Histology of Muscle Flashcards Preview

Skin MS: Week 4 > Histology of Muscle > Flashcards

Flashcards in Histology of Muscle Deck (65):
1

General Features of Skeletal Muscle 

1.   striated (voluntary)

2.   T-tubule system

3.   well-developed sarcoplasmic reticulum

4.   multinucleated

5.   nuclei located at cell periphery (just inside sarcolemma)

2

A band

broad, dark-staining band

anisotropic 

3

I band

narrower, light-staining band

isotropic bond

4

Z-disk

dense-staining, narrow

bisects I band

distance between two Z-disks = sarcomere

5

H band

pale-staining, narrow

bisects A-band

Located at the middle of the sarcomere

6

M-line

thin

bisects H band

7

Functional unit of the myofibril 

sarcomere

8

Sarcomere length varies as a function of degree of ________

contraction of muscle cell 

9

Actin filaments 

thin

extend from Z-disks to edge of H-band 

10

myosin filaments

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 

 

11

M line

at center of H-band

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

12

Z disk 

Q image thumb

(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

13

network of cisterns or membranous tubules running between and around myofibrils

form collars at AI junctions

Skeletal muscle - sarcoplasmic reticulum 

14

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

Sarcoplasmic reticulum 

15

Forms T-tubules

Sarcolemma

16

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

AI junction between two collars of SR 

17

Triads

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

2 triads/sarcomere 

18

Actin is made up of ____

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

19

Myosin  = _______ and _________

4 light chains and 2 heavy chains 

20

Light chain Myosin

Meromyosin

Long molecular subunits -rigid

packed together longitudinally to form backbone of myosin filament 

21

Heavy chain myosin

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

22

Globular head of heavy chain meromyosin

 

Cross bridge from thick myosin filament to actin filament

ATPase activity w/ actin-binding sites

23

No cross bridges at ________ line

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

24

Tropomyosin

Fibrous, arranged head to tail in linear series

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

25

Troponin complex

TnT: binds entire troponin molecule to tropomyosin

TnC: great affinity for Ca

Tnl: binds to actin, preventing actin-myosin interactions

26

Ca 

binds to TnC

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

27

alpha-actinin

component of Z-disk

holds actin filaments in register by binding them in parallel array

28

Titin

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

Nebulin

long, non-elastic protein

two molecules of nebulin wrap around each thin filaments

help anchor thin filament to Z-disk

30

Changes in banding patterns during contraction 

A-band remains constant

I-band becomes smaller

Z-disc come closer together (sarcomere shortens)

H-band narrows and is eventually obliterated 

31

sheath of fine connective tissue surrounding individual muscle

      fibers

endomysium

32

perimysium

(1) connective tissue sheath around groups of muscle fibers (fascicles)

(2) continues as a major component of a tendon

33

outermost sheath of connective tissue; surrounds entire muscle

epimysium 

34

Vascular supply to skeletal muscle

a.   larger arteries follow perimysium

b.   arterioles penetrate fascicles

c.   capillaries parallel individual myofibers

35

subneural apparatus

(1) secondary synaptic clefts formed by infolding of sarcolemma

(2) acetylcholinesterase located at surface of sarcolemma

36

Motor units

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

37

Muscle spindles

 

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

Sensory innervation of muscle spindle

[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

Motor innervation of muscle spindle 

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

40

Golgi tendon organs 

(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

Embryologic origins of skeletal muscle 

1.   loose mesenchyme -->  myoblasts

2.   myoblasts fuse --> multinucleate myotubes

a.   myofilaments appear

(1) irregularly arranged at first

(2) gradually become aligned into myofibrils

42

Hypertrophy of muscle d/t ____________

increase in size of fibers, not number

43

General featurs of Cardiac Muscle 

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

Cardiac muscles cells have _________ nucleus/nuclei located ________

1 nucleus 

centrally located 

45

myofibrils of cardiac muscle cells appearance

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

46

Intercalated disks 

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

T-tubules in cardiac muscle 

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

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

48

Sarcoplasmic reticulum in cardiac muscle 

[1] less developed than that of skeletal muscle

[2] simple plexiform arrangement of tubular elements

[a]  no terminal cisternae

49

diads

cardiac muscle

T-tubule + terminal portion of adjacent sarcoplasmic reticulum 

50

Fat droplets abundant in ________ muscle

cardiac 

51

Atrial granules 

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

Connective tissue of Cardiac muscle

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

Vascular supply to cardiac cells

1.   excellent: vessels are derived from coronary arteries

2.   lymphatic drainage present

54

Nerve supply to cardiac muscle

1.   branches of sympathetic and parasympathetic terminate on muscle cells

55

Purkinje fibers

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

Embryological origins of cardiac muscle

1.   mesoderm -->  myoblasts

2.   no fusion of myoblasts

57

General features of smooth muscle 

No striations

No t-tubules

involuntary 

58

Locations of smooth muscle

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

functions of smooth muscle

contractility, conductivity, production of extracellular products 

60

Connective tissue contributions of smooth muscle cells 

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

Dense bodies

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

Caveolae

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

Contractile mechanism for smooth muscle 

1. Ca calmodulin form a complex

2. Ca++-calmodulin complex activates myosin light chain kinase

3. myosin light chain kinase phosphorylates one of the two light chains associated with the myosin molecule head

4.   phosphorylation of the light chain exposes an 'actin-binding' site on the myosin molecule

64

Innervation of smooth muscle

  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

Regneration of smooth muscle

1.   smooth muscle cells retain mitotic capability (e.g., pregnant uterus)

2.   smooth muscle cells can also be formed from pre-existing pericytes