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BIOSCI 107 Part Two > Muscles: Skeletal Muscle part 2 > Flashcards

Muscles: Skeletal Muscle part 2 Flashcards

1
Q

Isotonic Contraction

A

Shortening, Tension constant, Velocity variable

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2
Q

Isometric Contraction

A

No shortening, Length constant, Tension variable

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3
Q

When is maximum active force generated in an isometric contraction?

A

When there is the greatest amount of actin and myosin overlap to produce the greatest number of cross-bridges

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4
Q

What is the optimal length for the greatest amount of tension/force

A

2-2.2μm

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5
Q

What does a length greater/smaller than the optimal length do to the amount of tension/force generated?

A

The amount of tension generated decreases

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6
Q

What occurs in lengths <2.0 µm that results in reduced force?

A

At lengths <2.0 µm filaments collide and interfere with each other reducing force developed

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7
Q

What occurs in lengths >2.2 µm that results in reduced force?

A

At lengths >2.2 µm active forces decline as the extent of overlap between filaments reduces, reducing the number of cross bridges

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8
Q

Equation for total tension

A

Total tension = active + passive force

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9
Q

Elastic components of muscle

A

Elastin

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10
Q

What is passive force

A

The connective tissue that resists stretch at a certain length (acts against the stretch)

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11
Q

What is active tension dependent on?

A

Sacromere length (actin and myosin overlap)

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12
Q

When is passive tension NOT generated

A

When there is no contraction occurring

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13
Q

What occurs a muscle is stimulated through a contraction

A

There is a “twitch” - peak in length v. stress graph due to active force and cross bridge cycle

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14
Q

What happens as active force decreases due to a muscle being stretched out?

A

Passive tension increases

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15
Q

What is Excitation-contraction coupling

A

a sequence of events that converts APs in a muscle fibre to a contraction

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16
Q

What is a motor unit?

A

a motor neuron and all the muscle fibers it innervates (nerve touches at neuromuscular junction)

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17
Q

What is the first stage of excitation contraction coupling?

A

ACh released into neuromuscular junction

AP travels down motor neuron. At axon terminal Ca2+ channels open, Ca2+ enters axon terminal → vesicles containing ACh to fuse with terminal membrane, releasing ACh into neuromuscular junction (synaptic cleft), a specialized synapse

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18
Q

What is the second stage of excitation contraction coupling

A

Activation of ACh receptors

Binding of ACh to receptors on muscle end plate → opening of ligand (ACh) gated ion channels. Opening of channels allows movement of mainly Na+ into muscle cell making it less -ve (end plate potential). Effects of Ach = short lasting as acetylcholinesterase (enzyme) rapidly breaks down Ach

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19
Q

What is the third stage of excitation contraction coupling

A

A Muscle Action Potential is triggered

If sufficient ligand gated channels are opened the end plate potential reaches threshold. Voltage gated Na+ channels open and an AP is triggered. AP is then propagated along the sarcolemma into the T tubule system

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20
Q

What is the fourth stage of excitation contraction coupling

A

Calcium is released from the SR

The AP is conducted down the t-tubules coming in close contact with the SR → voltage gated Ca2+ channels in the SR opening (Ca channel directly connected to voltage sensor). Ca2+ is released into the cytosol

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21
Q

What is the fith stage of exciatation contraction coupling

A

Ca2+ binds with troponin

When [Ca2+] reach a critical threshold the myosin binding sites on the actin filament are exposed allowing the cross-bridge cycle to occur

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22
Q

What occurs after Ca2+ binds to troponin

A

The cross bridge cycle

Cross-bridge formation, Power stroke, Detachment, Energization of myosin head

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23
Q

How does excitation-contraction coupling end

A

Contraction ends when Ca2+ levels decrease

Ca is actively pumped back into SR via Ca2+-ATPase pumps. Troponin moves tropomyosin back covering myosin binding site. Muscle “twitch” is complete

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24
Q

The 4 types of channels involved in excitation contraction coupling

A
  1. ACh ligand channel that allows Na+ to enter postsynaptic membrane
  2. Na+ voltage gated channels which allow Na+ influx to cause an AP
  3. Ca2+ voltage gated channels which release Ca2+ into the cytosol to cause a contraction
  4. Ca2+ ATPase which pumps Ca2+ back into the SR
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25
Q

What is the function of creatine phosphate

A

For brief periods (<15s) creatine phosphate can act as an ATP “store”

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26
Q

What type of metabolism is the use of creatine phosphate

A

Anaerobic (no O2)

27
Q

How long can creatine phosphate be used for

A

<15s

28
Q

Creatine phosphate + ADP = ?

A

creatine + ATP

29
Q

What is anaerobic glycolysis?

A

Short intense exercise: fast, inefficient metabolism

30
Q

How long is anaerobic the dominant system of muscle metabolsim

A

10-30s of maximal effort

31
Q

What builds up during anaerobic metabolism and what does this cause?

A

lactate and H+ limits duration to max 120s

32
Q

Is oxygen needed in anaerobic metabolism?

A

No

33
Q

What is aerobic metabolism

A

Efficient, but slow metabolsim ∴ good blood supply. Important for postural muscles and endurance exercise. Using aerobic respiration produces lots of ATP.

34
Q

Does aerobic metabolism require oxygen

A

Yes

35
Q

Maximum wattage of aerobic respiration

A

300W

36
Q

What is the Vo2 max

A

Aerobic exercise capacity (a breaking point) where you cannot exercise anymore

37
Q

What type of muscle fibre is type 1

A

slow oxidative

38
Q

What type of muscle fibre is type 2

A

fast glycolytic

39
Q

Max ATPase rate of type 1 muscle fibres

A

slow

40
Q

Max ATPase rate of type 2 muscle fibres

A

fast

41
Q

SR pumping capacity of type 1 muscle fibres

A

moderate

42
Q

SR pumping capacity of type 2 muscle fibres

A

high

43
Q

Diameter of type 1 muscle fibres

A

small

44
Q

Diameter of type 2 muscle fibres

A

large

45
Q

Mitochondira/myoglobin/blood supply of type 1 muscle fibres

A

high

46
Q

Mitochondira/myoglobin/blood supply of type 2 muscle fibres

A

low

47
Q

Glycolytic capacity of type 1 muscle fibres

A

moderate

48
Q

Glycolytic capacity of type 2 muscle fibres

A

high

49
Q

Primary ATP pathway of type 1 muscle fibres

A

aerobic

50
Q

Primary ATP pathway of type 2 muscle fibres

A

anerobic glycolysis

51
Q

What are type 1 motor units

A

(“slow twitch”): Units with neurons innervating slow efficient aerobic cells (maintaining posture, walking) innervates type 1 muscle fibres

52
Q

What are type 2 motor units

A

(“fast twitch”): Units with the neurons innervating the large fibres that fatigue rapidly but develop large forces (jumping, weight lifting) innervates type 2 muscles fibres

53
Q

What is the regulation of force dependent on?

A
  1. Increase no. of AP down one motor unit (twitches merge = force increase but same number of cells involved) Rate of stimulation of individual motor units
  2. No. or motor units recruited (depends on what muscle is needed for changes the amount of force needing to be developed → no. of muscle fibres recruited)
54
Q

When are large anaerobic fibres recruited?

A

Last

55
Q

When are small aerobic fibres recruited?

A

First

56
Q

What type of fibre is the most fatigue RESISTANT

A

type 1 (small aerobic)

57
Q

What type of muscle fibre uses the least amount of voltage

A

type 1

58
Q

What happens as more motor units are recruited/used

A

the tension increases

59
Q

How many twitchs does a single stimulus cause?

A

A single twitch: A single stimulus is delivered causing the muscle to contract and relax

60
Q

How long is the twitch compared to the length of the AP in skeletal muscle

A

Twitch is multiple times the length of an AP (voltage change)

61
Q

Complete Tetanus meaning (in relation to stimuli)

A

There is no relaxation of the muscle fibers between stimuli

62
Q

When occurs when there is a low stimulation frequency (i.e. temporal summation)?

A

The twitch turns into an unfused (incomplete) tetanus: If another stimulus is applied before the muscle relaxes completely, then more tension results. This is temporal (or wave) summation and results in unfused (or incomplete) tetanus

63
Q

What occurs when there is a high stimulation frequency?

A

The twitch turns into a fused (complete) tetanus: At higher stimulus frequencies, there is no relaxation at all between stimuli.

64
Q

What does an increased frequency of stimuli cause?

A

Increased frequency = Temporal Summation

BIOSCI 107 Part Two (17 decks)

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