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histology exam 1 > skeletal muscle > Flashcards

skeletal muscle Flashcards

1
Q

myocyte

A

indiv. muscle cell

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2
Q

muscle fiber

A

many myocytes fused together

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3
Q

myofibrils

A

contractile elements

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4
Q

sarcoplasm

A

muscle cytoplasm

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5
Q

muscle plasma membrane

A

sarcolemma

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6
Q

skeletal muscle appearance

A

-cells are multinucleate
-nuclei migrate to periphery of cell
-striated fibers
-assembled into sarcomeres

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7
Q

can skeletal muscle proliferate?

A

no

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8
Q

endomysium

A

CT that surrounds individual muscle fibers

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9
Q

fascicles

A

several fibers bound together

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10
Q

perimysium

A

CT that surrounds fascicles

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11
Q

muscle

A

formed from many fascicles

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12
Q

epimysium

A

CT that surrounds entire muscle, continuous with tendinous attachment

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13
Q

where do blood vessels tend to follow in skeletal muscle?

A

along CT (epi- and perimysium for support)

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14
Q

two major types of skeletal Mm fibers

A

fast twitch & slow twitch

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15
Q

type I skeletal muscle fibers

A

slow twitch

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16
Q

slow twitch fibers

A

-“slow” myosin
-small fibers w/ large amount of myoglobin
-use 1’ aerobic respiration for oxidative metabolism
-large # of mitochondria (ATP for energy)
-resistant to fatigue
-generate only moderate muscle tension
-common in peripheral limbs

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17
Q

type II skeletal muscle fibers

A

fast twitch

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18
Q

fast twitch fibers

A

-“fast” myosin
-large fibers with less myoglobin & fewer mitochondria
-use 1’ anaerobic glycolysis for energy production
-abundant glycogen
-extensive sarcoplasmic reticulum for rapid Ca release
-fatigue rapidly, but generate high muscle tension for short bursts of activity

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19
Q

what types of skeletal muscle fibers present in muscle?

A

both (type I and type II)

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20
Q

where are you most likely to see more type I skeletal muscle fibers?

A

in muscles used constantly
ex: leg muscles for standing

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21
Q

type IIA skeletal muscle fibers

A

oxidative & fatigue resistant

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22
Q

type IIB skeletal muscle fibers

A

glycolytic & fatigue sensitive

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23
Q

what happens during peak periods of exertion for skeletal muscle?

A

both type I and type II fibers metabolize glycogen via anaerobic glycolysis to produce ATP –> intermediate metabolites (e.g., lactic acid) –> precipitate as crystals in Mm –> tearing of Mm fibers & pain after heavy exertion

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24
Q

what happens during severe oxygen debt?

A

ischemia, muscle cramps, and even cell death

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25
Q

extreme exertion can lead to…

A

rhabdomyolysis (breakdown of actin & myosin) & subsequent kidney failure due to release of myoglobin & clogging of glomeruli

26
Q

during normal exercise Mm fibers can develop…

A

micro-tears

27
Q

hypertrophy

A

increase in cell size

28
Q

what causes hypertrophy of muscle cells?

A

exercise causes an increase in number of mitochondria & increase in volume of contractile proteins; splitting & branching of individual Mm fibers

29
Q

hyperplasia

A

production of new Mm fibers
relatively rare

30
Q

atrophy

A

decrease in cell size

31
Q

what causes atrophy of muscle cells?

A

-disuse
-immobilization can cause denervation

32
Q

sarcopenia

A

loss of skeletal muscle fibers and Mm mass
comes with increasing age

33
Q

satellite cells

A

-small cells adjacent to sarcolemma
-proliferate following injury and then differentiate into myoblasts

34
Q

what are the two types of mechanoreceptors in skeletal muscle?

A

neuromuscular spindles & neurotendinous spindles

35
Q

what do mechanoreceptors do in skeletal muscle?

A

-prevent overstretching & tearing of Mm
-used in postural reflexes
-coordination

36
Q

neuromuscular spindles

A

-located within belly of Mm
-sensitive to changes in length

37
Q

neurotendinous spindles

A

-located within the tendon
-sensitive to changes in tension

38
Q

skeletal muscle ultrastructure

A

-individual Mm fibers composed of myofibrils
-myofibrils composed of numerous myofilaments (or contractile proteins) in parallel bundles
-myofibrils arranged in sarcomeres

39
Q

what are the two types of myofilaments?

A

actin & mysoin

40
Q

actin

A

thin filament

41
Q

myosin

A

thick filament

42
Q

sarcomere structure

A

-A band: actin & myosin overlap
-I band: only actin
-Z-discs: located in I band
-M line: middle line of sarcomere; located in A band

43
Q

Z-discs

A

act as anchoring points for actin myofilaments

44
Q

during Mm contraction ___ shorten, but ____ remain the same length

A

sarcomeres; myofilaments

45
Q

sliding filament theory of Mm contraction

A

-thick & thin filaments slide over one another via energy from ATP
-sarcomere is shortened due to repeated binding & unbinding of actin & myosin filament
-ratchet-like, or “walk-along” mechanism

46
Q

neuromuscular junction

A

site where skeletal muscle innervated by nerves

47
Q

motor end plate (NMJ)

A

terminal portion of axon surrounded by myelin that rests on sarcolemma

48
Q

terminal bouton

A

similar to motor end plate by unmyelinated

49
Q

synaptic cleft

A

space b/w motor end plate & sarcolemma

50
Q

what bridges the synaptic cleft?

A

chemical neurotransmitter
generally acetylcholine

51
Q

transverse tubule system (T-tubules)

A

-extensive network of tubules continuous with sarcolemma
-indirectly links extracellular space with ER & intracellular environment

52
Q

triad

A

ends of T-tubules bounded by terminal cisternae of ER on either side

53
Q

what travels down the T-tubules?

A

electrical stimulation of neuron –> influx of Na+ into neuron –> wave of depolarization down axon –> release of neurotransmitter, binding to receptor proteins –> wave of depolarization of Mm fiber

54
Q

Ca reservoirs in skeletal muscle

A

sarcoplasmic reticulum & terminal cisternae

55
Q

sliding filament mechanism

A

influx of Na+ ions into cytoplasm from T-tubules triggers depolarization of sarcolemma –> release of Ca from ER & terminal cisternae into cytoplasm during contraction –> Ca causes conformational change in troponin, which interacts with tropomyosin (bound to actin), exposing myosin-binding sites on actin filament –> myosin binding causes conformational change in myosin head & sliding of myosin past actin
myosin heads repeatedly bind & unbind to actin in presence of Ca and Pi, causing contraction

56
Q

what ions activate sliding filament mechanism?

A

Ca

57
Q

each muscle fiber exhibits what type of response?

A

all or none; either it contracts or it doesn’t

58
Q

graded response

A

total number of muscle fibers contracting @ any given time determine strength of overall contraction

59
Q

motor unit (skeletal muscle)

A

-group of muscle fibers supplied by single motor neuron
-stimulation of a motor neuron results in contraction of all muscle fibers within that motor unit

60
Q

recruitment (skeletal muscle)

A

increase in number of motor units firing within a muscle

61
Q

muscular dystrophy

A

-degenerative wasting disease
-Mm weakness due to genetic defect in Mm protein
-can cause cell death
-one form affects the protein dystrophin

62
Q

myasthenia gravis

A

-autoimmune disease caused by production of antibodies to Ach receptors
-causes Mm weakness
-treatment with Achase inhibitors

histology exam 1 (13 decks)

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