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AGRC1041 > muscle physiology 1&2 > Flashcards

muscle physiology 1&2 Flashcards

1
Q

outer membrane of muscle fiber is the

A

sarcolemma

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2
Q

each muscle fiber is innervated by

A

one motor neuron, making up the motor unit

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3
Q

muscle fiber is made up of smaller subunits called

A

myofibrils

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4
Q

myofibrils made up of repeating

A

sarcomeres, basic contractile unit of muscle fiber

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5
Q

sarcomere, the basic contracile unit of myofibrils has a disk at each end called the

A

z disk

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6
Q

lots if small thin filaments, called _____, are attached to the z disks, extending towards the middle of the sarcomere

A

actin

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7
Q

A band

A

one region of the repeated sarcomere remains relatively constant in length during contraction

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8
Q

I band

A

rich in thinner filaments, made of actin , changed its length along with the sarcomere during contraction

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9
Q

sliding filament theory

A

states that the sliding of actin past myosin generates muscle tension

because actin is tethered to the Z disks or Z bands, any shortening of the actin filament would result in shortening or sarcomere and therefore the muscle

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10
Q

sarcomeres have proteins

A

actin (thin filaments) and
myosin (thick fillaments)

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11
Q

actin; thin or thick

roped together with ____

A

thin filaments

tropomyosin

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12
Q

myosin; thin or thick

heads interact with

A

thick filaments

heads interact with actin

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13
Q

myosin heads and actin filaments are arranged

A

360 degrees all around these filaments

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14
Q

tropomyosin molecules (that link the actin togtehr) also hold on to a

A

troponin complex

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15
Q

troponin complex 3 subunits

A
  • troponin T (bound to tropomyosin)
  • troponin I
  • troponin C (binds calcium)
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16
Q

when troponin C binds calcium, what occurs

A
  • change in shape
  • moves tropomyosin off the active site on actin –> enables interactin between actin and myosin
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17
Q

how actin and myosin filaments interact is called the process of

A

cross-bridge cycling

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18
Q

when the myosin heads bind to the active site on actin (when troponin C binds calcium) it forms a

at this point we’ve got ___ bound to myosin head

A

crossbridge

ADP

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19
Q

when myosin head binds to active site on actin we get a conformational change; moves the actin, this is called a

A

power stroke= force

ADP released from myosin head during the power stroke

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20
Q

during the power stroke (when myosin head binds to active site on actin we get a conformational change; moves the actin) the myosin cross bridges are rotating

at this point the ADP that was bound to myosin head is

A

towards the centre of the sarcomere; shortening the length of the sarcomere

released

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21
Q

one the ADP is released from myosin head during the power stroke, ____ binds to the myosin head

A

ATP

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22
Q

ATP binding to the myosin head causes a

A
  • change in shape of myosin; decreases affinity of myosin heads for the actin filaments
  • causes a release (myosin heads detach from actin)
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23
Q

after the myosin heads are detached from the actin, what do the myosin heads do with the ATP

A

cleave or hydrolyze it

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24
Q

myosin heads cleaving the ATP provides the energy for the myosin head

A

to undergo another conformational change, which recocks the myosin head: myosin head is displaced towards the pos end of the actin and then once in this position, myosin head has energy it needs to undergo another power stroke; repeats cycle

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25
Q

cross bridge cycling keeps on repeating as long as you have _____ and _____

A

ATP and calcium

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26
Q

muscle fiber contraction; how does it begin

A
  • action potential arrives along motor neuron innervating that fiber
  • acetylcholine (the neurotransmitter) is released from the presynaptic terminal of the motor neuron, opens sodium ion channels leading to action potenial in sarcolemma
  • action potential travels along the T tubules
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27
Q

describe what occurs during transduction of the electrical signal across the T-tubule membrane

A
  • action potential spreads down T-tubule
    activates dihydropyridine (DHP) receptors which line the T-tubule
  • DHP receptors tethered to calcium release channels
  • calcium diffuses out of sarcoplasmic reticulum into sarcoplasm
  • calcium initiates contraction
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28
Q

muscle relaxation

A
  • signal from motor neuron stops
  • acetylcholinesterase breaks down acetylcholine
  • allows sarcolemma and T-tubules to repolarise (resting membrane potenital)
  • calcium concentration in sarcoplasm decreases
  • troponin shields the binding sites on actin
  • blocks the myosin/actin interaction
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29
Q

how is calcium pumped out during muscle relaxation

A
  • voltage-gated calcium channels in sarcoplasmic reticulum close
  • calcium ions pumped from cytosol (sarcoplasm) into sarcoplasmic reticulum
  • sarcoendoplasmic reticulum calcium ATPase (SIRCA)
  • requires energy
  • pumping calcium against concentration gradient
  • results in tropomyosin covering up binding sites on actin strands
  • muscles will also stop contracting if they run out of ATP
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30
Q

motor unit includes the

A

alpha motor neuron and all the skeletal muscle fibers it innervates

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31
Q

activity of motor neurons produce

A

contraction: all or nothing fashion

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32
Q

____ motor units recruited first

A

smallest

larger ones recruited later for larger/stronger motions

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33
Q

Which of the following molecules is bound to myosin, when the myosin head binds to the actin site?

A

ADP

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34
Q

Which of the following is NOT a step in the muscle contraction process?

A.
Calcium binds to troponin C, which moves tropomyosin from the active site on the actin filament

B.
ATP binds to myosin causing the dissociation of the myosin head from the actin filament

C.
ADP molecule released during the power stroke

D.
Hydrolysis of ATP allows for the cocking of the myosin head

E.
Tropomyosin covering the active site on actin

A

E.
Tropomyosin covering the active site on actin

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35
Q

Which of the following is activated by membrane depolarisation within the T-tubule of a skeletal myocyte?

A

Dihydropyridine receptor (DHP)

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36
Q

Which neurotransmitter is responsible for the initiation of skeletal muscle contraction?

A

Acetylcholine

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37
Q

Which of the following allows for Ca2+ to re-enter the sarcoplasmic reticulum and terminate the muscle contraction?

A

Sarco/endoplasmic reticulum calcium-ATPase (SERCA)

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38
Q

Which of the following statements is TRUE regarding muscle developing maximum tension during active contraction?

A.
The muscle tension is inversely proportional to the length of the muscle

B.
The muscle develops maximum tension at the optimal length

C.
The muscle tension is directly proportional to the length of the muscle

D.
The muscle develops maximum tension when it is stretched the most

A

B.
The muscle develops maximum tension at the optimal length

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39
Q

Which of the following is the first component of the motor unit?

A

Alpha-motor neuron

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40
Q

smooth muscle in blood vessels function

A

control diameter, regulate blood flow

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41
Q

smooth muscle in lung airways function

A

control diameter, regulate air flow

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42
Q

smooth muscle in urinary system function

A

push urine through ureter, tone of bladder, internal spinchter

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43
Q

smooth muscle in male reproductive tract function

A

secretion, propels semen

44
Q

smooth muscle in females reproductive tract function

A

propels eye (fallopian tube), parturition (myometrium of uterus)

45
Q

smooth muscle in eye function

A

control of pupil diameter (iris muscle) and shape of lens

46
Q

smooth muscle in kidney function

A

regulate blood flow

47
Q

smooth muscle in skin function

A

hair erection (piloerection)

48
Q

single unit smooth muscle

A

act as a single unit, in unison
electrically coupled by gap junctions

49
Q

multi unit smooth muscle

A

muscle cells act independently allows finer control, more graded response

50
Q

sphincters contraction/relaxation

A

normally contracted, when relaxes something passes then returns back to contracted

51
Q

blood vessels and airways contraction/relaxation

A

normally partially contracted (tone)

52
Q

esophagus and urinary bladder contraction/relaxations

A

opposite of sphincters; normally relaxed, contracts when something passes

53
Q

stomach intestines contraction/relaxation

A

when physically activate lots of oscillations between contraction and relaxation

54
Q

smooth muscle is not _____ unlike skeletal muscle

A

striated

55
Q

dense bodies in smooth muscle

A

dense areas of membrane also help to maintain that
structural relationship of thick and thin filaments

56
Q

which muscle can shorten to greater degree; smooth or skeletal muscle

A

smooth

57
Q

is smooth muscle organized into sarcomeres

A

no

Smooth muscle still has actin and myosin, thin filaments and
thick filaments. However, it’s not organised into sarcomeres. Instead, it has a large number of intermediate filaments that help maintain its structural integrity

58
Q

what do smooth muscles have for electrical and chemical communication

A

gap junctions

59
Q

smooth muscle is _____ coupled

A

mechanically

60
Q

smooth muscle has tropomyosin but no toponin, what does it use instead

A

calmodulin

61
Q

smooth muscle has bundles of _____ anchored to the dense bodies, what do they do

A

non contractile intermediate filaments

serve to anchor the thin actin filaments

62
Q

smooth muscle sequesters large amounts of _____ ions in the extracellular fluid within _____

A

calcium
caveolae

63
Q

caveolae

A

small invagination in smooth muscle cell membrane (sarcolemma)

64
Q

2 main ways to get smooth muscle to contract

A

CICR (calcium induced calcium release)
ligand mediated

65
Q

ligand mediated way of smooth muscle contraction

A
  • a hormone or a neurotransmitter
    to bind to a receptor
  • This binding of to the G‐protein coupled receptor causes an enzymatic second messenger signal pathway to release calcium into the cell
  • May have no direct nerve
    supply
  • Respond to stimuli in the ECF
  • Stimulates IP3 formation
  • IP3 binds to IP3-gated Ca2+
    channel in sarcoplasmic reticulum
  • Ca2+ released into cytosol
65
Q

CICR way of smooth muscle contraction

A

-The first way is via an electrical potential spreading across the membrane
- which opens up calcium channels
- This influx of
calcium, causes calcium‐induced calcium release from the sarcoplasmic reticulum
- This calcium‐induced calcium release is also known as CICR. - - calcium enters into
the smooth muscle cell from the extracellular fluid, which engages a calcium channel
to release more calcium
- so calcium influx stimulates calcium release from sarcoplasmic reticulum

66
Q

in smooth muscle calcium channels are located in the

A

caveolus

67
Q

in CICR the calcium that comes into the cell from the caveolus isn’t really involved with the contraction of the smooth muscle to a great degree; most of the contraction is
induced from what is released from the

A

sarcoplasmic reticulum

68
Q

smooth vs skeletal muscle contraction

A

SKELETAL
- intracellular Ca2+ concentration is sensed by troponin
- moves tropomyosin (thin filament regulation)
- exposes binding sites on actin
- which allows actin-myosin interaction
- leads to cross bridge cycling
- causes contraction

SMOOTH
- intracellular Ca2+ is sensed by calmodulin
- which activates MLCK (thick filament regullation)
- which phosphorylates myosin
- which allows actin-myosin interaction
- leads to cross bridge cycling
- causes contraction

69
Q

smooth vs skeletal muscle which is thin filament regulation and which is thick

A

In skeletal muscle, the troponin moves tropomyosin off the active site. This movement of troponin is known as thin filament regulation. thin
filament: actin. So it’s regulating the thin filament.

In smooth muscle, calmodulin
activates myosin light chain kinase. This activation of myosin light chain kinase is
known as thick filament regulation. thick filament: Myosin. So calmodulin
is regulating the thick filament.

70
Q

in smooth muscle ___ is being regulated

in skeletal muscle ____ is being regulated

A

myosin
actin

71
Q

when Ca2+ binds to calmodulin in smooth muscle contraction, the calmodulin-calcium complex activates an enzyme:

A

myosin light chain kinase (MLCK) which phosphorylates the myosin head

72
Q

2 mechanisms to relax smooth muscle

A
  • pump calcium out of cell using calcium ATPase or via a sodium-calcium exchanger
  • sequester calcium back into sarcoplasmic reticulum
73
Q

is cardiac muscle striated

A

yes

74
Q

does cardiac muscle have sarcomeres with actin and myosin like skeletal muscle

A

yes

75
Q

what are some differences between cardiac muscle and skeletal muscle

A
  • cells branch
  • gap junctions present at intercalated discs where cells bind together
  • contraction is synchronized
  • energy from aerobic respiration
76
Q

one alpha motor unit innervates

A

many skeletal muscle fibers

77
Q

each muscle consists of a number of mixed ____ of different fiber types

A

motor units

78
Q

for a weak contraction of the whole muscle only one or a few of its motor units are activated, which motor units are recruited first

A

smallest motor units recruited first

larger ones recruited later for larger/stronger motions

79
Q

what determines the number of muscle fibers per motor unit and the number of motor units per muscle

A

the specific function of the muscle

80
Q

the smaller the muscle unit, the ____ the control of movement

A

finer

81
Q

what is a twitch

A

When a motor neuron innervating the muscle fibre has an action potential, when it
“fires”, it causes a brief increase in the intracellular concentration of calcium ions, and actin‐myosin binding. The result is a brief contraction called a ‘twitch’

82
Q

what is recruitment

A

a whole muscle is controlled by the firing of lots of motor axons. The motor
nerves control movement by adjusting the number of motor axons firing, therefore
controlling the number of twitching muscle fibres. This is a process known as
‘recruitment‘.

aka the process of activating more motor units to increase the strength of contraction

83
Q

in recruitment, why are smaller, fine motor units recruited first

A

because their neurons are
smaller and reach the excitation threshold more quickly than larger neurons

84
Q

summation

A

adding together individual twitch contractions to increase the intensity of the whole muscle contraction

85
Q

the force of
contraction increases by increasing

A

the frequency of contractions

86
Q

tetany

A

sustained contraction of a muscle; result of a rapid succession of nerve impulses delivered to the muscle

87
Q

refractory period

A

brief period of time in which muscle cells will not respond to a stimulus

88
Q

if muscle is stimulated anytime during refractory period it will

A

not respond

89
Q

Stimulating after refractory period but before complete recovery will lead to

A

second contraction on top of
first one, resulting in summation

90
Q

what has a longer refractory period; cardiac or skeletal muscle

A

cardiac; to prevent heart from going into tetany

91
Q

tetanus and cross bridge cycling

A
  • Sustained elevation in Ca2+ permits greater cross-bridge cycling
  • Frequency of action potentials increases
  • Duration of elevated cytosolic Ca2+ concentration increases
  • Contractile activity increases
  • Maximum tetanic contraction reached
92
Q

With tetanus, the maximum number of cross‐bridge
binding sites remain uncovered, so that

A

cross‐bridge cycling and tension development is at its peak

93
Q

active force regulation

A

Types and number of motor units recruited
More motor units = greater force

94
Q

passive force regulation

A

related to initial muscle length; what is ideal length for force generation

95
Q

to determine total muscle tension have to add together

A

active and passive tension

96
Q

Which of the following structures allows “single-unit” smooth muscle to contract in a coordinated manner?

A

Gap junctions

97
Q

Which of the following functions is attributed to the smooth muscle located in the skin?

A

Hair erection

98
Q

Which of the following is NOT a feature of smooth muscle?

A

Striations

99
Q

Which of the following is usually contracted in its normal state?

A

A sphincter

100
Q

Where in the myocyte are the smooth muscle calcium-induced release channels located?

A

Sarcoplasmic reticulum

101
Q

Which of the following initiates the activation of the IP3 pathway in the sarcoplasmic reticulum?

A

Hormonal activation of a GPCR

102
Q

Which protein in smooth muscle has a similar function as troponin does in skeletal muscle?

A

Calmodulin

103
Q

Which type of stimulation generates the highest tension in the muscle over time?

A

Fused tetanus

104
Q

Which of the following is the first component of the motor unit?

A

Alpha-motor neuron

105
Q

Which of the following statements is TRUE regarding muscle developing maximum tension during active contraction?
A.
The muscle develops maximum tension when it is stretched the most

B.
The muscle tension is inversely proportional to the length of the muscle

C.
The muscle tension is directly proportional to the length of the muscle

D.
The muscle develops maximum tension at the optimal length

A

D.
The muscle develops maximum tension at the optimal length

AGRC1041 (20 decks)

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