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Biology > Muscle structure and contraction > Flashcards

Muscle structure and contraction Flashcards

1
Q

What happens in a reflex action?

A
  1. Stimulus (heat)
  2. Pain receptor-stimulated
  3. Signal sent along sensory neuron
  4. Signal passed along relay neuron (message sent to brain)
  5. Signal sent along motor neuron
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2
Q

Muscles

A
  • Effectors
  • Carry out a response to a stimulus
  • Bring about movement
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3
Q

Three types of muscle

A
  • Cardiac
  • Smooth
  • Skeletal
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4
Q

Cardiac muscle

A
  • Found in heart
  • Involuntary
  • No conscious
  • Striated
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5
Q

Smooth muscle

A
  • Found in walls of blood vessels and digestive systems
  • Involuntary
  • No conscious control
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6
Q

Skeletal muscle

A
  • Found attached to the bone
  • Voluntary
  • Conscious control
  • Striated

Contract - pulling on incompressible bone to move them
- Can’t push - must work in antagonistic pairs = opposing actions

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7
Q

Antagonistic examples

A
  • Biceps and triceps

- Hamstring and quadriceps

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8
Q

What are skeletal muscles made of?

A
  • Tiny muscle fibres - Myofibrils
  • Made up of 2 types of myofilaments (even smaller)
  • The fibres line up parallel to each other to maximise strength and increase power
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9
Q

Muscle is an example of tissue

A
  • Made up of many similar cells = work together to carry out specific function
  • Movement
  • Separate muscle cells fuse together into muscle fibres - share nuclei and cytoplasm = SARCOPLASM
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10
Q

Sarcoplasm

A
  • Mainly found around muscle fibres

- Contains many mitochondria = ATP in respiration and ER

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11
Q

Two myofilaments

A
  • Actin and Myosin
  • Both fibrous proteins
  • Arranged in repeated units - Sacromeres
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12
Q

Actin

A
  • Protein filament
  • Thinner
  • Made up of 2 strands twisted around each other
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13
Q

Myosin

A
  • Protein filament
  • Thicker
  • Long rod shaped tails with bulbous heads
  • Project the side
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14
Q

Sarcomere structure

A
  • Myofibrils - striated - alternating light and dark coloured bands
  • Light = I bands - only actin - no overlap with myosin
  • Dark = A bands - overlapping actin and myosin
  • End of each A band - lighter coloured area - H-Zone - myosin filaments - no overlap with actin
  • Centre of I band - Z line - distance between z lines in sacromere
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15
Q

What do skeletal muscles contain?

A
  • Mixture of slow and fast twitch fibres

- Proportion may change depending on location and function of muscle

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16
Q

Two types of muscle fibre

A
  1. Fast twitch

2. Slow twitch

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17
Q

Fast twitch

A
  • Quick and powerful contraction
  • Tire quickly - act for short period
  • Dominant in athletes for power events
  • Appear dark stained
18
Q

Fast twitch muscle adaptions

A
  • Aneraboic respiration
  • Thicker + more numerous myosin filaments
  • High concentration of glycogen
  • Rely on glycolysis - ATP production = rapid contraction
  • Lots of ATPase to synthesis ATP from ADP and Pi
  • Lots of phosophocreatine - molecule rapidly generate ATP
    = Lactic acid can build up
19
Q

Slow twitch

A
  • Slow, less powerful contraction
  • Don’t tire quickly - act over a longer period
  • More common in endurance exercise (tennis)
  • White
20
Q

Slow twitch muscle adaptions

A
  • Aerobic respiration
  • Lots of mitochondria to supply ATP
  • High conc of myoglobin - stores o2
  • Numerous blood vessels deliver o2 and glucose
  • Contraction is delayed due to complex aerobic reactions
21
Q

Silent filament mechanism

A
  • Theory of muscle contraction

- Actin and myosin don’t get shorter = slide past each other = overall size of sacromere + muscle decrease

22
Q

Sacromere is contracted

A
  • Shorter I band
  • Z lines move closer together
  • Little/no H zone (myosin)
  • A band remains the same width as the myosin filaments have not become shorter
23
Q

Muscle proteins

A
  • Actin
  • Myosin
  • Tropomyosin
  • Troponin
24
Q

Actin

A

Binding sites

25
Q

Tropomyosin

A
  • Forms long threads that are wound around actin filaments - prevent myosin-binding
  • Muscle relaxed
26
Q

Myosin

A
  • Tails
  • 2 bulbous heads at one end
  • Heads fit into the binding sites on actin
27
Q

Cross bridges

A
  • Relaxed muscles - tropomyosin molecules block binding sites of the actin
  • Myosin heads = resting position
  • ADP + Pi bound to myosin head
  • CA2+ stimulates - troponin = tropomyosin to change shape which exposes the binding site on actin
  • Myosin head attach = cross-bridge + head tilts
  • Moves the actin filament along = sarcomere is shorter
  • ADP molecule detaches
28
Q

Power stroke

A
  • Movement of myosin
  • Dragging actin = power stroke
  • Myosin cross bridge binds to actin molecule
  • Cross bridge bends - pulling thin myofilament inward
  • Cross bridge at end of power stroke + returns to original conformation
  • Cross bridge binds to more distal actin molecule = repeat
29
Q

Detachment

A
  • ATP attaches to each myosin head
    = detach from actin-binding site
  • ATP hydrolysed by ATPase = energy for myosin head to return to original position

REPEAT
- Myosin head + ADP molecule reattaches itself further along the actin filament

30
Q

Sarcolemma

A
  • Cell membrane of a striated muscle fibre cell
31
Q

Sarcoplasmic Reticulum

A
  • System of flattened membranes

- Stores and pumps out Ca2+ ions

32
Q

Sarcomeres

A
  • Repeated units of myosin and actin in the muscle
33
Q

Troponin

A
  • Globular protein

- Moves tropomyosin so myosin can bind

34
Q

Muscle relaxation

A
  • Nerve stimulation stops
  • Ca2+ are actively transported back to SR - energy from hydrolysis of ATP
  • Reabsorption of Ca2+ allows tropomyosin to block the actin filament again
  • Myosin heads no longer bind to actin filament = muscle no longer contracts
  • Sarcomere will lengthen
35
Q

ATP

A
  • Hydrolysed to ADP + Pi = energy
  • For myosin heads to return to their original position
  • Reabsorption of Ca2+ into SR by active transport
36
Q

ATP synthesis

A
  • Synthesised in small amounts in anaerobic respiration
  • Larger amounts in aerobic respiration - series of reactions - can be slow (not immediate)
  • Generated more rapidly anaerobically using phosphocreatine
  • Stored in muscle + acts as a reserve supply of phosphate which can combine with ADP to make ATP
  • Phosphocreatine store - replenished using phosphate from ATP when the muscle is relaxed.
37
Q

ATP synthesis formula

A

Phosphocreatine + ADP = creatine + ATP - energy

ATP + creatine = ADP + phosphocreatine

38
Q

Neuromuscular junction

A
  • The point where a motor neurone meets a muscle fibre
  • Lots of them along a muscle - enable muscle fibres to contract simultaneously
    = Muscle action fast and powerful
  • Action to transmit the message across the synapse - same as in a cholinergic synapse (acetylcholine)
39
Q

What happens when acetylcholine diffuses to the postsynaptic membrane

A
  • Causes SR to release its store of Ca2+ into the myofibrils
  • Calcium binds to troponin on thin filament = changes shape, moving tropomyosin into the groove in the process
  • Myosin cross bridges can now attach + cross bridge cycle can take place
40
Q

Motor unit

A
  • Motor fibres supplied by a single motor neurone
41
Q

Small force

A
  • Only a few units are stimulated
42
Q

Large force

A
  • A lot of units are stimulated

Biology (16 decks)

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