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NYCC Histology > Muscle > Flashcards

Muscle Flashcards

1
Q

Nuclei of skeletal muscle

A

Multinucleated, peripherally placed under sarcolemma

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2
Q

Skeletal muscle cell structure

A

Long, cylindrical, multibucleated
Length varies up to few mm to 1m

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3
Q

Satellite cells

A

Small population of reserve progenitor cells remain adjacent to many mature skeletal muscle cells

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4
Q

Endomysium

A

Delicate layer of reticular fibers that immediately surrounds individual muscle fibers

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5
Q

Perimysium

A

Thicker layer of CT that surrounds fascicles

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6
Q

Fascicle

A

Bundle of muscle fibers

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7
Q

Epimysium

A

Thick external sheath of dense CT that surrounds the entire collection of fascicles that make up the muscle
- Carries/supports larger nerves, blood vessels and lymphatics

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8
Q

Myofibrils

A

Bundle of myofilaments (actin & myosin)

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9
Q

Basic functional unit of muscle cell

A

Sarcomere

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10
Q

Sarcomere

A
  • basic functional repetitive contractile subunit of striated muscle
  • segment of myofibril between two Z lines
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11
Q

Z line

A

Bisects light (I) band, anchors adjacent thin filaments (actin)

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12
Q

H band

A

Bisects dark (A) band
Only myosin, adjecent to actin

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13
Q

M line

A

Bisects H band
Adjacent thick filaments (myosin) link

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14
Q

I bands during contraction

A
  • Actin filament slides past myosin filaments
  • Shortens during contraction
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15
Q

A bands during contraction

A

Individual myosin filaments do not move, width does not change

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16
Q

H band during contraction

A

Narrows as actin overlaps myosin

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17
Q

What are the contractile units of skeletal muscle

A

Myofilaments (actin & myosin)

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18
Q

What are the striations shown in longitudinal sections of skeletal muscle?

A

Alternating dark & light bands due to organized parallel arrangement of myofibrils

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19
Q

Dark bands

A

A bands - mark extent of myosin filaments, actin overlaps

20
Q

Light bands

A

I bands - contain only actin

21
Q

Primary proteins of thin myofilaments

A

F-actin, tropomyosin, Troponin

22
Q

F-actin

A

Forms double stranded helix

23
Q

Tropomyosin

A

Double helix of 2 polypeptides, forms filaments that run in the groove between F-actin molecules in the thin filament
- in resting muscle works with Troponin to mask myosin binding sites

24
Q

Troponin

A

Complex of 3 subunits:
- Troponin-C (TnC) - smallest subunit, binds Ca in initiating contraction
- Troponin-T (TnT) - binds to tropomyosin, anchoring Troponin complex
- Troponin-I (TnI) - Binds to actin inhibiting actin-myosin interaction

25
Q

Thick myofilament structure

A
  • 2 heavy chains twisted together as myosin tails, and 4 light chains
  • globular projections containing he 4 light chains form head at 1 end of heavy chain
26
Q

Sarcoplasmic reticulum

A
  • Smooth ER of muscle cell
  • forms highly organized tubular networks around myofibrils, extending between A-I junctions
27
Q

Terminal cisternae

A

At the A-I junction, SR forms ring-like channel

28
Q

Function of terminal cisternae

A

Reservoir for Ca

29
Q

Transverse (T) tubule system

A

Numerous tubular invaginations of the sarcolemma reach to the A-I junction

30
Q

The T-tubule and 2 terminal cisternae form ______

A

a triad

31
Q

Function of triad complex

A

Triggers Ca release when sarcolemma is depolarized to initiate contraction of Sarcomeres

32
Q

Repair & healing of skeletal muscle

A
  • mature skeletal muscle cells are permanent (non-dividing)
  • limited ability to repair via satellite cells
  • more typically, fibroblasts repair injury site with scar tissue
33
Q

Epicardium

A

External CT covering around heart muscle (myocardium), lined by mesothelium

34
Q

Intercalated discs

A

Junctions between cardiac muscle cells forming strong intercellular adhesion and gap junctions

35
Q

Gap junction

A

Allow for communication allowing cardiac muscle to act as a syncytium allowing informational macromolecules to pass rapidly from cell to cell

36
Q

Cardiac vs skeletal muscle fibers

A
  • Sarcomeres organized and function similarly to skeletal muscle
  • myofibrils sparser than skeletal muscle (moth eaten appearance)
  • Autonomic nerves regulate contraction
37
Q

Repair and healing of cardiac muscle

A
  • permanent cells (non-dividing)
  • lack satellite cells - very little potential to regenerate after injury (most likely from nearby stem cells)
  • myocardial infarction - healing by fibroblasts laying down scar tissue
38
Q

Motor end plates / neuromuscular junctions

A

Contact made by terminal branches of motor axons with the skeletal muscle fiber

39
Q

Smooth muscle characteristics

A
  • non-striated, random placement of actin & myosin (no Sarcomeres)
  • elongated cells with tapered ends, one central nucleus
  • cells linked by gap junctions
  • No T-tubule system (disorganized SR)
40
Q

Smooth muscle contractile proteins

A

myosin light-chain kinase (MLCK) and calmodulin

41
Q

Calmodulin

A

Ca binding protein

42
Q

Dense bodies

A

Attachment sites in cell membrane anchoring Actin myofilaments

43
Q

Location of smooth muscle

A

Major muscle component of blood vessels, digestive, respiratory, urinary, and reproductive tracts

44
Q

Repair and healing in smooth muscle

A

Capable of more active regenerative response - stabile (quiescent) cells

45
Q

What structure is located in the I-band and attaches to the thin filaments?

A

Z-line

NYCC Histology (21 decks)

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