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Biology Paper 2 (5-8) > Skeletal muscles are stimulated to contract by nerves and act as effectors > Flashcards

Skeletal muscles are stimulated to contract by nerves and act as effectors Flashcards

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1
Q

Which muscle is found in the heart?

A
  • cardiac
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2
Q

Which muscle is involuntary?

A
  • cardiac
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3
Q

Which muscle is found most in the body?

A
  • skeletal
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4
Q

Which muscle is found along arteries and veins?

A
  • smooth
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5
Q

Which muscle is also involuntary?

A
  • smooth
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6
Q

Which muscle is really thick?

A
  • cardiac
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7
Q

Which muscle is able to be controlled when it relaxes and contracts?

A
  • skeletal
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8
Q

Which muscle is often around the joints?

A
  • skeletal
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9
Q

Which muscle contracts in a different way to the other two?

A
  • skeletal
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10
Q

Which muscle is usually found in pairs, working antagonistically?

A
  • skeletal
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11
Q

Structure of the smooth muscle

A
  • cells are spindle shaped with one central nucleus
  • contractile filaments irregularly arranged
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12
Q

Why are the contractile filaments irregularly arranged?

A
  • so that the contraction is not in one direction as in skeletal muscle
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13
Q

Structure of cardiac muscle

A
  • cells branch and connect with each other
  • specialised striated muscle that does not fatigue
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14
Q

Why do cells in cardiac muscle branch and connect with each other?

A
  • to assist the passage of nerve impulses through the muscle
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15
Q

Structure of skeletal muscle

A
  • muscle fibres
  • myofibril
  • protein filaments
  • fascicles
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16
Q

Muscle fibres

A
  • cells that make up skeletal muscle
  • they have fused together and share nuclei and cytoplasm
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17
Q

Fascicles

A
  • bundles of muscle fibres
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18
Q

Myofibril

A
  • bundle of protein filaments wrapped in endomysium (found in muscle fibres) that make up the muscle fibres
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19
Q

Protein filaments

A
  • when bundled together and wrapped in endomysium, make up myofibril
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20
Q

Actin

A
  • thinner, globular protein with twisted chains
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21
Q

Tropomyosin

A
  • forms long thing threads around actin filaments with troponin proteins present
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22
Q

Troponin

A
  • proteins present in tropomyosin wound around d actin filaments
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23
Q

Myosin

A
  • thicker fibre made of two proteins (fibrous protein arranged into a filament made up of several hundred molecules, the tail) and (globular protein which forms a bulbous head which protrudes from filament)
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24
Q

Sarcomere

A
  • section of myofibril that appears banded due to filaments present
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25
Q

Light band

A
  • I (isotopic) band - filaments don’t overlap
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26
Q

Dark band

A
  • A (anisotropic) band - filaments do overlap
27
Q

Neuromuscular junction

A
  • part where a motor neurone meets (synapses with) a skeletal muscle fibre.
28
Q

What does multiple junctions along the length of a muscle allow for?

A
  • rapid and powerful contraction when simultaneously stimulated by action potentials
29
Q

What do all muscle fibres supplied by a single motor neurone act as?

A
  • a single functional motor unit
30
Q

What does the number of units stimulated depend on?

A
  • the force required
31
Q

Sarcolemma

A
  • term for the cell membrane that encloses each muscle cell
32
Q

Sarcoplasm

A
  • cytoplasm of muscle cell
33
Q

What is the epimysium?

A
  • outer layer of muscle
34
Q

What is the perimysium?

A
  • inner layer of muscle
35
Q

What is the fasciculus?

A
  • giant muscle bundle
36
Q

What is tendon?

A
  • joins muscle to bone
37
Q

What is the Z zone?

A
  • light band section
38
Q

What is the H zone?

A
  • dark filaments only section
39
Q

What is the M zone?

A
  • middle of the dark band
40
Q

How does the body prevent overstimulation of the muscle as this neuromuscular junction?

A
  • breakdown of the acetylcholine neurotransmitter
41
Q

When the muscle contracts (actin fibres move inwards) what would happen to the length of the I band, A band, H zone, Z lines and sarcomere length?

A
  • All decrease except nothing happens to A band
42
Q

Describe muscle stimulation

A
  • action potential reaches neuromuscular junction, causing calcium ion channels to open
  • allowing calcium ions to move into the axon terminal
  • these ions cause the synaptic vesicles to fuse with the pre synaptic membrane and release molecules or neurotransmitter into the synaptic cleft
  • diffuses across the gap and binds with receptors on the post synaptic membrane causing it to depolarise
  • The action potential travels deep into the muscle fibre through a system of T –tubules that branch through the sarcoplasm
  • tubules are in contact with the endoplasmic reticulum of the muscle fibre (sarcoplasmic reticulum) which has actively absorbed calcium ions from the sarcoplasm in the muscle fibre
  • action potential opens the calcium ion channels in the sarcoplasmic reticulum and calcium ions diffuse back into the sarcoplasm down a diffusion gradient
43
Q

Muscle contraction first stages

A
  • calcium ions are released from sarcolemma after stimulation from the T system
  • calcium ions bind to the troponin and it changes shape
  • troponin displaces tropomyosin and exposes the myosin binding sites that were previously blocked
44
Q

Muscle contraction 1

A
  • The bulbous heads of the myosin attach to the binding sites on the actin filaments to form a cross-bridge – they have ADP attached to
    them which puts them in a state allowing them to do this
45
Q

Muscle contraction 2

A
  • the myosin heads change position to achieve a lower energy state and slide the actin filaments past the stationary myosin – we say that it ‘pushes the actin along with a power stroke’– the
    molecule of ADP is also released from the head in the process
46
Q

Muscle contraction 3

A
  • ATP binds to the bulbous heads of myosin and causes it to become detached
47
Q

Muscle contraction 4

A
  • Calcium then activates the enzyme ATPase which hydrolyses the ATP back to ADP. This provides the energy to “re-cock” the heads back into their normal position (recovery stroke), and the ADP stays attached to the myosin head – the cycle can begin again
48
Q

Muscle relaxation

A
  • When nervous stimulation ceases, calcium ions are actively transported back into the sarcoplasmic reticulum using energy from the hydrolysis of ATP
  • Troponin reverts to its normal shape allowing tropomyosin to re-block the actin filament binding site. Myosin heads are now unable to bind to actin filaments and the muscle relaxes - actin filaments slide back to their original position
49
Q

How might ATP production change compared to if you walked or sprinted and why might you want to respire anaerobically?

A
  • ATP production increases
  • anaerobic respiration quicker way of making ATP than aerobic respiration
50
Q

Why can intense exercise rapidly fatigue muscles?

A
  • lactate build up
51
Q

Why after exercise is lactate oxidised back into pyruvate to be aerobically respired?

A
  • make sure that the chemical energy locked up in lactate is not wasted
52
Q

Anaerobic respiration in muscles produces lactate (also known as lactic acid). Lactate lowers pH. Explain how this could lead to muscle fatigue and soreness.

A
  • lower pH increases concentration of H+ ions
  • H+ ions can alter hydrogen bonds and ionic bonds in proteins
  • changing tertiary structure
  • actin, myosin and tropomyosin could be less effective
  • active site of ATPase could change shape meaning it is not complementary to its substrate
  • preventing enzyme substrate complexes forming
  • less ATP regenerated
53
Q

What does phosphocreatine do?

A
  • regenerates ATP
54
Q

How does phosphocreatine regenerate ATP?

A
  • chemical that is stored in muscle and acts as a reserve supply of phosphates
  • During exercise, phosphocreatine phosphorylates ADP to ATP, so more ATP becomes available
  • at rest, ATP phosphorylates creatine back to phosphocreatine
55
Q

What are the two types of muscle fibres?

A
  • slow twitch and fast twitch
56
Q

What do fast twitch fibres mainly use and why?

A
  • anaerobic respiration
  • quicker process for producing ATP than aerobic respiration so fast fibres are better for short bursts of intense exercise
57
Q

What do slow twitch fibres mainly use and why?

A
  • aerobic respiration
  • yields more ATP per glucose molecules so slow fibres are better for endurance
58
Q

What are the main differences between slow and fast fibres?

A
  • slow fibres have many capillaries whereas fast fibres have fewer capillaries
  • slow fibres have higher myoglobin concentration whereas fast fibres have lower myoglobin concentrations
  • slow fibres have lower phosphocreatine concentration whereas fast fibres have higher phosphocreatine concentration
  • slow fibres have lower glycogen concentration whereas fast fibres have higher concentration of glycogen
59
Q

Why does a slow fibre have more capillaries than a fast fibre does?

A
  • provides lots of oxygen for the slow fibres so they can maintain a high rate of aerobic respiration
60
Q

Why do fast fibres have more phosphocreatine than slow fibres?

A
  • to help provide ATP quick enough for short bursts of intense exercise
61
Q

Why do fast fibres contain higher glycogen concentrations than slow fibres?

A
  • Fast fibres contract quicker than slow fibres
  • Fast fibres need to produce ATP quicker
  • Fast fibres mainly use anaerobic respiration
  • Less ATP per glucose is produced using anaerobic respiration
  • Fast fibres need to respire a lot of glucose
  • Large glycogen stores are needed in fast fibres to release enough glucose via hydrolysis
62
Q

Differences between myoglobin and haemoglobin

A
  • myoglobin contains one polypeptide chain whereas haemoglobin contains four polypeptide chains
  • myoglobin contains one haem group whereas haemoglobin contains four haem groups
  • myoglobin has oxygen store in muscle fibres whereas hameoglobin carries oxygen in red blood cells
  • myoglobin has no cooperative oxygen binding whereas haemoglobin has cooperative oxygen binding
63
Q

What is cooperative oxygen binding?

A
  • one oxygen binding makes it easier for the next one to bind
64
Q

Using the graph suggest why is myoglobin an excellent oxygen store?

A
  • Myoglobin has an extremely high affinity for oxygen (greater than haemoglobin)
  • it gives oxygen up at very low partial pressures
  • when it does release oxygen, it does so rapidly
  • this will help prolong aerobic respiration
  • and delay anaerobic respiration
  • and in turn, delay lactate production

Biology Paper 2 (5-8) (12 decks)

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