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Histology > Muscle Tissue > Flashcards

Muscle Tissue Flashcards

1
Q

Cardiac muscle blood supply

A

-receives extensive blood supply through a network of capillaries

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2
Q

F-actin

A

-double-stranded helical filament (composed of G-actin)

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3
Q

Sarcomere characteristics

A
  • portion of a myofibril between two adjacent Z-disks
  • basic contractile unit of skeletal muscle
  • measures 2-3 microns
  • sarcomere of individual myofibrils are in register in one muscle fiber, so the entire muscle cell exhibits cross-striations.
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4
Q

Smooth muscle contraction

A
  • driven by the high Ca++ concentration in the sarcoplasm

- relaxed muscle cells the highest concentration of Ca++ is in the sarcoplasmic reticulum

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5
Q

Smooth muscle fibers in the dermis of the skin

A

-attached to the hair follicles and form so called arrectores pilorum muscles

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6
Q

Troponin T binds to?

A

-binds to tropomyosin, anchoring the Troponin complex

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7
Q

T-tubular system

A
  • formed by deep invaginations of the sarcolemma

- allow the impulse to travel down into the cell and excite the terminal cisternae of the sarcoplasmic reticulum

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8
Q

Lateral portion of intercalated disks

A
  • runs parallel to the myofilaments
  • contains communication, of gap junctions that provide ionic continuity b/t adjacent cardiac muscle cells and allow the signal to contract to pass from cell to cell and generate a wave of contraction
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9
Q

I-band

A
  • pale area formed primarily by thin filaments
  • proteins such as Titian and nebulin are also found in the I-band
  • is bisected by the Z-line (Z-disk)
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10
Q

Fascicles

A

-formed by connective tissue sheath

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11
Q

Reticular fibers of smooth

A

-important role in the force transduction in the smooth muscle tissue

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12
Q

Myoglobin

A
  • an oxygen-binding protein

- gives muscle it’s red color. May store glycogen. DM pt’s can lower sugar by working out

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13
Q

2 principle components of myofibril

A

-thick and thin filaments

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14
Q

Excitation of smooth muscle

A
  • neural stimulation occurs through the postganglionic fibers of the autonomic nervous system
  • neurotransmitter is released in the close proximity of a muscle cell and has to diffuse to the muscle sells through the CT that surrounds the muscle cells
  • impulse transmission from cell to cell occurs through gap junctions
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15
Q

Nuclei of smooth muscle

A
  • centrally placed and long (cigar-shaped) with tapered ends

* similar looking to fibroblasts

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16
Q

What does conductivity allow muscle cells to do?

A

-allows muscle cells to transmit electrical impulse to other cells and to receive impulses from nerve cells.

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17
Q

Two pairs of Myosin II light chains?

A
  • attach to the heads.

- they are essential and regulatory (structural support)

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18
Q

Organization of skeletal muscles

A

-consist of fascicles or bundles of skeletal muscle fibers surrounded by a connective tissue sheath

Ex. Biceps->fascicles->skeletal muscle fiber (cell)->myofibril->myofilaments (thin/thick)

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19
Q

Nuclei of skeletal muscle cells?

A
  • are peripheral in location and are found immediately beneath the sarcolemma.
  • are peripheral because they are pushed near sarcolemma by myofibrils. This is unique to skeletal muscle
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20
Q

Gower’s sign

Trendelenburg (waddling) gait

A
  • use forelimbs to push off hindlimbs to erect pelvis and upper body.
  • variation of muscle fibers
  • CT taking up place of fibers (endomysial)
  • nuclei in abundance means inflammation
  • numerous macrophages

Signs of Duchenne muscular dystrophy

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21
Q

Troponin C binds to?

A
  • binds to Ca++, which is an essential step in the initiation of the muscular contraction.
  • smallest subunit
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22
Q

What 3 things does sarcoplasm of skeletal muscle cells contain?

A
  • numerous myofibrils (found inside of fibers)
  • numerous filamentous mitochondria
  • myoglobin
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23
Q

Thick filament are formed by?

A
  • formed by hundreds of myosin molecules.

- Myosin II molecules is the muscle myosin

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24
Q

Skeletal muscle contraction

A
  1. resting muscle cell, myosin-binding site on the actin filament is concealed by tropomyosin filament
  2. Presence of high concentration of Ca++ ions, Ca++ binds to Troponin C
  3. Changes the spatial configuration of the Troponin molecule and causes the tropomyosin filament to shift->opens myosin-binding site on the actin filament
  4. Myosin starts “walking” along the actin fibers
  5. Myosin uses ATP to slide the actin along, myosin is an ATPase
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25
Q

How is a skeletal muscle fiber (skeletal muscle cell) formed?

A

-“cells” of the skeletal muscle is actually a multinucleated syncytium.

Syncytium is cytoplasm that is shared

-takes a long time and a lot of effort to repair

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26
Q

Thick filament (smooth)

A

-formed by Myosin II

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27
Q

Troponin I binds to?

A

-binds to actin inhibiting the interaction with myosin

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28
Q

Mechanical stimulation of smooth

A

-passive stretching of the organ, can lead to the initiation of a muscular contraction

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29
Q

Long-term contraction of smooth muscle

A

-secondary mechanism that requires minimum energy

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30
Q

Satellite cells

A
  • after injury they become activated, proliferate and give rise to new myoblasts, which fuse to from a new fiber
  • extensive damage results in the formation of a CT scar
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31
Q

6 types of accessory proteins found in the skeletal muscle

A
  • Titin (thick)
  • Myomesin (thick)
  • Alpha-Actinin
  • Nebulin
  • Desmin
  • Dystrophin
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32
Q

Arrangement of microfibrils

A
  • composed of thin and thick filaments

- thin (actin) filaments are arranged in a hexagonal array with 6 thin filaments surrounding 1 thick (myosin) filament

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33
Q

Depolarized membrane of sarcolemma

A
  • develops a positive membrane potential when it becomes more permeable for Na+ ions
  • depolarization of membrane of muscle cell starts a cascade of reactions that cause muscular contraction
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34
Q

Epimyseum

A
  • most external thick layer of connective tissue that surrounds a group of fascicles that constitutes a named muscle
  • dense CT collagen type 1
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35
Q

Filamentous mitochondria location and function?

A
  • lie between myofibrils and close to the sarcolemma.

- represent the source of ATP for the myofibrils

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36
Q

Adherens junctions (fasciae adherentes) of transverse portion of intercalated disks

A
  • connect the microfilaments of the two neighboring cardiac muscle cells.
  • similar to the zonula adherentes found in the epithelial cells
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37
Q

Myofibril

A
  • make up skeletal muscle fiber.
  • extend the whole length of the muscle fiber.
  • individual myofibril is striated
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38
Q

Dystrophin

A

-membrane-associated protein complex that links actin cytoskeleton to the extracellular matrix stabilizing the thin filaments

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39
Q

Myomesin

A

-holds the thick filaments in register at the M-line

Note: M-line runs through the middle of the H-zone

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40
Q

M-line

A

-line formed by accessory proteins, such as myomesin that hold the thick filaments in register

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41
Q

Nebulin

A
  • attached to the Z-disk and runs parallel to thin filaments.
  • anchor the thin filaments and to regulate the length of thin filaments during muscular fiber development
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42
Q

T-tubules of cardiac muscles

A
  • large and found at the Z-disks and not at the junction of A and I bands like skeletal muscle fibers
  • contraction is Ca++ dependent and similar to contraction of skeletal muscle
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43
Q

Skeletal muscle origin?

A

-originate from myoblasts (myocytes line up) that fuse with each other to form long multinucleated postmitotic myotubes

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44
Q

What causes muscle contractility?

A
  • actin
  • myosin
  • ATP
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45
Q

Skeletal muscle that is attached to bone function

A

primarily for locomotion, respiration, and other functions

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46
Q

Latch state of smooth muscle

A
  • caused by the decrease of ATP activity while the myosin head is attached to actin
  • causes prolonged contraction used to sustain the tone of blood vessels
  • condition resembles the rigor Morris of the skeletal muscle
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47
Q

Two heavy chains of Myosin II characteristics?

A
  • form coiled alpha-helices and two globular heads that exhibit ATPase and motor activity.
  • globular heads contain binding sites for actin and ATP
  • is a dimer
48
Q

Sarcoplasm of smooth muscle

A
  • contains myofilaments and organelles (numerous mitochondria)
  • myofilaments of smooth muscle cells are more randomly distributed throughout the cytoplasm than in skeletal muscle and are poorly organized
49
Q

How does muscle respond to:
Aging?
Exercise?
Disuse?

A
  • increasing in diameter
  • hypertrophy
  • atrophy
50
Q

What causes skeletal muscle striation?

A

-due to arrangement of filaments in the cytoplasm

51
Q

Cardiac muscle fibers arrangement

A
  • fibers are formed by individual cells that are about 100 micrometers long
  • different from the skeletal muscle fibers, which are formed by a syncytium
52
Q

What does Myosin II consist of?

A
  • 2 heavy chains

- 2 light chains

53
Q

Microstructues of a muscular fiber

A

-composed of hundreds of myofibrils that span the entire length of the muscle cell

54
Q

Excitation of smooth muscle steps

A
  1. Ca++ is releases into sarcoplasm
  2. Ca++ binds calmodulin (specific to smooth muscle)
  3. Ca++/calmodulin complex binds to caldesmon releasing it from actin and opening the myosin-binding site on F-actin
  4. Ca++/calmodulin complex activates myosin light-chain kinase (has to unfold)
55
Q

Chemical stimulation of smooth muscle contraction

A

-elicited by various hormones, angiotensin II (kidney), vasopressin, etc

56
Q

Smooth muscle (simplest type of muscular tissue) characteristics?

A
  • does not exhibit cross striation in the cytoplasm, contractile filaments are not well organized inside the cell
  • specialized for slow/rhythmic prolonged contractions of visceral organs, can provide rapid and precise contraction (eye)
  • involuntary
57
Q

Specialized plasmalemma (plasma membrane) term?

A

-sarcolemma

58
Q

Tropomysin

A
  • forms filaments that lie in the grooves between the two actin monomers.
  • in the resting muscle tropomyosin masks the myosin-binding sites on the actin filament (sits over the actin binding site)
59
Q

Smooth muscle regeneration and blood supply

A
  • moderate blood supply through capillaries in the CT immediately surrounding the muscle cells (uses less energy than skeletal and cardiac)
  • capable of active regenerative response. Can go through mitosis and replace the damaged or lost cells
60
Q

Transverse portion of intercalated disks

A
  • runs across the fiber at a right angle, contains anchoring junctions that provide mechanical stability for the tissues and prevent cells from being pulled apart during contraction
  • two parts: adherens junctions and desmosomes
61
Q

H-zone

A
  • pale area in the middle of the A-band that contains thick filaments
  • has no thin filaments
62
Q

Microstructure of a myofibril

A

-myofibril exhibits striations formed by alternating dark (A-bands) and light (I-bands) regions

A=anisotropic (same value when measured in different directions)
I=isotropic (different value when measured in different directions)

63
Q

Purkinje fibers

A
  • cardiac conduction cells
  • modified for the conduction of electric impulses in a way similar to nerve cells
  • from nodes and bundles including the sinoatrial and atrioventricular nodes and the bundle of His
64
Q

Titin

A
  • largest protein that anchors the thick filaments to the Z-disk
  • extends to the M-line
  • function is to keep the thick filaments in their position in the central part of the sarcomere
65
Q

Membrane triads

A
  • formed by sarcolemma and the sarcoplasmic reticulum.

- on triad consists of one T-tubule and two cisternae of sarcoplasmic reticulum running parallel to it

66
Q

Z-line (Z-disk)

A
  • composed of accessory proteins and its major function is to provide anchoring points for thin filaments and to support the architecture of the myofibril
  • bisects I-band
67
Q

Smooth muscle in walls of larger hollow organs:

A
  • walls of veins, arteries and lymphatic vessels
  • extramural part of large ducts of glands
  • GI tract, from distal esophagus to the anal canal
  • M/F reproductive tract (ductus deferents, uterus, vagina)
  • urinary system (bladder, ureter)
68
Q

Cardiac muscle regeneration

A
  • no ability of regeneration
  • localized injury result in the replacement of muscle cells with fibrous CT that forms a scar
  • function is lost in area of scar
  • injury and repair is seen in the myocardial infarction
69
Q

What do accessory proteins do?

A

-provide attachment of filaments to the Z-disk and attachment of Z-disks to each other and to the sarcolemma.

70
Q

Dense bodies of smooth muscle

A
  • anchoring points of thin filaments, formed by a-actinin.
  • are anchored into the network of intermediate filaments by desmin
  • dense bodies are somewhat analogous to the Z-disks of skeletal muscle fibers
  • thick filaments are scattered throughout the sarcoplasm
71
Q

Skeletal muscle innervation?

A

-voluntary

72
Q

Desmin

A

-an intermediate filament that forms a lattice that surrounds Z-disks and attaches them to one another and also attaches Z-disks to the plasma membrane

73
Q

Where are accessory proteins found?

A

-primarily in the Z-disk and in the M-line

74
Q

What happens in phosphorylation in smooth muscle contraction?

A

-myosin light-chain kinase phosphorylares the regulatory (light) chain of the myosin molecule
-when light regulatory chain is phosphorylated, myosin molecule unfolds and actin-binding site on the myosin head becomes open and myosin binds to actin
A. Filaments slide at an angle
B. Cell shortens, nucleus folds and becomes corkscrew-shaped
C. Slow action (1 second) ant it often takes over a second to achieve the contraction

75
Q

Action potential of muscle cell

A

-brief positive going changes in the membrane potential that are propagated along the length of the membrane at a speed up to 120 m/sec

76
Q

F-actin and tropomyosin (smooth)

A

F-actin: principal component of thin filaments in the smooth muscle
Tropomyosin: wraps around actin in a fashion similar to skeletal muscle
-no troponin is present in the thin filaments of smooth muscle

77
Q

Communicating junctions of smooth muscle

A
  • found interconnecting individual muscle cells
  • small molecules or ions can pass through junctions from cell to cell and regulate contraction of the entire bundle of muscle cells
  • can initiate contraction of neighboring muscle cells by allowing ions to pass through gap junctions and depolarize plasma membranes of other cells
78
Q

Proteins that make up thin filaments

A
  • F-actin
  • Tropomysin
  • Troponin complex (Troponin T, I, and C)
79
Q

Visceral skeletal muscle location and function

A
  • tongue, pharynx, and the proximal 1/3 of esophagus.

- aid with swallowing and speech

80
Q

Characteristics of skeletal muscle fibers?

A
  • numerous cross striations
  • voluntary
  • are quick, but usually get tired fast: use up energy quick
81
Q

Endomysium

A

-most internal layer of reticular fibers that surround individual muscle fibers

82
Q

Location of smooth muscles (broad)

A
  • walls of larger hollow organs
  • iris and ciliary body
  • present in dermis of skin
83
Q

Smooth muscle of iris and ciliary body

A

-responsible for the constriction and dilation of the pupil

84
Q

Cardiac conducting system

A

-heartbeat is initiated, coordinated, and regulated by modified cardiac muscle cells that form the cardia conducting system

85
Q

A-band

A
  • Contains both thick and thin filaments.
  • central part is called the H-zone (only thick filaments)
  • overlap b/t thick and thin filaments cause darker part of A-band
86
Q

Sarcoplasmic reticulum

A
  • highly speacialized form of smooth endoplasmic reticulum and is used as a depot of Ca++
  • when excited, the sarcoplasmic reticulum releases Ca++ into cytoplasm initiating the muscular contraction
87
Q

Smooth muscle fiber location? Striated? Innervation?

A
  • found in the walls of the internal organs (GI tract and middle walls of blood vessels)
  • do not show striations in the cytoplasm
  • involuntary
88
Q

Specialized smooth endoplasmic reticulum term?

A

-sarcoplasmic reticulum

89
Q

Cardiac muscle cell organelles

A
  • centrally placed rounded nuclei
  • myofibrils pass around the nucleus outlining a nuclear region where most organelles, including numerous mitochondria are concentrated, as well as inclusions, such as glycogen granules
  • large flattened mitochondria are densely packed b/t the myofibrils
90
Q

Troponin complex, what does it attach to?

What are the three globular subunits?

A
  • -attached to tropomysin
  • Troponin T, Troponin I, Troponin C

FYI: tested for for possible MI

91
Q

Fusiform cells

A

-smooth muscle cells are elongated spindle shaped (fusiform cells) and are 20-200 micrometers in length (20 in walls of small blood vessels and 500 in the pregnant uterus)

92
Q

Skeletal muscle location

A

-attached to the skeleton and are also present in some visceral organs.

93
Q

Caveolae-like invaginations of sarcolemma

A
  • act as sarcolemmal vesicles and deliver the depolarization to the chambers of sarcoplasmic reticulum, located beneath the caveolae
  • may act similar to T-tubules of skeletal muscle
94
Q

Desmosomes (maculae adherentes) of the transverse portion of intercalated disks

A

-connect intermediate filaments (formed by desmin) of two adjacent cells

95
Q

Skeletal muscle contraction

-What happens with the I and A band? H-zone?

A
  • due to the sliding of filaments which results in the shortening of the sarcomere, while the length of individual filaments does not change
  • length of A-band does not change during contraction
  • I-band and H-zone shrink during contraction due to the increase of overlap between thick and thin filaments
96
Q

Action potential

A
  • travels along the membrane

- descends down into the cell along the T-tubules, which causes excitation of the SR and release of Ca++ into sarcoplasm

97
Q

Skeletal muscle relaxation

A
  1. Following depolarization, Ca++activated ATPase membrane pumps transport Ca++ back into the sarcoplasmic reticulum. Ca++ disassociates from the Troponin C
  2. Troponin complex returns to its original configuration and pulls the tropomyosin filament over the myosin binding site blocking the actin-myosin interaction. This stops the contraction unless there are new waves of depolarization coming with the nerve impulses
  3. Rapid action that only takes 30 msec
98
Q

Cardiac muscle fiber location? Innervation?

A
  • found in the heart
  • striated
  • involuntary

FYI: Evolved from smooth muscle but structurally like skeletal muscle

99
Q

Caldesmon

A
  • smooth muscle-specific actin-binding protein that masks the myosin-binding site on the actin fibers
  • opens Ca++ binding site when Ca++ is near
100
Q

Terminal cisternae (formed by long chambers of sarcoplasmic reticulum)

A
  • run parallel to the T-tubules on both sides
  • contain high concentration of Ca++ ions
  • running near the boundary of A-band and I-band
101
Q

Alpha-Actinin

A

-anchors thin filaments into the Z-disk

102
Q

Smooth muscle relaxation

A
  • Ca++ is pumped back into sarcoplasmic reticulum
  • Ca++ levels in the sarcoplasm drop
  • Calmodulin disassociates from the light-chain kinase, which deactivates the latter
  • myosin is dephosphorylated and becomes inactive (folds to cover actin binding site)
  • Caldesmon binds to the myosin-binding site on the actin filament
  • slow action, has a prolonged effect on the tissue and requires very little energy spent compared to the skeletal muscle (10% of ATP that skeletal muscle uses)
103
Q

Sarcoplasmic reticulum of cardiac muscle

A
  • not as well-developed as in the skeletal muscle
  • no large terminal cisternae; instead there are small chambers that run parallel to the T-tubules only on one side of the tubule forming diads
104
Q

Myosin II of smooth muscle

A
  • composed of two heavy polypeptide chains and four light chains
  • only binds to actin when phosphorylated
  • Myosin molecule is folded (inactive!) when dephosphorylated
105
Q

Muscle cells of cardiac

Shape and arrangement?

A
  • rectangular in outline
  • formed by long chains of muscle cells that attach to each other like cars in a train
  • connections b/t individual cells are marked with intercalated disks
  • when two cells attach there is branching of muscle fibers
106
Q

Cardiac muscle characteristics

A
  • exhibit cross-striations (same arrangement of contractile filaments as skeletal)
  • involuntary (rhythmic contractions to pump blood through the cardiovascular system)
107
Q

Connective tissue role in muscles?

A
  • protection and force transduction

- provides passage for nerves and blood vessels that supply the muscle

108
Q

Most smooth muscle is slow, what smooth muscle is fast?

A
  • ciliary muscle of the eye is fast

- erector pili of the skin is also smooth muscle

109
Q

Electric capacitor of Sarcolemma

A
  • voltage inside cell is negative
  • outside cell is 0
  • is a negative membrane potential in a resting cell, achieved by actively pumping Na+ ions out of the cell
110
Q

Perimysium

A

-thicker layer of collagenous connective tissue that surrounds groups of muscle fibers, known as fascicles

111
Q

Sarcolemma of skeletal muscle fibers forms long process called ______? What is _____ important for?

A

T-tubules. (Only found in skeletal muscle)

T-tubules that extend into the cytoplasm are important for carrying the wave of depolarization deep into the sarcoplasm.

FYI: action potential in a neuron is along the surface. In muscle cells the action potential runs inside the cell through T-tubules

112
Q

Cytoplasm of muscle cells term?

A

-sarcoplasm

113
Q

Intercalated disks of cardiac

A
  • represent junctions b/t individual muscle cells

- step-like Junction that consists of transverse and lateral portions

114
Q

Skeletal muscle fiber

A

-multinucleated cell or syncytium

115
Q

Thin filaments of smooth muscle

A

-similar to skeletal but w/out Troponin complex

116
Q

Arrangement of contractile filaments within the myofibrils?

A
  • arrangement is regular and gives the myofibrils “striated” appearance.
  • all the myofibrils are in register within the skeletal muscle fiber, so the whole fiber exhibits characteristic transverse striations.

Histology (5 decks)

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