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Histology (Emily) > Lecture 6 - Muscle > Flashcards

Lecture 6 - Muscle Flashcards

1
Q

Smooth muscle cell (muscle fiber)

A

non-striated unicellular muscle fibers connected by gap junctions. Call each cell a “fiber”, like skeletal muscle cells. Are shorter than muscle cells/fibers.

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2
Q

Skeletal muscle cells (muscle fiber)

A

big, multinucleated striated fibers, also unicellular.

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3
Q

Cardiac muscle cells (myocyte)

A

myocytes connect to make a multicellular fiber. Each cell only has one nucleus. Striated and connected by intercalated disks.

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4
Q

Non-muscle cells w/ contractile properties

A
  • Myoepithelial - epithelial that contract mammary glands
  • Myofibroblasts
  • Myoid cells - testis, squeeze contents through tubules
  • Perineurial – surround nerves
  • Pericytes – stem cells of blood vessels. Around capillaries.
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5
Q

Thin filaments are ____.

Thick filaments are ____.

A 
Thin = Actin
Thick = Myosin
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6
Q

Sarcolemma

A

plasma membrane of muscle cells

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7
Q

Sarcoplasmic reticulum

A

smooth ER of muscle cells

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8
Q

External lamina

A

type IV collagen, reticular fibers (type III collagen) – like any other basement membranes. Goes around entire cell.

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9
Q

Satellite Cells

A

Pluripotential stem cells located b/t external lamina and sarcolemma for limited skeletal muscle regeneration (activated by injury); can also become bone or cartilage (Remember, skeletal muscle cells do NOT divide. They are terminally differentiated)

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10
Q

Myositis Ossificans

A

Follows an episode of trauma to the skeletal muscle divisions of satellite cells lead to formation of skeletal muscle fibers however some cells differentiate into cartilage and bone producing cells evolves into painless, hard muscle mass

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11
Q

Types of skeletal fiber

A
  1. Red (Aerobic, type I)
  2. White (Anaerobic, Type IIb)
  3. Intermediate fibers (Type IIa)
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12
Q

Red (Aerobic, Type I)

A

Slow oxidative; slow-twitch, prolonged contractions = Leg muscle!

Elevated myoglobin, cytochrome, mitochondria, ATPase activity

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13
Q

White (Anaerobic, Type IIb)

A

Fast glycolytic; fast-twitch, rapid contractions = Chicken breast! Can respond fast but not used regularly.

Decrease myoglobin, cytochrome, mitochondria, elevated glycogen

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14
Q

Intermediate fibers (Type IIa)

A

Fast oxidative glycolytic, fatigue resistant, pink, aneorobic, yet oxidative (so basically in between red and white function)

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15
Q

Skeletal muscle formation from large to small

A

Muscle fascicles (group of muscle cells) fibers (single muscle cell) myofibrils (formed by arrangement of myofilaments/sarcomeres) sarcomeres and myofilaments (thin & thick filaments)

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16
Q

What is being reduced when atrophy occurs after injury/cast?

A

Muscle fibril! It is not that the cell (muscle fiber) would disappear. The myofilament arrangement that makes up the muscle fibrils are reduced, so the answer is muscle fibril, NOT fiber (single cell)

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17
Q

______ holds skeletal muscle together and channel vascular and nerve.

A

Connective tissue (collagen IV)

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18
Q

Epimysium

A

Surrounds muscle (deep invested fascia), dense irregular CT; on the surface of muscle belly

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19
Q

Perimysium

A

Surrounds fasicles, or groups of muscle fibers

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20
Q

Endomysium

A

Delicate CT between surrounding individual muscle fibers

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21
Q

Fibers are made of ____

A

Myofibrils formed from myofilaments (actin, myosin II). Myofilaments are the actual contractile elements of striated muscle. Myofibrils are surrounded by a well-developed sarcoplastic reticulum (sER).

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22
Q

Sarcomere

A

Basic contractile unit of striated muscle; segment of myofibril btw 2 Z-lines

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23
Q

Z-line

A

It bisects the I band (actin/thin filament); where actin filaments anchor w/ alpha-actinin

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24
Q

M-line

A

It bisects the light H band (myosin/thick filament). It’s a narrow dense line. “Middle” of sarcomere where myosine fibrils connect with C proteins. Stays constant during contraction. “Inside” A band.

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25
Q

I-band

A

light band only actin filaments (shrinks w/ muscle contraction) = in the pic above, the lighter pink parts are I-band! And notice the thin line within the I-band = Z-line!

26
Q

H-band/zone

A

light band directly around M-line that has only myosin filaments (shrinks w/ contraction); located inside A-band

27
Q

A-band

A

dark band, myosin filaments w/ sometimes overlapping actin filaments; “All” so both actin & myosin; essentially the length of thick filament! Stays constant! = in the pic above, the darker pink parts are A-band!

28
Q

Thin filaments

A

contain F-actin, tropomyosin, and troponin. Responsible for light bands.

29
Q

Thick filaments

A

contain only myosin II. Responsible for dark bands.

30
Q

Sacromere Proteins: Titin

A

attaches Z-line to M-line (anchors myosin to Z-line), largest known protein!

31
Q

Sacromere Proteins: Tropomyosin

A

makes the myosin-binding site on actin, sits in groove of actin filament

32
Q

Sacromere Proteins: Troponin (TnT, TnC, TnI)

A

TnC binds Ca++ which allows contraction; TnT binds to tropomyosin, and TnI inhibits muscle contraction

33
Q

Sacromere Proteins: Tropomodulin

A

keeps actin from growing beyond proper length

34
Q

Sacromere Proteins: Alpha-actinin

A

anchors actin to z-line

35
Q

Sacromere Proteins:

C Protein

A

myosyn binding protein. holds myosin at M line

36
Q

5 steps of muscle contraction:

A
  1. Attachment: Myosin head is tightly bound to the actin molecule of the thin filament.
  2. Release: myosin head becomes uncoupled from the thin filament. Caused by ATP binding to the myosin.
  3. Bending: myosin head, as a result of hydrolysis of ATP, advances a short distance in relation to the thin filament. ADP and phosphate remain bound.
  4. Force generation: myosin head releases inorganic phosphate and the power stroke occurs
  5. Reattachment: Cycle repeats itself.
37
Q

What must be available for the rxn between actin and myosin?

A

Ca2+, then must be removed after - accomplished by the sarcoplasmic reticulum.

38
Q

Where is a reservoir for Ca2+?

A

Terminal Cisterna (where the two adjacent sarcoplasmic reticulums meet the A and I bands)

39
Q

Transverse tubular system

A

contains numerous tubular invaginations of the plasma membrane, each one is called a T tubule. Located between 2 terminal cisterna of the sarcoplasmic reticulum (makes up the triad).

40
Q

What do the T tubules contain?

A

voltage-sensor proteins, are activated when the plasma membrane is depolarized.

41
Q

What happens when the proteins on the t-tubule are depolarized?

A

This twisting ffects the conformation of the Ca2+-release channels on the adjacent terminal cisternae open and allows Ca2+ into the sarcoplasm.

42
Q

Duchenne Muscular Dystrophy

A

x-linked recessive, absence of dystrophin (anchors actin to sarcolemma), hence fibers become disorganized, cell size changes, nuclei incorporated into cell, lots of fibrosis, sarcomeres unorganized, inefficient contraction, muscle tissue degenerates over time.

Filaments contract but are not connected to plasma membrane leads to problems in effective muscle contractions.

43
Q

Rigor mortis that begins at moment of death is caused by what?

A

The concentration of ATP is too low!

44
Q

What kind of innervation does cardiac muscle have?

A

autonomic innervation

Has the ability to contract by itself (conducting system of the heart via purkinje fibers); looks more globular, lighter, and glycogen filled cells, next to the lumen of the chamber of heart.

45
Q

Which two types of muscle are striated?

A

skeletal and cardiac

46
Q

Intercalcated disks

A

In cardiac muscle - crossbands

47
Q

DIAD in Cardiac Muscle

A

1 sarcoplasmic reticulum + 1 T-tubule (unlike skeletal that has 2 SR)

1 T-Tubule per sarcomere found at Z-line (unlike skeletal that has 2 at A-I junction)

48
Q

Purkinje fibers:

A

pecialized cardiac muscle cells. Found below/lining the endocardium, larger than cardiac muscle, stain lighter, less fibrous propagate action potentials and can generate impulses by themselves.

49
Q

Intercalated Disks:

A

cell-to-cell junctions for communication

50
Q

Transverse Intercalated Disks

A
  • Fascia adherens, desmosomes. Dark lines. Responsible for enduring mechanical stress = connect cells end-to-end = cardiac fiber formation! Run parallel to striations but perpendicular to fibers.
51
Q

Lateral Intercalated Disks

A

gap junctions, desmosomes = side-by-side to communicate and relay signal; run with fibers!

52
Q

Do cardiac muscle cells have satellite cells?

A

No satellite cells in cardiac muscle don’t have regeneration of cardiac muscle.

53
Q

SMOOTH MUSCLE

A

Autonomic innervation, slow prolonged contractions, - elongated, single nucleus (central, corkscrew when contracted), external lamina, gap-junctions

54
Q

Does smooth muscle have striations?

A

No

55
Q

Dense bodies

A

In smooth muscle where actin is anchored (replaces Z-lines, still made of alpha-actin).

56
Q

Caveolae

A

Vesicles that deliver calcium to smooth muscle (no T-tubules, underdeveloped sER)

57
Q

What are two signs that it is smooth muscle?

A

Dense bodies, blood vessels.

58
Q

Where is smooth muscle?

A

Lines tubular organs (i.e. GI tract, uterus, etc.)

59
Q

Oxytocin is delivered to initiate uterine muscle contraction via what channels?

A

Activating calcium release channels via second messenger!

60
Q

What are differences in smooth muscle contraction?

A
  • No T system, caveolae instead
  • Ca++ delivered in vesicles!
  • Myosin heads all along shaft instead of just at end.
  • Contraction by direct ANS stimulation, also hormonal

Histology (Emily) (8 decks)

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