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E2 NSP > Skeletal Muscle > Flashcards

Skeletal Muscle Flashcards

1
Q

Skeletal muscles contain ______
muscle fibers

A

multinucleate

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2
Q

The muscle fiber is surrounded by a cell
membrane called a ________

A

sarcolemma

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3
Q

he sarcolemma is attached to strands of
connective tissue called the ________

A

endomysium

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4
Q

Bundles of muscle fibers are grouped
together by a connective tissue sheath
called the _____

A

perimysium

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5
Q

The muscle fiber bundles that form the
muscle are contained within an outer
sheath of connective tissue called the
________

A

epimysium

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6
Q

The connective tissues are connected to
______ and to the tendons that attach
the muscle to the bones

A

each other

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7
Q

Skeletal muscle fibers are divided into
__________

A

myofibrils

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8
Q

The myofibrils are separated from each
other by longitudinal vesicles called the
__________

A

sarcoplasmic reticulum.

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9
Q

The ____________ contains the calcium that is used to initiate the contractile
process

A

sarcoplasmic reticulum

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10
Q

The myofibrils are divided into ________, which are the functional units responsible for muscle contraction

A

sarcomeres

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11
Q

Sarcomeres are composed of thick and thin
filaments and are bounded by a band of protein called the ____________

A

Z line

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12
Q

The thin filaments contain two helical chains of ____________.

A

actin

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13
Q

Thin filament have a long filamentous protein called _______ that lies in the groove
formed by the two intertwined actin
chains.

A

tropomyosin

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14
Q

what binds to tropomyosin?

A

troponin

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15
Q

A globular portion of the myosin molecule, called the __________, projects out of the thick filament.

A

cross bridge

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16
Q

The thick filaments are held together by transversely organized proteins called
______. These proteins are responsible for the formation of the M line

A

myomesin

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17
Q

A large elastic protein called ______ connects the M line to the Z line. Titin not only stabilizes the structure, it creates the elasticity that opposes passive stretching of the muscle and allows the muscle to spring back to its original length after being stretched

A

titin

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18
Q

what is exitation-contraciton EC coupling?

A

Generation of the muscle action
potential and depolarization of the T-tubule (initiation of muscle contraction)

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19
Q

Skeletal muscle fibers are activated by what kind of motor neuron?

A

α-motoneurons

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20
Q

how many α-motoneurons innervate a single muscle fiber?

A

one

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21
Q

what is a motor unit?

A

the motor neuron and all the fibers it innervates

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22
Q

when the motor neuron fires what happens to the muscle fibers?

A

all muscle fibers it innervates are activated

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23
Q

what are the first two steps of EC coupling?

A
  • Generation of the muscle action potential and depolarization of the T- tubule
  • The release of calcium from the sarcoplasmic reticulum
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24
Q

what are the third and froth step of EC?

A
  • The binding of calcium to troponin
    and the initiation of the cross bridge cycle
  • The re-accumulation of calcium within the SR
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25
how is Ca released from the sarcoplasmic reticulum?
-depolarized membrane causes Ca release from SR
26
what are the Ca channels on SR called?
ryanodine receptors
27
what do DHP receptors do?
coupled to ryanodine receptor and bocks Ca release when membrane is polarized
28
what happens when t tube depolarize?
Depolarization of the T-tubule causes the charged protein to move towards the DHP receptor, unblocking the Ca2+ release channel within the ryanodine receptor
29
Troponin C (TnC), which contains binding sites for ______.
calcium
30
Troponin T (TnT), which binds the troponin complex to _____ and______
tropomyosin and actin
31
Troponin I (TnI), which keeps the troponin complex tied to actin and inhibits the interaction between the _____ and _____
myosin cross bridge and actin
32
what initiates the cross bridge cycle?
Ca bind to trop C
33
The binding of calcium to troponin C causes __________________
troponin I to separate from tropomyosin and actin
34
The movement of TnI allows tropomyosin ________________
to move away from the myosin binding sites on actin.
35
what is the first two steps of the sliding filament theory?
1. The enzyme catalyzing the hydrolysis of ATP, actin-myosin ATPase, is contained within the cross bridge and is activated when the myosin molecule binds to actin. 2. The ATP is bound to myosin as a high- energy complex referred to as myosin ADPPi
36
what is the third and forth step of the sliding filament theory?
3. When the cross bridge bends, ADP and Pi are released from myosin. 4. The thin filament detaches from myosin when a new molecule of ATP binds to the myosin molecule.
37
When skeletal muscle contracts, _____ sides over the _______ filaments.
the thin filaments slide over the thick (The movement of the thin filaments over the thick filaments is produced by the cross bridge cycle)
38
how is Ca removed from the cross bridge?
Ca pumps (SERCA)
39
The removal of calcium from the cytoplasm causes calcium to ________
dissociate from TnC (TnI separates from TnC and rebinds to tropomyosin. - Tropomyosin returns to its position covering the myosin binding sites on actin. - Cross bridge cycling stops)
40
what occurs in the atent period of the twitch contraction?
This is the period of time from the action potential to the onset of contraction. The time delay is due to the excitation- contraction coupling
41
what occurs during the contraction phase of twitch contraction?
This is the time that tension is developing due to the cross-bridge cycling
42
what occurs during the relaxation phase of the twitch contraction?
This is the time that the tension is decreasing (i.e., relaxing) and is longer than the contraction phase. This is due to the amount of time it takes to get all the Ca2+ sequestered.
43
what is an isometric contraction?
total length of muscle does not change
44
what is preload?
initial length of the muscle prior to contraction
45
what factors impact the force produced by an isometric contraction?
* The preload (i.e., the overlap between thick and thin filaments). * The number of muscle fibers activated. * The frequency of action potentials generated by the muscle.
46
what is an isotonic contraction?
muscle develops force and shortens
47
what is afterload?
load lifted by the muscle when it shortens
48
what are the phases of isotonic contraction?
* It contracts isometrically until the force developed is equal to the afterload. * It shortens isotonically at a constant velocity until it shortens as much as it is capable of shortening. * It contracts isometrically until it begins to relax.
49
how is the velocity of shortening during an isotonic contraction related to the afterload
inversely proportional to
50
how is The amount of shortening that occurs during an isotonic contraction related to the afterload
is inversely proportional
51
The force produced during an isometric contraction depends on _________
the length of the fibers
52
The force produced by a muscle depends on the number of __________________
myosin cross bridges that bind to actin during the contraction
53
The relationship between the preload and the force of contraction is called the ____________
length-tension relationship
54
The maximum number of cross bridges can bind to the thin filament when the initial sarcomere length is between ____ and ___
2.0 um and 2.2 um
55
The resistance to stretch depends on what?
the elastic properties of titin and other proteins in parallel with the thick and thin filaments.
56
how does the CNS vary the amount of force generated by a muscle?
varying the number of a motor neurons that are active
57
what is a twitch contraction?
the contractile force generated my one action potential
58
why can AP summate?
Because the duration of a twitch is greater than the duration of an action potential, the contractions produced by successive action potentials can summate
59
is Ca present during contraction?
no, Although the calcium released by a single action potential activates all of the contractile protein, the calcium is removed from the myoplasm before the contractile force reaches its full potential
60
when does tetanus occur?
occurs when the frequency of action potentials is high enough to prevent any relaxation of contraction between action potentials and the force
61
how are contractie proteins connected to the bones?
elastic structures series called elastic component
62
what are the phases of isotonic contraction?
* It contracts isometrically until the force developed is equal to the afterload. * It shortens isotonically at a constant velocity until it shortens as much as it is capable of shortening. * It contracts isometrically until it begins to relax.
63
what happens if you increase afterload?
* Increases the latency + force between muscle and shortening. * Decreases the velocity/amount of shortening.
64
The characteristics of an isotonic twitch depend upon ____________
the magnitude of the load being lifted
65
the heavier the load what changes occur?
(1) the latent period is longer, (2) the velocity of shortening (distance shortened per unit of time) is slower, (3) the duration of the twitch is shorter, and (4) the distance shortened is less (good graph on slide)

E2 NSP (8 decks)

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