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Physiology > muscles 1 > Flashcards

muscles 1 Flashcards

1
Q

Cardiac muscle

A
  • 200-300 micro metres long
    • Single nucleus
    • Striated
    • Involuntary
    • Responsible for contraction of the heart
    • Has intercalated disks
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2
Q

intercalated disks

A

○ Cardiac muscle cells branch and are interconnected by intercalated disks
○ Connected by gap junctions - electrically connected

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3
Q

Smooth muscle

A
  • Involuntary
    • Lines internal structures eg. Digestive tract, veins/arteries, respiratory passage ways
    • Small elongated, thin spindle shaped cells
    • Single nucleus
    • Non-striated - smooth
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4
Q

Muscle fibre

A
  • Surrounded by endomysium
    • Contains myofibrils
    • The cell
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5
Q

Myofibrils

A
  • Surrounded by sarcoplasmic reticulum
    • Consists of sarcomeres
    • Thing inside the cell (100s of em)
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6
Q

Sarcomere

A
  • Contains
    ○ thick filaments
    ○ Thin filaments
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7
Q

actin is attached to

A

Z disk

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8
Q

actin is attached to Z disc by

A

a-actinin

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9
Q

myosin thick filament is attached to

A

Z disk

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10
Q

myosin thick filament is attach to Z disc by

A

titin

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11
Q

how is tension created in the sarcomere

A

actin and myosin pull on each other

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12
Q

Actin (thin) filaments

A
  • Double helix of polymerised G-actin (F-actin)

- Tropomyosin and troponin complexes are embedded in the cleft of the twisted chains

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13
Q

Tropomyosin

A

○ Tropomyosin is filamentous and spans the lengths of the filament

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14
Q

Myosin (thick) filaments

A
  • Thick filaments are comprised of many myosin molecules

○ 1.6 micro metres long x 12nm wide

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15
Q

Sarcomeres change during contraction

A
  • Shorted
    • I bands and H zone shorten
    • A bands do not change in length
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16
Q

A bands

A

length of myosin thick filaments

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17
Q

I bands

A

distance between mysosin thick filaments

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18
Q

H bands

A

distance between actin think filaments

19
Q

4 steps of actin myosin cross bridge

A
  1. Myosin binds actin
    - Myosin head attached reversibly to high affinity active sites on the actin thin filament
    1. Myosin ‘power stroke’ pulls actin filament, contracting sarcomere
      • ADP released, freeing ATP-binding site
    2. ATP binding releases myosin from actin
      • Conformational change
    3. ATP hydrolysis drives re-cocking of myosin to high energy state, but is not required for power stroke
20
Q

Sliding filament model

A
  • The lever movement pulls on the actin filament relative to the myosin head (~5nm) producing force
    • Thick and thin filaments interdigitate and slide relative to each other
21
Q

tension is proportional to

A

○ Proportional to the number of actin-myosin crossbridges

○ Ie. Amount of overlap

22
Q
  • Length-tension curve
A

○ The tension generated by a sarcomere can be predicted from sarcomere length ie. Overlap

23
Q

In relaxed muscle

A

§ Tropomyosin ™ blocks the myosin binding site on actin filaments preventing crossbridge formation
§ Tropomyosin is regulated by the tropomyosin complex

24
Q

troponin complex

A

Tn-T, Tn-I, Tn-C

25
Q

Tn-T binds to

A

tropomyosin

26
Q

Tn-I binds to

A

Tn-C and actin

27
Q

Tn-C binds to

A

Ca ions

28
Q

how does troponin work

A

○ When Tn binds Ca its conformation changes pulling tropomyosin out of the myosin binding site so myosin thick filament can bind

29
Q

How is Ca regulated

A
  • Action potential -> opens dihydropyridine receptor (DHPR) -> opens ryanodine receptor (RyR) -> releases Ca2+ from the sarcoplasmic reticulum
30
Q

sarcoplasmic reticulum

A

endoplasmic reticulum and muscle

surrounds each myofibril

31
Q

SERCA

A

calcium ATPases / calcium pumps
on the sarcoplasmic reticulum
sequesters calcium to cause relaxation

32
Q

dihydropyridine receptor

A

on the outside of the cell

voltage gated

33
Q

ryanodine receptor

A

mechanically gated calcium channel
gated by dihydropyridine receptor
on the sarcoplasmic reticulum inside the cell

34
Q

DHPR does

A

voltage gated

mechanically pushes the RyR receptor

35
Q

T tubule

A

part of the plasma membrane that brings the action potential closer to the interior of the muscle fibre

36
Q

numero muscular junction

A

where the nerve talks to muscle
motor end plate
cholinergic synapse

37
Q

motor neurone secretes

A

acetyl choline

38
Q

Nicotinic Ach receptor

A

§ Ionotropic - ligand-gated Na+ channel
§ Always excitatory
lets sodium into the cell to cause an action potential which travels down the T tubule

39
Q

How does contraction stop

A
  • Motorneuron AP stops
    • Ach degraded at the synapse by AChE
    • Muscle AP stops - DHPR - RyR close
    • Ca -ATPase pumps remove cytoplasmic Ca so calcium sequestered back into the sarcoplasmic reticulum
    • Troponin-tropomyosin complex blocks cross bridges, causing relaxation (if ATP is present)
40
Q

excitation/contraction event called

A
  • This whole event is called a twitch
41
Q

latent period

A

time between action potential and coupling

42
Q

excitation contraction coupling

A

Because a twitch is slow, theres time for >1 AP

Wave summation progressively increases [Ca2+] which increases tension

43
Q

maximum tension

A
  • Maximum tension (tetanus) Is reached when all actin + myosin are forming crossbridges

Physiology (13 decks)

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