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Neuronal Communication > Sliding Filament Model > Flashcards

Sliding Filament Model Flashcards

1
Q

what happens to myosin filament during contraction?

A

myosin filaments pull actin filaments inwards towards the centre of sarcomere.

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2
Q

what happens when the myosin filaments pulls the actin filament towards the centre of the sacromere?

A
  • light band becomes narrower.
  • Z lines move closer together which shortens the sacromere.
  • The H-zone becomes narrower.
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3
Q

what happens to the dark bands during contraction?

A

the dark bands stay the same width the myosin filaments themselves have no yet shortened, but overlap the actin filaments by a greater amount.

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4
Q

what causes movement?

A

the simultaneous contraction of lots of sarcomeres causes myofibrils and muscle fibres contract. when sarcomeres return to their original length the muscle relaxes.

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5
Q

why do myosin filaments have hinged globular heads?

A

it allows them to move forwards or backwards.

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5
Q

what forms the myosin filament?

A

several hundred myosin molecules

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6
Q

where are actin-myosin binding sites located?

A

on the actin filament.

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7
Q

what is the name of the protein that often blocks the actin-myosin binding site?

A

tropomyosin. held in place by the protein troponin.

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8
Q

what happens when a muscle is in a resting state?

A

actin myosin binding sites are blocked by tropomyosin. this means that myosin cannot bind with actin and filaments can’t slide past each other.

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9
Q

what happens when a muscle is stimulated to contract?

A
  1. myosin heads form bonds with actin filaments.
  2. myosin heads change angle in unison which pulls the actin filament along the myosin filament.
  3. myosin then detaches from the actin and its head returns to its original angle, using ATP.
  4. myosin reattaches further along the actin filament and the process occurs again.
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10
Q

what are the bonds called between myosin heads and actin filaments?

A

actin-myosin cross bridges.

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11
Q

what is a neuromuscular junction?

A

the point where the motor neurone and skeletal muscle fibre meet.

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12
Q

what triggers muscle contraction?

A

when an action potential arrives at a neuromuscular junction.

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13
Q

why are there many neuromuscular junctions along muscle?

A

to ensure that all muscle fibres contract simultaneously.

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14
Q

what happens when an action potential reaches the neuromuscular junction?

A
  1. it stimulates calcium ion channels to open.
  2. calcium ions diffuse into the synapse into the synaptic knob, where they cause synaptic vesicles to fuse with the presynaptic membrane.
  3. Acetylcholine is released into the synaptic cleft by exocytosis and diffuses across the synapse.
  4. it binds to receptors on the postsynaptic membrane (sarcolemme.) this opens sodium ion channels and results in depolarisation.
  5. acetylcholine is broken down by acetylcholinesterase into chlorine and ethanoic acid. this prevents the muscle from being overstimulated.
  6. choline and ethanoic acid diffuse back into the neurone, where they are recombined into acetylcholine, using the energy provided by the mitochondria.
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15
Q

how does the depolarisation of the sarcolemma travel deep into muscle fibre?

A

by spreading through the T-tubules.

16
Q

are T tubules in contact with the sarcoplasmic reticulum?

A

yes.

17
Q

where does the sarcoplasmic reticulum get the stored calcium ions?

A

it actively absorbs calcium ions from the sarcoplasm.

18
Q

what happens when an action potential reaches the sarcoplasmic reticulum?

A

it stimulates calcium ion gates to open. calcium ions diffuse down their concentration gradient, flooding the sarcoplasm with calcium ions.

19
Q

what causes tropomyosin to move away from actin myosin binding sites?

A

calcium ions bind to troponin causing it to change shape. it pulls on tropomyosin and moves it away from actin myosin binding sites.

20
Q

what activates the ATPase activity of the myosin?

A

calcium ions in the sarcoplasm.

21
Q

how does the myosin head return to its original position?

A

calium ions present in sarcoplasm actvates ATPase activity of myosin. this hydrolyses ATP to ADP and inorganic phosphate. releasing energy which the myosin head uses to return to its original position.

22
Q

does muscle contraction require lots of energy?

A

yes.

23
Q

what provides energy for muscle contraction?

A

hydrolysis of ATP into ADP and phosphate.

24
Q

what are the main ways ATP is generated?

A
  • aerobic respiration
  • anaerobic respiration.
  • creatine phosphate.
25
Q

how does aerobic respiration generate ATP?

A
  • most of ATP used by muscle cells is regenerated from ADP during oxidative phosphorylation.
  • aerobic respiration is only used for periods of low-intensity exercise as it requires oxygen.
26
Q

how does anaerobic respiration generate ATP

A
  • in very active muscles, oxygen is used up more quicklythan blood supply can replace it.
  • ATP is made by glycolysis but since no oxygen is present, pyruvate is converted into lactic acid.
  • if lactic acid builds up in muscles, this could result in muscle fatigue.
27
Q

how does creatine phosphate generate ATP?

A
  • creatine phosphate is stored in muscles.
  • creatine phosphate acts as reserve supply of phosphate which is available to combine with ADP reforming ATP .
  • store of phosphate used up quickly.
28
Q

how can muscle activity be monitored with sensors?

A

monitor electrical activity in a muscle.

29
Q

what can be measured with sensors?

A

the strength of a muscle contraction or to track muscle fatigue levels.

30
Q

what is muscle fatigue?

A
  • a long-lasting reduction of the ability to contract and exert force.
  • normally localised and occurs after prolonged relatively strong muscle activity.
  • can be helpful for promoting muscle growth but is usually harmful as serious injury is most likely to occur.
31
Q

what is an electromyogram?

A

a record of electrical activity in a muscle during an activity.

32
Q

why is detecting muscle fatigue important?

A
  • for research into human-computer interactions.
  • sport injuries and perfomance.
  • ergonomics
  • prosthetics.
33
Q

what does a typical experiment into muslce fatigue look like?

A
  • subject performing a set task such as moving a limb in a specified manner. a signal is acquired using sensors attached to the skin, which is recorded and processed to reveal characteristics of muscle during that exercise.
34
Q

what changes in signal are required to identify fatigue?

A
  • an increase in the mean amplitude of the signal.
  • a decrease in the frequency of the signal.
  • disruption to the overall pattern existing within the signal.

Neuronal Communication (10 decks)

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