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BIO 241 [Exam #3] > Chapter 12 - Muscle Physiology > Flashcards

Chapter 12 - Muscle Physiology Flashcards

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1
Q

What are the three types of muscle?

A
  • skeletal muscle
  • smooth muscle
  • cardiac muscle
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2
Q

How do the types of muscle differ from each other?

A

differ based on:
- appearance (shape, # nuclei, striations)
- control (voluntary/involuntary)
- function

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3
Q

Describe the characteristics of cardiac muscle

A
  • branched
  • striated
  • uninucleated
  • involuntary control
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4
Q

Describe the characteristics of skeletal muscle

A
  • tubular
  • striated
  • multinucleated
  • voluntary control
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5
Q

Describe the characteristics of smooth muscle

A
  • spindle-shaped
  • nonstriated
  • uninucleated
  • involuntary control
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6
Q

muscle tissue consists of _________ ______

A

muscle cells

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7
Q

What is an alternate name of “muscle cell”

A

muscle fiber

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8
Q

How would you describe the organization of skeletal muscle in general

A

tubes within a tube

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9
Q

Name the skeletal muscle organization from largest to smallest structure

A
  1. skeletal muscle
  2. muscle fascicle
  3. muscle fiber/cell
  4. myofibrils
  5. myofilaments
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10
Q

Name the different types of skeletal muscle coverings

A
  • epimysium
  • perimysium
  • endomysium
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11
Q

Define epimysium, perimysium, and endomysium

A

epimysium: surrounds entire skeletal muscle

perimysium: surrounds the fascicle

endomysium: surrounds the fiber

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12
Q

What surrounds a skeletal muscle fiber (hint: not the endomysium)

A

sarcolemma (similar to cell membrane)

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13
Q

What structure of skeletal muscle is surrounded by a sarcolemma and contains the sarcoplasmic reticulum (SR)?

A

skeletal muscle fiber/cell

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14
Q

What is the function of the SR?

A

stores Ca2+

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15
Q

What is the function of the sarcolemma?

A

surrounds skeletal muscle fiber (similar to CM)

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16
Q

What is the infolding of the sarcolemma and is something an AP can travel down?

A

T tubule

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17
Q

What are myofilaments, what are 2 general types of myofilaments, and how are myofilaments arranged?

A

Smallest structural unit of skeletal muscle; contains sarcomeres

Two types of myofilaments:
Thick filament - myosin
Thin filament - actin (+2 others)

Arrangement:
Into a sarcomere that has dark and light patterns = striations

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18
Q

What structural unit of skeletal muscle is arranged into a sarcomere?

A

myofilaments

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19
Q

A sarcomere is ________ a cell

A

NOT

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20
Q

Define a sarcomere. Draw and label all of the different parts of a sarcomere

A

Basic contractile unit of skeletal muscle that consists of thick and thin myofilaments that have varying amounts of overlap = striations (IS NOT A CELL)

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21
Q

Myosin is a ______ filament, whereas actin is a _______ filament. Myosin and actin are considered _________

A

thick
thin
myofilaments

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22
Q

What is the reason that skeletal muscle has striations (what are striations due to)?

A

overlap between thick and thin myofilaments = striations

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23
Q

A sarcomeres ________ can vary. It can _______ or __________

A

length
shorten
elongate

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24
Q

What area does a sarcomere cover?

A

the distance between two adjacent
Z-discs

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25
Q

Name all the bands/discs/lines found in a sarcomere

A

MIZAH
- M line
- I band
- Z discs/line
- A band
- H band

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26
Q

Describe the M line of a sarcomere

A

helps hold down myosin

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27
Q

Describe the I band of a sarcomere

A

100% thin filament (actin); no overlap

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28
Q

Describe the Z discs/lines of a sarcomere

A

in center/bisects I band

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29
Q

Describe the A band of a sarcomere

A

contains entire length of myosin; varying amounts of overlap with actin

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30
Q

Describe the H band of a sarcomere

A

100% myosin and in center of A band; no overlap with actin

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31
Q

Name only the thin filaments that make up a sarcomere

A

actin
tropomyosin
troponin

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32
Q

What type of thin filament contains myosin binding sites?

A

actin

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33
Q

Define actin (thin filament) and function

A

thin, consists of 2 twisted strands of actin molecules

has myosin binding site

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34
Q

Define tropomyosin (thin filament) and function

A

long, fibrous protein, intertwined with actin filament

covers up myosin-binding sites of actin when muscle is relaxed

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35
Q

What thin filament covers up myosin-binding sites of actin when muscle is relaxed

A

tropomyosin

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36
Q

Define troponin (thin filament)

A

globular protein that sits on top of tropomyosin
contains Ca2+ binding sites (contraction)

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37
Q

What thin filament contains Ca2+ binding sites?

A

troponin

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38
Q

What does myosin consists of? (hint: what is its general structure)

Which part interacts with the thin filament?

A

myosin head
hinge
tail

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39
Q

What contains actin binding sites and ATP binding sites?

A

myosin head

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40
Q

What binding sites does myosin contain?

A

actin binding sites
ATP binding sites

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41
Q

What happens at the actin-binding site (on myosin)?

A

binds to actin
(both actin and myosin binding sites interact/bind to each other)

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42
Q

What happens at the ATP binding site (on myosin)?

A

catalyzes hydrolysis of ATP (ATP -> ADP + Pi)

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43
Q

When ATP is present on myosin, ______ between actin and myosin -> ___________

A

detachment
relaxation

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44
Q

When ADP is present on myosin, _______ between actin and myosin -> _________

A

attachment
contraction

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45
Q

Where would you specifically find a myosin-binding site, actin-binding site, and ATP-binding site?

A

Myosin binding site: actin
Actin binding site: myosin head
ATP binding site: myosin head

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46
Q

What is the sliding filament theory?

A

is the sliding between thick and thin myofilaments to change sarcomere size

47
Q

When a muscle contracts, __________ __________

A

sarcomeres shorten

48
Q

TRUE or FALSE: The H band contains the entire thick filament

A

False, it only has a portion of it that does not overlap with the thin filament

49
Q

TRUE or FALSE: The I band contains only actin

A

True, I band contains 100% actin

50
Q

TRUE or FALSE: Actin and myosin must bind to each other when the sarcomere shortens

A

True

51
Q

TRUE or FALSE: The length of actin shortens, but the length of myosin does not change when a sarcomere shortens

A

False, neither actin nor myosin length change

52
Q

What filament slides toward the M line

A

thin filament (actin)

53
Q

Which part(s) of the sarcomere shorten or change in size when skeletal muscle contracts?

A

H and I band shorten (HI and BYE); Distance between M line and Z discs shorten

54
Q

Neither ______ or ________ change in ________ during a muscle contraction

A

actin (thin)
myosin (thick)
length

55
Q

Why is Ca2+ necessary for skeletal muscle contraction? (What is the function of Ca2+)

A

Ca2+ binds to troponin, which changes it shape and position of tropomyosin shifts to expose myosin binding sites on actin filaments

56
Q

Define a “cross-bridge”

A

Attachment between myosin (head) and actin

57
Q

TRUE or FALSE: During the power stroke, myosin moves toward the M-line/center of the sarcomere

A

False, actin is the filament that slides toward the M-line (myosin remains stationary)

58
Q

Define a “power stroke” and what is the result of such an event? What step in the Sliding Filament Throy happened immediately before and immediately after the power stroke?

A

Power stroke happens when Pi falls off from the myosin head and moves laterally toward the tail

Before power stroke: Pi falls off
After power stroke: ADP falls off

59
Q

Regarding the cross bridge, what happens when ATP is present on the myosin head?

A

Myosin head will detach from the myosin binding site on actin

60
Q

What happens chemically and physically/mechanically to the myosin head when ATP gets hydrolyzed?

A

ATP is hydrolyzed into ADP + Pi to return the myosin head to its original position

61
Q

What is the Ca2+ pump and when/why would it function/operate?

A

Ca2+ pump located on the SR and functions to move Ca2+ ions from “cytoplasm” (sarcoplasm) back into SR -> will allow for muscle relaxation

62
Q

Define the NMJ. What is usually found in this space?

A

Neural Muscular Junction: Synapse between motor neuron and muscle cells

ACh (NT/Ligand/Chemical)+ AChE

63
Q

How does the myosin head get repositioned once ADP and Pi fall off?

A

ATP will bind to ATP binding site and will be hydrolyzed into ADP and Pi. This reenergizes myosin head to return to its original position

64
Q

Skeletal muscle cells can have _______

A

AP (action potentials)

65
Q

What is the goal of excitation-contraction coupling in skeletal and cardiac muscle?

A

release Ca2+ from SR -> contraction

66
Q

What are the functions of the nicotinic ACh receptor? (What does it act as?)

A
  1. ionotropic receptor for ACh
  2. LG-Na+ channel
67
Q

What is the RMP for skeletal muscle cells?

A

-70mV to -95mV

68
Q

The nicotinic ACh receptor requires binding of ______ ACh molecules

A

2

69
Q

Regarding the skeletal muscle AP graph, label the following: RMP, threshold, peak of AP, initial depolarization,rapid depolarization, repolarization, hyperpolarization, VG-Na+ channel first opens, VG-Na+ channel first closes, VG-K+ channel first open, LG-ion channel first opens

A

check answer on review question doc

70
Q

What is an EPP and how does it get generated?

A

End Plate potential is the initial depolarization (analogous to EPSP)

Is generated by the influx of Na+ through the opening of the nicotinic ACh receptor (LG-Na+ channel)

71
Q

What is a T tubule, DHP receptor, and Ryanodine receptor? What is the relationship between these three things?

A

T tubule: infolding of sarcolemma

DHP receptor: VG-Ca+ channels

Ryanodine receptors: Ca2+ release channels on SR membrane

Between all of these, an AP will travel down the T tubule and activate the DHP receptor. It is coupled with the ryanodine receptor and it will also become activated.

72
Q

Regarding skeletal muscle excitation-contraction couplings, what is meant by the phrase “calcium-induced, calcium released”?

A

An outside source of Ca2+ is needed to flow through the DHP receptor (into the cytoplasm) to induce the release of Ca2+ out of the SR via the Ryanodine receptor

73
Q

Describe how the sliding filament theory works

A
  1. skeletal muscle fiber stimulated by motor neuron at the NMJ

series of interactions occur in prior to step 2

  1. Ca2+ released from SR and intracellular Ca2+ concentration increases
  2. Ca2+ binds to troponin and troponin changes shape
  3. the position of tropomyosin shifts to expose the myosin binding sites on actin
  4. If ADP + Pi is present on myosin head, it attaches to actin (known as cross bridge)
  5. Pi falls off from myosin head and moves laterally toward tail (power stroke)
  6. power stroke causes thin filament (actin) to slide along thick filament (myosin) and moves thin filament toward center of sarcomere

sarcomere shorten and whole skeletal muscle tissue contracts

  1. ADP falls off after power stroke -> ATP binding site now empty
  2. New ATP binds to myosin head -> detaches from actin
  3. ATP hydrolyzed into ADP + Pi -> reenergizes myosin head to return to original position
  4. Ca2+ transported back to SR via Ca2+ pump (for relaxation purposes)
74
Q

What falls off AFTER power stroke?

A

ADP

75
Q

What happened to the myosin head to cause it to perform the power stroke?

A

Pi fell off from the myosin head -> power stroke

76
Q

How does the myosin head get reenergized to return to its original position?

A

ATP binds to empty ATP binding site on myosin head and hydrolyzed into ADP + Pi = reenergized to original position

77
Q

What is the value of threshold for an AP of skeletal muscle cells?

A

-65mV

78
Q

Explain excitation-contraction coupling in skeletal muscle

A
  1. AP reaches axon terminal of motor neuron (NT vesicles fuse as a result of influx of Ca2+ due to opening of VG Ca2+ channel)
  2. ACh released into NMJ
  3. ACh binds to nicotinic ACh receptor on sarcolemma of skeletal muscle cell
    (receptor + channel)
  4. Na+ diffused into skeletal muscle cell -> initial depolarization (EPP)
  5. Once EPP reach threshold (-65mv) -> VG-Na+ ch. open -> more Na+ diffuses in = skeletal muscle cell AP STARTS
  6. AP travels along sarcolemma down to the T tubules
  7. AP activated DHP receptors (VG-Ca2+ channels) on T tubules
  8. extracellular Ca2+ diffuses in -> intracellular Ca2+ increases
  9. activation of DHP receptor activates its coupled receptor, Ryanodine receptors (Ca2+ release channels) on SR membrane
  10. Ca2+ diffuses out of SR and into cytoplasm (process known as Ca2+ induced Ca2+ released mechanism)
  11. intracellular Ca2+ increases and initial Ca2+ triggers more Ryanodine receptors to open via positive feedback
  12. Ca2+ that was released from the SR (intracellular) will bind to troponin and initiates contraction (sliding filament theory)

CA2+ USED FOR CONTRACTION COMES FROM SR NOT EXTRACELLULARLY

79
Q

What happens to skeletal muscle if the nicotinic ACh receptor is blocked? What happens if the VG-Ca2+ channels are blocked?

A

Both would lead to no contraction of skeletal muscle

(Na+ cannot flow through nicotinic ACh receptor to begin EPP and Ca2+ cannot flow through VG-Ca2+ channels to initiate Ca2+ induced, Ca2+ released mechanism -> no contraction)

80
Q

VG-Ca2+ channels in skeletal muscle cells are also known as…

A

DHP receptors

81
Q

What is Acetylcholinesterase, what is its function, and where is it present?

A

AChE is an enzyme that degrades ACh to decrease [ACh] at the NMJ -> relaxation

82
Q

What are the ways in which skeletal muscle relaxes?

A
  • ryanodine receptors inhibited via negative feedback (bc of high intracellular Ca2+) to stop release of Ca2+ via SR
  • Ca2+ pump (on SR) pumps cytoplasmic Ca2+ back into SR
  • use AChE (acetylcholinesterase) to clear out/degrade ACh at the NMJ
83
Q

A __________ in Ca2+ in skeletal muscle will lead to relaxation

A

decrease

84
Q

What is rigor mortis? (just define it)

A

rigidity or stiffness of the body after death that peaks at about 10-12 hours after death

85
Q

What is rigor mortis caused by?

A

due to prolonged contraction (lots of Ca2+) of skeletal muscle because once someone has passed, no ATP is made, so the myosin head cannot detach from actin. Therefore, the cross-bridge cannot break and Ca2+ cannot be pumped back into SR (both require ATP). Body will remain in contracted state

86
Q

What types of muscle(s) are controlled by the SNS (somatic NS) and ANS (autonomic NS)?

A

SNS - skeletal muscle
ANS - smooth and cardiac

87
Q

Where is smooth muscle found in the body?

A

DRUBB

  • digestive organs
  • reproductive tracts
  • urinary tracts
  • bronchioles
  • blood vessel walls
88
Q

TRUE or FALSE: Smooth muscle have actin and myosin arranged into sarcomeres

A

False, thick and thin filaments in smooth muscle are NOT arranged into sarcomeres

89
Q

Structurally, how is smooth muscle different from skeletal muscle

A
  • Thin and Thick filaments are NOT arranged into sarcomeres
  • Actin is attached to dense bodies (in skeletal muscle actin is attached to Z discs)
  • No troponin (Ca2+ binds to Calmodulin instead -> Ca2+-Calmodulin complex)
  • Few/no SRs
  • Caveoles (shallow infoldings) instead of T tubules
  • No NMJ
90
Q

Because smooth muscle does not have troponin, what does Ca2+ bind to?

A

binds to calmodulin to form Ca2+-Calmodulin complex

91
Q

Ca2+ from the __________ environment leads to contraction in smooth muscle

A

extracellular (comes from Ca2+ diffused from VG-Ca2+ channels)

92
Q

Ca2+ from the __________ environment leads to contraction in skeletal muscle

A

intracellular (comes from the Ca2+ released from SR via RyR)

93
Q

Why don’t you have an NMJ in smooth muscle?

A

because NT are released over a larger area from varicosities of autonomic neurons

94
Q

If smooth muscle have very few SRs, then what is the source of Ca2+ needed for smooth muscle contraction? What does this Ca2+ bind to?

A

Extracellular Ca2+ (that diffuses in via VG-Ca2+ channels @ threshold)

Ca2+ binds to Calmodulin to form the Ca2+-Calmodulin complex

95
Q

Define a varicosity

A

Axon-like swelling of autonomic neurons (ANS) that contain and release NTs

96
Q

What pathways can stimulate smooth muscle?

A

neuronal pathways (by autonomic neurons)
endocrine pathways (by hormones)

97
Q

What are the two types of stimulation in a neuronal pathway of smooth muscle?

A
  • extrinsic stimulation
  • intrinsic stimulation
98
Q

Compare extrinsic stimulation and intrinsic stimulation for smooth muscle. Provide examples

A

extrinsic stimulation: stimulus originates outside smooth muscle tissue
-> ex: external stimulus -> CNS -> PNS -> ANS -> PANS and SANS -> effects tissue

intrinsic stimulation: stimulus originates within the body/tissue
-> ex: enteric nervous system (GI tract; has its own NS)

99
Q

What are some examples of NT that are a part of smooth muscle extrinsic and intrinsic stimulation?

A

ACh
Epinephrine
Nitric Oxide (NO)

100
Q

Know the RMP and threshold values for smooth muscle AP graph

A

RMP = -60mV
Threshold = -40mV

101
Q

What structure is calmodulin analogous to in skeletal muscle?

A

troponin

102
Q

In smooth muscle, what happens at the end of RMP?

A

LG-ion channels open to create graded depolarization/potential

103
Q

What are graded potentials?

A

are the initial depolarization in smooth muscle

(EPP is the initial depolarization in skeletal muscle)

104
Q

Regarding smooth muscle excitation-contraction coupling, list the enzymes that can lead to contraction, and which enzymes lead to relaxation. Also, for each of these enzymes, state if it is active/inactive and phosphorylated/dephosphorylated

A

CONTRACTION

  • Ca2+-Calmodulin
  • MLCK (active)
  • MLC - phosphorylated
  • Myosin Phosphatase - phosphorylated (inactive)
  • Rho kinase (active)

RELAXATION

  • MLCK - phosphorylated (inactive)
  • MLC
  • Myosin Phosphatase (active)
  • Myosin Phosphatase Phosphatase (active)
  • Rho kinase - phosphorylated (inactive)
  • PKG (active)
105
Q

Describe excitation-contraction coupling in smooth muscle

A
  1. RMP is at -60mV
  2. stimulation -> LG ion channels open -> graded potentials
  3. if threshold reached at -40mV, VG-Ca2+ channels open -> Ca2+ diffuse in -> sharp rise in Ca2+
  4. Ca2+ binds to calmodulin -> Ca2+-Calmodulin Complex formed
  5. Ca2+-Calmodulin dephosphorylates MLCK (inactive) -> MLCK (active)
  6. MLCK (active) phosphorylates MLC (“active”) -> cross-bridge attachment -> contractoin
106
Q

How does smooth muscle relax?

A

myosin phosphatase (active) dephosphorylates MLC -> breaks cross bridge -> relaxation

107
Q

TRUE or FAlSE: Cardiac muscle is striated

A

True, it contains sarcomeres similar to skeletal muscle

108
Q

What types of muscle(s) contain sarcomeres?

A

skeletal and cardiac muscle

109
Q

Define gap junctions

A

site at which cardiac muscle cells are connected (intercalated discs) and allows for traveling of AP from one cell to another

110
Q

Define myocardium

A

a mass of cardiac muscle cells connected to each other via gap junctions

111
Q

What type of muscle(s) does not need nerve stimulation to generate an AP?

A

cardiac muscle

112
Q

Define a pacemaker

A

The region (SA node) at which an AP in cardiac muscle begins; located in right atrium

113
Q

Why is heart rate able to increase or decrease?

A

it can be influenced by ANS (SANS-increase HR and PANS-decrease HR) and hormones

BIO 241 [Exam #3] (3 decks)

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