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MD2002 > Sarcomere Structure > Flashcards

Sarcomere Structure Flashcards

1
Q

What are muscle fiber bundles called ?

A

Fasiculi

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2
Q

What layers of connective tissue are present in skeletal muscle and what do they cover ?

A

Epimysium - dense sheath on the surface
Perimysium - between fasiculi
EndoWmysium - between muscle fibers

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3
Q

What is the diameter of a skeletal muscle fiber ?

A

50-100 μ

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4
Q

What is a Sarcolemma ?

A

“cell membrane of a striated muscle fiber cell.”

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5
Q

What is the sarcoplasm ?

A

Intracellular fluid that fills spaces between myofibrils

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6
Q

What are myofibrils predominantly made of ?

A

Actin and myosin filaments

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7
Q

What is a sarcomere ?

A

The portion of a myofibril that lies between two successive Z disks

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8
Q

What is the diameter of a myofibril ?

A

1-2 μ

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9
Q

What is the main protein making up thick filaments ?

A

Myosin

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10
Q

What is the structure of thick filaments ?

A

Tail = 2 intertwined heavy chains

2 globular heads extending out forming cross-bridge =
Heavy and light chains (each head) + binding sites for actin and ATP (myosin-ATPase) (on each head)

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11
Q

What is the length of myosin in a sarcomere ?

A

1.6 μm

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12
Q

What is the length of actin in a sarcomere ?

A

1 μm

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13
Q

What are the main proteins making up thin filaments ?

A

Actin, tropomyosin and troponin (forming a complex with each other)

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14
Q

Which of the proteins making up the thin filaments are contractile ? Regulatory ?

A

Actin - contractile

Tropomyosin and troponin - regulatory

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15
Q

What is the structural specificity of actin in thin filaments ?

A

Each G actin has a binding site for myosin

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16
Q

What is the function of tropomyosin in the thin filament ?

A

Overlaps binding sites on actin for myosin and inhibits interaction when in the relaxed state

17
Q

What is the function of troponin in the thin filament ?

A

Binds Ca2+ reversibly and once bound changes conformation to pull tropomyosin away from the myosin interaction sites.

18
Q

How does Ca2+ binding to troponin regulate skeletal muscle contraction ?

A

Because it moves the tropomyosin away and allows myosin to interact with the actin.

19
Q

Where is nebulin found within the sarcomere ? What is its function ?

A

In the thin filament

Helps align actin

20
Q

Where is titin found within the sarcomere ? What is its function ?

A

Connects the Z line to the M line.

Provides elasticity and stabilises myosin

21
Q

What are all the structural proteins found in the sarcomere ?

A

Titin (connectin)
Z-line protein (alpha-actinin)
M-line proteins (myomesin, M-protein)
Nebulin

22
Q

What are all the contractile proteins found in the sarcomere ?

A

Actin
Myosin
Tropomyosin
Troponin Complex

23
Q

What is the A band made of ?

A

primarily myosin filaments in the region of overlap

24
Q

What is the I band made of ?

A

Actin filaments bisected by Z-line

25
Q

What is the H zone made of ?

A

Only myosin filaments

26
Q

What happens to the sarcomere as a whole, the H zone, A band, and I band upon contraction ?

A

Sarcomere as a whole shortens
H zone and I band shorten
A band stays constant

27
Q

Which feature of T tubules allows the fluid within to be continuous with external environment ?

A

Their walls are continuous with the sarcolemma

28
Q

What structure contains intracellular structures and organelles ?

A

Sarcoplasmic reticulum

29
Q

What is a terminal cisternae ? What is their function ?

A

“enlarged areas of the sarcoplasmic reticulum surrounding the transverse tubules. Store calcium and release it when an action potential courses down the transverse tubules, eliciting muscle contraction.”

30
Q

What is the function of the sarcoplasmic reticulum ?

A

Ca2+ storage and release following membrane excitation.

31
Q

How are sarcoplasmic reticulum and T-tubules connected ?

A

With junctions

32
Q

What is the structure of the junction connecting sarcoplasmic reticulum and T-Tubules ?

A

Two integral membrane proteins:

  • One in the T-tubule membrane (modified voltage-sensitive Ca2+ channel called dihydropyridine (DHP) receptor, which acts as a voltage sensor)
  • One in the membrane of the sarcoplasmic reticulum ( ryanodine receptor, which forms a Ca2+channel)
33
Q

What is a triad ?

A

T tubule with terminal cisternae on both sides

MD2002 (77 decks)

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