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Applied Exercise Physiology > Week 4 - Skeletal Muscle > Flashcards

Week 4 - Skeletal Muscle Flashcards

1
Q

Describe the functions of skeletal muscle

A

Force production for locomotion and breathing, postural support, heat production during cold stress, and acting as an endocrine organ

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2
Q

What are the types of connective tissue surrounding skeletal muscle

A

Epimysium (entire muscle)
Perimysium (fascicles)
Endomysium (muscle fibres)
Basement membrane (below endomysium)
Sarcolemma (muscle cell membrane)

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3
Q

Describe the microstructure of muscle fibres

A

Myofibrils (Actin & Myosin)
Sarcomere (Z line, M line, H zone, A band, I band)

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4
Q

Describe the role of satellite cells

A

Satellite cells play a key role in muscle growth and repair by increasing the number of nuclei in mature muscle fibres

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5
Q

Describe the event that occurs in the neuromuscular junction

A
  1. ACh released into the synaptic cleft
  2. ACh binds to nicotinic receptors on the motor endplate
  3. Cation-selective ion channels open in the motor endplate
  4. Local depolarisation of the motor endplate
  5. Depolarisation of muscle cell membrane
  6. Raised intracellular Ca2+ concentration
  7. Muscle contraction
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6
Q

What is the sliding filament model

A

Muscle shortening occurs due to the movement of actin filament over the myosin filament

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7
Q

Describe the contribution of energy in muscle contraction

A

Myosin ATPase breaks down ATP as fibre contracts.
Sources of ATP: PCr, Glycolysis, Oxidative phosphorylation

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8
Q

Describe the steps to Excitation-Contraction Coupling

A
  1. Signal from motor nerve fibre enters synaptic knob
  2. Synaptic vesicles release acetylcholine across synaptic cleft and to the Ach receptors on the sarcolemma of muscle fibre
  3. Release of Ach causes excitation of muscle fibre, which then travels to the T tubule and causes depolarisation
  4. Depolarisation opens calcium ion channels from sarcoplasmic reticulum and terminal cisterna of sarcoplasmic reticulum
  5. Calcium ion bind to troponin on actin molecule which causes a shift in the position of tropomyosin so that the myosin binding sites on actin are exposed. An ATP is used in this step
  6. Energised myosin cross-bridge binds to the active site on actin and pulls on the actin molecule to produce a back and forth movement
  7. Ach release stops, and the muscle fibre is repolarised
  8. Calcium is pumped from the cytosol into the sarcoplasmic reticulum
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9
Q

Define muscle fatigue

A

Fatigue = a decline in muscle power output
Occurs from decrease muscle force production and muscle shortening velocity

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10
Q

Describe the mechanisms of muscle fatigue in heavy exercise

A

Decreased calcium release from sarcoplasmic reticulum
Accumulation of metabolites (Pi, H+, free radicals) that inhibit myofilament sensitivity to calcium

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11
Q

Describe the mechanisms of muscle fatigue at moderate intensity

A

Increased radical production (modification of cross-bridge head)
Glycogen depletion
Accumulation of Pi + H+ does not contribute to fatigue during moderate intensity exercise

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12
Q

What causes exercise-associated muscle cramps

A

Hyperactive motor neurons in the spinal cord
High-intensity exercise can alter muscle spindle and golgi tendon organ function.
Increased excitatory activity of muscle spindles and reduced inhibitory effect of the golgi tendon organ

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13
Q

What are some strategies to alleviate EAMS

A

Passive stretching often relieves this type of muscle cramp
Possible that activating ion channels in the mouth could send inhibitory signals to the spinal cord, but inhibit overactive motor neurons

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14
Q

Define Isotonic, Isokinetic and Isometric

A

Isotonic: Muscle tension remains unchanged where muscle length decreases
Isokinetic: Muscle length decreases with constant velocity
Isometric: Muscle contracts but does not change in length

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15
Q

What are the 3 main types of muscle fibres

A

Type I (Slow)
Type IIa (Mixed)
Type IIx (Fast)

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16
Q

How are muscle fibres typed

A

Contractile properties
Muscle biopsy
Oxidative capacity
Immunohistochemical staining
Gel electrophoresis

17
Q

What factors determine the speed of muscle contraction and relaxation

A

Muscle twitch
Contraction-calcium released from SR
Relaxation-reuptake of calcium into SR
Speed of shortening is greater in fast fibres

18
Q

What factors determine the force regulation in muscle fibres

A

Number and types of motor units recruited
Muscle length
Firing rate of motor neurons
Contractile history of muscle

19
Q

Define the term motor unit

A

Each mature muscle fibre is innervated by a single axon

20
Q

What do motoneurons supplying larger faster motor units have

A

Larger cell bodies
Larger diameter axons
greater number of axonal branches
Sparse afferent innervation
More complex and extensive motor end plate of neuromuscular junction

21
Q

Describe the muscle force-velocity relationship

A

At any absolute force exerted by the muscle, the speed of movement is greater in muscles with a higher percentage of fast-twitch fibres

At any given velocity of movement, the peak power generated is greater in a muscle with higher percentage of fast-twitch fibres

Maximum velocity of shortening is greatest at the lowest force

22
Q

What occurs to strength and muscle power with aging

A

Strength is lost with age and appear greater for lower body
Muscle power lower in older group as it declines with age

23
Q

What are the factors that affect declining muscle aging

A

A loss of muscle mass
Muscle quality is reduced (fat accumulation in muscle increases)
Neuromuscular alterations (Denervation and less motor units as age increases)

24
Q

Define denervation and collateral reinnervation

A

Denervation: disconnect of muscle fibre to motor neuron

Collateral reinnervation: muscle fibre reconnects to an adjecent motor axon neuron

25
Q

What are some excitation-coupling processes on muscle function other than older age

A
  1. Changes in excitation-contraction coupling (decrease release of calcum)
  2. Changes in sarcoplasmic reticulum function (decrease calcium uptake)
  3. Slowing of myosin molecule
  4. Reduce actomyosin cross bridges
26
Q

Define Henneman Size principle

A

Consistent pattern of recruitment
Small motor units = low force
Large motor units = high force

Slow have easily excited motor neurons
Fast motor units have higher threshold (harder to excite)

27
Q

Describe the crossbridge cycle

A
  1. ATP binds to myosin head.
  2. ATP hydrolysis into ADP + Pi but remain on myosin head.
  3. Pi dissociate from myosin; forms new cross bridge.
  4. Powerstroke occurs, shortening the muscle.
  5. ADP dissociates from myosin; awaits another ATP molecule
28
Q

What are the muscle force velocity relationships in muscle fibres

A
  • At any absolute force exerted by the muscle, the speed of the movement is greater in muscles with higher percentage of fast-twitch fibres
  • Maximum velocity of shortening is greatest at the lowest force
  • At any given velocity of movement, the peak power generated is greater in a muscle with a higher percentage of fast-twitch fibres
  • The peak power increases with velocity up to movement speed of 200 to 300 degrees
29
Q

What is needed for muscle contraction to continue, and what happens what it ceases

A
  1. Shortening continues as long as ATP is available and Ca2+ can bind onto troponin
  2. When neural activity ceases, Ca2+ is removed from SR by Ca2+, tropomyosin moves into active site and muscle relaxes
30
Q

How does denervation and collateral re-innervation alter muscle characteristics

A

Increased co-expression of myosin isoforms
Decreased force output
Decreased velocity of contraction and thus power
Increases size of motor unit (less efficient)
Preserves from muscle mass but not all

31
Q

Muscle characteristics of master athletes

A

Muscle deterioration not as severe but still present

Applied Exercise Physiology (13 decks)

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