3. Skeletal Muscle Physiology

Question 1

Requirements for Skeletal Muscle Contraction

• Activation:
– ____ at neuromuscular junction.
• Excitation-contraction coupling:
– Generation and propagation of an ____ along the
sarcolemma, which causes…
• Final trigger: a rise in intracellular ____.

Answer 1

neural stimulation
action potential
Ca2+

Question 2

Neuromuscular Transmission and Excitation-Contraction Coupling

• Muscle innervation by myelinated nerve fibers from motor neurons in the spinal cord.
• ____: The parent axon and all the muscle fibers that it innervates.
• Neuromuscular junction: specialized structure of nerve terminals associated with target muscle.
• Nerves transmit a membrane depolarization signal (action potential; to be studied in BS-IV) to the muscles.
• Axon terminal releases ____ into the synaptic cleft in response to the action potential.

Answer 2

motor unit

acetylcholine (ACh)

Question 3

Neuromuscular Transmission and Excitation-Contraction Coupling: 1. Resting Membrane Potential

• Nervous system:
– Controls muscle contractions through
action potentials.
• Resting membrane potentials:
– Membrane voltage difference across membranes (____) caused by ____ differences on the two sides of a membrane.
– Normal (resting) potential is negative:
• Muscle cells: ____ mV.

Every cell at the level of its membrane has an electrical charge, and this electrical charge is distributed differently extracellularly and intracellularly > polarized; when you have a resting cell > slight difference in the amount of charge on both sides > the inner side is slightly more ____ than the outer side (polarization)

Due to differential ____ and ____

Answer 3

polarization
ion concentration
-70/-90

negative
transports
permeabilities

Question 4

Neuromuscular Transmission and Excitation-Contraction Coupling: 2. Action Potential

• Action potential:
– Change in membrane potential from a negative resting potential to a ____ potential (depolarization), and back to the negative resting potential (____).
– Used to transmit signals (e.g. nerve impulse).
– Amplitude (strength) ____ with distance from initial site

AP > change in membrane potential at level at any PM > goes from negative to positive (on the inside, this is depolarization, now ____ mV from -70 mV) > due to the influx of ____ ions

The AP transmits itself ____ > once passes a point > repolarization via the trafficking of ____ ions

Answer 4

positive
repolarization
constant

+25
Na+

sequentially
K+

Question 5

Neuromuscular Transmission and Excitation-Contraction Coupling: 3. Neurotransmitter Release

• ACh stored in neuronal synaptic vesicles.
• AP travels down the nerve fiber (1).
• Depolarization opens ____ channels (2).
• Influx of Ca+2 (3): synaptic vesicles fuse with the membrane (4) and release ACh into the synaptic cleft (5).

Answer 5

voltage-gated Ca2+

Question 6

Excitation-Contraction Coupling: End Plate Potential

1. Local depolarization (end plate potential):
   – Resting muscle membrane potential: -70/-90 mV.
   – Nicotinic ACh receptors at the ____:
   • ____ ion channels:
   –Binding of ACh induces a conformational
   change in the channel to open to the ____ movement of positive ions (____&raquo_space; K+ > Ca2+).
   – Net result: + charge enters cell, so voltage inside cell rises (becomes less negative), i.e. depolarization (____) to ~ ____ mV.

Creation of local depolarization at the level of the end plate (due to the traffic of Na+ ions) > end plate potential (not an ____ at this point, but will create one)

Answer 6

sarcolemma
ACh-gated
inward
Na+
end plate potential
~0
action potential

Question 7

Excitation-Contraction Coupling: End Plate Potential
2. Generation and propagation of the AP:
– End plate potential propagates along the ____.
– Change in voltage opens ____ Na+ channels: Na+ influx → plasma membrane depolarization.
– If ____ is reached, an AP is generated: local depolarization spreads.

Answer 7

sarcolemma
voltage-gated
treshold

Question 8

Excitation-Contraction Coupling: End Plate Potential
3. Repolarization:
– ____ channels close and ____ channels open.
– K+ ____ through the open K+ channels.
– Loss of + charge returns membrane to its
negative resting potential.

Answer 8

Na+
voltage-gated K+
exits

Question 9

Excitation-Contraction Coupling: 1. Role of T Tubules

• ____ is required for myofilament contraction.
• Ca2+ must be liberated from the SR.
• Therefore, current must penetrate deeply into the muscle fiber.
• But… skeletal muscle fibers are too large to produce current flow deep inside the cells.
• Solution: APs are transmitted along the ____ which extend to the proximity of the SR.
• APs in the T tubules cause Ca2+ release in the vicinity of the myofibrils, causing contraction.
• The overall process is called ____.

Answer 9

Ca2+
T tubules
excitation-contraction coupling

Question 10

Excitation-Contraction Coupling: 2. Release of Ca2+
• Voltage change (action potential) in the T tubules activates the ____.
• Activation of DHP receptors opens Ca2+ release channels (____) in the SR.
• Channels open for a few ____, releasing Ca2+ into the sarcoplasm.
• High [Ca2+] in the vicinity of the myofibrils causes their contraction.

DHPR are activated by a change in polarity (inner side of membrane is polarized) > ____ to the Ca-release channels in the SR > once DHPR are activated, it’ll force these channels open > resulting in an expulsion of Ca2+ ions from the SR released in vicinity of the myofibrils

Answer 10

dihdropyridine (DHP) receptors
ryanodine receptor channels
milliseconds

mechanically linked

Question 11

Excitation-Contraction Coupling: 3. Re-uptake of Ca2+

• Repolarization:
• Causes ____ receptors to close the Ca2+ release channels in
the SR.
• Ca2+ is pumped back into the SR by a ____ (____: Sarco/Endoplasmic RetiCulum ATPase).
• Inside the SR, the protein ____ serves to concentrate stored Ca2+ .
• Low [Ca2+] in the vicinity of the myofibrils stops their contraction.

Answer 11

DHP
Ca2+ pump
SERCA
calsequestrin

Question 12

Contraction of Skeletal Muscle: The Calcium Switch

• Absence of Ca2+ (____ M):
–____ binds Ca2+ → shift in position of tropomyosin: ____ within the groove between the two actin chains.
–Myosin-binding sites on actin are exposed: myosin binds tightly to actin (cross-bridge).
–Cross-bridge cycling occurs, over and over, as long as ____ is high and ____ is available.
–When nervous stimulation ceases, Ca2+ is pumped back into SR and contraction ends.

Since Ca2+ control in skeletal muscle is at the thin filaments: ____

(In smooth muscle > ____-linked Ca regulation)

Answer 12

10-9
tropomyosin/troponin complex

10-5
troponin C
deeper
[Ca2+]
ATP
actin-linked regulation
myosin

Question 13

Contraction of Skeletal Muscle: Cross-bridge Cycle

1. Binding of myosin to actin:
   • Myosin head is bound to ____→ high-energy conformation and high affinity for actin.
   • ATP has been hydrolyzed but energy can not be released until myosin head can interact with actin: requires activation of ____ by Ca2+

Answer 13

ADP + Pi

tropomyosin

Question 14

Contraction of Skeletal Muscle: Cross-bridge Cycle

2. Powerstroke:
   • Release of ____ → ____ in the myosin head: “power stroke” that moves actin and myosin filaments relative to each other.

Answer 14

Pi

conformational change

Question 15

Contraction of Skeletal Muscle: Cross-bridge Cycle

3. Rigor:
   • Release of ____ → conformational change in myosin to a ____.
   • Myosin remains ____ to actin subunit.
   • Myosin in a conformation with high affinity for ____ (lower affinity for ____).

Answer 15

ADP
low-energy form
bound
ATP
actin

Question 16

Contraction of Skeletal Muscle: Cross-bridge Cycle

4. Unbinding of myosin and actin:
   • Binding of ATP to the myosin head: conformational change → unbinding from ____.

ATP binds to the ____ domain of the myosin head following release of binding to actin

Answer 16

actin

ATPase

Question 17

Contraction of Skeletal Muscle: Cross-bridge Cycle

5. Cocking of the myosin head:
   • ATP hydrolysis by the ATPase activity at the myosin head.
   • Released energy forces the myosin head into its ____
   from where the cycle can repeat itself (“____” model).

Hydrolyzes ATP into ADP and Pi > ____ the myosin (preparing it to “shoot” and act upon actin) and will restart the cycle if calcium is present

Answer 17

high-energy conformation
walk-along
cocks

Question 18

Every time we go around one cross-bridge cycle we burn ____ per myosin head, and we move the actin filament to the left

Answer 18

1 ATP

Question 19

Neuromuscular Transmission and Excitation-Contraction Coupling: Summary

1. Arrival of an action potential at the neuromuscular junction and induction of ____ release.
2. Activation by ACh of ____ channels and depolarization of the sarcolemma (action potential).
3. Transmission of the action potential: ____ depolarization of the sarcolemma, including T tubule system.
4. Activation of the ____ receptors.
5. Ca2+ release from the SR (____ channels).
6. Binding of Ca2+ to ____ at the thin (actin) myofilament.
7. Troponin/tropomyosin conformational unmasking of myosin-binding sites on actin.
8. Start of the cross-bridge cycle.

Answer 19

ACh
nicotinic ACh-gated Na+
sequential
DHP receptors
ryanodine
troponin C

Question 20

Energetics of Skeletal Muscle Contraction

First immediate source of energy > ____ stores of ATP (relatively low); if contraction lasts longer than ____ seconds, these stores are depleted

The cell then switches to the use of ____ (ATP carrier); after these are depleted (____ seconds) > uses ____ from use of imported glucose from liver or intracellular stores of glycogen, or as a more stable source of energy the cell will use the ____

Answer 20

intracellular
1-2
creatine phosphate
8
glycolysis
Krebs/TCA/ox. phos.

Question 21

Energetics of Skeletal Muscle Contraction

• Efficiency of muscle contraction: ____ (at the ATP level).
• Energy consumption:
– ____ (contraction).
– ____ (SERCA; relaxation).
– ____ (ion balance restoration during repolarization).

• Muscle cells require modest levels of ATP when at rest, and substantial amounts of ATP during intense contraction.
• Energy sources (in order of use):
– Hydrolysis of ATP stores:
• 1-2 seconds.
– Hydrolysis of phosphocreatine.
– Glycogenolysis and anaerobic glycolysis.
– Oxidative metabolism.

Answer 21

40-45%
myosin ATPase
Ca2+-ATPase
Na+/K+-ATPase

Question 22

Energetics of Skeletal Muscle Contraction

• Hydrolysis of ____:
– 5-8 seconds.
– Shuttles phosphate groups from mitochondria to myofibrils.

Following hydrolysis of ATP stores

Phosphocreatine is the result of phosphorylation of ____ with ATP > now it is a carrier of ATP > migrate to myofibrils to myosin, and there is creatine phosphokinase (located within the ____ of the sarcomere, where the reverse reaction takes place)

Before contraction, cell has free ATP in storage and as phosphocreatine (eventually also gets depleted after 8 seconds, and must be regenerated in mitochondria or glycolytic pathway)

Answer 22

phosphocreatine
creatine
H line

Question 23

Energetics of Skeletal Muscle Contraction

 • Glycogenolysis and anaerobic glycolysis:
– O2 supply to muscle is limited - \_\_\_\_
exercise.
– Anaerobic glycolysis to \_\_\_\_ and
fermentation to \_\_\_\_: low energy
efficiency.
– Accumulation of lactate: muscle
\_\_\_\_. 
– Time scale: \_\_\_\_.

Glycolytic pathway is an ____ method of producing ATP

Has two advantages: very ____ pathway to produce energy, and quickly mobilizes the stores of carbs already present in muscle as glycogen

Answer 23

intense
pyruvate
lactate
soreness
minutes
inefficient

quick

Question 24

Energetics of Skeletal Muscle Contraction

• Oxidative metabolism:
– Sustained, long-term contraction (e.g. aerobic
exercises).
– Requires adequate \_\_\_\_ supply:
• High rate of \_\_\_\_ (breathing). 
• High heart \_\_\_\_.
• Vasodilation.

– For 2-4 h: 50% of energy from ____.
– >4 h: ____ stores.
– Following exercise, respiration is still increased
(____) because oxidative phosphorylation continues to:
• Replenish ____ and ____ stores.
• Convert ____ to pyruvate to glucose in the
liver.

Answer 24

O2
lung ventilation
contraction rate

carbohydrates
lipid
oxygen deficit phenomenon
creatine-P
glycogen
lactate

Question 25

Energetics of Skeletal Muscle Contraction

If muscle that is contracting is one of the sustained, long contracting (____), then main mechanism to obtain energy is TCA/ox phos in the mitochondria

Can use carbs, fatty acids, AA; but in order for ox phos to take place > needs a good supply of O2 (aerobic process)

Overall, a very ____method in obtaining ATP

Even after exercise has stopped, the body is still using oxygen almost as comparably as when contraction was taking place; because once contraction stops the muscle has to return to resting parameters: has to restore stores of ____, and has to reassemble the glycogen stores, body also has to convert all excess lactate back to pyruvate and glucose (____, uses a lot of ATP)

Answer 25

red
efficient
ATP
gluconeogenesis

Question 26

Mechanical Properties of Skeletal Muscle

• Twitch:
• Muscle contraction in response to a ____
stimulus.

• Force:
• ____: relaxation begins before contraction is fully established.
• Phases:
• Lag or latent phase: transmission of the AP and liberation of ____.
• Contraction phase: ____.
• Relaxation phase: reuptake of ____.

Answer 26

single
low
Ca2+
cross-bridge
Ca2+

Question 27

Mechanical Properties of Skeletal Muscle Contraction: Summation

• ____: Addition of individual twitch contractions to increase the intensity of overall muscle contraction.
• Types of summation mechanisms:

Temporal (or frequency) summation:
• Increase in force via greater neural discharge frequency: ____.
• Increase of ____.

Spatial (or multiple fiber) summation:
• Recruitment of motor units: ____.
• Increase in the number of ____ contracting simultaneously.

Single twitch usually never reaches the ____ that a muscle can generate

Temporal > increase in force > due to increase in ____ of stimulation (rate coding) > increase the rate of contraction

Spatial > recruitment/activation of variable number of ____ (one motor neuron and all the skeletal muscle fibers that are innervated) (number coding) > increase in motor units that contract simultaneously

Answer 27

summation
rate coding
contraction rate

number coding
motor units

maximum possible force

frequency

motor units

Question 28

Repeated Stimulation: Temporal Summation

• Contraction for periods longer than a twitch requires ____ neural stimulations.
• Temporal summation or frequency increase:

A. Contraction in response to a single AP:
____.

B. Summed response to a second stimulation
during the ____ period:
• Second release of Ca2+ → Reactivation of ____ → two individual responses, increase in ____.

C. Two stimulations in quick succession:
• [Ca2+] still high + 2nd release of Ca2+ → increase in ____ and ____ of contraction.

Answer 28

repeated

twitch

relaxation
cross-bridge
force

force
duration

Question 29

Repeated Stimulation: Temporal Summation

• Frequency increase:
– Next contraction occurs before the ____ is over.
– Total strength of contraction (tension) rises ____.
– As frequency of APs increase, frequency of ____ increases
– Muscle does not completely ____ between contractions.

Answer 29

preceding contraction
progressively
contraction
relax

Question 30

Repeated Stimulation: Temporal Summation

Tetanus:
Sustained contraction due to rapid and repeated stimulation.

– IncompleteT etanus:
• Time for Ca2+ to be recycled through the ____ between APs → Muscle fibers ____ relax between contractions.

– Complete (or Fused) Tetanus:
• Frequency of stimulation above critical level
(tetanic fusion frequency ≈ ____ stimuli/sec).
• Contractions fuse together, appear ____ and
____.
• Depolarization events overlap:
– Sarcoplasm ____ remains high.
– Cross-bridge cycling continues without
____.

If we continue to increase the frequency of stimuli > reach ____

If rate of stimulation is even higher > complete tetanus > the curve is smooth, you don’t see a decrease in the force that the muscle is generating > the concentration of Ca is sarcoplasm is always high and activating the actin filaments > cross-bridge is continuing without any relaxation

Answer 30

SR
partially

20-60
smooth
continuous
[Ca2+]
relaxation

Question 31

Repeated Stimulation: Temporal Summation

High Forces during Tetanus:
– Several fold higher than a twitch: high
____ ratio.
– Reasons:
• [Ca2+]remainshigh.
• Biomechanical: full extension of ____ of muscles (i.e. myofilaments, tendons, CT).

Once reaching tetanic state > forces generated are much more than single twitch > reflects the ____ possible force generated by the muscle

Reason why it’s much higher > muscle is not only composed of muscle cells > there are other components (____, connected to bones, etc.) > single twitch: cell may contract, but not enough ____ for connective tissue to fully extend (reorganize elastin molecules) > increase frequency > increase the contraction of non-muscle components and you achieve contraction as an organ

Answer 31

tetanus/twitch
elastic

maximum
elastin
time

Question 32

Spatial Summation of Muscle Contraction

• Motor Units:
– Group of fibers innervated by a ____.
– Fine motor control from few fibers: ~____ fibers/motor unit.
– Powerful movements from large numbers: ~____ fibers/motor unit.

Answer 32

single motor neuron
5
100

Question 33

Spatial Summation of Muscle Contraction

• Activation (“____”) for motor control: ____ of force.
• Fibers within a single motor unit are distributed throughout a muscle.
• Total force produced is determined by the number of ____ activated at one time.

Stimulate MU A and then stimulate A again, the second contraction is stronger (____ summation)

Stimulate MU A then MU B together (____ summation), the summed force is a much higher force when combined than when each work individually

Answer 33

recruitment
modulation
motor units
temporal
spatial

Question 34

Spatial Summation of Muscle Contraction

• Size principle:
• Small motor units → ____ threshold for action potentials →
activated (“recruited”) before ____ motor units.
• Graded force output:
• Increase in force by ____ steps during weak contraction.
• ____ steps when large amounts of force are required.

Every muscle is comprised of heterogeneous mix of MU; and there are also different types of muscle fibers > the spatial summation can be very fine (stimulating only a few muscle fibers) or more widespread (where the entire muscle organ is stimulated)

How is the NS doing this? > size principle: smaller MU has a ____ threshold to a response for an AP (activated more easily), so they are recruited before the large MU (basis of graded force output)

Answer 34

lower
large
small
greater

lower

Question 35

Spatial Summation

• Differences in threshold:
– Smaller motor units driven by ____ motor nerve fibers.
– Have small ____ in the spinal cord.
– Smaller motor neurons and smaller nerve fibers are more ____ than larger ones.

Smaller MU have nerves that are smaller in ____, and they respond better to AP (more excitable, lower threshold)

Answer 35

small
motor neurons
excitable

diameter

Question 36

Spatial Summation

• Hypothetical example of multiple fiber summation:
– Smallest motor units: very ____ threshold of excitation.
– Largest motor units: very ____ threshold of excitation.
• In the following slides:
– Number of motor units activated in response to increased amounts of nerve excitation.
– Relationship to force exerted by the muscle.

Answer 36

low

high

Question 37

Initial two small MU that have been activated produce a ____ percentage of force

Once you stimulate the moderate MU the force increases more than the ____ MU

The last MU (large) produces the largest ____ of force, requires a ____ stimulus in order to be activated

Answer 37

small
smaller
proportion
very high

Question 38

Mechanics of Skeletal Muscle Contraction: Types of Contraction

1. Isometric:
   – No change in ____ but increase in ____.
2. Isotonic:
   – Change in ____ with constant ____.

Answer 38

muscle length
tension
muscle length
tension

Question 39

Mechanics of Skeletal Muscle Contraction: 1. Isometric Contraction

• Isometric = “____ length”.
• Isometric contraction recording:
– Muscle attached to a rigid support: no muscle shortening is allowed during contraction.
– Experiment: Length of muscle is adjustable at rest (relaxed) but held ____ during contraction.
– Measurement of ____ in response to a single stimulus at a ____ muscle length:
• Isometric force increases relatively ____.
• Isometric ____ is slightly slower than
contraction.
• NO actual movement → NO ____ is
carried out but energy is consumed to maintain force.

Bottom graph > length of muscle remains constant > pre-stretch vs resting length > the tension (isometric) graph changes from one length to another > the muscle is generating no physical work according to the formula (distance = 0), but the muscle is still using ____ in order to contract

Answer 39

equal
constant
isometric force
fixed
rapidly
relaxation
physical work

energy

Question 40

Mechanics of Skeletal Muscle Contraction: 1. Isometric Contraction

• ____ relationship:
– Relationship between initial length and force
generated.

– Optimal length of contraction:
• Due to ____.
• Maximum force of contraction: ____.
• ____ decreases rapidly beyond normal length

By changing lengths, you get a curve located here: when muscle is too long > the force the muscle exerts is much lower; if compress the muscle (too short) > the force the muscle exerts is also lower than the muscle at resting length, but equal to the tension in the stretched muscle

Correlated with the degree of overlap of thick and thin filaments in contractile mechanism; each muscle has optimal length to contract = the length at which the force can exist is the highest > this is where the position of ____ between myosin and actin filaments are optimal; in the other cases the degree of overlap is ____, thereby resulting in a low cross-bridge cycle (3, stretched); if muscle is compressed, there is no more space to reduce the size between the two ____, cannot generate a great force (1)

Answer 40

length-tension
myofilament overlap
normal resting length
force

overlap
optimal
Z disks

Question 41

Mechanics of Skeletal Muscle Contraction: 1. Isometric Contraction

• Length-tension curves:
– Relationship between initial length and force
generated.

– Active force:
• Increase in ____ during contraction.
• Due to ____.

– Optimal length of contraction:
• Maximum force of contraction: ____.
• Force decreases ____ beyond normal length.

– Passive force:
• Dependent on the presence of ____ tissue (“____”)

The total force of the muscle is increasing while stretching, but contradicts what he said > the reason it increases: because of a huge increase in ____ (due to the presence of connective tissue, non-muscle cells), not due to the actual generation of tension from skeletal muscle cells

Answer 41

force (tension)
myofilament overlap

normal resting length
rapidly

conenctive
elastic elements

passive force

Question 42

Mechanics of Skeletal Muscle Contraction: 2. Isotonic Contraction

Isotonic: “equal ____”.
Isotonic contraction recording:
– Experiment: Muscle attached to a rigid frame
and to weights (load) that the muscle lifts.
– Muscle can ____ and exert constant ____.
– Change in muscle length during contraction.
– Actual movement → ____ is carried
out and ____ is consumed to maintain force.

The shape is very different from isometric experiment, where the top ____; also receive the degree of shortening > length decreases

Answer 42

force
shorten
force
physical work
energy

plateaus

Question 43

Mechanics of Skeletal Muscle Contraction: 2. Isotonic Contraction

1. Initially, contraction is ____.
2. After sufficient force is generated, muscle shortens and lifts the load: ____
   contraction.
   • Muscle force = weight force → ____ force line (upper panel)
3. Relaxation (lengthening) at constant
   force: ____ relaxation.
4. Muscle relaxes back to its original length:
   ____ relaxation.

Answer 43

isometric
isotonic
flat
isotonic
isometric

Question 44

Mechanics of Skeletal Muscle Contraction

Duration of the isometric contraction depends on the ____:

A. Light load:
• Short ____ phase.
• Longest ____ phase.
• Low ____.

B. Increase (e.g. doubling) in load:
• Longer ____ phase.
• Shorter ____ phase.
• Higher (e.g. double) ____.

C. Load too high (e.g. tripling) for the muscle to lift:
• Only ____ contraction.
• Higher ____ (e.g. triple).

When load is light (just A) > the isotonic contraction is efficient and it contracts very quickly (high ____, and the force is relatively low)

Double the weight > the muscle takes ____ in order to contract, and it’s not as much as before, but the force that the muscle has to exert has ____

Triple the weight > the muscle cannot ____ > completely isometric contraction (no change in length), but an increase in force (not enough to move the load), but this is the ____ generated by this muscle

Answer 44

load
isometric
isotonic
force

isometric
isotonic
force

isometric
force

slope

longer
doubled

contract
maximal force

Question 45

Mechanics of Skeletal Muscle Contraction: 2. Isotonic Contraction

Force-velocity relationship:
• How much weight can a muscle lift, and how fast can it lift it?

Experiment:
• Isotonic recording with A (heavy) > B > C > D (light) loads.
• Measurement of initial velocity:
• Speed at which muscle begins to shorten.
• Indicated by the slope of the ____ contractions.

Results:
• ____ loads are lifted quicker: VD > VC > VB so if load = 0 → ____ (greatest possible contraction speed).
• VA = 0 (isometric contraction) → A ≥ ____ capability of the muscle (____).

Answer 45

isotonic
Vmax
maximal force
Fmax

Question 46

Mechanics of Skeletal Muscle Contraction: 2. Isotonic Contraction

Force-velocity curve:
• Also known as ____ curve.
• ____ relationship. Results:
• ____ loads are lifted quicker: VD > VC > VB so if load = 0 → ____ (greatest possible contraction speed).
• VA = 0 (isometric contraction) → A ≥ ____.

Answer 46

stress-velocity
inverse
lighter
Vmax
Fmax

Question 47

Mechanics of Skeletal Muscle Contraction: 2. Isotonic Contraction

 Power curve:
• Muscle DOES \_\_\_\_: Force ×Distance.
• Rate of physical work: \_\_\_\_.
• Power output graph:
• At Vmax: force ≈ 0 → power output = \_\_\_\_.
• At Fmax: NO displacement (distance = 0) →
power output = \_\_\_\_.
• Maximum power output ≈ \_\_\_\_.

• Maximum power output occurs at the muscle length with the highest ____ (amount of power produced for a given metabolic energy unit).

There is a point where there is a maximal power output > muscle is using ____ at the highest efficiency > correlates with the muscle at ____ (the optimal overlap of myofilaments)

Answer 47

physical work
power output
0
0
0.3Fmax

metabolic efficiency

energy stores
rest

Question 48

Mechanics of Skeletal Muscle Contraction: 2. Isotonic Contraction

• Velocity:
• Maximal at \_\_\_\_ load (Vo).
• Decreases with \_\_\_\_ load.
• V = 0 when load is equal to the \_\_\_\_ the muscle can generate
(\_\_\_\_ force).

• If load is increased past that point, the muscle will
actually be able to still sustain the load up to ____ times maximum force (cross-bridges are still able to remain attached to actin).
• At greater loads, cross-bridges are unable to sustain the load, rapid ____ occurs, and the muscle can ____.

Extend the curve to the right > up to vertical line is combination of velocity-tension curve > no more power output here > but if we measure velocity and place more weight > the muscle begins to lengthen > due to the fact that the overlap between myofilaments generates just enough force to prevent the ____ of the cell (safety mechanism)

Answer 48

zero
increasing
isometric

1.6
lengthening
break

overextensions

Question 49

Speed of Contraction

Eye muscle after stimulation is very ____ to contract and relax

Soleus takes ____ longer to contract than the muscles in the eye

Answer 49

quick

50X