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Skin MS: Week 4 > Histology of Muscle > Flashcards

Histology of Muscle Flashcards

1
Q

General Features of Skeletal Muscle

A
  1. striated (voluntary)
  2. T-tubule system
  3. well-developed sarcoplasmic reticulum
  4. multinucleated
  5. nuclei located at cell periphery (just inside sarcolemma)
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2
Q

A band

A

broad, dark-staining band

anisotropic

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3
Q

I band

A

narrower, light-staining band

isotropic bond

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4
Q

Z-disk

A

dense-staining, narrow

bisects I band

distance between two Z-disks = sarcomere

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5
Q

H band

A

pale-staining, narrow

bisects A-band

Located at the middle of the sarcomere

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6
Q

M-line

A

thin

bisects H band

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7
Q

Functional unit of the myofibril

A

sarcomere

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8
Q

Sarcomere length varies as a function of degree of ________

A

contraction of muscle cell

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9
Q

Actin filaments

A

thin

extend from Z-disks to edge of H-band

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10
Q

myosin filaments

A

thick

extend from one end of A-band to other end of A-band

thin cross bridges extend from each myosin filament towards neighboring actin filaments

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11
Q

M line

A

at center of H-band

contains myomesin, C protein and other proteins that interconnect thick myosin filaments to maintain their specific lattice arrangement

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12
Q

Z disk

A

(a) region where attachment of the ends of the actin filaments in adjacent sarcomeres occurs
(b) appears filamentous and somewhat electron dense
(c) contains alpha-actinin

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13
Q

network of cisterns or membranous tubules running between and around myofibrils

form collars at AI junctions

A

Skeletal muscle - sarcoplasmic reticulum

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14
Q

________ binds and releases Ca (membranes contain voltage-gated Ca-release channels)

A

Sarcoplasmic reticulum

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15
Q

Forms T-tubules

A

Sarcolemma

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16
Q

T-tubules typically seen at ___________ between _________ (skeletal muscle)

A

AI junction between two collars of SR

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17
Q

Triads

A

T-tubule + 2 lateral cisternae of SR (skeletal muscle)

2 triads/sarcomere

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18
Q

Actin is made up of ____

A

G-actin (globular) and F-actin - composed of 2 helically wound G-actin polymers

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19
Q

Myosin = _______ and _________

A

4 light chains and 2 heavy chains

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20
Q

Light chain Myosin

A

Meromyosin

Long molecular subunits -rigid

packed together longitudinally to form backbone of myosin filament

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21
Q

Heavy chain myosin

A

Heavy meromyosin

Long molecular subunits, more flexible

2 components - rod-like portion lies parallel to backbone of filament, globular head = crossbridge from thick myosin filament to actin filament

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22
Q

Globular head of heavy chain meromyosin

A

Cross bridge from thick myosin filament to actin filament

ATPase activity w/ actin-binding sites

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23
Q

No cross bridges at ________ line

A

M- line (globular heads directed away from midpoint of myosin filament)

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24
Q

Tropomyosin

A

Fibrous, arranged head to tail in linear series

helically wound along grooves of F-actin helix (blocks actin-myosin binding)

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25
Q

Troponin complex

A

TnT: binds entire troponin molecule to tropomyosin

TnC: great affinity for Ca

Tnl: binds to actin, preventing actin-myosin interactions

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26
Q

Ca

A

binds to TnC

Binding to TnC induces a conformational shift in tropomyosin, exposing previously blocked active sites on the actin filament (myosin binding sites)

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27
Q

alpha-actinin

A

component of Z-disk

holds actin filaments in register by binding them in parallel array

28
Q

Titin

A

Large, linear elastic protein

Helps position myosin filaments precisely within the sarcomere

extends from each half of a myosin filament to the Z-disc (like a spring)

29
Q

Nebulin

A

long, non-elastic protein

two molecules of nebulin wrap around each thin filaments

help anchor thin filament to Z-disk

30
Q

Changes in banding patterns during contraction

A

A-band remains constant

I-band becomes smaller

Z-disc come closer together (sarcomere shortens)

H-band narrows and is eventually obliterated

31
Q

sheath of fine connective tissue surrounding individual muscle

fibers

A

endomysium

32
Q

perimysium

A

(1) connective tissue sheath around groups of muscle fibers (fascicles)
(2) continues as a major component of a tendon

33
Q

outermost sheath of connective tissue; surrounds entire muscle

A

epimysium

34
Q

Vascular supply to skeletal muscle

A

a. larger arteries follow perimysium
b. arterioles penetrate fascicles
c. capillaries parallel individual myofibers

35
Q

subneural apparatus

A

(1) secondary synaptic clefts formed by infolding of sarcolemma
(2) acetylcholinesterase located at surface of sarcolemma

36
Q

Motor units

A

consist of a motor neuron and the muscle fibers innervated by it

37
Q

Muscle spindles

A

Small specialized muscle fibers (inrafusal fibers) enclosed in connective tissue capsule

Central - nuclear bag fibers, nuclear chain fibers

capsules - internal immediately surrounds intrafusal, external capsule surrounds internal capsule

38
Q

Sensory innervation of muscle spindle

A

[1] large diameter fibers form annulospiral or primary endings around mid-portions of nuclear bag and nuclear chain fibers

[2] smaller diameter afferent fibers form flower spray or secondary endings on the intrafusal fibers some distance from the mid-region

39
Q

Motor innervation of muscle spindle

A

efferent fibers form motor end plates on either side of the mid-region of the intrafusal fibers

40
Q

Golgi tendon organs

A

(1) spindle-shaped bodies comprised of collagen and enclosed by a thin capsule
(2) afferent (sensory) nerve fibers penetrate between the collagen fibers
(3) sensitive to stretching forces on the tendon

41
Q

Embryologic origins of skeletal muscle

A
  1. loose mesenchyme –> myoblasts
  2. myoblasts fuse –> multinucleate myotubes
    a. myofilaments appear
    (1) irregularly arranged at first
    (2) gradually become aligned into myofibrils
42
Q

Hypertrophy of muscle d/t ____________

A

increase in size of fibers, not number

43
Q

General featurs of Cardiac Muscle

A
  1. striated (involuntary)
  2. T-tubule system
  3. sarcoplasmic reticulum less well developed than in skeletal muscle
  4. single nucleus/cell
  5. nucleus located at center of cell
  6. intercalated disks are a diagnostic feature of this tissue
44
Q

Cardiac muscles cells have _________ nucleus/nuclei located ________

A

1 nucleus

centrally located

45
Q

myofibrils of cardiac muscle cells appearance

A

branch and sometimes blend with adjacent myofibrils, sarcomeres/a-bands/i-bands/z-discs all present

46
Q

Intercalated disks

A

a. dark cross-bands; frequently appear step-like
b. occur where a Z-disk should be observed
c. mark spots of cell-to-cell attachments

represent a complex of several types of cell-to-cell junctions

[1] gap junctions (nexuses)

[2] desmosomes

[3] fascia adherens (serve as anchoring points for actin filaments)

47
Q

T-tubules in cardiac muscle

A

[1] larger (wider) than those in skeletal muscle

[2] located at Z-lines instead of at A-I junction

48
Q

Sarcoplasmic reticulum in cardiac muscle

A

[1] less developed than that of skeletal muscle

[2] simple plexiform arrangement of tubular elements

[a] no terminal cisternae

49
Q

diads

A

cardiac muscle

T-tubule + terminal portion of adjacent sarcoplasmic reticulum

50
Q

Fat droplets abundant in ________ muscle

A

cardiac

51
Q

Atrial granules

A

a. unique to atrial cardiac muscle cells
b. contain atrial natriuretic peptide which functions to lower blood pressure

[1] decreased renal tubules capability to resorb (conserve) sodium and water

52
Q

Connective tissue of Cardiac muscle

A
  1. each cardiac muscle cell is surrounded by a fine net of reticular and collagenous fibers
  2. collagenous and elastic fibers occur between bundles of cells
53
Q

Vascular supply to cardiac cells

A
  1. excellent: vessels are derived from coronary arteries
  2. lymphatic drainage present
54
Q

Nerve supply to cardiac muscle

A
  1. branches of sympathetic and parasympathetic terminate on muscle cells
55
Q

Purkinje fibers

A

Specialized muscle fibers - conduction system of cardiac muscle

a. myofibrils reduced in number
b. contain more sarcoplasm
c. nuclei more rounded
d. large diameter
e. lack T-tubules
f. more glycogen

56
Q

Embryological origins of cardiac muscle

A
  1. mesoderm –> myoblasts
  2. no fusion of myoblasts
57
Q

General features of smooth muscle

A

No striations

No t-tubules

involuntary

58
Q

Locations of smooth muscle

A

walls of hollow viscera (most of the gastrointestinal tract; portions of reproductive and urinary tracts, walls of blood vessels, larger ducts of some compound glands, respiratory passages, and small bundles in the skin)

59
Q

functions of smooth muscle

A

contractility, conductivity, production of extracellular products

60
Q

Connective tissue contributions of smooth muscle cells

A

a. every cell is surrounded by a thin external lamina that separates the plasma membrane of adjacent smooth muscle cells
b. reticular fibers are prevalent in the external lamina: help harness the force of contraction

61
Q

Dense bodies

A

comparable to Z-disks of skeletal and cardiac muscle

(1) contain a-actinin
(2) serve as anchor sites for actin-myosin filament bundles as

well as intermediate filaments

Located along inner aspects of the sarcolemma, scattered throughout cytoplasm

62
Q

Caveolae

A

pinocytotic-like

(1) may function as the equivalent of the T-tubule in skeletal and cardiac muscle
(2) may also work in concert with the sarcoplasmic reticulum to modulate Ca++ availability

63
Q

Contractile mechanism for smooth muscle

A
  1. Ca calmodulin form a complex

  1. Ca++-calmodulin complex activates myosin light chain kinase
  2. myosin light chain kinase phosphorylates one of the two light chains associated with the myosin molecule head
  3. phosphorylation of the light chain exposes an ‘actin-binding’ site on the myosin molecule
64
Q

Innervation of smooth muscle

A
  1. sympathetic innervations: synaptic vesicles contain norepinephrine
  2. parasympathetic innervation: synaptic vesicles contain acetylcholine
  3. variations in numbers of cells in a group that are innervated
65
Q

Regneration of smooth muscle

A
  1. smooth muscle cells retain mitotic capability (e.g., pregnant uterus)
  2. smooth muscle cells can also be formed from pre-existing pericytes

Skin MS: Week 4 (10 decks)

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