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Histology Exam 1 > Muscles > Flashcards

Muscles Flashcards

1
Q

What is a myocyte?

A

individual muscle cell, also called a muscle fiber

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2
Q

What is the name for a muscle cytoplasm?

A

sarcoplasm

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3
Q

What is the name for the plasma membrane/ plasmalemma in a muscle cell?

A

sarcolemma

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4
Q

What are the three types of muscle cells and what are they derived from?

A

skeletal muscle, smooth muscle, and cardiac muscle
mesodermally derived

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5
Q

What is skeletal muscle responsible for?

A

movement of the skeleton; under voluntary motor control

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6
Q

How much of the body mass is skeletal muscle?

A

40%

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7
Q

How long are individual skeletal muscle fibers?

A

80-100 um in diamete and up to 35 cm (1ft)

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8
Q

Characteristics of skeletal muscle cells?

A

multinucleate and form syncytia due to fusion of myoblasts into a mutinucleate myotube during development

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9
Q

What is synyctia?

A

a single cell or cytoplasmic mass containing several nuclei

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10
Q

What happens when nuclei migrate to periphery of cell?

A

they lose the ability to proliferate

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11
Q

What is endomysium?

A

connective tissue that surrounds individual muscle fibers

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12
Q

What is a fasicle?

A

several fibers bound together

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13
Q

What is perimysium?

A

connective tissue that surrounds fascicles

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14
Q

What is many fascicles formed together called?

A

muscle

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15
Q

What is epimysium?

A

connective tissue that surrounds entire muscle - continous with tendinous attachment

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16
Q

What is type 1 fibers?

A

slow myosin
small fibers with large amount of myoglobin
use 1’ aerobic respiration for oxidative metabolism
large # of mitochondria
resistant to fatigue, but generate only moderate muscle tension
common in peripheral limbs

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17
Q

What is type 2 fibers?

A

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

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18
Q

What are intermediate fibers?

A

type 2a = oxidative and fatigue resistant
type 2b = glycolytic and fatigue sensitive

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19
Q

What occurs during periods of peak exertion?

A

type 1 and type 2 fibers metabolize glycogen via anaerobic glycolysis to produce ATP = intermediate metabolites (lactic acid) = precipitate as crystals in muscle cells = tearing of muscle fibers and pain after heavy exertion

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20
Q

What occurs if oxygen debt is severe?

A

ischemia and muscle cramps, even cell death

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21
Q

What is ischemia?

A

an inadequate blood supply to an organ or part of the body

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22
Q

What can extreme exertion lead to?

A

acute rhabdomyolysis (breakdown of actin and myosin)
myoglobinuric nephrosis (kidney failure)

due to release of myoglobin and clogging of glomeruli

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23
Q

What happens to muscle fibers during normal exercise?

A

muscle fibers develop micro-tears

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24
Q

What happens to muscle size during exercise?

A

muscle cells increase in size (hypertrophy) due to increase in mitochondria and increase in volume of contractile proteins (splitting/branching of individual muscle fibers)

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25
Q

What is relatively rare for muscle fibers to do?

A

produce new muscle fibers

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26
Q

What happens to muscle size when muscle is not used efficiently?

A

muscle cells decrease in size (atrophy) due to immobilization (e.g. splint, cast) denervation (nerve damage = muscle atrophy)
with old age, also get progressive loss of skeletal muscle fibers (sarcopenia) not replaced = decrease in number and muscle mass

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27
Q

What are satellite cells?

A

precursors to skeletal muscle cells and are responsible for the ability of muscle tissue to regenerate. ie These embryonic cells remain in the adult and can replace damaged muscle fibers to some degree.

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28
Q

What is something skeletal muscle has limited ability to do?

A

regenerate following injury

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29
Q

What are mechanoreceptors?

A

a sense organ or cell that responds to mechanical stimuli such as touch or sound

their are two types of proprioceptors: neuromuscular spindles and neurotendious spindles

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30
Q

What are intrafusal fibers?

A

modified skeletal muscle fibers associated with modified nerve endings

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31
Q

What are neuromuscular spindles?

A

muscle spindles located within belly of muscles - sensitive to change in length

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32
Q

What are neurotendinous spindles?

A

golgi tendon organs located within tendon - sensitive to changes in tension

Mechanoreceptors

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33
Q

What do neuromuscular and neurotendinous spindles prevent?

A

overstretching and tearing of muscles; used in postural reflexes, coordination

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34
Q

What are myofibrils composed of?

A

numerous myofilaments or contractile proteins in parallel bundles

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35
Q

What are individual muscle fibers composed of?

A

myofibrils

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36
Q

What are the two types of myofilaments?

A

actin (6-8um) and myosin (15um)

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37
Q

Actin and myosin present in what ratio in skeletal muscle?

A

2:1

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38
Q

What is the arrangement of skeletal muscle?

A

parallel arrangement of contractile proteins = striated appearance in longitudinal section

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39
Q

How do actin and myosin cause striations?

A

actin and myosin overlap in A band, but not I band

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40
Q

What are sacromeres?

A

functional units of muscle cells (myofibrils are arranged into sarcomeres)

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41
Q

What acts as anchoring points for actin myofilaments?

A

z-discs

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42
Q

What is the sliding filament theory of muscle contraction?

A

during muscle contraction, sarcomeres shorten, but myofilaments remain same length

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43
Q

What occurs during muscle contraction?

A

due to thick and thin filaments sliding over one another via energy from ATP = shortening of sarcomere, via repeated binding and unbinding of actin and myosin

44
Q

What is the mechanism of muscle contraction referred to?

A

ratchet-like or “walk-along” mechanism

45
Q

What are neuromuscular junctions?

A

sites where skeletal muscles are innervated by motor nerves

46
Q

What is the motor end plate? Rests where and is surrounded by what?

A

a chemical synapse that is formed at the sites where the terminal branches of the axon contact a target muscle cell

rests on sarcolemma and is surrounded by myelin

47
Q

What is a terminal bouton?

A

the specialized presynaptic terminal at the end of an axon

similar to motor end plate, but unmyelinated

48
Q

What is a synaptic cleft?

A

space between motor end plate of nerve and sarcolemma of muscle

it is bridged by the chemical neurotransmitter = acetylcholine

49
Q

How does an action potential move down a t-tubule?

A

electrical stimulation of neuron = influx of sodium into neuron = wave of depolarization down axon = release of neurotransmitter = binding to receptor proteins = wave of depolarization of muscle fibers

50
Q

Define t-tubule. What do they do?

A

transverse tubule system

invaginations of the plasma membrane, which are present exclusively in striated muscle. Their role is to maintain the SR calcium store under the tight control of membrane depolarization via the voltage sensor channel DHPR

51
Q

What are t-tubules continous with?

A

sacrolemma (plasma membrane of skeletal muscles)

52
Q

What do t-tubules indirectly link?

A

extracellular space with ER and intracelular environment

53
Q

What are t-tubules bounded by?

A

enlarged terminal cisternae of ER on either side; forms triad

54
Q

What is the sliding filament mechanism?

A

influx of sodium ions into cytoplasm from t-tubules triggers depolarization of sacrolemma = release of calcium from ER and terminal cisternae into cytoplasm during contraction

55
Q

What acts as a Ca reservoir during muscle relaxation? What is necessary during muscle contraction?

A

sarcoplasmic reticulum and terminal cisternae acts as Ca reservoir
Calcium is necessary for muscle contraction

56
Q

What does Ca cause when released for contraction?

A

conformational change in troponin, which interacts with tropomyosin molecules (bound to actin), exposing myosin-binding site on actin filament

57
Q

Myosin binding causes conformational change in what?

A

myosin head and sliding of myosin past actin

58
Q

What causes contraction in a muscle?

A

myosin heads repeatedly bind and unbind to actin in presence of Ca and Pi, causing contraction

59
Q

What is a specific function of skeletal muscle fibers?

A

exhibit all or nothing response - either contract or doesn’t

60
Q

What determines the strength of overall contraction?

A

total number of muscle fibers contracting (graded response)

61
Q

What is a motor unit?

A

a group of muscle fibers supplied by single motor neurons

62
Q

What causes contraction of all muscle fibers within a motor unit?

A

stimulation of a motor neuron

63
Q

What is recruitment in skeletal muscles?

A

the process by which different motor units are activated to produce a given level and type of muscle contraction

WHICH - increases the number of motor units firing within a muscle

64
Q

What is muscular dystrophy? What causes it?

A

degenerative wasting disease = muscle weakness due to genetic defect in muscle protein = cell death

cause = defect in dystrophin protein

65
Q

What is dystrophin?

A

part of a group of proteins (a protein complex) that work together to strengthen muscle fibers and protect them from injury as muscles contract and relax

66
Q

What is myasthenia gravis? What is used to treat it?

A

autoimmune disease caused by production of antibodies to acetylcholine receptors = muscle weakness

drugs that are used to treat myasthenia gravis act on acetylcholinesterase to stop the breakdown of acetylcholine

67
Q

What is acetylcholineesterase? What does it do? What do Achase inhibitors do?

A

Some acetylcholinesterase breaks down acetylcholine.

acetylcholinesterase inhibitors increase the amount of acetylcholine available and so help muscle activation and contraction

68
Q

What kind of contractility is used in smooth muscles?

A

inherent contracticility - rhythmic, wave-like contractions independent of neurological stimulation (peristalsis)

69
Q

How are smooth muscle fibers arranged? What are they specialized to do?

A

bound together into highly irregular, branching fascicles, specialized for prolonged contractions with low force

70
Q

What size are smooth muscles? What is a distinct characteristic of them? What do they look like on a stain?

A

smaller than skeletal muscle (2um and 2-200um long)

single, central nuclei with the same organization of muscle fibers as skeletal muscle - endo, peri, and epimysium

in pictures- rounded edges, tightly packed nuclei, and uniform in size - commonly confused with connective tissue

71
Q

What is the ratio of actin: myosin in smooth muscle?

A

15:1 ratio, but randomly arranged

72
Q

Do smooth muscle have striations? What are other features of smooth muscle that are important to know?

A

No. Myofilaments (actin and myosin) are not arranged in sacromeres, rather they are intracytoplasmic structures called dense bodies.

73
Q

What are dense bodies?

A

Dense bodies are functionally equivalent to z-discs in skeletal muscle - provide attachment sites for actin

found in smooth muscle

74
Q

What does smooth muscle lack? What does it use to activate myosin?

A

lacks: troponin complex that controls myosin binding, t-tubule system, and terminal cisternae of ER

uses calmodulin - binds calcium and activates myosin cross-binding

75
Q

What does the cell membrane of smooth muscle contain? What does smooth muscle rely on?

A

cell membrane has caveolae
relies on diffusion of extracellular calcium for contraction

76
Q

What is smooth muscle influenced by? What kind of innervation does it have?

A

autonomic nervous system, hormones, and local metabolites

most smooth muscle has dual sympathetic and parasympathetic innercation and is involuntary - response depends on receptor type (alpha or beta)

77
Q

Smooth muscle of the gut has what kind of innervation?

A

sympathetic stimulation (fight or flight) = inhibitory
parasympathetic stimulation (rest or digest) = stimulatory

78
Q

Smooth muscle can be single unit or multi unit - what does that mean?

A

single unit = tonic smooth muscle = fibers contract as a unit (ex: visceral sm mm of gut)

multi unit = phasic smooth mm = individual m fibers contract independently (ex: erector pili mm)

79
Q

What is an ability of smooth muscle? What can smooth muscle cells develop from?

A

retains ability to divide and repair itself following injury

develop from endothelial cells, pericytes of blood vessels, and fibroblasts

80
Q

What are myoepithelial cells?

A

glandular epithelial cell differentiation

thin layer above the basement membrane but generally beneath the luminal cells

81
Q

What is cardiac muscle? What is it surrounded by?

A

(or myocardium) makes up the thick middle layer of the heart

myocardium is surrounded by a thin outer layer called the epicardium (AKA visceral pericardium) and an inner endocardium

82
Q

What is the outer/inner layer of cardiac muscle made up of?

A

outer, fibrous, connective tissue layer and inner serous layer (continous with epicardium) containing mesothelial cells

83
Q

What does the pericardium contain? What is it used for?

A

pericardial fluid
lubrication

84
Q

What is the epicardium?

A

outermost layer
simple squamous mesothelium on external surface of heart

85
Q

What is the epicardium supported by?

A

underlying fibroblastic connective tissue and adipose tissue

86
Q

Where are blood vessels and nerves located in cardiac muscle?

A

within subepicardial layer

87
Q

What is the heart protected by?

A

adipose tissue layer

88
Q

What is myocardium? What does it contain?

A

cardiac myself itself, thicker in ventricles than atria

endo, peri, and epimysium

89
Q

What is myocardium composed of?

A

thick, collagenous, connective tissue skeleton composed of fibroblasts and collagen

90
Q

What are the features of cardiac myocytes?

A

one centrally located nucleus (ocassionally two)

fibers are striated, but involuntary (autonomic control)

91
Q

What is the arrangement of contractile proteins in cardiac mm?

A

into sarcomeres similar to skeletal muscle - but contain intracellular dead, not triad, composed of one t-tubule and one cisterns of ER, located at z-disc

(skeletal muscle has 2 cisternae and t-tubules

92
Q

What is endocardium? What is it supported by? What fibers are present in it?

A

lines atria and ventricles, covers heart valves, simple squamous endothelium

supported by sub endothelial fibroblastic connective tissue, interspersed with reticular fibers and smooth muscle

thicker in atria than vesicles

purkinje fibers located within subepi- and endocardial layers

93
Q

What is lamina fibrosa?

A

layer of fibrous connective tissue that covers cardiac valves which are covered by endothelium

94
Q

What is os cordis?

A

a large constant bone lying near the junction of the interatrial and interventricular septa of the beef heart and extending anteriorly into the AV valve rings, especially the right

95
Q

What are intercalated discs?

A

unique to cardiac muscle, specialized connections between cells
enhance spread of contractile stimulus between cells
allow synnchronous contrations

also provide increased surface area for attachment of myofibrils between adjacent cells

96
Q

What are intercalated discs made up of?

A

cell junctions = desmosomes, fascia adherens, and gap junctions

97
Q

What are desmosomes?

A

bind individual myocytes together laterally and on ends

98
Q

What are fascia adherens?

A

like zonula adherens, but join ends of muscle fibers

99
Q

What are gap junctions?

A

located laterally, provie ionic communication between cells, synchronize contractions, and allow muscle to behave as syncitium

100
Q

What does the conduction system of the heart consist of

A

SA node, AV node, Bundle of His, and Punkinje fibers

all consist of highly modified cardiac myocytes that coordinate conduction, joined by extensive gap junctions

101
Q

Why are conduction systems paler colored when stained in comparison to surrounding muscle?

A

due to higher glycogen content

102
Q

What is the SA node? Where is it located? What does it generate?

A

“pacemaker”
located at junction of superior vena cava and RA
generates impulses that induce contraction of atria

103
Q

What stimulates the AV node? Where is it located? What does it do?

A

impulse traveling across atria
located between RA and V
delays impulse, gives atria time to contract

104
Q

What is the interventricular septum? How does conduction travel through it?

A

separates the left ventricle and the right ventricle
impulse travels down the IVS via bundle of His into L and R Av bundles within IVS

105
Q

After the interventricular septum, where does the conduction travel to?

A

fibers further subdivide in ventricular myocardium and ramify into Purkinje fibers within subendo- and subepicardium of ventricular free wall, gradually merge with myocardium, initiate ventricular contraction

106
Q

What is the rhythm of the SA node modulated by?

A

autonomic nervous system

sympathetic stimulation = from sympathetic ganglia increase per hour

parasympathetic stimulation = from vagus nerve decrease per hour

Histology Exam 1 (6 decks)

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