x000A;I-band and H-zone start to disappear
What are the four steps of the crossbridge cycle? Start from the beginning of muscle relaxation. Which step is the rate-limiting step?
1. ATP binds to myosin, actin-myosin complex dissociates
&#x000A;4. Hydrolysis products of the ATPase reaction are released from myosin (rate-limiting step)
List the steps of generating an action potential in a muscle cell during excitation-contraction coupling.
1. Action potential generated in alpha-motoneuron and travels down axon
&#x000A;5. Sodium flows into the muscle cell, causing the depolarization of the muscle cell (from negative to positive)
List the steps of excitation-contraction coupling, starting from the moment the muscle cell is depolarized to the removal of calcium from the cytosol of the cell. Do not list the steps of the crossbridge cycle.
1. Action potential travels along sarcolemma until enters a T-tubule, is sensed by a T-tubular voltage sensor, and causes a shape change of the sensor, in turn causing a shape change in the sarcoplasmic reticulum's Ca2+ channels
What are the 5 factors that affect force production in a muscle?
1. physiological cross-sectional area (PCSA)
&#x000A;5. rate coding
What is the relationship between PCSA and force production in a muscle?
direct relationship between PCSA and force production
&#x000A;the more sarcomeres in parallel, the higher the force produced
What does muscle pennation angle do? Do pennated muscles produce less/more force than fusiform?
allows packing of a large number of fibers in to a small anatomical CSA
&#x000A;pennated muscles generally produce more force than fusiform
If two muscles have an equal mass, but one has longer fibers than the other, which muscle will produce greater force? What are the tradeoffs for this muscle?
the one with shorter fibers will produce greater force
&#x000A;it will have a small range of motion and the fibers will be slower
What is the formula for PCSA? What assumptions can we make when calculating PCSA? How can we reduce the formula to one that makes it easy to quickly compare the PCSA's of two different muscles? What is the reduced relationship?
PCSA = ((muscle mass in grams) x cos (angle of pennation))/((muscle density in grams per cubic centimeters) x (muscle fiber length))
&#x000A;What is happening to the thick and thin filaments in each case?
a. force production greatly decreases; thick filaments bump into Z-lines
&#x000A;
At what length range do most muscle fibers operate? What is this range called?
~2.0 - 2.3 micrometers
&#x000A;plateau region
Describe the muscle-length tension curve.
1. start with short sarcomere length and increase muscle length up to the muscle's optimal length: the tension developed is entirely active tension produced within the sarcomere by the degree of myofilament overlap
What are the two types of forces at work that combine to get the total tension on a muscle?
two forces: 1. passive, due to connective tissue architecture; 2. active/developed, due to amount of myofilament overlap
What happens to the muscle beyond its optimal length?
stretch sarcomeres to a point where myofilament overlap decreases, decreasing force production
How would the length-tension curve differ between pennated and fusiform muscles?
pennated muscles have more muscle fibers packed into a particular CSA while fusiform muscles have fewer muscle fibers and more connective tissue; therefore, the passive tension curve would be less steep than that for the pennated muscle, causing the total length-tension curve to plummit beyond the muscle's optimal length and climb sharply as tension on the connective tissue continues to increase with muscle length.
Why does muscle force production decrease with greater shortening/lengthening velocity?
at a given time, the number of myosin crossbridges in contact with actin decreases as shortening/lengthening velocity increases
What are the three types of muscle contractions? Describe each.
1. concentric: muscle shortens while it is activated
How would you get the greatest production of force during eccentric contractions? What is special about the state the muscle is in during eccentric contraction? What is the effect of velocity on force production during eccentric contractions?
by using involuntary contractions (external electrical stimulation) rather than voluntary
In what order are alpha-motoneurons recruited to produce increasing force? What is the name of this rule of order?
in increasing axon diameter; for low force contractions, motor units with small alpha-motoneurons are recruited, and for increasing force production, larger alpha-motoneurons are recruited.
What are the three types of motor units based on alpha-motoneuron size? What kind of muscle fibers does each unit type contain?
Slow (S) units: Type I or slow oxidative (SO) muscle fibers
Contrast the number of muscle fibers and strength of each type of motor unit.
S: small number of fibers, low force producing
Under what circumstances would the normal recruitment order of motor units not be followed? Is this a common circumstance? What drives motor unit recruitment?
During novel, eccentric contractions and during sudden movements
What is rate coding?
discharge frequency for an alpha-motoneuron
What is the relationship between force production and stimulation frequency?
force increases sigmoidally with stimulation frequency
To increase force production, but still remaining below 50% MVC, what does the body do? When increasing to a higher force level (> 50-80% MVC)?
< 50% MVC: increases motor unit recruitment and increases rate coding of motor units already active
What factors affect muscle shortening velocity?
load imposed on the muscle
What is the relationship between load imposed on a muscle and its shortening velocity? What happens to the shortening velocity when no load is applied and when the load is at its maximum for a particular muscle?
The greater the load, the lower the shortening velocity. When load is zero, the muscle can shorten at its maximal shortening velocity (Vmax). When load is so great that the muscle cannot shorten the contraction becomes isometric; the load at this point is called the maximal isometric force (Po)
What is the relationship between a muscle's fiber length (normal length, not stretching length) and its shortening velocity? What explains this relationship?
the longer the fiber length, the greater the shortening velocity
What is the relationship between the type of motor unit recruited and muscle shortening velocity? Why is this the case?
fast twitch fibers shorten faster (2x-4x) than slow twitch
Is there a great variation in fiber type composition between individuals? Between men and women? How does female fiber size compare to male fiber size?
wide variation in fiber type between individuals, but not between men and women
What is the difference in CSA between Type I and Type II fibers? The difference in force produced per CSA?
CSA and force per CSA are both the same for Type I and Type II fibers within the same species
What determines whether a person has more Type I than Type II muscle fibers? For which fiber type(s) is fiber type composition a decent predictor of performance?
genetics, for the most part, and innervation: if you cross-innervate a fast muscle with a nerve from a slow muscle, the fast muscle takes on contractile characteristics of a slow muscle (and vice versa)
What are the effects of resistance training, decreased used, no use (as in spinal cord injury) and endurance training on PSA?
Effect on PSA:
how many muscle fibers are there in a typical muscle?
100's to 1000's
How many muscle fibers are in a single fascicle and what covers the fascicle?
10's to 100's\\u000Aperimysium
What's the diameter of a typical muscle fiber? How long are muscle fibers typically?
diameter = 100 micrometers or 0.1 mm\\u000Alength = 1 cm to 10's of cm
How many myofibrils are there per muscle fiber?
~1000
What are the 2 contractile structures/units of muscle tissue?
myofibril and sarcomere
What's the diameter of a typical myofibril?
1 micrometer
What makes up a myofibril?
sarcomeres aligned in series
How long is a typical sarcomere?
2.5 micrometers
With a muscle fiber that is 10 cm long, how many sarcomeres are aligned in series within each of the fiber's myofibrils?
10 cm / 2.5 micrometers =\\u000A10 x 10^2- meters / 2.5 x 10^6- meters =\\u000A4.0 x 10^4 =\\u000A40,000 sarcomeres in a 10 cm long fiber
What makes up myofilaments?
Thin filaments made up of actin, troponin, and tropomyosin\\u000AThick filaments made up of myosin only
What components make up a myosin molecule and what chemical is used to determine the components?
Heavy meromyosin (site of crossbridge and ATPase activity), subdivided into an S-1 segment (head of myosin) and an S-2 segment (neck of myosin)\\u000ALight meromyosin (tail of myosin)\\u000APapain is used to cleave the myosin molecule
How is a single myosin molecule more typically subdivided? What division determines the shortening velocity of a muscle fiber?
two myosin heavy chains (MHC)\\u000Afour myosin light chains (MLC)\\u000AMHC forms the backbone of the head and tail regions\\u000AMLC are arranged on the head portion only\\u000AThe type of MHC mostly determines shortening velocity
What are the two regulatory proteins involved in crossbridge cycling and what do they generally do? How are these two proteins differ in function during crossbridge cycling?
troponin and tropomyosin\\u000Ainitiate and terminate contraction\\u000Atropomyosin physically blocks the interaction between actin and myosin while the muscle is at rest\\u000Atroponin has an affinity for calcium, and when calcium binds to troponin, troponin changes shape, pulls on tropomyosin, and causes the tropomyosin to expose the binding sites on actin
How is muscle functionally organized (2 ways)?
Motor unit and sarcomere
What does a motor unit consist of?
one alpha-motoneuron and all the muscle fibers it innervates, which usually all lie within one fascicle, but the fibers do not necessarily lie next to each other
What's the range for the number of fibers in a motor unit?
10-15 up to the 1000's
Describe the parts of the sarcomere
extends from one Z-line to the next\\u000AA-bands are the regions that contain thick filaments\\u000AH-zone is the part of the A-band that only contains thick filaments (no thin)\\u000Abisected by the M-line\\u000AI-band contains only thin filaments and is bisected by the Z-lines
What happens to the bands/lines in a sarcomere during contraction?
Z-lines move closer together\\u000AI-band and H-zone start to disappear
What are the four steps of the crossbridge cycle? Start from the beginning of muscle relaxation. Which step is the rate-limiting step?
1. ATP binds to myosin, actin-myosin complex dissociates\\u000A2. ATP is hydrolyzed by ATPase, energy released to cock the myosin head\\u000A3. In presence of calcium, myosin binds with actin, energy stored in cocked crossbridge moves the thin filament past the thick filament\\u000A4. Hydrolysis products of the ATPase reaction are released from myosin (rate-limiting step)
List the steps of generating an action potential in a muscle cell during excitation-contraction coupling.
1. Action potential generated in alpha-motoneuron and travels down axon\\u000A2. When the action potential reaches the axon terminal, vesicles in the axon terminal release Ach into the synaptic cleft\\u000A3. ACh binds to receptors on the sarcolemma (muscle side of neuromuscular junction)\\u000A4. Binding of ACh to the sarcolemma receptors causes sodium channels to open on the sarcolemma\\u000A5. Sodium flows into the muscle cell, causing the depolarization of the muscle cell (from negative to positive)
List the steps of excitation-contraction coupling, starting from the moment the muscle cell is depolarized to the removal of calcium from the cytosol of the cell. Do not list the steps of the crossbridge cycle.
1. Action potential travels along sarcolemma until enters a T-tubule, is sensed by a T-tubular voltage sensor, and causes a shape change of the sensor, in turn causing a shape change in the sarcoplasmic reticulum's Ca2+ channels\\u000A3. Ca2+ is released from the SR into the cell and binds to troponin, beginning the crossbridge cycle\\u000A4. Action potentials from the alpha-motoneuron end and release of Ca2+ from SR stops\\u000A5. Ca2+ ATPase pumps move calcium from the cytosol back into the SR
What are the 5 factors that affect force production in a muscle?
1. physiological cross-sectional area (PCSA)\\u000A2. muscle length\\u000A3. muscle shortening/lengthening velocity\\u000A4. number of motor units recruited\\u000A5. rate coding