Physiology of Skeletal Muscle Contraction

Question 1

The basic unit of skeletal muscle is the multinucleated …

Answer 1

The basic unit of skeletal muscle is the multinucleated myofiber

Question 2

… are long filaments that run parallel to each other to form muscle (myo) fibers

Answer 2

Myofibrils are long filaments that run parallel to each other to form muscle (myo) fibers

Question 3

… are long filaments that run parallel to each other to form muscle (myo) fibers

Answer 3

Myofibrils are long filaments that run parallel to each other to form muscle (myo) fibers

Question 4

The … are the contractile proteins in the myofibers that are arranged into groups that cause the cytoplasm to appear repetitively banded (or striated).

Answer 4

The myofilaments are the contractile proteins in the myofibers that are arranged into groups that cause the cytoplasm to appear repetitively banded (or striated).

Question 5

Sarcomere

• Each sarcomere consists of a central …-band (thick filaments) and two halves of the …-band (thin filaments).
• The …-band from two adjacent sarcomeres meets at the Z-line. The central portion of the …-band is the M-line, which does not contain actin.

Answer 5

• Each sarcomere consists of a central A-band (thick filaments) and two halves of the I-band (thin filaments).
• The I-band from two adjacent sarcomeres meets at the Z-line. The central portion of the A-band is the M-line, which does not contain actin.

Question 6

Sarcomere

• Each sarcomere consists of a central A-band (… filaments) and two halves of the I-band (… filaments).
• The I-band from two adjacent sarcomeres meets at the …-line. The central portion of the A-band is the M-line, which does not contain …

Answer 6

• Each sarcomere consists of a central A-band (thick filaments) and two halves of the I-band (thin filaments).
• The I-band from two adjacent sarcomeres meets at the Z-line. The central portion of the A-band is the M-line, which does not contain actin.

Question 7

The myofilaments include thick filaments, composed mainly of …, and thin filaments composed mainly of …

Answer 7

The myofilaments include thick filaments, composed mainly of myosin, and thin filaments composed mainly of actin.

Question 8

Skeletal muscles are tissues comprising … and … filaments, which require adenosine triphosphate (ATP) to produce muscle contractions

Answer 8

Skeletal muscles are tissues comprising actin and myosin filaments, which require adenosine triphosphate (ATP) to produce muscle contractions

Question 9

Tropomyosin (TPM)

• Controls whether … and … interact
• Sits on … filament in groove of double helix
• At rest, TPM covers … binding site for …
• Thus, TPM blocks …-… interaction
• Pulled out of the way when muscle is active

Answer 9

• Controls whether actin and myosin interact
• Sits on thin filament in groove of double helix
• At rest, TPM covers actin’s binding site for myosin
• Thus, TPM blocks actin-myosin interaction
• Pulled out of the way when muscle is active

Question 10

Tropomyosin (TPM)

• Controls whether actin and myosin interact
• Sits on thin filament in groove of double helix
• At rest, TPM covers actin’s binding site for myosin
• Thus, TPM blocks actin-myosin interaction
• Pulled out of the way when muscle is active

Answer 10

• Controls whether actin and myosin interact
• Sits on thin filament in groove of double helix
• At rest, TPM covers actin’s binding site for myosin
• Thus, TPM blocks actin-myosin interaction
• Pulled out of the way when muscle is active

Question 11

Cross bridge cycling

• … pulling …, consuming …, and resetting
• Controlled by calcium
• … pulled during … power stroke

Answer 11

• Myosin pulling actin, consuming ATP, and resetting
• Controlled by calcium
• Actin pulled during myosin power stroke

Question 12

Troponin (Tn): 3 subunits

• Troponin proteins control whether
  
  • tropomyosin allows or blocks …-… interaction
• Troponin is made up of 3 subunits (in this order):
  
  • troponin T (T = tropomyosin-binding)
  • troponin C (C = calcium-binding)
  • troponin I (I = inhibitory / binds to actin)

Answer 12

• Troponin proteins control whether
  
  • tropomyosin allows or blocks actin-myosin interaction
• Troponin is made up of 3 subunits (in this order):
  
  • troponin T (T = tropomyosin-binding)
  • troponin C (C = calcium-binding)
  • troponin I (I = inhibitory / binds to actin)

Question 13

Troponin (Tn): 3 subunits

• Troponin proteins control whether
  
  • tropomyosin allows or blocks actin-myosin interaction
• Troponin is made up of 3 subunits (in this order):
  
  • troponin …
  • troponin …
  • troponin …

Answer 13

• Troponin proteins control whether
  
  • tropomyosin allows or blocks actin-myosin interaction
• Troponin is made up of 3 subunits (in this order):
  
  • troponin T (T = tropomyosin-binding)
  • troponin C (C = calcium-binding)
  • troponin I (I = inhibitory / binds to actin)

Question 14

Cross Bridge Cycle (illustration)

• REACTIONS
  
  • 1 Myosin releases …
  • 2 Myosin head … …
  • 3 Myosin binds actin
  • 4 Power stroke

Answer 14

• REACTIONS
  
  • 1 Myosin releases actin
  • 2 Myosin head cleaves ATP
  • 3 Myosin binds actin
  • 4 Power stroke

Question 15

Cross Bridge Cycle (illustration)

• REACTIONS
  
  • 1 Myosin releases actin
  • 2 Myosin head cleaves ATP
  • 3 Myosin … actin
  • 4 … stroke

Answer 15

• REACTIONS
  
  • 1 Myosin releases actin
  • 2 Myosin head cleaves ATP
  • 3 Myosin binds actin
  • 4 Power stroke

Question 16

Excitation-Contraction Coupling

• describes the rapid communication between electrical events occurring in the plasma membrane of skeletal muscle fibres and …+ release from the …, which leads to contraction.

Answer 16

• describes the rapid communication between electrical events occurring in the plasma membrane of skeletal muscle fibres and Ca2+ release from the SR, which leads to contraction.

Question 17

Excitation-Contraction Coupling

• describes the rapid communication between electrical events occurring in the plasma membrane of skeletal muscle fibres and Ca2+ release from the SR, which leads to contraction.
• In skeletal muscle there is a direct … connection between calcium channels of membrane and calcium release channels of sarcoplasmic reticulum
  
  • membrane … -> membrane calcium channels undergo a … change -> SR calcium release channels undergo a conformational change that opens them -> calcium flows from SR to cytosol

Answer 17

• describes the rapid communication between electrical events occurring in the plasma membrane of skeletal muscle fibres and Ca2+ release from the SR, which leads to contraction.
• In skeletal muscle there is a direct physical connection between calcium channels of membrane and calcium release channels of sarcoplasmic reticulum
  
  • membrane depolarises -> membrane calcium channels undergo a conformational change -> SR calcium release channels undergo a conformational change that opens them -> calcium flows from SR to cytosol

Question 18

Excitation-Contraction Coupling

• describes the rapid communication between electrical events occurring in the plasma membrane of skeletal muscle fibres and Ca2+ release from the SR, which leads to contraction.
• In skeletal muscle there is a direct physical connection between calcium channels of membrane and calcium release channels of sarcoplasmic reticulum
  
  • membrane depolarises -> membrane calcium channels undergo a conformational change -> SR calcium … channels undergo a conformational change that … them -> calcium flows from SR to …

Answer 18

• describes the rapid communication between electrical events occurring in the plasma membrane of skeletal muscle fibres and Ca2+ release from the SR, which leads to contraction.
• In skeletal muscle there is a direct physical connection between calcium channels of membrane and calcium release channels of sarcoplasmic reticulum
  
  • membrane depolarises -> membrane calcium channels undergo a conformational change -> SR calcium release channels undergo a conformational change that opens them -> calcium flows from SR to cytosol

Question 19

Excitation-Contraction Coupling

• describes the rapid communication between electrical events occurring in the plasma membrane of skeletal muscle fibres and Ca2+ release from the SR, which leads to contraction.
• In skeletal muscle there is a direct physical connection between calcium channels of membrane and calcium … channels of sarcoplasmic reticulum
  
  • membrane depolarises -> membrane calcium channels undergo a … change -> SR calcium release channels undergo a … change that opens them -> calcium flows from SR to cytosol

Answer 19

• describes the rapid communication between electrical events occurring in the plasma membrane of skeletal muscle fibres and Ca2+ release from the SR, which leads to contraction.
• In skeletal muscle there is a direct physical connection between calcium channels of membrane and calcium release channels of sarcoplasmic reticulum
  
  • membrane depolarises -> membrane calcium channels undergo a conformational change -> SR calcium release channels undergo a conformational change that opens them -> calcium flows from SR to cytosol

Question 20

… = the link (molecular process) between the depolarisation of the membrane (with a tiny influx of calcium) and the consequent huge increase in cytosolic calcium that then leads to contraction

Answer 20

E-C coupling = the link (molecular process) between the depolarisation of the membrane (with a tiny influx of calcium) and the consequent huge increase in cytosolic calcium that then leads to contraction

Question 21

… = one long multi-nucleate muscle cell

Answer 21

Myofibre = one long multi-nucleate muscle cell

Question 22

… = organelle, string of sarcomeres

Answer 22

Myofibril = organelle, string of sarcomeres

Question 23

… = thick or thin filament (molecules)

Answer 23

Myofilament = thick or thin filament (molecules)

Question 24

Contraction = when ends of sarcomere (… lines) are pulled toward each other by … filament pulling … filaments

Answer 24

Contraction = when ends of sarcomere (z lines) are pulled toward each other by myosin filament pulling actin filaments

Question 25

Troponin: how it works

• … Ca2+ bind to troponin C (C = calcium binding),
  
  • In heart TnC only binds to … Ca2+ ions
• TnC changes …
• … change in TnC “shuts off” TnI
• tropomyosin-troponin leaves F-actin groove
• unmasks the myosin binding site on actin
• next myosin heads make cross bridges (cycling) to actin
  
  • Myosin breaks down ATP
  • Myosin pulls thin filaments

Answer 25

• 4 Ca2+ bind to troponin C (C = calcium binding),
  
  • In heart TnC only binds to 3 Ca2+ ions
• TnC changes conformation
• conformational change in TnC “shuts off” TnI
• tropomyosin-troponin leaves F-actin groove
• unmasks the myosin binding site on actin
• next myosin heads make cross bridges (cycling) to actin
  
  • Myosin breaks down ATP
  • Myosin pulls thin filaments

Question 26

Troponin: how it works

• 4 Ca2+ bind to troponin C (C = calcium binding),
  
  • In heart TnC only binds to 3 Ca2+ ions
• TnC changes conformation
• conformational change in TnC “shuts off” Tn…
• tropomyosin-troponin leaves …-actin groove
• unmasks the myosin … site on actin
• next myosin heads make cross bridges (cycling) to actin
  
  • Myosin breaks down ATP
  • Myosin pulls thin filaments

Answer 26

• 4 Ca2+ bind to troponin C (C = calcium binding),
  
  • In heart TnC only binds to 3 Ca2+ ions
• TnC changes conformation
• conformational change in TnC “shuts off” TnI
• tropomyosin-troponin leaves F-actin groove
• unmasks the myosin binding site on actin
• next myosin heads make cross bridges (cycling) to actin
  
  • Myosin breaks down ATP
  • Myosin pulls thin filaments

Question 27

Troponin: how it works

• 4 Ca2+ bind to troponin C (C = calcium binding),
  
  • In heart TnC only binds to 3 Ca2+ ions
• TnC changes conformation
• conformational change in TnC “shuts off” TnI
• tropomyosin-troponin leaves …-actin groove
• unmasks the myosin binding site on actin
• next myosin heads make … bridges (cycling) to actin
  
  • Myosin breaks down ATP
  • Myosin pulls thin filaments

Answer 27

• 4 Ca2+ bind to troponin C (C = calcium binding),
  
  • In heart TnC only binds to 3 Ca2+ ions
• TnC changes conformation
• conformational change in TnC “shuts off” TnI
• tropomyosin-troponin leaves F-actin groove
• unmasks the myosin binding site on actin
• next myosin heads make cross bridges (cycling) to actin
  
  • Myosin breaks down ATP
  • Myosin pulls thin filaments

Question 28

Troponin: how it works

• … Ca2+ bind to troponin C (C = calcium binding),
  
  • In heart TnC only binds to 3 Ca2+ ions
• TnC changes conformation
• conformational change in TnC “shuts off” TnI
• tropomyosin-troponin leaves F-actin groove
• unmasks the myosin binding site on actin
• next myosin heads make cross bridges (cycling) to actin
  
  • Myosin breaks down …
  • Myosin pulls … filaments

Answer 28

• 4 Ca2+ bind to troponin C (C = calcium binding),
  
  • In heart TnC only binds to 3 Ca2+ ions
• TnC changes conformation
• conformational change in TnC “shuts off” TnI
• tropomyosin-troponin leaves F-actin groove
• unmasks the myosin binding site on actin
• next myosin heads make cross bridges (cycling) to actin
  
  • Myosin breaks down ATP
  • Myosin pulls thin filaments

Question 29

Total TnI = marker for total muscle …

Answer 29

Total TnI = marker for total muscle breakdown

Question 30

Cardiac TnI = marker for … …

Answer 30

Cardiac TnI = marker for myocardial infarct

Question 31

Cardiac Tn… = marker for myocardial infarct

Answer 31

Cardiac TnI = marker for myocardial infarct

Question 32

Cross bridge cycling

• Molecular cycle of actin-myosin interaction
• Mechanism of Contraction at … level
• Contraction depends on binding of … heads to … filaments (actin) at specific binding sites
• In resting state of sarcomere, myosin heads are blocked from binding to actin by tropomyosin, which occupies the specific binding sites (in F-actin double helical groove)

Answer 32

• Molecular cycle of actin-myosin interaction
• Mechanism of Contraction at Molecular level
• Contraction depends on binding of myosin heads to thin filaments (actin) at specific binding sites
• In resting state of sarcomere, myosin heads are blocked from binding to actin by tropomyosin, which occupies the specific binding sites (in F-actin double helical groove)

Question 33

Cross bridge cycling

• Molecular cycle of actin-myosin interaction
• Mechanism of Contraction at Molecular level
• Contraction depends on binding of myosin heads to thin filaments (actin) at specific binding sites
• In … state of sarcomere, myosin heads are … from binding to actin by …, which occupies the specific binding sites (in F-actin double helical groove)

Answer 33

• Molecular cycle of actin-myosin interaction
• Mechanism of Contraction at Molecular level
• Contraction depends on binding of myosin heads to thin filaments (actin) at specific binding sites
• In resting state of sarcomere, myosin heads are blocked from binding to actin by tropomyosin, which occupies the specific binding sites (in F-actin double helical groove)

Question 34

Force generation vs. sarcomere length

• Fill in blanks

Answer 34

• Between A & B: the degree of filament overlap is directly proportional to force muscle can generate.
• When the effect of small shortening of one sarcomere is multiplied by many sarcomeres in a myofibril and the shortening of many myofibrils together is summed, the whole muscle fibre shortens.
• Shortening of many muscle fibres is manifest as contraction of the entire muscle with change in muscle length

Question 35

Cross Bridge Cycle (illustration)

• REACTIONS
  
  • 1 - Myosin releases actin
  • 2 - Myosin head … ATP
  • 3 - Myosin binds actin
  • 4 - …. …

Answer 35

• REACTIONS
• 1.Myosin releases actin
• 2.Myosin head cleaves ATP
• 3.Myosin binds actin
• 4.Power stroke

Tropomyosin: The important thing to notice in the animation (you can animate this by running this powerpoint in slide show mode (shift-F5) is that the tropomyosin (long blue string) rolls up and down. It turns out that myosin (top and left) can only interact with specific bits of the actin molecule. In the absence of calcium, this active site of actin is covered by tropomyosin. In the presence of calcium (yellow balls that fly in to cartoon), tropomyosin is rolled away from actin’s active site because the calcium causes troponin (3 purple beads connected to one another, one of which is connected to the blue tropomyosin) to drag tropomyosin down (i.e. away from the active site of actin). This allows myosin to interact with actin at its active site.

Question 36

Cross Bridge Cycle - Explanation

Answer 36

Tropomyosin: The important thing to notice in the animation (you can animate this by running this powerpoint in slide show mode (shift-F5) is that the tropomyosin (long blue string) rolls up and down. It turns out that myosin (top and left) can only interact with specific bits of the actin molecule. In the absence of calcium, this active site of actin is covered by tropomyosin. In the presence of calcium (yellow balls that fly in to cartoon), tropomyosin is rolled away from actin’s active site because the calcium causes troponin (3 purple beads connected to one another, one of which is connected to the blue tropomyosin) to drag tropomyosin down (i.e. away from the active site of actin). This allows myosin to interact with actin at its active site.

Question 37

Rigor Mortis

• After death, … ceases to occur, depleting the corpse of oxygen used in the making of Adenosine triphosphate (ATP).
• ATP depleted after death
• Muscle cell does not resequester Ca2+ into …
  
  • ­ Increase in … Ca2+
• Ca2+ allows crossbridge cycle contraction
  
  • Until ATP & creatine-P run out
• W/o ATP -> myosin stops just after power stroke
  
  • With myosin still bound to actin
  • Rigor mortis ends when muscle tissue degrades after 3 days

Answer 37

• After death, respiration ceases to occur, depleting the corpse of oxygen used in the making of Adenosine triphosphate (ATP).
• ATP depleted after death
• Muscle cell does not resequester Ca2+ into SR
  
  • ­ Increase in Cytosolic Ca2+
• Ca2+ allows crossbridge cycle contraction
  
  • Until ATP & creatine-P run out
• W/o ATP -> myosin stops just after power stroke
  
  • With myosin still bound to actin
  • Rigor mortis ends when muscle tissue degrades after 3 days

Question 38

Rigor Mortis

• After death, respiration ceases to occur, depleting the corpse of oxygen used in the making of Adenosine triphosphate (ATP).
• ATP depleted after death
• Muscle cell does not resequester Ca2+ into SR
  
  • ­ Increase in Cytosolic Ca2+
• Ca2+ allows … cycle contraction
  
  • Until … & …-P run out
• W/o ATP -> myosin stops just after power stroke
  
  • With myosin still bound to actin
  • Rigor mortis ends when muscle tissue degrades after 3 days

Answer 38

• After death, respiration ceases to occur, depleting the corpse of oxygen used in the making of Adenosine triphosphate (ATP).
• ATP depleted after death
• Muscle cell does not resequester Ca2+ into SR
  
  • ­ Increase in Cytosolic Ca2+
• Ca2+ allows crossbridge cycle contraction
  
  • Until ATP & creatine-P run out
• W/o ATP -> myosin stops just after power stroke
  
  • With myosin still bound to actin
  • Rigor mortis ends when muscle tissue degrades after 3 days

Question 39

Rigor Mortis

• After death, respiration ceases to occur, depleting the corpse of oxygen used in the making of Adenosine triphosphate (ATP).
• ATP depleted after death
• Muscle cell does not resequester Ca2+ into SR
  
  • ­ Increase in Cytosolic Ca2+
• Ca2+ allows crossbridge cycle contraction
  
  • Until ATP & creatine-P run out
• W/o ATP -> myosin stops just after … …
  
  • With myosin still bound to …
  • Rigor mortis ends when muscle tissue degrades after 3 days

Answer 39

• After death, respiration ceases to occur, depleting the corpse of oxygen used in the making of Adenosine triphosphate (ATP).
• ATP depleted after death
• Muscle cell does not resequester Ca2+ into SR
  
  • ­ Increase in Cytosolic Ca2+
• Ca2+ allows crossbridge cycle contraction
  
  • Until ATP & creatine-P run out
• W/o ATP -> myosin stops just after power stroke
  
  • With myosin still bound to actin
  • Rigor mortis ends when muscle tissue degrades after 3 days

Question 40

Rigor Mortis

• After death, respiration ceases to occur, depleting the corpse of oxygen used in the making of Adenosine triphosphate (ATP).
• ATP depleted after death
• Muscle cell does not resequester Ca2+ into SR
  
  • ­ Increase in Cytosolic Ca2+
• Ca2+ allows crossbridge cycle contraction
  
  • Until ATP & creatine-P run out
• W/o ATP -> myosin stops just after power stroke
  
  • With myosin still bound to actin
  • Rigor mortis ends when muscle tissue degrades after … days

Answer 40

• After death, respiration ceases to occur, depleting the corpse of oxygen used in the making of Adenosine triphosphate (ATP).
• ATP depleted after death
• Muscle cell does not resequester Ca2+ into SR
  
  • ­ Increase in Cytosolic Ca2+
• Ca2+ allows crossbridge cycle contraction
  
  • Until ATP & creatine-P run out
• W/o ATP -> myosin stops just after power stroke
  
  • With myosin still bound to actin
  • Rigor mortis ends when muscle tissue degrades after 3 days

Question 41

ATP, creatine phosphate and creatine phosphokinase

• Creatine found in muscle …
  
  • Phosphorylated to creatine …
  • This is how energy is stored in muscle
• When cross bridge cycling hydrolyses ATP to ADP + Pi, creatine phosphate donates a high energy phosphate to ADP restoring it to ATP
• ATP levels must be kept stable – buffering & regeneration
• The reaction is catalysed in both directions by the enzyme creatine phosphokinase (a/k/a CK, CPK)

Answer 41

• Creatine found in muscle fibres
  
  • Phosphorylated to creatine phosphate
  • This is how energy is stored in muscle
• When cross bridge cycling hydrolyses ATP to ADP + Pi, creatine phosphate donates a high energy phosphate to ADP restoring it to ATP
• ATP levels must be kept stable – buffering & regeneration
• The reaction is catalysed in both directions by the enzyme creatine phosphokinase (a/k/a CK, CPK)

Question 42

ATP, creatine phosphate and creatine phosphokinase

• Creatine found in muscle fibres
  
  • Phosphorylated to creatine phosphate
  • This is how energy is stored in muscle
• When cross bridge cycling … ATP to ADP + Pi, creatine phosphate donates a high energy phosphate to ADP restoring it to …
• ATP levels must be kept stable – buffering & regeneration
• The reaction is catalysed in both directions by the enzyme creatine … (a/k/a CK, CPK)

Answer 42

• Creatine found in muscle fibres
  
  • Phosphorylated to creatine phosphate
  • This is how energy is stored in muscle
• When cross bridge cycling hydrolyses ATP to ADP + Pi, creatine phosphate donates a high energy phosphate to ADP restoring it to ATP
• ATP levels must be kept stable – buffering & regeneration
• The reaction is catalysed in both directions by the enzyme creatine phosphokinase (a/k/a CK, CPK)

Question 43

Creatine vs creatinine

• Creatine is a small molecule that can accept high energy phosphate bonds from …
• Creatine-phosphate is the above molecule after phosphate has been added to it
• Creatine-… (CPK) is the enzyme the adds phosphate to creatine
  
  • This is a plasma marker of muscle destruction
  • It is a large molecule detected by antibodies
• Creatine-kinase (CK) is just another name for creatine phosphokinase (above). They are the same thing.
• Creatinine is a diagnostic marker of kidney function. It is a breakdown product of creatine.

Answer 43

• Creatine is a small molecule that can accept high energy phosphate bonds from ATP
• Creatine-phosphate is the above molecule after phosphate has been added to it
• Creatine-phosphokinase (CPK) is the enzyme the adds phosphate to creatine
  
  • This is a plasma marker of muscle destruction
  • It is a large molecule detected by antibodies
• Creatine-kinase (CK) is just another name for creatine phosphokinase (above). They are the same thing.
• Creatinine is a diagnostic marker of kidney function. It is a breakdown product of creatine.

Question 44

Creatine vs creatinine

• Creatine is a small molecule that can accept high energy phosphate bonds from …
• Creatine-phosphate is the above molecule after phosphate has been added to it
• Creatine-phosphokinase (CPK) is the enzyme the adds phosphate to creatine
  
  • This is a plasma marker of muscle …
  • It is a large molecule detected by …
• Creatine-kinase (CK) is just another name for creatine phosphokinase (above). They are the same thing.
• Creatinine is a diagnostic marker of kidney function. It is a breakdown product of creatine.

Answer 44

• Creatine is a small molecule that can accept high energy phosphate bonds from ATP
• Creatine-phosphate is the above molecule after phosphate has been added to it
• Creatine-phosphokinase (CPK) is the enzyme the adds phosphate to creatine
  
  • This is a plasma marker of muscle destruction
  • It is a large molecule detected by antibodies
• Creatine-kinase (CK) is just another name for creatine phosphokinase (above). They are the same thing.
• Creatinine is a diagnostic marker of kidney function. It is a breakdown product of creatine.

Question 45

Creatinine is a diagnostic marker of … function. It is a breakdown product of creatine.

Answer 45

Creatinine is a diagnostic marker of kidney function. It is a breakdown product of creatine.

Question 46

Creatine-kinase (CK) is just another name for creatine … - They are the same thing.

Answer 46

Creatine-kinase (CK) is just another name for creatine phosphokinase - They are the same thing.

Question 47

Calcium triggers contraction

• There are … Ca2+ gradients
  
  • … vs. … free Ca2+
  • … vs. … free Ca2+
• Efflux of Ca2+ from sarcoplasmic reticulum to cytoplasm provides most of calcium
  
  • Calcium entering cell from outside provides only small fraction of calcium needed for contraction

Answer 47

• There are two Ca2+ gradients
  
  • Extracellular vs. cytosolic free Ca2+
  • SR vs. cytosolic free Ca2+
• Efflux of Ca2+ from sarcoplasmic reticulum to cytoplasm provides most of calcium
  
  • Calcium entering cell from outside provides only small fraction of calcium needed for contraction

Question 48

Calcium triggers contraction

• There are two Ca2+ gradients
  
  • Extracellular vs. cytosolic free Ca2+
  • SR vs. cytosolic free Ca2+
• … of Ca2+ from … … to cytoplasm provides most of calcium
  
  • Calcium entering cell from outside provides only small fraction of calcium needed for contraction

Answer 48

• There are two Ca2+ gradients
  
  • Extracellular vs. cytosolic free Ca2+
  • SR vs. cytosolic free Ca2+
• Efflux of Ca2+ from sarcoplasmic reticulum to cytoplasm provides most of calcium
  
  • Calcium entering cell from outside provides only small fraction of calcium needed for contraction

Question 49

Depolarisation -> increased Ca2+

• … -> Depolarisation
• Active Nicotinic … -> net inward current
• depolarisation spread via …-Tubules
• Local action potentials trigger Ca2+ efflux from terminal cisternae
  
  • Across membrane of sarcoplasmic reticulum
  • Into the fibre cytoplasm

Answer 49

• ACh -> Depolarisation
• Active Nicotinic AChR -> net inward current
• depolarisation spread via T-Tubules
• Local action potentials trigger Ca2+ efflux from terminal cisternae
  
  • Across membrane of sarcoplasmic reticulum
  • Into the fibre cytoplasm

Question 50

Depolarisation -> increased Ca2+

• ACh -> Depolarisation
• Active … AChR -> net inward current
• depolarisation spread via T-…
• Local action potentials trigger Ca2+ efflux from … …
  
  • Across membrane of sarcoplasmic reticulum
  • Into the fibre cytoplasm

Answer 50

• ACh -> Depolarisation
• Active Nicotinic AChR -> net inward current
• depolarisation spread via T-Tubules
• Local action potentials trigger Ca2+ efflux from terminal cisternae
  
  • Across membrane of sarcoplasmic reticulum
  • Into the fibre cytoplasm

Question 51

Excitation-Contraction (EC) Coupling

• Excitation-contraction coupling = the molecular mechanism for how the … of the plasma membrane leads to the release of …+ into the cytoplasm followed by ….
• Ryanodine Receptor (RyR)
  
  • In SR membrane
  • Releases Ca2+
  • From SR
  • Triggered by voltage sensor on Ca2+ channel
• SERCA
  
  • In SR membrane
  • Pumps Ca2+ Back into SR
  • Needs ATP

Answer 51

• Excitation-contraction coupling = the molecular mechanism for how the depolarisation of the plasma membrane leads to the release of Ca2+ into the cytoplasm followed by contraction.
• Ryanodine Receptor (RyR)
  
  • In SR membrane
  • Releases Ca2+
  • From SR
  • Triggered by voltage sensor on Ca2+ channel
• SERCA
  
  • In SR membrane
  • Pumps Ca2+ Back into SR
  • Needs ATP

Question 52

Excitation-Contraction (EC) Coupling

• Excitation-contraction coupling = the molecular mechanism for how the depolarisation of the plasma membrane leads to the release of Ca2+ into the cytoplasm followed by contraction.
• … Receptor (RyR)
  
  • In SR membrane
  • Releases Ca2+
  • From SR
  • Triggered by voltage sensor on Ca2+ channel
• …
  
  • In SR membrane
  • Pumps Ca2+ Back into SR
  • Needs ATP

Answer 52

• Excitation-contraction coupling = the molecular mechanism for how the depolarisation of the plasma membrane leads to the release of Ca2+ into the cytoplasm followed by contraction.
• Ryanodine Receptor (RyR)
  
  • In SR membrane
  • Releases Ca2+
  • From SR
  • Triggered by voltage sensor on Ca2+ channel
• SERCA
  
  • In SR membrane
  • Pumps Ca2+ Back into SR
  • Needs ATP

Question 53

Excitation-Contraction (EC) Coupling

• Excitation-contraction coupling = the molecular mechanism for how the depolarisation of the plasma membrane leads to the release of Ca2+ into the cytoplasm followed by contraction.
• Ryanodine Receptor (RyR)
  
  • In SR membrane
  • … Ca2+
  • … SR
  • Triggered by voltage sensor on Ca2+ channel
• SERCA
  
  • In SR membrane
  • … Ca2+ … into SR
  • Needs …

Answer 53

• Excitation-contraction coupling = the molecular mechanism for how the depolarisation of the plasma membrane leads to the release of Ca2+ into the cytoplasm followed by contraction.
• Ryanodine Receptor (RyR)
  
  • In SR membrane
  • Releases Ca2+
  • From SR
  • Triggered by voltage sensor on Ca2+ channel
• SERCA
  
  • In SR membrane
  • Pumps Ca2+ Back into SR
  • Needs ATP

Question 54

Excitation-Contraction (EC) Coupling

• Excitation-contraction coupling = the molecular mechanism for how the depolarisation of the plasma membrane leads to the release of Ca2+ into the cytoplasm followed by contraction.
• Ryanodine Receptor (RyR)
  
  • In SR membrane
  • Releases Ca2+
  • From SR
  • Triggered by … sensor on Ca2+ channel
• S….
  
  • In SR membrane
  • Pumps Ca2+ Back into SR
  • Needs ATP

Answer 54

• Excitation-contraction coupling = the molecular mechanism for how the depolarisation of the plasma membrane leads to the release of Ca2+ into the cytoplasm followed by contraction.
• Ryanodine Receptor (RyR)
  
  • In SR membrane
  • Releases Ca2+
  • From SR
  • Triggered by voltage sensor on Ca2+ channel
• SERCA
  
  • In SR membrane
  • Pumps Ca2+ Back into SR
  • Needs ATP

Question 55

SERCA = Smooth endoplasmic Reticulum Calcium ATPase = a … pump in the sarcoplasmic reticulum (smooth endoplasmic reticulum) membrane of a muscle cell. It … free cytosolic calcium back into the SR; thus it … calcium and requires … to do so.

Answer 55

SERCA = Smooth endoplasmic Reticulum Calcium ATPase = a calcium pump in the sarcoplasmic reticulum (smooth endoplasmic reticulum) membrane of a muscle cell. It pumps free cytosolic calcium back into the SR; thus it resequesters calcium and requires ATP to do so.

Question 56

Tetany: molecular basis

• A … AP -> Ca2+ release from SR -> …
• Ca2+ ions are rapidly pumped back into SR -> end of …
• Frequent APs -> insufficient Ca2+ resequestration -> summation of contraction

Answer 56

• A single AP -> Ca2+ release from SR -> twitch
• Ca2+ ions are rapidly pumped back into SR -> end of twitch
• Frequent APs -> insufficient Ca2+ resequestration -> summation of contraction

Question 57

Tetany: molecular basis

• A single AP -> Ca2+ release from SR -> twitch
• Ca2+ ions are rapidly pumped back into SR -> end of twitch
• … APs -> insufficient Ca2+ … -> … of contraction

Answer 57

• A single AP -> Ca2+ release from SR -> twitch
• Ca2+ ions are rapidly pumped back into SR -> end of twitch
• Frequent APs -> insufficient Ca2+ resequestration -> summation of contraction

Question 58

Sarcomere length

• Below is a graph of sarcomere spacing (i.e. sarcomere length) vs. tension.
• For each segment (e.g. between A-B or between B-C), what is the relative length of the sarcomeric A band to the sarcomeric I band?

Answer 58

Question 59

Contractile properties - muscle cells

• muscle fibres are divided into 2 main types:
  
  • … twitch (type I – ‘red’ – oxidative, small diam.)
    
    • High myoglobin, many mitochondria
  • … twitch (type II – ‘white’ – nonoxidative, wide diam.)
    
    • Lower myoglobin, increased energy from glycolysis
• fibre types differ in:
  
  • aerobic (slow) vs anaerobic
  • faster calcium re-uptake (fast)
  • maximum tension produced (fast)
  • fatigue resistance (slow)

Answer 59

• muscle fibres are divided into 2 main types:
  
  • slow twitch (type I – ‘red’ – oxidative, small diam.)
    
    • High myoglobin, many mitochondria
  • fast twitch (type II – ‘white’ – nonoxidative, wide diam.)
    
    • Lower myoglobin, increased energy from glycolysis
• fibre types differ in:
  
  • aerobic (slow) vs anaerobic
  • faster calcium re-uptake (fast)
  • maximum tension produced (fast)
  • fatigue resistance (slow)

Question 60

Contractile properties - muscle cells

• muscle fibres are divided into 2 main types:
  
  • slow twitch (type I – ‘…’ – oxidative, small diam.)
    
    • High myoglobin, many mitochondria
  • fast twitch (type II – ‘…’ – nonoxidative, wide diam.)
    
    • Lower myoglobin, increased energy from glycolysis
• fibre types differ in:
  
  • aerobic (which are …) vs anaerobic
  • faster calcium re-uptake (which are…)
  • maximum tension produced (fast)
  • fatigue resistance (slow)

Answer 60

• muscle fibres are divided into 2 main types:
  
  • slow twitch (type I – ‘red’ – oxidative, small diam.)
    
    • High myoglobin, many mitochondria
  • fast twitch (type II – ‘white’ – nonoxidative, wide diam.)
    
    • Lower myoglobin, increased energy from glycolysis
• fibre types differ in:
  
  • aerobic (which are slow) vs anaerobic
  • faster calcium re-uptake (fast)
  • maximum tension produced (fast)
  • fatigue resistance (slow)

Question 61

Contractile properties - muscle cells

• muscle fibres are divided into 2 main types:
  
  • slow twitch (type I – ‘red’ – oxidative, small diam.)
    
    • … myoglobin, many mitochondria
  • fast twitch (type II – ‘white’ – nonoxidative, wide diam.)
    
    • … myoglobin, increased energy from glycolysis
• fibre types differ in:
  
  • aerobic (slow) vs anaerobic
  • faster calcium re-uptake (fast)
  • maximum tension produced (… fibres)
  • fatigue resistance (… fibres)

Answer 61

• muscle fibres are divided into 2 main types:
  
  • slow twitch (type I – ‘red’ – oxidative, small diam.)
    
    • High myoglobin, many mitochondria
  • fast twitch (type II – ‘white’ – nonoxidative, wide diam.)
    
    • Lower myoglobin, increased energy from glycolysis
• fibre types differ in:
  
  • aerobic (slow) vs anaerobic
  • faster calcium re-uptake (fast)
  • maximum tension produced (fast fibres)
  • fatigue resistance (slow fibres)

Question 62

Slow twitch muscle fibres

• Type … – ‘…’ – oxidative, small diam
• High myoglobin, many mitochondria
• Aerobic/anaerobic?
• Fatigue resistant

Answer 62

• Type I – ‘red’ – oxidative, small diam
• High myoglobin, many mitochondria
• Aerobic
• Fatigue resistant

Question 63

Slow twitch muscle fibres

• Type I – ‘red’ – oxidative, small diam
• … myoglobin, many mitochondria
• Aerobic
• … resistant

Answer 63

• Type I – ‘red’ – oxidative, small diam
• High myoglobin, many mitochondria
• Aerobic
• Fatigue resistant

Question 64

Fast twitch muscle fibres

• Type II – ‘white’ – nonoxidative, wide diam
• Lower myoglobin, increased energy from glycolysis
• Anaerobic
• … calcium re-uptake
• … tension produced

Answer 64

• Type II – ‘white’ – nonoxidative, wide diam
• Lower myoglobin, increased energy from glycolysis
• Anaerobic
• Faster calcium re-uptake
• Maximum tension produced

Question 65

Fast twitch muscle fibres

• Type … – ‘…’ – nonoxidative, wide diam
• Lower myoglobin, increased energy from glycolysis
• Anaerobic
• Faster calcium re-uptake
• Maximum tension produced

Answer 65

• Type II – ‘white’ – nonoxidative, wide diam
• Lower myoglobin, increased energy from glycolysis
• Anaerobic
• Faster calcium re-uptake
• Maximum tension produced

Question 66

Fast twitch muscle fibres

• Type II – ‘white’ – nonoxidative, wide diam
• … myoglobin, increased energy from …
• Aerobic/Anaerobic?
• Faster calcium re-uptake
• Maximum tension produced

Answer 66

• Type II – ‘white’ – nonoxidative, wide diam
• Lower myoglobin, increased energy from glycolysis
• Anaerobic
• Faster calcium re-uptake
• Maximum tension produced

Question 67

Basis of muscle fibre types

Answer 67

Question 68

Distribution of fibre types

• Muscles contain mixtures of fibre types, composition depends on muscle action:
  
  • s… = 80% type I (slow), 20% type IIA
  • vastus lateralis = mixture of type I, IIA, IIX
• Proportions depend on …

Answer 68

• Muscles contain mixtures of fibre types, composition depends on muscle action:
  
  • soleus = 80% type I (slow), 20% type IIA
  • vastus lateralis = mixture of type I, IIA, IIX
• Proportions depend on physical fitness:
  
  • Inactive
  • Moderately active
  • Endurance athlete
  • Anaerobic athlete

Question 69

Distribution of fibre types

• Muscles contain mixtures of fibre types, composition depends on muscle action:
  
  • soleus = …% type I (slow), …% type IIA
  • vastus … = mixture of type I, IIA, IIX
• Proportions depend on physical fitness:
  
  • Inactive
  • Moderately active
  • Endurance athlete
  • Anaerobic athlete

Answer 69

• Muscles contain mixtures of fibre types, composition depends on muscle action:
  
  • soleus = 80% type I (slow), 20% type IIA
  • vastus lateralis = mixture of type I, IIA, IIX
• Proportions depend on physical fitness:
  
  • Inactive
  • Moderately active
  • Endurance athlete
  • Anaerobic athlete

Question 70

Distribution of fibre types

• Muscles contain mixtures of fibre types, composition depends on muscle action:
  
  • soleus = 80% type I (…), 20% type IIA
  • vastus lateralis = mixture of type I, IIA, IIX
• Proportions depend on physical fitness:
  
  • Inactive
  • Moderately active
  • Endurance athlete
  • Anaerobic athlete

Answer 70

• Muscles contain mixtures of fibre types, composition depends on muscle action:
  
  • soleus = 80% type I (slow), 20% type IIA
  • vastus lateralis = mixture of type I, IIA, IIX
• Proportions depend on physical fitness:
  
  • Inactive
  • Moderately active
  • Endurance athlete
  • Anaerobic athlete

Question 71

Distribution of fibre types

• Muscles contain mixtures of fibre types, composition depends on muscle action:
  
  • soleus = 80% type I (slow), 20% type IIA
  • vastus lateralis = mixture of type I, IIA, IIX
• … depend on physical fitness:
  
  • Inactive
  • Moderately active
  • Endurance athlete
  • Anaerobic athlete

Answer 71

• Muscles contain mixtures of fibre types, composition depends on muscle action:
  
  • soleus = 80% type I (slow), 20% type IIA
  • vastus lateralis = mixture of type I, IIA, IIX
• Proportions depend on physical fitness:
  
  • Inactive
  • Moderately active
  • Endurance athlete
  • Anaerobic athlete

Question 72

Exercise and adaptation

• Normal gastrocnemius - T1 and T2 Fibres mixed together, some dark (T1) some light (T2)
• … runner - Very little T1 (slow) most T2 (fast)
• … … runner - Very little T2 (fast) a lot more T1 (slow)

Answer 72

• Normal gastrocnemius - T1 and T2 Fibres mixed together, some dark (T1) some light (T2)
• Sprint runner - Very little T1 (slow) most T2 (fast)
• Long Distance runner - Very little T2 (fast) a lot more T1 (slow)

Question 73

Exercise and adaptation

• Normal gastrocnemius - T1 and T2 Fibres mixed together, some dark (T1) some light (T2)
• Sprint runner - Very little T1 (… twitch) most T2 (… twitch)
• Long Distance runner - Very little T2 (… twitch) a lot more T1 (… twitch)

Answer 73

• Normal gastrocnemius - T1 and T2 Fibres mixed together, some dark (T1) some light (T2)
• Sprint runner - Very little T1 (slow) most T2 (fast)
• Long Distance runner - Very little T2 (fast) a lot more T1 (slow)

Question 74

Co-ordination of muscle contraction

• 3 types of co-ordination
• … Units
  
  • Recruitment & size principle
• T…
• Fusion of myocytes into long myofibres

Answer 74

• 3 types of co-ordination
• Motor Units
  
  • Recruitment & size principle
• Tetany
• Fusion of myocytes into long myofibres

Question 75

Co-ordination of muscle contraction

• 3 types of co-ordination
• Motor Units
  
  • … & size principle
• Tetany
• … of … into long myofibres

Answer 75

• 3 types of co-ordination
• Motor Units
  
  • Recruitment & size principle
• Tetany
• Fusion of myocytes into long myofibres

Question 76

Motor units

• Definition: A … alpha motor … and all muscle fibres it …
• Functions as a single … unit of skeletal muscle
• all muscle fibres in a single motor unit are of the same type
  
  • (e.g. slow oxidative, fast oxidative, fast glycolytic).

Answer 76

• Definition: A single alpha motor neuron and all muscle fibres it innervates.
• Functions as a single contractile unit of skeletal muscle
• all muscle fibres in a single motor unit are of the same type
  
  • (e.g. slow oxidative, fast oxidative, fast glycolytic).

Question 77

Motor units

• Definition: A single … motor neuron and all muscle fibres it innervates
• Functions as a single contractile unit of skeletal muscle
• all muscle fibres in a single motor unit are of the … …

Answer 77

• Definition: A single alpha motor neuron and all muscle fibres it innervates.
• Functions as a single contractile unit of skeletal muscle
• all muscle fibres in a single motor unit are of the same type
  
  • (e.g. slow oxidative, fast oxidative, fast glycolytic).

Question 78

Motor Units: Variety

• In … muscles responsible for powerful gross contractions, a single motor neuron may synapse on 1000 fibres
• In … muscles mediating precision movement a single motor neuron may synapse with as few as 2 – 3 muscle fibres
• Type and function of the lower motor neuron determines the muscle fibre,
• There are different sorts of motor units in a single muscle

Answer 78

• In large muscles responsible for powerful gross contractions, a single motor neuron may synapse on 1000 fibres
• In small muscles mediating precision movement a single motor neuron may synapse with as few as 2 – 3 muscle fibres
• Type and function of the lower motor neuron determines the muscle fibre,
• There are different sorts of motor units in a single muscle

Question 79

Motor Units: Variety

• In large muscles responsible for powerful gross contractions, a single motor neuron may synapse on 1000 fibres
• In small muscles mediating precision movement a single motor neuron may synapse with as few as 2 – 3 muscle fibres
• Type and function of the … motor neuron determines the muscle fibre,
• There are different sorts of motor units in a single muscle

Answer 79

• In large muscles responsible for powerful gross contractions, a single motor neuron may synapse on 1000 fibres
• In small muscles mediating precision movement a single motor neuron may synapse with as few as 2 – 3 muscle fibres
• Type and function of the lower motor neuron determines the muscle fibre,
• There are different sorts of motor units in a single muscle

Question 80

Motor Units: Variety

• In large muscles responsible for powerful gross contractions, a single motor neuron may synapse on 1000 fibres
• In small muscles mediating precision movement a single motor neuron may synapse with as few as 2 – 3 muscle fibres
• Type and … of the lower motor neuron determines the muscle …,
• There are different sorts of motor units in a single muscle

Answer 80

• In large muscles responsible for powerful gross contractions, a single motor neuron may synapse on 1000 fibres
• In small muscles mediating precision movement a single motor neuron may synapse with as few as 2 – 3 muscle fibres
• Type and function of the lower motor neuron determines the muscle fibre,
• There are different sorts of motor units in a single muscle

Question 81

Contraction: Force Generation

• Iso… – generates a variable force while length of muscle remains unchanged.
• Iso… – generates a constant force while the length of the muscle changes.

Answer 81

• Isometric – generates a variable force while length of muscle remains unchanged.
  
  • “Iso” = same, “metric” = length
• Isotonic – generates a constant force while the length of the muscle changes
  
  • “tonic” = tone = tension/force

Question 82

Contraction: Force Generation

• Isometric – generates a … force while length of muscle remains ….
• Isotonic – generates a … force while the length of the muscle …

Answer 82

• Isometric – generates a variable force while length of muscle remains unchanged.
  
  • “Iso” = same, “metric” = length
• Isotonic – generates a constant force while the length of the muscle changes
  
  • “tonic” = tone = tension/force

Question 83

Types of force generation

• Using example: picking up a drinking glass
• Stage 1: iso… – force increases, joint does not move
  
  • Muscle Force < force of gravity –> force increases
    
    • biceps and brachioradialis generate force by … contraction as muscles have not yet shortened
• Stage 2: iso… – force remains the same, arm moves
  
  • Glass moves upward in response to force
    
    • An … contraction starts as the force generated by the muscles overcomes gravitational and inertial forces keeping glass on the table
• Glass starts to rise as the muscles shorten and the elbow bends and force generated by the muscle is constant as the glass is moving

Answer 83

• Using example: picking up a drinking glass
• Stage 1: isometric – force increases, joint does not move
  
  • Muscle Force < force of gravity –> force increases
    
    • biceps and brachioradialis generate force by isometric contraction as muscles have not yet shortened
• Stage 2: isotonic – force remains the same, arm moves
  
  • Glass moves upward in response to force
    
    • An isotonic contraction starts as the force generated by the muscles overcomes gravitational and inertial forces keeping glass on the table
• Glass starts to rise as the muscles shorten and the elbow bends and force generated by the muscle is constant as the glass is moving

Question 84

Types of force generation

• Using example: picking up a drinking glass
• Stage 1: isometric – force …, joint does …
  
  • Muscle Force < force of gravity –> force increases
    
    • biceps and brachioradialis generate force by isometric contraction as muscles have not yet shortened
• Stage 2: isotonic – force remains the …, arm …
  
  • Glass moves upward in response to force
    
    • An isotonic contraction starts as the force generated by the muscles overcomes gravitational and inertial forces keeping glass on the table
• Glass starts to rise as the muscles shorten and the elbow bends and force generated by the muscle is constant as the glass is moving

Answer 84

• Using example: picking up a drinking glass
• Stage 1: isometric – force increases, joint does not move
  
  • Muscle Force < force of gravity –> force increases
    
    • biceps and brachioradialis generate force by isometric contraction as muscles have not yet shortened
• Stage 2: isotonic – force remains the same, arm moves
  
  • Glass moves upward in response to force
    
    • An isotonic contraction starts as the force generated by the muscles overcomes gravitational and inertial forces keeping glass on the table
• Glass starts to rise as the muscles shorten and the elbow bends and force generated by the muscle is constant as the glass is moving

Question 85

Types of force generation

• Using example: picking up a drinking glass
• Stage 1: isometric – force increases, joint does not move
  
  • Muscle Force < force of gravity –> force increases
    
    • biceps and brachioradialis generate force by isometric contraction as muscles have not yet shortened
• Stage 2: isotonic – force remains the same, arm moves
  
  • Glass moves upward in response to force
    
    • An isotonic contraction starts as the force generated by the muscles overcomes gravitational and inertial forces keeping glass on the table
• Glass starts to rise as the muscles … and the elbow bends and force generated by the muscle is … as the glass is moving

Answer 85

• Using example: picking up a drinking glass
• Stage 1: isometric – force increases, joint does not move
  
  • Muscle Force < force of gravity –> force increases
    
    • biceps and brachioradialis generate force by isometric contraction as muscles have not yet shortened
• Stage 2: isotonic – force remains the same, arm moves
  
  • Glass moves upward in response to force
    
    • An isotonic contraction starts as the force generated by the muscles overcomes gravitational and inertial forces keeping glass on the table
• Glass starts to rise as the muscles shorten and the elbow bends and force generated by the muscle is constant as the glass is moving

Question 86

Types of muscular force generation

• Muscle contraction ≠ (necessarily) muscle …
• … – force during contraction – tossing a ball into air
• … (negatives) – force during muscle elongation
  
  • e.g. when “braking” or when the weight of the object is overwhelming – catching a ball
• Both types of force generation can occur in one behaviour
• Proprioception controls force gen. based on length and stretch

Answer 86

• Muscle contraction ≠ (necessarily) muscle shortening
• Concentric – force during contraction – tossing a ball into air
• Eccentric (negatives) – force during muscle elongation
  
  • e.g. when “braking” or when the weight of the object is overwhelming – catching a ball
• Both types of force generation can occur in one behaviour
• Proprioception controls force gen. based on length and stretch

Question 87

Types of muscular force generation

• Muscle contraction ≠ (necessarily) muscle shortening
• Concentric – force during … – tossing a ball into air
• Eccentric (negatives) – force during muscle …
  
  • e.g. when “braking” or when the weight of the object is overwhelming – catching a ball
• Both types of force generation can occur in one behaviour
• … controls force gen. based on length and stretch

Answer 87

• Muscle contraction ≠ (necessarily) muscle shortening
• Concentric – force during contraction – tossing a ball into air
• Eccentric (negatives) – force during muscle elongation
  
  • e.g. when “braking” or when the weight of the object is overwhelming – catching a ball
• Both types of force generation can occur in one behaviour
• Proprioception controls force gen. based on length and stretch

Question 88

Types of muscular force generation

• Fill in the blanks

Answer 88

Question 89

A … contraction is a type of muscle activation that causes tension on your muscle as it shortens

Answer 89

A concentric contraction is a type of muscle activation that causes tension on your muscle as it shortens

Question 90

… contraction occurs when the total length of the muscle increases as tension is produced.

Answer 90

Eccentric contraction occurs when the total length of the muscle increases as tension is produced. (For example, the lowering phase of a biceps curl constitutes an eccentric contraction.)

Question 91

Recruitment: Size principle

• as the initial … contraction occurs:
  
  • more and more motor units are recruited starting with … ones and progressively adding … ones
  • Allows fine gradation of force for … movements
• In drinking glass example:
  
  • more and bigger motor units recruited until the glass starts moving and the contraction becomes isotonic

Answer 91

• as the initial isometric contraction occurs:
  
  • more and more motor units are recruited starting with smaller ones and progressively adding larger ones
  • Allows fine gradation of force for small movements
• In drinking glass example:
  
  • more and bigger motor units recruited until the glass starts moving and the contraction becomes isotonic

Question 92

Recruitment: Size principle

• as the initial … contraction occurs:
  
  • more and more motor units are recruited starting with smaller ones and progressively adding larger ones
  • Allows fine gradation of force for small movements
• In drinking glass example:
  
  • more and bigger motor units recruited until the glass starts moving and the contraction becomes …

Answer 92

• as the initial isometric contraction occurs:
  
  • more and more motor units are recruited starting with smaller ones and progressively adding larger ones
  • Allows fine gradation of force for small movements
• In drinking glass example:
  
  • more and bigger motor units recruited until the glass starts moving and the contraction becomes isotonic

Question 93

Upper vs Lower Motor Neurons

• Lower motor neuron disease
  
  • Leads to …
  • Leads to Muscle …
• Upper motor neurone disease
  
  • Spasticity, hypertonia

Answer 93

• Lower motor neuron disease
  
  • Weakness
  • Muscle atrophy
• Upper motor neurone disease
  
  • Spasticity, hypertonia

Question 94

Upper vs Lower Motor Neurons

• Lower motor neuron disease
  
  • Weakness
  • Muscle atrophy
• Upper motor neurone disease
  
  • S…, H…

Answer 94

• Lower motor neuron disease
  
  • Weakness
  • Muscle atrophy
• Upper motor neurone disease
  
  • Spasticity, hypertonia

Question 95

… = muscle is over-contracted when at rest

Answer 95

Hypertonia = muscle is over-contracted when at rest (IN UPPER MOTOR NEURONE DISEASE)

Question 96

… = muscle has involuntary spasms of activity that resist relaxation. They are VELOCITY-dependent, and often one-way (ie there is resistance to flexion but no resistance to extension)

Answer 96

Spasticity = muscle has involuntary spasms of activity that resist relaxation. They are VELOCITY-dependent, and often one-way (ie there is resistance to flexion but no resistance to extension) (IN UPPER MOTOR NEURONE DISEASE)

Question 97

… motor neuron = signal starts (dendrites) in the brain (especially the motor cortex) and extends to (axon) the spinal cord, where it forms a synapse with a … motor neuron.

Answer 97

Upper motor neuron = signal starts (dendrites) in the brain (especially the motor cortex) and extends to (axon) the spinal cord, where it forms a synapse with a lower motor neuron.

Question 98

… = muscle wasting, muscle becomes smaller (and weaker) due to disuse. Often caused by loss of neural input to the muscle fibre.

Answer 98

Atrophy = muscle wasting, muscle becomes smaller (and weaker) due to disuse. Often caused by loss of neural input to the muscle fibre. (IN LOWER MOTOR NEURON DISEASE)

Question 99

Stretch Reflex

• Controls Muscle Length
• … Muscle Force
• Lack of patellar reflex = … sign

Answer 99

• Controls Muscle Length
• Increases Muscle Force
• Lack of patellar reflex = Westphal’s sign

Question 100

Stretch Reflex controls muscle … and increases muscle …

Answer 100

Stretch Reflex controls muscle length and increases muscle force (lack of patellar reflex - westphal’s sign)

Question 101

Patellar Reflex

• Sensory spindle fibre = Muscle Spindle Fibre
  
  • Detects …, i.e. Length
  • Proprioception
• Spindle is … to other muscle fibres
• Ipsilateral Spinal reflex
• Monosynaptic

Answer 101

• Sensory spindle fibre = Muscle Spindle Fibre
  
  • Detects Stretch, i.e. Length
  • Proprioception
• Spindle is Parallel to other muscle fibres
• Ipsilateral Spinal reflex
• Monosynaptic

Question 102

Patellar Reflex

• Sensory spindle fibre = Muscle Spindle Fibre
  
  • Detects Stretch, i.e. Length
  • P…
• Spindle is Parallel to other muscle fibres
• Ipsilateral … reflex
• Monosynaptic

Answer 102

• Sensory spindle fibre = Muscle Spindle Fibre
  
  • Detects Stretch, i.e. Length
  • Proprioception
• Spindle is Parallel to other muscle fibres
• Ipsilateral Spinal reflex
• Monosynaptic

Question 103

The patellar reflex is a clinical and classic example of the … reflex arc.

Answer 103

The patellar reflex is a clinical and classic example of the monosynaptic reflex arc.

Question 104

The Monosynaptic Stretch Reflex

• A monosynaptic reflex, such as the knee jerk reflex, is a simple reflex involving only one synapse between the sensory and motor neurone.
• The pathway starts when the muscle spindle is … (caused by the tap stimulus in the knee jerk reflex). The muscle spindles are responsible for detecting the … of the muscles fibres.
• When a … is detected it causes action potentials to be fired by Ia afferent fibres. These then synapse within the spinal cord with α-motoneurones which innervate … fibres. The antagonistic muscle is inhibited and the agonist muscle contracts i.e. in the knee jerk reflex the quadriceps contract and the hamstrings relax.

Answer 104

• A monosynaptic reflex, such as the knee jerk reflex, is a simple reflex involving only one synapse between the sensory and motor neurone.
• The pathway starts when the muscle spindle is stretched (caused by the tap stimulus in the knee jerk reflex). The muscle spindles are responsible for detecting the length of the muscles fibres.
• When a stretch is detected it causes action potentials to be fired by Ia afferent fibres. These then synapse within the spinal cord with α-motoneurones which innervate extrafusal fibres. The antagonistic muscle is inhibited and the agonist muscle contracts i.e. in the knee jerk reflex the quadriceps contract and the hamstrings relax.

Question 105

Muscle Spindle

• A spindle consists of 3-12 … fibres
• Gamma motor neurons increase …
  
  • Drive contraction of edge of intrafusal fibres
  • Sensors from muscle spindle are:
    
    • Called Type 1a and Type 2
    • Wrap around the intrafusal fibres
    • Detect stretch (ie length) of central non-contracting region using stretch receptors
• Spindle is like a thermostat that regulates the relationship between muscle length and muscle contractility
  
  • ie the relationship between neural drive and force generation

Answer 105

• A spindle consists of 3-12 intrafusal fibres
• Gamma motor neurons increase sensitivity
  
  • Drive contraction of edge of intrafusal fibres
  • Sensors from muscle spindle are:
    
    • Called Type 1a and Type 2
    • Wrap around the intrafusal fibres
    • Detect stretch (ie length) of central non-contracting region using stretch receptors
• Spindle is like a thermostat that regulates the relationship between muscle length and muscle contractility
  
  • ie the relationship between neural drive and force generation

Question 106

Muscle Spindle

• A spindle consists of 3-12 intrafusal fibres
• … motor neurons increase sensitivity
  
  • Drive contraction of edge of intrafusal fibres
  • Sensors from muscle spindle are:
    
    • Called Type 1a and Type 2
    • Wrap around the intrafusal fibres
    • Detect … (ie …) of central non-contracting region using … receptors
• Spindle is like a thermostat that regulates the relationship between muscle length and muscle contractility
  
  • ie the relationship between neural drive and force generation

Answer 106

• A spindle consists of 3-12 intrafusal fibres
• Gamma motor neurons increase sensitivity
  
  • Drive contraction of edge of intrafusal fibres
  • Sensors from muscle spindle are:
    
    • Called Type 1a and Type 2
    • Wrap around the intrafusal fibres
    • Detect stretch (ie length) of central non-contracting region using stretch receptors
• Spindle is like a thermostat that regulates the relationship between muscle length and muscle contractility
  
  • ie the relationship between neural drive and force generation

Question 107

Muscle Spindle

• A spindle consists of 3-12 intrafusal fibres
• Gamma motor neurons increase sensitivity
  
  • Drive contraction of edge of intrafusal fibres
  • Sensors from muscle spindle are:
    
    • Called Type 1a and Type 2
    • Wrap around the intrafusal fibres
    • Detect stretch (ie length) of central non-contracting region using stretch receptors
• Spindle is like a thermostat that regulates the relationship between muscle … and muscle …
  
  • ie the relationship between neural drive and force generation

Answer 107

• A spindle consists of 3-12 intrafusal fibres
• Gamma motor neurons increase sensitivity
  
  • Drive contraction of edge of intrafusal fibres
  • Sensors from muscle spindle are:
    
    • Called Type 1a and Type 2
    • Wrap around the intrafusal fibres
    • Detect stretch (ie length) of central non-contracting region using stretch receptors
• Spindle is like a thermostat that regulates the relationship between muscle length and muscle contractility
  
  • ie the relationship between neural drive and force generation

Question 108

Muscle Spindle

• A spindle consists of 3-12 intrafusal fibres
• Gamma motor neurons increase sensitivity
  
  • Drive contraction of edge of intrafusal fibres
  • Sensors from muscle spindle are:
    
    • Called Type 1a and Type 2
    • Wrap around the intrafusal fibres
    • Detect stretch (ie length) of central non-contracting region using stretch receptors
• Spindle is like a thermostat that regulates the relationship between muscle length and muscle contractility
  
  • ie the relationship between … drive and … generation

Answer 108

• A spindle consists of 3-12 intrafusal fibres
• Gamma motor neurons increase sensitivity
  
  • Drive contraction of edge of intrafusal fibres
  • Sensors from muscle spindle are:
    
    • Called Type 1a and Type 2
    • Wrap around the intrafusal fibres
    • Detect stretch (ie length) of central non-contracting region using stretch receptors
• Spindle is like a thermostat that regulates the relationship between muscle length and muscle contractility
  
  • ie the relationship between neural drive and force generation

Question 109

Muscle Spindle Reflex: Relevance

• Absence of this reflex = … Sign
  
  • Receptor damage
  • Femoral nerve damage
  • Peripheral nerve disease
    
    • e.g. Peripheral …
• In upper motor neuron disease
  
  • Can lead to hypertonia and spasticity
  • UMN inhibits normal descending inhibitory input to spinal interneurons
  • The spindle reflex becomes over-sensitive
    
    • Can attempt to contract muscle all the time

Answer 109

• Absence of this reflex = Westphal’s Sign
  
  • Receptor damage
  • Femoral nerve damage
  • Peripheral nerve disease
    
    • e.g. Peripheral Neuropathy
• In upper motor neuron disease
  
  • Can lead to hypertonia and spasticity
  • UMN inhibits normal descending inhibitory input to spinal interneurons
  • The spindle reflex becomes over-sensitive
    
    • Can attempt to contract muscle all the time

Question 110

Muscle Spindle Reflex: Relevance

• Absence of this reflex = Westphal’s Sign
  
  • Receptor damage
  • Femoral nerve damage
  • Peripheral nerve disease
    
    • e.g. Peripheral Neuropathy
• In … motor neuron disease
  
  • Can lead to hypertonia and spasticity
  • … inhibits normal descending inhibitory input to spinal interneurons
  • The spindle reflex becomes over-…
    
    • Can attempt to contract muscle all the time

Answer 110

• Absence of this reflex = Westphal’s Sign
  
  • Receptor damage
  • Femoral nerve damage
  • Peripheral nerve disease
    
    • e.g. Peripheral Neuropathy
• In upper motor neuron disease
  
  • Can lead to hypertonia and spasticity
  • UMN inhibits normal descending inhibitory input to spinal interneurons
  • The spindle reflex becomes over-sensitive
    
    • Can attempt to contract muscle all the time

Question 111

Muscle Spindle Reflex: Relevance

• Absence of this reflex = Westphal’s Sign
  
  • Receptor damage
  • … nerve damage
  • … nerve disease
    
    • e.g. Peripheral Neuropathy
• In upper motor neuron disease
  
  • Can lead to hyper… and s…
  • UMN inhibits normal descending inhibitory input to spinal interneurons
  • The spindle reflex becomes over-sensitive
    
    • Can attempt to contract muscle …

Answer 111

• Absence of this reflex = Westphal’s Sign
  
  • Receptor damage
  • Femoral nerve damage
  • Peripheral nerve disease
    
    • e.g. Peripheral Neuropathy
• In upper motor neuron disease
  
  • Can lead to hypertonia and spasticity
  • UMN inhibits normal descending inhibitory input to spinal interneurons
  • The spindle reflex becomes over-sensitive
    
    • Can attempt to contract muscle all the time

Question 112

Tendon Reflex

• Protects from …
• … Muscle Force -> dropping the load
  
  • Sensor firing -> decreased contraction

Answer 112

• Protects from overloading
• Decreases Muscle Force -> dropping the load
  
  • Sensor firing -> decreased contraction

Question 113

Tendon Reflex

• Protects from overloading
• Decreases Muscle Force -> dropping the load
  
  • Sensor firing -> … contraction

Answer 113

• Protects from overloading
• Decreases Muscle Force -> dropping the load
  
  • Sensor firing -> decreased contraction

Question 114

Tendon Reflex

• Sensor to Spinal Cord
• Interneuron to motor neuron
• Motor neuron …
• Motor neuron to muscle

Answer 114

• Sensor to Spinal Cord
• Interneuron to motor neuron
• Motor neuron inhibited
• Motor neuron to muscle

Question 115

Tendon Reflex

• Sensor = … Tendon Organ
  
  • Detects …
  • In series with muscle
  • In tendon
    
    • Near border with muscle
• Disynaptic
• Ipsilateral Spinal reflex

Answer 115

• Sensor = Golgi Tendon Organ
  
  • Detects Tension
  • In series with muscle
  • In tendon
    
    • Near border with muscle
• Disynaptic
• Ipsilateral Spinal reflex

Question 116

Tendon Reflex

• Sensor = Golgi Tendon Organ
  
  • Detects Tension
  • In … with muscle
  • In tendon
    
    • Near … with muscle
• Disynaptic
• Ipsilateral Spinal reflex

Answer 116

• Sensor = Golgi Tendon Organ
  
  • Detects Tension
  • In series with muscle
  • In tendon
    
    • Near border with muscle
• Disynaptic
• Ipsilateral Spinal reflex

Question 117

Tendon Reflex

• Sensor = Golgi Tendon Organ
  
  • Detects Tension
  • In series with muscle
  • In tendon
    
    • Near border with muscle
• …synaptic
• Ipsilateral Spinal reflex

Answer 117

• Sensor = Golgi Tendon Organ
  
  • Detects Tension
  • In series with muscle
  • In tendon
    
    • Near border with muscle
• Disynaptic
• Ipsilateral Spinal reflex

Question 118

Tendon Reflex

• Sensor = Golgi Tendon Organ
  
  • Detects Tension
  • In series with muscle
  • In tendon
    
    • Near border with muscle
• Disynaptic
• … Spinal reflex

Answer 118

• Sensor = Golgi Tendon Organ
  
  • Detects Tension
  • In series with muscle
  • In tendon
    
    • Near border with muscle
• Disynaptic
• Ipsilateral Spinal reflex

Question 119

Like the stretch reflex, the tendon reflex is …lateral

Answer 119

Like the stretch reflex, the tendon reflex is ipsilateral

Question 120

The … … reflex is a response to extensive tension on a tendon. It helps avoid strong muscle contractions which could tear the tendon from either the muscle or bone.

Answer 120

The Golgi tendon reflex is a response to extensive tension on a tendon.[7] It helps avoid strong muscle contractions which could tear the tendon from either the muscle or bone.

Question 121

Summary - Physiology of Skeletal Muscle Contraction

• Fibre types differ in oxidative metabolism
  
  • … red
  • … white
• … unit determines fibre type
• Balance of force to length
  
  • … principle
  • … reflex
    
    • Allows for “braking”: eccentric —> isometric

Answer 121

• Fibre types differ in oxidative metabolism
  
  • Slow red
  • Fast white
• Motor unit determines fibre type
• Balance of force to length
  
  • Size principle
  • Stretch reflex
    
    • Allows for “braking”: eccentric —> isometric

Question 122

Muscle contraction is dependent on calcium in the … being … - most of this calcium comes from the … …

Answer 122

Muscle contraction is dependent on calcium in the cytosol being raised - most of this calcium comes from the sarcoplasmic reticulum (very little from outside the cell)