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CAPS 390 > muscles > Flashcards

muscles Flashcards

1
Q

what is the organization of skeletal muscle?

A

myofilaments -> sarcomeres -> myofibrils -> muscle fiber -> fascicle (bundle of muscle fiber) -> muscle

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2
Q

epimysium

A

dense collagenous connective tissue that surrounds entire muscle

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3
Q

perimysium

A

collagenous connective tissue that surrounds bundles of muscle fibers called fascicles

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4
Q

endomysium

A

fine sheath of connective tissue composed of reticular fiber that surrounds individual muscle

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5
Q

myotendinous junction

A

finger-like extensions of the muscle fibers insert into the connective tissue of the tendon

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6
Q

basal lamina

A

specialized layer of extracellular matrix that supports and separates epithelial cells from the underlying connective tissue

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7
Q

how does the basal lamina provide structural support to the cell?

A

it binds to the myofiber via dystroglycan-containing complex

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8
Q

how does basal lamina connect to the actin (cytoskeleton)?

A

basal lamina -> transmembrane protein alpha-dystroglycan then beta -> dystrophin -> actin

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9
Q

myofibers

A

long, cylindrical and striated
multinucleated with nuclei located at the periphery (at the edge)

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10
Q

myofibrils

A

aligned in parallel
separated by mitochondria and sarcoplasmic reticulum
composed of filaments called myofilaments

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11
Q

sarcoplasmic reticulum

A

smooth endoplasmic reticulum
forms an interconnected network of tubules
surrounds each myofibrils
forms chambers called terminal cisternae on either side of the t-tubules

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12
Q

terminal cisternae

A

chamber formed by SR on either side of the t-tubules

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13
Q

when is Ca2+ stored and released?

A

stores Ca2+ when muscle is at rest
released in the sacroplasm when muscle is stimulated

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14
Q

t-tubules

A

deep invagination of sacrolemma
perpendicular to the length of myofiber

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15
Q

how many terminal cisternae are next to the t-tubule?

A

two tc and a single t-tubule form a triad junction

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16
Q

how are Ca2+ released?

A

action potential runs along the sarcolemma, reaches the T-tubules, and activates DHPRs.
DHPRs are mechanically coupled to RyRs, which release Ca²⁺ from the sarcoplasmic reticulum into the sarcoplasm, where it initiates muscle contraction.

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17
Q

which side does the myosin head face and why?

A

it faces outwards because the actin binding site and myosin ATPase site is on it (for contraction to occur)

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18
Q

what happens when Ca2+ is at low concentration?

A

myosin binding sites on actin are masked by tropomyosin

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19
Q

TnI
TnC
TnT

A

TnI - binds to actin
TnC - binds to Ca2+
TnT - binds to myosin

20
Q

what is the movement of troponin upon stimulation?

A

SR releases Ca2+ into the sarcoplasm
Ca2+ binds to troponin -> changes its conformation
shift in the position of tropomyosin
unmasking of myosin binding sites
myosin binding to actin

21
Q

what happens to the actin when muscle contracts?

A

slides but doesn’t shorten
overlap with myosin

22
Q

what happens to the myosin when muscle contracts?

A

shortens and overlap with actin

23
Q

are skeletal muscle voluntary or involuntary? striated or smooth?

A

voluntary and striated

24
Q

what is a motor end plate?

A

a specialized domain of the sarcolemma
highly excitable
responsible for initiating the action potential that propagates across the myofiber -> muscle contraction

25
Q

what is a neuromuscular junction?

A

the junction/synapse of the axon terminal of a motor neuron with the motor end plate

26
Q

how does the electrical signal travel from the brain/spinal cord to the muscle to cause contraction?

A
  1. signal originates in the brain/spinal cord
  2. action potential travels down the axons of motor neuron
  3. reaches the axon terminal at the neuromuscular junction
  4. ACh are released into the synaptic cleft
  5. ACh binds to the receptor on the motor end place and depolarize muscle membrane
  6. action potential propagates across sarcolemma into the t-tubules
  7. t-tubules signals SR to release Ca2+ into muscle fiber
  8. Ca2+ bind to proteins in muscle fiber allowing actin and myosin to slide past each other
27
Q

where are ACh receptors located?

A

they are located on the sarcolemma (PM of muscle cell), at the motor end plate

28
Q

are axons myelinated?

A

they are generally myelinated outside the muscle cell and unmyelinated at the end of the axon at the neuromuscular junction

29
Q

where are the ACh neutransmitter stored in?

A

in the synaptic vesicles

30
Q

is the junction of muscle fiber folded?

A

yes

31
Q

how is Ca2+ restored after muscle contraction?

A

they are pumped back from the sarcoplasm to the SR via ATPase

32
Q

what happens in duchenne muscular dystrophy?

A

the link between the actin cytoskeleton and the basal lamina (with dystrophin and dystroglycan complex) in lost
-> disorganized sarcomeres

33
Q

where is the cardiac muscle located?

A

in the heart where it forms a thick layer called myocardium

34
Q

is cardiac muscle striated and voluntary?

A

it is striated and involuntary

35
Q

how are the characteristics of cardiac fibers and how are they joined together?

A

they are short and branched striated fibers and joined by intercalated disks

36
Q

zonula adherens

A

anchor actin myofilament of the terminal sarcomeres to the PM (transverse part of cardiac muscle)

37
Q

desmosomes

A

bind fibers together preventing their separation during contraction cycles (transverse part of cardiac muscle)

38
Q

gap junction in cardiac muscle

A

rapid flow of information between fibers

39
Q

how many t-tubule and terminal cisternae are present in cardiac muscle?

A

one t-tubule and one terminal cisternae that forms a diad

40
Q

what are the characteristics of smooth muscle?

A

found in the GI tract, respiratory tract, around blood vessels
involuntary
non-striated fibers and spindle-shaped and tapered

41
Q

how many nucleus are in smooth muscle?

A

mono-nucleated
(one central nucleus per fiber)

42
Q

is there t-tubules and SR cisternae for smooth muscle?

A

no

43
Q

tunica media

A

it is made up of smooth muscle cells and elastic tissue

44
Q

how does the tunica media differ in arteries and veins?

A

tunica media is thicker in arteries to sustain higher blood pressure

45
Q

what are the 2 types of smooth muscle layer?

A

longitudinal - push food down
circular - constricts to prevent food from going up

46
Q

what are the contractile apparatus of smooth muscle?

A

consist of myosin and actin filaments attached to dense bodies in the sarcoplasm or PM plaques

47
Q

what do smooth muscles have instead of t-tubules?

A

caveolae - small flasked-shaped invaginations of the membrane

CAPS 390 (5 decks)

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