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Physiology of physical activity > Lecture 5 > Flashcards

Lecture 5 Flashcards

1
Q

What are 4 key differences between the muscles of the eye and the biceps muscle?

A

Muscles of Eye vs biceps muscle:
Small size of motor units vs large size of motor units
- 10-15 fibre innervated by 1 motor neuron vs 1000+ fibre stimulated by 1 motor neuron
large number of motor units vs small number of motor units
- Allows for PRECISE movement vs allows for gross/powerful movement

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2
Q

What are 3 factors of the force of muscle contraction at the fiber level? 2 factors at the whole muscle level?

A

At the fibre level:
1) Frequency of stimulation
– takes time to take up slack and stretch the series elastic components
2) Relative size (diameter) of the muscle fibres
– the bulkier the muscle (greater cross-sectional area), the greater its strength
3) Muscle fibre and sarcomere length:
– muscles contract strongest when muscle fibers are 80-120% of their normal resting
length

At the whole muscle level:
4) Recruitment: number of muscle fibres stimulated
– the more motor units recruited, the stronger the contraction
5) Size Principle
– small force = small motor units, large force = large motor units

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3
Q

What is a muscle twitch? What are the 3 phases?

A

A muscle twitch is the response of a muscle to a single action
potential of its motor neuron.
The fibres contract quickly and then relax

Latent Period
Period of Contraction
Period of Relaxation

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4
Q

What is going on during the period of contraction and the period of relaxation?

A

Period of Contraction –cross bridges are active and the muscle shortens if the tension is great enough to overcome the load

Period of Relaxation – Ca2+is pumped back into SR and muscle tension decreases to
baseline level 10-100 ms

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5
Q

What are the 2 main categories of muscle fibers? What are the 2 subtypes of the 2nd main category of muscle fiber?

A

– Type I (Slow twitch, oxidative)
– Type II (Fast twitch, glycolytic)

» Type IIa fast oxidative glycolytic
» Type IIx fast glycolytic

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6
Q

What are 5 defining characteristics of each type of muscle fiber?

A 
-Type I slow oxidative fibres  
Small / weak contraction
Aerobic respiration
‘red fibres’
Twitch = 200 ms
Very Efficient & Non-fatiguable
-Type IIa fast oxidative-glycolytic fibres:
Intermediate / Strong contraction
Anaerobic & Aerobic 
Respiration
Twitch = 100 ms
Quick & Less fatiguable than IIx
-Type IIx fast glycolytic fibres:
Very Strong
Anaerobic respiration
‘white fibres’ 
Twitch = 50 ms
Highly fatiguabl
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7
Q

What is the difference in size and colour of type 1 and type 2 fibers? Which muscle fiber types have the strongest contraction, from strongest to weakest?

A

Type 1=red and smaller

Type 2=white and larger

Type 2 X
Type 2 A
Type 1

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8
Q

What is the difference in myosin ATPase for type 1 and type 2 fibers?

A
  • Type I
  • slow myosin ATPase
  • Generates force slowly
  • Type II
  • Fast myosin ATPase
  • Generates force quickly
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9
Q

How resistant is each muscle fiber type to fatigue?

A
  • Type I: fatigue resistant
  • Type IIa: moderately fatigable
  • Type IIx: very fatigable
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10
Q

What are the 4 key factors in the generation of force?

A
  • Frequency of stimulation
  • Number of motor units activated
  • Muscle fibre and sarcomere length
  • Speed of Contraction
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11
Q

How do muscles respond to a higher stimulation frequency?

A

– If second electrical shock is administered before complete relaxation of muscle.
• Repeated action potential hit fibre
– Second contraction is stronger until max tension is reached

  • More rapidly delivered stimuli result in incomplete tetanus –sustained but quivering contraction
  • Stimulus 30 X /sec – max tension but slight relaxation between contractions
  • If stimuli are given quickly enough, complete tetanus results –smooth, sustained contraction with no relaxation period
  • Stimulus 100 X /sec
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12
Q

How does motor unit recruitment relate to muscle force generation?

A

• Contraction stimulus determined by effort
– Greater effort = greater efferent signal
– Stimulating more muscle fibres to contract
More muscle fibres contracting → greater force
- Remember a muscle = bundle of muscle fibres
– Recruitment occurs at the level of the motor unit
• Movements requiring low effort recruit smaller, slow motor units
• Movements requiring large effort recruit large motor units

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12
Q

How does motor unit recruitment relate to muscle force generation?

A

• Contraction stimulus determined by effort
– Greater effort = greater efferent signal
– Stimulating more muscle fibres to contract
More muscle fibres contracting → greater force
- Remember a muscle = bundle of muscle fibres
– Recruitment occurs at the level of the motor unit
• Movements requiring low effort recruit smaller, slow motor units
• Movements requiring large effort recruit large motor units

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13
Q

What is henneman’s size principle? What is the reasoning behind this?

A

Order of motor unit recruitment is related to - size of motor units

  • Small units recruited first
  • Large units recruited last

Larger neurons are more difficult to depolarize to threshold
Requires greater synaptic input
- Small neurons excited first (low input TYPE I)
- next large neurons (high input TYPE II)

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14
Q

How is the amount of force generation controlled?

A

Amount of tension/force controlled by SIZE & NUMBER of stimulated fibres

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15
Q

What are the 3 potential actions during a muscle contraction?

A

isometric
shortening(isotonic)
lengthening(isotonic)

16
Q

What is a unique feature of isometric contractions?

A

The cross bridges generate force, but do not move the thin filaments

No change in overall muscle length

In isometric contractions, increasing muscle tension (force) is measured

17
Q

What is the definition of an isotonic contraction? What are the two types?

A

In isotonic contractions, the muscle changes length and moves the load. Once sufficient tension has developed to move the load, the tension remains relatively constant through the rest of the contractile period.

Two types of isotonic contractions:
Concentric contractions – the muscle shortens and does work
Eccentric contractions – the muscle contracts as it lengthens

18
Q

Which type of isotonic contraction leads to DOMS?

A

Eccentric actions place a stretch on the sarcomeres to the point where the myofilaments may experience strain, otherwise known as exercise induced delayed
onset muscle soreness (DOMS)

19
Q

What are key differences between slow and fast motor units?

A

Slow motor units contain slow fibres:
• Myosin with long cycle time and therefore uses ATP at a slow rate.
• Many mitochondria, so large capacity to replenish ATP.
• Economical maintenance of force during isometric
contractions and efficient performance of repetitive slow
isotonic contractions.

Fast motor units contain fast fibres:
• Myosin with rapid cycling rates.
• For higher power or when isometric force produced by slow motor units is insufficient.
• Type IIa fibers are fast and adapted for producing sustained power.
• Type IIx fibers are faster, but non-oxidative and fatigue rapidly.

20
Q

What happens to performance because of aging? what specific thing declines with aging? What is the result of this decline?

A

Performance declines, despite maintenance of physical activity

Number of motor units declines during aging so more fibers per muscle unit

  • FF motor units get smaller in old age and decrease in number
  • S motor units get bigger with no change in number
  • Decreased rate of force generation and POWER!!
21
Q

How does aging affect muscle injury(3 things)?

A

• Muscles in old animals are more susceptible to contraction-induced
injury than those in young or adult animals.
• Muscles in old animals show delayed and impaired recovery following
contraction-induced injury.
• Following severe injury, muscles in old animals display prolonged,
possibly irreversible, structural and functional deficits.

22
Q

Are muscle tissues prone to disorder? what’s one exception?

A

• Muscle tissues experience few disorders
– *Heart muscle is the exception
– Skeletal muscle – remarkably resistant to infection
– Smooth muscle – problems stem from external irritants

23
Q

What is muscular dystrophy? What are the 2 types?

A

Muscular dystrophy – a group of inherited muscle destroying disease
• Affected muscles enlarge with fat and connective tissue
• Muscles degenerate

  • Types of muscular dystrophy:
  • Duchenne muscular dystrophy
  • Myotonic dystrophy
24
Q

How did muscular dystrophy use to be classified? How is it classified now?

A
  • Muscular dystrophies have in the past been classified based on subjective and sometimes subtle differences in clinical presentation, such as age of onset, involvement of particular muscles, rate of progression of pathology, mode of inheritance.
  • Since the discovery of dystrophin, numerous genetic disease loci have been linked to protein products and to cellular phenotypes, generating models for studying the pathogenesis of the dystrophies.

Proteins localized in the nucleus, cytosol, cytoskeleton, sarcolemma, and ECM

25
Q

What are 2 other types of muscle tissue disorders?

A

• Myofascial pain syndrome – pain is caused by tightened bands of muscle fibers

• Fibromyalgia – a mysterious chronic-pain syndrome
– Affects mostly women
– Symptoms – fatigue, sleep abnormalities, severe musculoskeletal pain, and headache

Physiology of physical activity (11 decks)

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