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BMS150 test 2 > skeletal muscle (wk8) > Flashcards

skeletal muscle (wk8) Flashcards

1
Q

fascicles

A

made of linearly aligned muscle fibers (myofiber)

  • The muscle fiber is a single, multi-nucleated, elongated cell
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2
Q

what is each muscle fibre in a facile made of

A

many sarcomeres, arranged linearlyw

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3
Q

what are sarcomeres made of

A

myofibrils (organelles)

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4
Q

epimysium

A

connective tissue sheath surrounding the whole muscle and extending from the tendons

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5
Q

perimysium

A

sheath surrounding each fascicle

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6
Q

endomysium

A

heath surround each individual muscle fibe

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7
Q

what is below the endoymysim

A

the sarcolemma – the cell membrane of the muscle cell.

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8
Q

how many myofibrils in each muscle fiber

A

Muscle fibers are large, multinucleated cells:
* Contain 1000 – 2000 myofibrils

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9
Q

what are myofibrils composed of

A

myofilaments

Each myofibril composed of many myofilaments, composed of:

  • Contractile proteins
    ▪ Actin
    ▪ Myosin
  • Regulatory proteins
    ▪ Tropomyosin
    ▪ Troponin
  • Additional accessory
    proteins
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10
Q

what are myofilaments composed o

A
  • Contractile proteins
    ▪ Actin
    ▪ Myosin
  • Regulatory proteins
    ▪ Tropomyosin
    ▪ Troponin
  • Additional accessory
    proteinsw
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11
Q

what is the contractile unit of skeletal muscle

A

Myofibrils are arranged into a series of sarcomeres, which form the contractile unit of skeletal muscle.

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12
Q

what 2 filaments are in a sarcomere

A

thick (myosin) and thin (actin)

Consist of interdigitating myofilaments, composed of:
* Thin filaments (made of actin)
* Thick filaments (made of myosin)

▪ The striated appearance of skeletal muscle is due to the overlapping of thick and thin filaments

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13
Q

what binds each sarcomere to a z disk

A

thin filament

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14
Q

what is in the center of a sarcomere and what’s it made of

A

M line made myosin/ thick filament

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15
Q

sarcomere: z disk and m line

A
  • Each sarcomere is bound by the Z-disk
    ▪ Thin filament attaches to the Z-disk
    ▪ Other proteins involved in stretch sensing and signal communication also attach to Z-disk.
  • At the center is the M-line
    ▪ Includes a variety of proteins to bind the myosin molecules within the thick filament
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16
Q

how do you get alternating light and dark bands in sarcomeres

A
  • Thick filaments lie between and partially interdigitate with thin filaments
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17
Q

light bands (I bands) vs dark bands (A bands)

A
  • Light bands (aka I bands) are regions of thin filaments that do not overlap with thick filaments
  • At the center of the light bands is the Z disk
  • Dark bands (aka A bands) are the region were the thick and thin filaments do overlap
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18
Q

in muscle contraction is it the light bands (I bands) or dark bands (A bands) that shorten

A

I band shortens (light)

During muscle contraction, the I band shortens, while the A band does not change in length

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19
Q

g actin vs f actin

A
  • Monomer:G-actin
  • Polymer: F-actin
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20
Q

thin filaments are made of how much actin?

A

▪ Thin filaments are composed of two strands of F-actin wound together.

▪ F-actin is the major constituent of the thin filament

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21
Q

how can myosin bind actin?

A

▪ Each G-actin monomer has a binding site for myosin

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22
Q

how are thick filaments made?

A

Arranged into thick filaments composed of many myosin units. Each unit is composed of head & tail regions
* Head region forms cross-bridges that interact with adjacent actin filaments
▪ Many myosin units are arranged in staggered position into a thick filament

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23
Q

how is a cross bridge formed

A

head region of myosin forms cross bridge that interacts with adjacent actin filaments (G actin monomer has binding site)

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24
Q

3 biochemical features of myosin head region

A

▪ ATPase activity
▪ Actin-binding region
▪ ATP binding region

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25
Q

what does tropomyosin associate with

A

actin

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26
Q

what are the 2 contractile proteins

A

▪ Actin
▪ Myosin

27
Q

what are the 2 regulatory proteins

A

▪ Tropomyosin
▪ Troponin

28
Q

When a skeletal muscle is in a relaxed state what does tropomyosin bind to

A

When a skeletal muscle is in a relaxed state, tropomyosin molecules cover the myosin-binding site on G-actin monomers
* This prevents cross-bridge formation between actin and myosin

29
Q

what prevents the cross bridge formation between actin and myosin

A

tropomyosin
=relaxed

and troponin I is also there (inhibtirou)

30
Q

what does troponin associate with

A

actin

31
Q

what are the 3 subunits of the complex troponin forms

A

troponin I, troponin T, troponin C

32
Q

what do troponin I, troponin T, troponin C all bind to

A
  • Troponin C - binds to Calcium
  • Troponin T - binds to Tropomyosin
  • Troponin I – binds to actin and inhibits contraction
33
Q

Troponin C - binds to..?

A

calcium

34
Q

Troponin T - binds to …?

A

tropomyosin

35
Q

troponin I- binds to..?

A

binds to actin and inhibits contraction

36
Q

what inhibits and what allows for cross bridge formation?

A

troponinC and T allows for cross bridge

tropomyosin and troponin I inhibits formation

i think

37
Q

how do the 3 subunits of troponin work?

A

When calcium binds to Troponin C, The troponin complex undergoes a conformational change and Troponin T “pulls” tropomyosin and Troponin I off of the myosin-binding site of G-actin subunits

38
Q

where is sarcolemma?

A

The plasma membrane of the muscle fiber is called the sarcolemma

39
Q

what does the sarcolemma contain?

A

Contains invaginations called transverse Tubules (aka T- tubules)
* Allows the action potential to be carried deep into the muscle fiber
* Continuous with the extracellular fluid

40
Q

use of t tubules in sarcolema

A

-carry AP deep in muscle fibers
-continuous with ECF

41
Q

The sarcolemma and T-tubules closely associate with…?

A

the sarcoplasmic reticulum

42
Q

what is found in high concentrations of the sarcoplasmic reticulum?

A

Sarcoplasmic reticulum is a specialized endoplasmic reticulum containing high concentrations of calcium

43
Q

what are terminal cistern

A

Terminal cisternae of the sarcoplasmic reticulum are specialized regions that associate with the T-tubules

44
Q

what is the muscle triad

A

The junction between T-tubules and sarcoplasmic reticulum cisterna is called the muscle triad

▪ Volume of T-tubule is large compared to the SR cisterna

45
Q

is [Ca2+] high or low in ECF

A

high

46
Q

how is a synapse formed at the neuromuscular junction

A

A motor nerve axon contacts each muscle fiber near the middle of the fiber, forming a synapse called the neuromuscular junction.

47
Q

what part of the sarcolemma is close to presynaptic terminal for synapse at neuromuscular junction

A

The region of the sarcolemma in closest contact with the presynaptic nerve terminal is called the motor end plate

48
Q

what is released at the motor nerve terminal and what does it bind

A

The motor nerve terminal releases acetylcholine (Ach), which binds to the nicotinic receptor on the sarcolemma.

49
Q

what happens when Ach binds nicotinic receptor at neuromuscular junction

A

▪ This gives rise to a graded, depolarizing end-plate potential.
▪ Activates voltage-gated sodium channels → triggering an action potential that propagates along the sarcolemma
▪ The skeletal muscle fibre action potential “looks” very similar to the neuron action potential (slightly longer duration, ~ 10 msec)

50
Q

which channels does Ach binding activate

A

v gated Na+ channels

51
Q

purpose of T tubule in action potential

A
  • The action potential propagates along the surface of the skeletal muscle fiber and penetrate deeper into the muscle fiber via the T-tubules
    ▪ This is the purpose of the T- tubule – to “bring” the action potential (travels along the sarcolemma) deep within the very large muscle fibres
    ▪ The action potential then signals to the sarcoplasmic reticulum
52
Q

what can action potential alongs T tubules activate in the sarcolemma?

A

L-type Ca2+ channels

53
Q

what does activation of the L-type Ca2+ channels in the sarcolemma trigger

A

triggers mechanical activation of Ryanodine receptors (RYR) on the surface of the SR terminal cisterna within the cell

54
Q

L-type Ca2+ channels activated?

A

mechanical activation of Ryanodine receptors (RYR)

55
Q

Where is most of the calcium that activates the skeletal muscles

A

Most of the calcium that activates the skeletal muscle sarcomere is from the SR, NOT the extracellular fluid

56
Q

how does l type ca2_ channel and RYR work

EC coupling

A
  • Opening of L-type Ca2+ channels and RYR allows Ca2+ to flow down its concentration gradient into the cytosol of the muscle fiber
    ▪ Calcium then binds to troponin (C subunit) to expose the binding sites for myosin
57
Q

whole muscle contraction

A
  • Typical muscle receives input from ~ 100 alpha-motor neurons
    ▪ The number of muscle fibers that each motor neuron innervates varies widely
  • All the muscle fibers innervated by a single nerve fiber is called a motor unit
    ▪ Often these complexes intermingle extensively
  • Allows motor units to contract in support of one another rather than entirely individually
58
Q

motor unit

A

All the muscle fibers innervated by a single nerve fiber

59
Q

What is the alpha-motor neuron-muscle fiber complex called?

A

neuromuscular junction

60
Q

how do you get a muscle contraction?

A

alpha motor neurons send many high frequency APs

61
Q

twitch vs tetanus

A

twitch is few APs with low frequency; tetanus is high AP with high frequency

62
Q

summation of skeletal muscle twitches –> tetany

A
  • A single action potential from a motor neuron barely causes any force development in the group of muscle fibres (motor unit) that it innervates
    ▪ Smooth, continuous, forceful contractions occur when the alpha-motor neuron sends many action potentials to a motor unit at a relatively high frequency
63
Q

tetany

A
  • Tetany = development of force (tension) in a muscle fibre due to many action potentials→greater and greater release of calcium from the SR
64
Q

fused tetany

A

▪Fused tetany→maximal force development in the muscle fibres of a motor unit – no individual “twitches” visible
▪Muscle has no time to “clear” calcium back to the SR

BMS150 test 2 (18 decks)

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