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Musculoskeletal > Skeletal muscle physiology > Flashcards

Skeletal muscle physiology Flashcards

1
Q

What are the 5 main functions of skeletal muscle?

A
  1. Maintenance of posture
  2. Purposeful movement in relation to external environment
  3. Respiratory movement
  4. Heat production
  5. Contribution to whole body metabolism
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1
Q

What are the 3 types of muscle?

A

Cardiac
Smooth
Skeletal

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2
Q

Which types of muscle are striated?

A

Skeletal
Cardiac

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3
Q

Which types of muscle are involuntary?

A

Smooth
Cardiac

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4
Q

Which type of muscle is voluntary?

A

Skeletal

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5
Q

What causes striation of muscle?

A

Alternation of dark bands (Myosin filaments) and light bands (Actin filaments)

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6
Q

Where does skeletal muscle receive its calcium for excitation contraction coupling?

A

Entirely from the sarcoplasmic reticulum

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7
Q

Where does cardiac muscle receive its calcium for excitation contraction coupling?

A

ECF and sarcoplasmic reticulum (Calcium induced calcium release)

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8
Q

What is meant by a motor unit?

A

This is a single alpha motor neurone and all the skeletal muscles fibres that it innervates

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9
Q

How many muscle fibres will be contained in a motor unit with fine movement requirements?

A

Only around 10

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10
Q

How many muscle fibres will be contained in a motor unit with power movement requirements?

A

100s to 1000s

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11
Q

What are some examples of muscles with fine motor requirements?

A

External eye muscles
Muscles of facial expression
Intrinsic hand muscles

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12
Q

What is meant by a muscle fibre?

A

One single muscle cell

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13
Q

How is a muscle fibre organised?

A

It is a bundle of myofibrils surrounded by a sarcoplasm, containing multiple nuclei and many mitochondria, all surrounded by a sarcolemma

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14
Q

What is the smallest contractile unit of the myofibril?

A

Sarcomere

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15
Q

What are the 5 zones of the sarcomere?

A

A-band
H-zone
M-line
I-band
Z-line

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16
Q

What is the A band?

A

This is the overlap between thick and thin filaments

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17
Q

What is the H zone?

A

This is the section containing only myosin thick filaments

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18
Q

What is the M line?

A

This is the line that passes vertically down the H zone at the centre of the thick filaments

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19
Q

What is the I band?

A

This is the section containing only actin thin filaments

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20
Q

What is the Z line?

A

This is the vertical line connecting the actin filaments

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21
Q

What is the sliding filament theory?

A

The theory that muscle tension is produced by the sliding of actin filaments over the myosin filaments

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22
Q

Describe the contraction stages of the sliding filament theory

A

Ca2+ binds to troponin, on tropomyosin fibres (Wrapped around the actin filaments), causing a conformational change allowing the uncovering of myosin binding sites on the actin filament

Ca2+ also causes excitation allowing the binding of myosin cross-bridges to myosin binding sites on actin

The actinomyosin cross-bridge then bends, via breakdown of ATP, allowing for a “power stroke” causing the release of ADP and Pi, as well as energy

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23
Q

Describe the relaxation stage of the sliding filament theory

A

ATP then binds to the cross-bridge, allowing for detachment of the cross-bridge from actin

The breakdown of this ATP into ADP and Pi then allows for resetting where the cross-bridge returns to its normal place

Ca2+ is actively taken up by the sarcoplasmic reticulum when there is no longer an action potential, meaning that tropomyosin can return to its normal place, preventing myosin binding to actin filaments

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24
Q

What causes rigour mortis in death?

A

Rigor mortis is caused by a lack of ATP due to cessation of metabolism, meaning that myosin cross-bridges cannot detach from actin, and Ca2+ cannot be pumped back into the sarcoplasmic reticulum, so muscle remain contracted

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25
Q

What is meant by excitation contraction coupling?

A

This is the process whereby the surface action potential results in activation of the contractile structures of the muscle fibre

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26
Q

Describe the process of excitation contraction coupling in skeletal muscle fibres

A

Ca2+ is released from the lateral sacs of the sarcoplasmic reticulum when the surface action potential spreads down the transverse T-tubules

27
Q

What are T-tubules?

A

These are extensions of the surface membrane that dip into the muscle fibre

28
Q

What are the 2 primary factors that affect skeletal muscle tension gradation?

A

Number of muscle fibres contracting
Tension developed by each contracting muscle type

29
Q

What is meant by asynchronous motor unit recruitment?

A

This means that while some motor units are contracting, others aren’t, resulting in a sub-maximal contraction, protecting against muscle fatigue

30
Q

What factors affect the tension developed by each contracting muscle fibre?

A

Frequency of contractions
Summation of contractions
Length of muscle fibre
Thickness of muscle fibre

31
Q

What is meant by twitch summation?

A

In skeletal muscle, the duration of action potential is much shorter than the duration of the resulting twitch

It is therefore possible to summate twitches to bring about stronger contraction through repetitive fast stimulation of skeletal muscle
This is because the latent period of the action potential will have passed before the twitch ends

32
Q

What will occur if a muscle fibre is re-stimulated after it has completely relaxed?

A

The second resulting twitch will be of the same magnitude as the first, as there is no summation of contractions

33
Q

What will occur if a muscle fibre is re-stimulated before it has completely relaxed?

A

The second twitch is added onto the first twitch, resulting in summation, and thus a greater level of contractility

34
Q

What will occur is the muscle fibre is stimulated so rapidly that it does not have an opportunity to relax between stimuli?

A

A maximal sustained contraction known as tetanus will occur

35
Q

What happens after a prolonged period of tetanus?

A

Tetanus cannot be sustained for long periods of time and fatigue will begin, unless the stimulus is stopped, meaning that contractility will decrease

36
Q

Why can cardiac muscle not be tetanised?

A

Cardiac membrane potential has a much longer refractory period

37
Q

What is meant by optimal length for maximal tetanic contraction?

A

This is the optimal length of a muscle so that there is an adequate overlap between myosin and actin, thus that maximal tetanic contraction can occur

38
Q

Why does percentage of maximal tetanic contraction decrease if the muscle fibre is too long?

A

Fewer thin-filament binding sites are accessible for binding with thick filament cross bridges

39
Q

Why does percentage of maximal tetanic contraction decrease if the muscle fibre is too short?

A

Fewer thin-filament binding sites are exposed to thick filaments because the thin filaments overlap with each other

40
Q

What are the 2 components of a skeletal muscle?

A

Contractile component
Series-elastic component

41
Q

What makes up the contractile component of the skeletal muscle?

A

The cross-bridge cycling with sarcomeres

42
Q

What makes up the series-elastic component of a skeletal muscle?

A

Transmission of tension to bone via the stretching and tightening of muscle connective tissue and tendons

43
Q

What are the 2 main types of skeletal muscle contraction?

A

Isotonic contraction
Isometric contraction

44
Q

What are the uses of isotonic muscle contractions?

A

Body movements and movement of objects

45
Q

What are the uses of isometric muscle contractions?

A

Supporting objects in fixed positions
Maintaining body posture

46
Q

What is meant by isotonic contraction?

A

Muscle tension remains constant as muscle length changed

47
Q

What is meant by isometric contraction?

A

Muscle tension develops at constant muscle length

48
Q

What are the 3 main differences between types of skeletal muscle fibre?

A

Enzymatic pathways for ATP synthesis
Resistance to fatigue
Activity of myosin ATPase

49
Q

What effect does myosin ATPase have on muscle contraction?

A

It determines the speed at which energy is made available for cross-bridging

50
Q

What is the usual number of types of muscle fibres contained in 1 motor unit?

A

1

51
Q

What are the 3 types of skeletal muscle fibre?

A

Slow oxidative (Type I)
Fast oxidative (Type IIa)
Fast glycolytic (Type IIx/IIb)

52
Q

What are the 3 main metabolic pathways for ATP production

A
  1. Transfer of high energy phosphate from creatinine phosphate to ADP to form ATP
  2. Oxidative phosphorylation (aerobic)
  3. Glycolysis - Pyruvic acid to lactic acid (Anaerobic)
53
Q

What are the characteristics and uses of slow oxidative skeletal muscle fibres?

A

Slow contraction speed
High resistance to fatigue
High capacity for oxidative phosphorylation
Many mitochondria
Low myosin ATPase

Used in prolonged, low work, aerobic activity (e.g. maintenance of posture, walking)

54
Q

What are the characteristics and uses of fast oxidative skeletal muscle fibres?

A

Fast speed of contraction
Intermediate resistance to fatigue
Intermediate levels of enzymes fro anaerobic glycolysis
High level of ATPase activity
High oxidative phosphorylation capacity

Used for both aerobic and anaerobic activity and are useful in prolonged relatively moderate work (e.g. jogging)

55
Q

What are the characteristics and uses of fast glycolytic skeletal muscle fibres?

A

Fast speed of contraction
Low resistance to fatigue (Lactic acid)
low oxidative phosphorylation capacity
High levels of anaerobic enzymes

Used in anaerobic activity such as short term, high intensity exercise (e.g. jumping)

56
Q

What is a reflex?

A

A stereotyped response to a specific stimulus

57
Q

What is the purpose of a stretch reflex?

A

This serves as a negative feedback that resists passive change in muscle length to maintain optimal resting muscle length

58
Q

Describe the pathway of the patellar tendon reflex?

A

When a hammer hits the patellar tendon, the sensory receptor is the muscle spindle itself and is activated by the muscle stretch

This causes the firing of the afferent neurones which synapse in the spinal cord with the alpha motor neurones that innervate the stretched muscle

Activation of the reflex results in contraction of the stretched muscle, in this case, the quadriceps femurs

59
Q

What are muscle spindles?

A

Muscle spindles are a collection of specialised muscle fibres that act as the sensory receptors for stretch reflex

60
Q

Where are muscle spindles found?

A

These are found within the belly of the muscles and run parallel to ordinary muscle fibres

61
Q

How are muscle spindles specialised?

A

They have sensory nerve endings known as annulospiral fibres which increase firing as the muscle is stretched

62
Q

What is the motor supply to the muscle spindles called?

A

Gamma motor neurones

63
Q

How do gamma motor neurones affect muscle spindles?

A

They just the level of tension in the muscle spindles to maintain their sensitivity to stretch (Stop them going loose)

64
Q
A

Musculoskeletal (123 decks)

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