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A&P Exam 2 > Chapter 10 - Muscle Tissue - PART 2 > Flashcards

Chapter 10 - Muscle Tissue - PART 2 Flashcards

1
Q

A typical thin filament contains _____ proteins

A

4

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2
Q

What are the 4 proteins that make up a thin filament?

A

F-actin
Nebulin
Tropomyosin
Troponin

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3
Q

The F in F-actin stands for….

A

Filamentous

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4
Q

Describe the structure and composition of F-actin

A

Twisted strand composed of two rows of 300-400 individual molecules of G-actin

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5
Q

A long strand of _____ exists along the F-actin strand in the _____ between the rows of G-actin molecules

A

A long strand of NEBULIN exists along the F-actin strand in the CLEFT between the rows of G-actin molecules

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6
Q

What protein holds the F-actin strand together?

A

Nebulin

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7
Q

Each G-actin molecule contains a _____ that can bind to _____(in thick filaments)

A

Each G-actin molecule contains a ACTIVE SITE that can bind to MYOSIN in thick filaments

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8
Q

Under resting conditions, is myosin bound to the active site of G-actin?

A

No

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9
Q

What protein complex prevents myosin binding to the active site of a G-actin molecule in resting conditions?

A

Troponin-tropomyosin complex

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10
Q

Describe how TROPOMYOSIN prevents myosin binding to the active site of a G-actin molecule

A

Tropomyosin covers the active sites on G-actin and prevents actin-myosin interaction.
Tropomyosin is a double stranded molecule that covers SEVEN active sites

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11
Q

Explain how TROPONIN prevents myosin binding to the active site of G-actin

A

Troponin molecule consists of 3 globular subunits.
1 subunit binds to tropomyosin, locking them together as a tropopnin-tropomyosin complex
1 subunit bonds to 1 G-actin molecule, holding the complex in its position
1 subunit has a receptor that binds 2 calcium ions. (In a resting muscle, intracellular Ca2+ conc is low and that binding site is empty)

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12
Q

A contraction can occur only when……

A

The Troponin-Tropomyosin complex changes position, exposing the active sites on actin

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13
Q

What triggers the Troponin-Tropomyosin complex to change position and expose the active sites of actin?

A

The binding of calcium ions to receptors on the Troponin molecules

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14
Q

The thin filaments are attached to the ___ on either end of a sarcomere

A

Z lines

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15
Q

Why is the Z line often called a Z disc?

A

The Z line in a sectional view looks more like a disc with an open meshwork

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16
Q

A thick filament contains about ____(#) ____ molecules

A

A thick filament contains about 300 MYOSIN molecules

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17
Q

What is known as a “cross-bridge”?

A

When the myosin heads interact with thin filaments during a contraction

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18
Q

The connections between the head and the tail functions as a ______ that lets the head ______

A

The connections between the head and the tail functions as a HINGE that lets the head PIVOT

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19
Q

When the head pivots, what does it do and why is this significant?

A

When it pivots, the head swings toward or away from the M line. This is a KEY STEP in muscle contraction

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20
Q

All myosin molecules are arranged with their _____ pointing towards the _______

A

Tails pointing towards the M line

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21
Q

Which band includes a central region where there are NO myosin heads?

A

The H band

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22
Q

Each thick filament has a core of ____

A

TITIN

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23
Q

In a normal resting sarcomere, the titin strands are….

A

Completely relaxed

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24
Q

When do titin’s become tense?

A

Only when some external force stretches the sarcomere

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25
Q

Explain 4 things that happen to a sarcomere during contraction

A
  1. The H bands and I bands of the sarcomere get smaller
  2. The zones of overlap get larger
  3. The Z lines move closer together
  4. The width of the A band remains CONSTANT
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26
Q

When Myofibrils get shorter, so does the _____

A

Muscle fiber

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27
Q

Give 2 reasons why muscle fibers get shorter when Myofibrils get shorter

A
  1. Myofibrils are attached to the sarcolemma at each Z line
  2. Myofibrils are attached at either end of the muscle fiber
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28
Q

What is the sliding filament theory?

A

The 4 observations of a sarcomere during contraction can only occur if the thin filaments are sliding towards the center of each sarcomere, alongside the thick filaments

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29
Q

under the sliding filament theory, do actin and myosin ever change their length?

A

NO - the thin just slides over the thick

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30
Q

When muscle cells contract, they pull on…

-what is this pull called?

A

the attached tendon fibers

this pull is called tension

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31
Q

tension is a ____ force

A

active force

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32
Q

what does it mean that tension is an active force?

A

energy must be expended to produce it

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33
Q

Before movement can occur, the applied tension must overcome what?

A

the object’s load/resistance (a passive force)

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34
Q

The load/resistance of an object is dependent on…

A

the weight, shape, and friction of the object

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35
Q

What happens when the applied tension exceeds the load?

A

the object moves

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36
Q

compression tends to force the object AWAY from…..

A

the source of the compression

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37
Q

tension tends to force the object….

A

TOWARDS the source of the tension

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38
Q

no movement can occur until the applied compression…..

A

exceeds the load/resistance of the object

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39
Q

muscle cells can ____ but they cannot _____

A

muscle cells can PULL but they cannot push

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40
Q

name the 5 steps of the contraction process

A
  1. Neural control
  2. Calcium release
  3. Thick-thin filament interaction
  4. Muscle fiber contraction
  5. Tension production
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41
Q

Under contraction, explain “neural control”

A

skeletal muscle is under neural control. contraction only occurs when skeletal muscle fibers are activated by neurons

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42
Q

the cell bodies of neurons are located where in the body?

A

the central nervous system (brain and spinal cord)

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43
Q

A neuron can activate a muscle fiber by stimulating its….

A

sarcolemma

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44
Q

When a neuron activates a muscle fiber by stimulating its sarcolemma, what process follows?

A

excitation-contraction coupling

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45
Q

Under contraction, explain “Calcium release”

A

The 1st step in excitation-contraction coupling is the release of CALCIUM IONS form the CISTERNAE of the SARCOPLASMIC RETICULUM

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46
Q

Under Contraction, explain the “thick-thin filament interaction”

A

the calcium ions released from the cisternae of the sarcoplasmic reticulum then trigger interactions between thick and thin filaments.

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47
Q

Under contraction, explain “muscle fiber contraction”

A

the interaction between the thick and thin filaments result in muscle fiber contraction and the CONSUMPTION of energy in the form of ATP

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48
Q

Under contraction, explain “tension production”

A

the thick and thin filament interactions produce ACTIVE TENSION

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49
Q

Describe the structural components of a sarcomere

A

each sarcomere has dark A bands and light I bands. The A band contains the M line, H band, and the zone of overlap.
Each I band contains thin filaments, but NO thick filaments.
Z lines mark the boundary between adjacent sarcomere

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50
Q

What is the smallest contractile unit of a striated muscle cell?

A

sarcomere

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51
Q

Sarcomeres are ____ of ____

A

Sarcomeres are BUNDLES of myofibrils

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52
Q

Why do skeletal muscle fibers appear striated when viewed through a light microscope?

A

Because the Z lines and thick filaments of myofibrils are aligned

53
Q

Where would you expect the greatest concentration of Ca2+ in resting skeletal muscle to be?

A

in the cisternae of the sarcoplasmic reticulum

54
Q

Skeletal muscle activity is under ____ control

A

neural

55
Q

Skeletal muscle fibers begin contraction with the release of…..

A

internal stores of calcium ions

56
Q

The release of calcium ions is under the control of…..

A

the nervous system

57
Q

where does communication between the nervous system and a skeletal muscle fiber occur?

A

at an intercellular connection known as a neuromuscular junction

58
Q

a neuromuscular junction could also be called a _____ junction

A

myoneural junction

59
Q

describe the 3 step process of a neuron stimulating a muscle fiber to contract

A
  1. in a resting sarcomere, the tropomyosin strands cover the active sites on the thin filaments, PREVENTING cross-bridge formation
  2. When calcium ions enter the sarcomere from the cisternae of the sarcoplasmic reticulum, they bind to troponin, which rotates and swings the tropomyosin away from the active sites
  3. Cross bridge formation then occurs and the contraction cycle begins
60
Q

What happens in cross bridge formation?

A

the head of myosin binds to the active site of actin to begin the contraction cycle

61
Q

The link between the generation of action potential in the sarcolemma and the start of a muscle contraction is called…..

A

excitation-contraction coupling

62
Q

where does excitation-contraction coupling occur?

A

at triads

63
Q

a triad consists of….

A

a T (transverse) tubule and 2 terminal cisternae

64
Q

on reaching a triad, the action potential signals…..

A

the release of calcium ions from the cisternae of the sarcoplasmic reticulum

65
Q

Why is calcium release from the cisternae of the sarcoplasmic reticulum almost an instantaneous effect on the sarcomere?

A

because the terminal cisternae are located at the zones of overlap where the thick and thin filaments interact

66
Q

What protein is the LOCK that keeps the active sites inaccessible and what is the KEY to that lock?

A

lock = troponin
key = calcium ions

67
Q

When a muscle fiber is at rest, what can you say about troponin?

A

the binding site for calcium is empty

68
Q

What does calcium binding do to troponin?

A

it changes the shape of the troponin molecule and weakens the bonds between troponin and actin. the troponin molecule then changes position, rolling the attached tropomyosin strand away from the active sites.
WITH THIS, THE CONTRACTION CYCLE BEGINS

69
Q

The power stroke refers to the ___ ____ of muscle contracion

A

molecular interactions

70
Q

Each power stroke ____ the sarcomere by about _____

A

SHORTENS the sarcomere by about 0.5%

71
Q

Why does the entire muscle shorten at the same rate?

A

because all the sarcomeres contract together

72
Q

The speed of the shortening of a muscle depends on…..

A

the cycling rate (the # of power strokes per second)

73
Q

The greater the load, the ______ the cycling rate

A

slower

74
Q

The myosin heads along a thick filament work together work together in a similar way to pull…..

A

a thin filament towards the center of the sarcomere

75
Q

each myofibril consists of a string of _____

A

sarcomeres

76
Q

In contraction, all of the ___ filaments are pulled towards _____

A

in contraction, all of the thin filaments are pulled towards the center of the sarcomeres

77
Q

Each skeletal muscle fiber has how many neuromuscular junctions?

A

1

78
Q

Can a single axon control more than one skeletal muscle fiber?

A

yes

79
Q

the cytoplasm of the synaptic terminal contains…..

A

vesicles filled with molecules of acetylcholine

80
Q

What is acetylcholine?

A

Acetylcholine is a neurotransmitter found in vesicles in the cytoplasm of the synaptic terminal

81
Q

What is a neurotransmitter?

A

a chemical released by a neuron to change the permeability (or other properties) of another cell’s plasma membrane

82
Q

What 2 structures contain the enzyme which breaks down acetylcholine?

A

the SYNAPTIC CLEFT and the MOTOR END PLATE

83
Q

What is the enzyme called that breaks down acetylcholine?

A

acetylcholinesterase (AChE)

84
Q

What is the synaptic cleft?

A

a narrow space that separates the synaptic terminal of the neuron from the opposing motor end plate

85
Q

What stimulates the release of acetylcholine from the vesicles within the cytoplasm of the synaptic terminal?

A

the arrival of action potential (an electrical impulse) at the synaptic terminal

86
Q

An action potential is a…..

A

sudden change in the transmembrane potential that travels along the length of the axon

87
Q

What happens when the action potential reaches the neuron’s synaptic terminal?

A

permeability changes in the membrane trigger the EXOCYTOSIS of acetylcholine into the synaptic cleft

88
Q

Exocytosis occurs as vesicles fuse with……

A

the neuron’s plasma membrane

89
Q

Where does acetylcholine get released to during exocytosis?

A

into the synaptic cleft

90
Q

After acetylcholine is released into the synaptic cleft, what happens next?

A

acetylcholine molecules diffuse across the synaptic cleft and bind to acetylcholine RECEPTORS on the surface of the motor end plate

91
Q

Acetylcholine binding to its receptor on the motor end plate triggers what?

A

alters the membrane’s permeability to sodium ions. Because the extracellular fluid contains a high concentration of sodium ions, sodium ions rush into the sarcoplasm

92
Q

The sudden rush of sodium ions into the sarcoplasm results in what?

A

results in the generation of action potential in the sarcolemma.

93
Q

After sodium ions are rushed into the sarcoplasm, what does acetylcholinesterase do?

A

it quickly breaks down the acetylcholine on the motor end plate and in the synaptic cleft, thus inactivating the Ach receptor sites

94
Q

list the 6 steps of the contraction cycle

A
  1. Contraction cycle begins
  2. Active site exposure
  3. Cross bridge formation
  4. Myosin head pivoting
  5. Cross bridge detachment
  6. Myosin reactivation
95
Q

Step 1: The contraction cycle begins

A

begins with the arrival of calcium ions within the zone of overlap

96
Q

Step 2: Active site exposure

A

the binding of calcium to troponin triggers the weakening of the bond between actin and the troponin-tropomyosin complex - changes position, rolling the tropomyosin molecule away from the active sites on actin and allowing interaction with the energized myosin heads

97
Q

Step 3: Cross-Bridge Formation

A

once the active sites on actin are exposed, the energized myosin heads bind to them, forming crossed bridges

98
Q

Step 4: Myosin Head Pivoting

A

The energy that was stored in the resting state is released as the myosin head pivots toward the M line. This is called the POWER STROKE

99
Q

In the contraction cycle, ADP and Pi are bound to…….

A

the head of myosin

100
Q

During the power stroke (step 4) what happens to ADP and Pi?

A

they are both released

101
Q

Step 5: Cross Bridge Detachment

A

When another ATP binds to the myosin head, the link between the myosin head and the active site on actin is broken. The active site is now exposed and able to form another cross bridge

102
Q

Step 6: Myosin Reactivation

A

Myosin reactivation occurs when the free myosin head splits ATP into ADP and Pi. The energy released is used to recock the myosin head

103
Q

in the resting sarcomere, each myosin head is…..

A

energized - charged with energy that will be used to power a contraction

104
Q

Each myosin head points _____ the M line in the resting position

A

away from

105
Q

When the myosin heads points away from the M line in the resting position, the myosin head is said to be _______

A

cocked

106
Q

Cocking the myosin head requires _____. How is it obtained??

A

energy that is obtained by breaking down ATP

107
Q

How long do ADP and Pi remain bound to the phosphate head during the contraction cycle?

A

they are released at step 4 - myosin head pivoting

108
Q

The contraction cycle is repeated ____ times each ____

A

several times each second

109
Q

The contraction cycle is repeated several times each second as long as which 2 conditions are met?

A

Calcium and ATP reserves are sufficient

110
Q

Calcium ion levels will remain elevated only as long as…..

A

action potentials continue to pass along the T tubules and stimulate terminal cisternae

111
Q

What happens to calcium when the stimulus of action potential is removed?

A

The calcium channels in the sarcoplasmic reticulum close and a calcium ion pump pulls ca2+ from the sarcoplasm and stores it within the terminal cisternae.
Troponin molecules then shift position, swinging the tropomyosin strands over the active sites and PREVENTING cross-bridge formation

112
Q

What would happen during contraction if neither end of the myofibril was held in position?

A

both ends move towards the center

113
Q

What would happen during a contraction if ONE end of the myofibril was held in position?

A

the free end will be pulled towards the fixed end

114
Q

Which is more rare in skeletal muscles - neither side of the myofibril is fixed or 1 end is fixed?

A

neither side is fixed is very seldom because usually 1 end is fixed

115
Q

If neither end of the myofibril can move, what can you say about sliding?

A

When neither end of the myofibril can move, thin and thick filament interactions consume energy and generate tension, BUT SLIDING CANNOT OCCUR (called isometric contraction)

116
Q

The duration of a contraction depends on which 3 things?

A
  1. The period of stimulation at the neuromuscular junction
  2. The presence of free calcium ions in the sarcoplasm
  3. The availability of ATP
117
Q

explain why the duration of a contraction is dependent upon “stimulation at the neuromuscular junction”

A

the acetylcholine released as a result of a single action potential is rapidly broken down by acetylcholinesterase. also, the permeability changes of the SR are very brief. therefore, a contraction will only continue if additional action potentials arrive at the synaptic terminal in rapid succession. When they do, a continual release of acetylcholine into the synaptic cleft produces a series of action potentials in the sarcolemma that keeps calcium levels elevated in the sarcoplasm. under these conditions, the contraction cycle will be repeated over and over

118
Q

explain why the duration of a contraction is dependent on the presence of free calcium ions in the sarcoplasm

A

if just 1 action potential arrives at the neuromuscular junction, Ca2+ concentrations in the sarcoplasm will quickly return to normal resting levels.

119
Q

2 mechanisms are involved in the process of calcium concentration in the sarcoplasm returning to normal resting levels with the arrival of just one action potential at the neuromuscular junction:

A
  1. Active Ca2+ transport across the sarcolemma and into the extracellular fluid
  2. Active Ca2+ transport of the sarcoplasmic reticulum
120
Q

Of the 2, which transport is far more important?

A

transport into the sarcoplasmic reticulum

121
Q

As Ca2+ concentrations in the sarcoplasm fall, what happens?

A

earlier events reverse themselves - calcium ions detach from troponin, troponin returns to its original position, and the active sites on myosin are again covered by tropomyosin

CONTRACTION HAS ENDED

122
Q

Do sarcomeres automatically return to their original length after contraction has ended?

A

no - external forces must act on the contracted muscle fiber to stretch the myofibrils and sarcomeres to their original dimensions

123
Q

Describe the neuromuscular junction

A

the neuromuscular junction is the synapse between a motor neuron and a muscle fiber. This connection enables communication between the nervous system and a skeletal muscle fiber

124
Q

How would a drug that blocks acetylcholine release affect muscle contraction?

A

Acetylcholine release is necessary for skeletal muscle contraction because it serves as the first step in the process, enabling cross bridge formation. A muscle’s ability to contract depends on the formation of cross bridges between myosin and actin myofilaments.
A DRUG THAT BLOCKS ACETYLCHOLINE RELEASE WOULD INTERFERE WITH CROSS-BRIDGE FORMATION AND PREVENT MUSCLE CONTRACTION.

125
Q

What would happen to a resting skeletal muscle if the sarcolemma suddenly became very permeable to Ca2+?

A

the intracellular concentration of Ca would increase, and the muscle would contract. In addition, because the amount of calcium ions in the sarcoplasm must decline for relaxation to occur, this might prevent the muscle form relaxing completely

126
Q

Predict what would happen to a muscle if the motor end plate failed to produce acetylcholinesterase

A

The motor end plate would be continuously stimulated by acetylcholine, locking the muscle in a state of contraction

127
Q

Describe the 5 steps in initiating muscle contraction (step 5 = muscle contraction begins)

A
  1. Acetylcholine is released, binding to the receptors
  2. Action potential reaches T tubule
  3. Sarcoplasmic reticulum releases Ca2+
  4. Active site exposure, cross-bridge formation
  5. Contraction begins
128
Q

Describe the 5 steps in muscle relaxation

A
  1. Acetylcholine is broken down by acetylcholinesterase
  2. Sarcoplasmic reticulum recaptures Ca2+ (conc in sarcoplasm declines)
  3. Active sites covered, no cross bridge interaction
  4. Contraction ends
  5. Relaxation occurs. passive return to resting length
129
Q

Ach is released from….

A

the synaptic terminal

A&P Exam 2 (19 decks)

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