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BIO108- GENERAL PHYSIOLOGY > LECTURE 8: MUSCULAR CONTRACTION > Flashcards

LECTURE 8: MUSCULAR CONTRACTION Flashcards

1
Q

Classification of muscle (morphological
and functional)

A

-smooth muscle
-striated muscle

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2
Q

Types of Striated muscle

A

-skeletal muscle
-cardiac muscle.

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3
Q

comprise muscle fibers, composed of thin and thick filaments

A

Striated Muscle

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4
Q

Location of Smooth Muscle

A

Internal Organs

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5
Q

Location of Striated muscle

A

attached to the skeleton

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6
Q

Most muscles contract when __________ send signals to them, initiating a series of events that cause the muscles to generate force and become ________

A

-neurons
-shorter

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7
Q

Each and every skeletal
muscle fiber in vertebrates
is innervated by a single
_______________ but a certain
neuron may innervate a
number of fibers.

A

motor neuron

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7
Q

Three principal kinds of movement:

A

– ameboid
– ciliary and flagellar
– muscular

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8
Q

The motor neurons are
__________ and only if they
send _______________ to the
muscles that the muscles
are activated.

A

-excitatory
-synaptic input

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9
Q

consists of a single motor neuron and all the muscle fibers it controls. and is the functional unit of skeletal muscle control

A

motor unit

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9
Q

contraction of skeletal muscle results from
___________________ travelling down somatic
motor axons originating in the CNS

A

action potentials

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9
Q

transfer of signal from nerve to muscle occurs
at the ____________________, also called
myoneural junction or motor endplate

A

neuromuscular junction

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9
Q

A special type of synapse exhibiting close
association between the membranes of a neuron and a muscle fibre

A

myoneural junction /motor endplate

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10
Q

-The synaptic contact between
a nerve fiber and a muscle
fiber
-Nerve impulses bring about
the release of a
neurotransmitter that cross
the synaptic cleft
-Signals the muscle fiber to
contract

A

Neuromuscular junction

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10
Q

The stimulus leading to contraction of a muscle
fiber is an action potential in a motor neuron that makes a ________ with the muscle fiber.

A

synapse

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11
Q

Muscle Contraction = ____________________

A

The active generation of tension within muscle fiber

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11
Q
  • consists of parallel multinucleate
    fibers (contains many myofibrils)
  • attached to bones or other
    anchor points through tough
    connective tissue bands (tendons)
A

skeletal muscles

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12
Q

sarcomeres, arranged end-to-end

A

myofibrils

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12
Q

fuse to form myotubes (synthesizes proteins
characteristic of muscle fibers and
differentiates into its adult form

A

myoblasts

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12
Q

myoblasts fuse to form
________ (synthesizes proteins
characteristic of muscle fibers and
differentiates into its adult form)

A

myotubes

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13
Q

thin filaments of
actin and thick filaments of myosin
(Interdigitate in a precise
geometric relationship

A

sarcomere

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14
Q

basic functional unit of striated
muscle

A

sarcomere

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15
Q

Structure of Sarcomere includes:

A

*Z line / Z disk
*A band
*H zone
*M line
*I band

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16
Q

contains α-actinin

A

Z line / Z disk

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17
Q

-anisotropic
-interdigitated thick and thin
filaments; densest portion; strongly polarizes visible light

A

A band

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18
Q

middle of the H zone; contain enzymes that are
important in energy metabolism

A

M line

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18
Q

contains only thick filaments (myosin); lighter portion

A

H zone

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19
Q

-isotropic
-between two A bands; does not
polarize light

A

I band

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19
Q
  • each myosin filament
    is surrounded by six thin
    filaments, and it shares these
    actin filaments with
    surrounding thick filaments
  • each actin filament is
    surrounded by three myosin
    filaments
A

region of overlap

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20
Q

each_____________ is surrounded by ______________, and it shares these
actin filaments with
surrounding thick filaments

A
  • myosin filament
    -six thin filaments
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21
Q
  • each ___________ is
    surrounded by __________________
A

-actin filament
-three myosin
filaments

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22
Q
  • twisted actin molecules
    -each has an active site where
    they interact with myosin
  • troponin complex – complex
    of 3 globular proteins;
    calcium dependent switch
  • Resting – active site covered
    by tropomyosin which is held
    in place by troponin
A

Thin filaments

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23
Q
  • Myosin
  • Head attaches to actin
    during contraction
  • Can only happen if
    troponin changes position,
    moving tropomyosin to
    expose active site
  • myosin heads – binding
    sites for ATP; form
    molecular cross bridges
    with actin filaments
A

Thick Filaments

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23
Q

complex of 3 globular proteins;
calcium dependent switch

A

troponin complex

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23
Q

– binding sites for ATP; form
molecular cross bridges
with actin filaments

A

myosin heads

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24
Q

-long, thin molecule (40 nm
long)
-made of 2 protein chains
forming helical filaments

A

Tropomyosin

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24
Q

globular proteins

A

Troponin complex

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24
Q

Troponin Subunits

A

-TnT
-TnC
-TnI

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24
Q
  • strongly attached to tropomyosin
A

TnT

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25
Q

binds calcium ions

A

TnC

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26
Q

induces tropomyosin to move, exposing
the active site

A

TnI

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27
Q

-composed of two identical heavy
chains (long and thin), and smaller
light chains

A

myosin molecule

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27
Q

Length and width of Myosin molecule

A
  • length : 150 nm
  • width : 2 nm
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28
Q

Length and width of globular double “head” region

A

-Length: 20 nm
-Width: 4 nm

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28
Q
  • contains enzymatic and
    actin-binding activity
A

globular double “head” region

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28
Q

calcium-binding proteins

A

light chains

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29
Q

Explain Sliding Filament Hypothesis (Contraction and Relaxation)

A

*Muscle contracts:
-sarcomeres shorten - thin (actin)
filaments actively slid along between the
thick (myosin) filaments
-process pulls the actin filaments closer to
the center of the sarcomere, and
because the thin filaments are anchored
in the Z disks, the sarcomeres become
shorter

*Muscle relaxes or stretched
- the overlap between thin and thick
filaments is reduced, and the
sarcomeres elongate

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30
Q

Who proposed Sliding Filament Hypothesis?

A

H. E. Huxley and A. F. Huxley (1954)

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30
Q
  • lengths of the thick
    filaments and of the thin
    filaments remain
    constant
    -filaments slide past one
    another, the I band
    narrows as the thin
    filaments slide toward
    the center of each A band
A

Sliding Filament Hypothesis

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31
Q

Sliding Filament Hypothesis: that cross-bridges are evenly distributed along each thick filament, except in the ________ where no cross-bridges are present.

A

bare zone

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31
Q

Sliding Filament Hypothesis: the force generated by a sarcomere is proportional
to the number of __________ binding myosin filaments to actin filaments

A

cross-bridges

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31
Q

Sliding Filament Hypothesis (graph): The structure of the bones and joints limits the range of movement is shown in?

A

plateau region of the graph

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31
Q

As the length of the sarcomeres
is changed, so is the amount of overlap between the actin and
myosin filaments

A

Length-tension relation

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31
Q

overlap between the thick and thin filaments
allows the largest number of cross-bridges to be formed

A

maximal

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31
Q

Sliding Filament Hypothesis (graph): When Tension drops off with increased length then _________________________________________.

A

thick and thin filaments overlap less and fewer cross-bridges can be formed

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31
Q

Sliding Filament Hypothesis (graph): drops off with decreased length is due to?

A

Thin Filaments colliding to one another preventing further shortening

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32
Q

Process of Sliding Filament Hypothesis

A
  1. A nerve signal reaches the muscle fiber, triggering the release of calcium ions from the sarcoplasmic reticulum
  2. Calcium ions bind to troponin molecules on the actin filaments, causing a conformational change that shifts tropomyosin, exposing the actin binding sites
  3. Myosin heads (cross-bridges) on the thick filaments attach to the exposed binding sites on the actin filaments.
  4. ATP is hydrolyzed (broken down) which provides the energy for the myosin heads to pivot and pull the actin filaments towards the center of the sarcomere, causing the filaments to slide past each other
  5. After the power stroke, ADP and Pi (inorganic phosphate) are released, and the myosin head detaches from the actin binding site
  6. When the nerve signal stops, calcium ions are actively pumped back into the sarcoplasmic reticulum, causing tropomyosin to re-cover the actin binding sites, preventing further cross-bridge formation and allowing the muscle to relax
33
Q

net result hydrolysis of
one molecule of ATP
(liberating energy -
generate force)

A

Cross-bridge Chemistry

34
Q

myosin and actin filaments associate and
dissociate in the presence of _____

A

ATP

34
Q

*myosin acts as an _______- hydrolyzing ATP

A

ATPase

34
Q

ATP binds to actomyosin, splitting the molecule into _____ and _______

A

actin and myosin

34
Q

actin rebinds to the ________, increasing the rate of release (ADP + Pi)

A

myosin

35
Q

thick and thin filaments slide
past one another driven by
changes in bonds between
_________________ and _________

A

myosin cross-bridges and actin

36
Q

myosin heads
are not bound to actin

A

relaxed state

36
Q

heads rotate (formation of a
series of bonds) - pulling on the
actin filament and causing it to
___________ the myosin filament.

A

slide past

36
Q

four separate binding sites
on the myosin head

A

M1 to M4

36
Q

Once activated myosin heads attach to ________

A

Actin

37
Q

M1 to M2 interact in _______________ with sites
on the actln filament

A

sequence (left to right)

38
Q

myosin head detaches only if ____ binds

A

ATP

39
Q

2 types of Muscle Contraction

A

-isometric contraction
-isotonic contraction

40
Q
  • length of a muscle is held fixed
    preventing it from shortening
A

isometric contraction

41
Q

muscle shortens as force is
generated

A

isotonic contraction

42
Q

smaller load

A

less force is generated, faster contraction

43
Q

maximal isometric
tension of this muscle is
_______. Once reach it cannot shorten further

A

100 g

44
Q

multiply the
force and the velocity
for each data point

A

Power-velocity curve

45
Q

maximal force of 100 g, the velocity of shortening is zero (isometric); force generated by a muscle drops as its speed of shortening increases

A

Force- velocity curve

46
Q

_____________________regulate the state of muscle contraction

A

free calcium ions

47
Q

muscle fibers generate tension once exposed to _________________

A

Ca2+ and Mg-ATP

48
Q

muscle fibers relax when _______ is removed, even if Mg-ATP is still present

A

-Ca2+
-Mg-ATP

49
Q

Force increases with increasing _____________ (up to some maximum value)

A

Ca2+ concentration

50
Q

___________ and __________
regulate binding between
myosin cross-bridges and
actin thin filaments

A

troponin and tropomyosin

51
Q

In _______________ condition troponin complex binds with actin and tropomyosin (preventing myosin cross-bridges from binding to actin)

A

Low Ca2+ concentration

52
Q

In an _________________ condition, troponin C binds Ca2+ changing the subunit affinities and causing the tropomyosin molecule to
move away from the myosin-binding site on actin

A

Increasing Ca2+

53
Q

Free calcium modulates both the ___________ and __________

A

ATPase activity and tension

54
Q

ATPase activity of myosin increases sigmoidally with the _______________ of the surrounding solution (10-8 M)

A

Ca2+ concentration

55
Q

Mg-ATP is removed once tension has
developed

A

rigor mortis

56
Q

when there is removal of Ca2+ and addition of
Mg-ATP

A

rigor is relieved

57
Q

AP is propagated in a
muscle fiber, it initiates a
brief contraction, a _____

A

twitch

58
Q

excitation-contraction coupling
occurs

A

latent period

59
Q

Process pf Excitation-Contraction Coupling

A
  1. Action potential in a motor neuron is activated.
  2. This causes a postsynaptic potential in the muscle fiber
  3. Which gives rise to a propagated muscle AP
60
Q

extensions of the plasma membrane that extend deep into the interior of each muscle fiber, associated with sarcoplasmic reticulum

A

Transverse tubules (T tubules)

61
Q

makes intimate contact
with T tubules

A

sarcoplasmic reticulum (SR)

62
Q

When an AP is conducted into the T tubule it causes the release of __________ stored in the neighboring sarcoplasmic
reticulum.

A

Ca2+ ion

63
Q

How does Ca2+ get into the SR?

A

SR sequesters calcium

64
Q

SR is capable of doing what?

A
  1. Driving the concentration of intracellular
    free Ca2+ so low that contraction is prevented
  2. remove Ca2+ from the myoplasm depends on the activity of proteins that bind and transport Ca2+ ions
65
Q
  • T tubule is at rest - calcium channels in the SR membrane are blocked by the “feet” of ryanodine receptors
  • T-tubule membrane depolarizes - voltage-sensitive dihydropyridine receptors convey the signal to the ryanodlne receptors, and the “plungers” blocking calcium channels in the SR membrane are removed (allowing Ca2+ to flow out of the SR lumen into the myoplasm)
A

Plunger model

66
Q

Plunger Model: free Ca2+ binds to _________, revealing cross-bridge binding
sites on actin molecules

A

troponin

67
Q

Plunger Model: ryanodine receptors
again block the calcium channels

A

membrane potential returns to rest

68
Q

-depolarization of the T-tubule membrane activates membrane-bound phosphodiesterase (PDE) - production of inositol 1,4,5-triphosphate (IP3) and diacylglycerol (DG) from the hydrolysis of phosphotidylinositol
-IP3 diffuses to the terminal cisternae of the SR - binds and activates receptors causing calcium channels of the SR to open
- allows calcium ions to leak out rapidly into the sarcoplasm for contraction to occur

A

Enzyme- (or messenger-)mediated mechanism

69
Q

What happens in the latent period?

A

1.initiation of an action potential in the muscle fiber,
2. propagation of the AP along the T tubules into the fiber,
3. release of Ca2+ from the sarcoplasmic reticulum
4. diffusion of the Ca2+ ions to troponin molecules
5. binding of Ca2+ to troponin
6. activation of myosin cross-bridges and their binding to actin thin filaments, and generation of force

70
Q

______________ by myosin cross-bridges as they cyclically attach to and detach from actin thin filaments

A

Hydrolysis of ATP

71
Q

ENERGETICS OF MUSCLE CONTRACTION

A

-Hydrolysis of ATP by myosin cross-bridges
-Pumping of Ca2+ during excitation-coupling
-Direct Phosphorylation
-Anaerobic Glycolysis
-Oxidative Phosphorylation of ADP

72
Q
  • high energy phosphates are
    transferred from creatine
    phosphate to ADP,
    regenerating AT
A

direct phosphorylation

73
Q

hydrolyzes glucose,
dephosphorylating ADP in the
process (lactate as byproduct)

A

anaerobic glycolysis

74
Q

regenerates ATP

A

oxidative phosphorylation of ADP

75
Q

Classification of Skeletal Muscle Fibers

A

-oxidative or glycolytic fibers, (by the source of ATP)
- fast-twitch or slow-twitch fibers, (by the speed of muscle contraction)

76
Q

Slow and fast oxidative fibers rely on _______ and _________

A

glucose and oxygen

77
Q

Fast glycolytic fibers rely on ______________

A

anaerobic glycolysis

78
Q

Muscles incur _____________ during anaerobic glycolysis

A

oxygen debt

79
Q

-contract very slowly and do not produce twitches
-found in the postural muscles of amphibians, reptiles, and birds, muscle spindles and extraocular muscles of mammals
-normally do not produce APs and they do not require an AP to spread excitation (innervating motor neuron runs the length of the muscle fiber and makes repeated synapses all along)
-myosin cross-bridges attach and detach very slowly (extremely slow shortening velocity and ability to generate isometric tension very efficiently)

A

Tonic Muscle Fiber

80
Q

-contract slowly and fatigue slowly
- they are found in mammalian postural muscles.
-They are characterized by a slow-to-moderate V, and slow Ca2+ kinetics.
-They generate all-or-none APs, so they contract in response to motor neuron input with all-or-none twitches.
-Like other twitch fibers, they typically
have one or at most a few motor endplates

A

Slow twitch (or type I) fibers

81
Q

-for slow, sustained contractions without fatigue
-contain extensive blood supply
-high density of mitochondria
-abundant stored myoglobin (protein that binds oxygen more tightly than hemoglobin does)
-important in maintaining posture in terrestrial
vertebrate

A

slow oxidative fibers (red muscles)

82
Q

Two kind of Fast fibers

A

-fast glycolytic fiber (white muscles)
-fast oxidative fiber

83
Q

-lacks efficient blood supply
-pale in color
-function anaerobically
-fatigue rapidly

A

fast glycolytic fiber (white muscles)

84
Q

-extensive blood supply
-high density of mitochondria and myoglobin
-function aerobically
-for rapid, sustained activities

A

fast oxidative fiber

85
Q

Types of stimulations according to strength

A

➢ subthreshold
➢ threshold
➢ submaximal
➢ maximal
➢ supramaximal

86
Q

not capable of inducing a response or muscle
contraction

A

subthreshold

87
Q
  • weakest stimulus capable of causing contraction
A

threshold

88
Q

intermediate between threshold and supramaximal

A

submaximal

89
Q

causes a maximal contraction wherein the overlap between the myofilaments is greatest

A

maximal

90
Q
  • beyond maximal stimulus
  • no higher contractions are observed because all the
    motor units have been activated.
A

supramaximal

91
Q

➢ A twitch results from a single action potential in a motor
neuron
➢Single stimulus-contraction-relaxation sequence
in a muscle fiber
➢Varies in duration

A

Muscle Twitch

92
Q

graph of tension development in
various muscles during a twitch contraction

A

myogram

93
Q

Muscle Twitch is divide into:

A

-Latent Period
-Contraction phase
-Relaxation Phase

94
Q

– starts at stimulus
– action potential sweeps across the sarcolemma and the sarcoplasmic reticulum releases calcium ions
– muscle fiber does not produce tension,
contraction has yet to begin

A

Latent period

95
Q

– tension rises to a peak
– calcium ions bind to troponin, active sites on thin
filaments are being exposed, and cross-bridge
interactions are occurring

A

Contraction Phase

96
Q

– calcium levels are falling, active sites are being
covered by tropomyosin, and the number of active
cross-bridges is declining

A

Relaxation phase

97
Q

Contraction of a whole muscle is ______, which
means that the extent and strength of its
contraction can be voluntarily altered

A

graded

98
Q

two basic mechanisms by which the
nervous system produces graded contractions:

A

– Varying the number of fibers that contract
– Varying the rate at which fibers are stimulated

99
Q

Muscle curves showing increasing amplitudes with increasing ____________

A

electrical intensity

100
Q

– Ger., ‘staircase’
– Gradual increase in muscular contraction due to rapidly
repeated stimulation
– Occurs when muscle is stimulated a second time
immediately after relaxation phase has ended
– First 30-50 stimulations
– Rise in tension due to increase of Ca2+ in the sarcoplasm
– Eventual depletion of chemical energy leading to fatigue
→ decreasing amplitude of muscle contraction

A

Treepe

101
Q

➢ Prolonged and strong contractions of the muscles
often lead to a familiar state called muscle fatigue.
➢ the rate of depletion of muscle glycogen = to the
increase in muscle fatigue.
➢ Hence, fatigue results mainly from the inability of the
contractile and metabolic processes of muscle fibers
to continue supplying the same work output.

A

Fatigue

102
Q

Interruption of blood flow through a contracting muscle leads to almost complete ____________. This occurs usually within a minute or two, because of the low nutrient supply and the loss of oxygen.

A

muscle fatigue

103
Q

Larger number of motor units stimulated, the greater effect of ___________.

A

contraction

104
Q

A smooth and steady increase in muscle tension is produced by increasing the number of motor units brought into play

A

motor unit recruitment

105
Q

____________ of multiple motor neurons results in stronger contractions

A

Recruitment

106
Q

A twitch results from a __________________ in a motor neuron

A

single action potential

107
Q

More rapidly delivered action potentials produce a graded contraction by ________________

A

summation

108
Q

➢ sustained
contraction of a muscle
brought about by the
application of a large number
of stimuli in rapid succession
leaving insufficient time for
relaxation.
➢The height of tetanic
contraction is greater than
the twitch produced by single
stimulation of the same
intensity because of the
summation of twitches

A

Tetanus

109
Q

Classification of Tetanus

A

-Incomplete Tetanus
-Complete Tetanus

110
Q

periods of incomplete relaxation take
place between the summated stimuli.

A

Incomplete tetanus

111
Q

-no relaxation occurs between stimuli
-the tension developed is about
four times that developed by the individual twitch contractions.

A

Complete Tetanus

BIO108- GENERAL PHYSIOLOGY (10 decks)

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