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Medicine Year 1 - Semester 2 - Part 1 > Skeletal Muscle Force Generation, Energy Usage & Fibre Type > Flashcards

Skeletal Muscle Force Generation, Energy Usage & Fibre Type Flashcards

(58 cards)

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1
Q

What are sarcomeres ?

A

Highly organised, functional units of skeletal and cardiac muscle.

They have a striated appearance.

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2
Q

State the contractile proteins

A

Actin (thin filaments)
Myosin (thick filaments)

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3
Q

Z disc

A

Defines the boundary of each sarcomere - thousands of sarcomeres can make up a single muscle myofibre

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4
Q

I band

A

Mainly actin filaments

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5
Q

A band

A

Mainly myosin and overlapping actin filaments

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6
Q

Describe sarcomere shortening

A

A band remains constant
H zone and I band both shorten

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7
Q

State the role of ATP in muscle contraction

A

Membrane potential
Ca2+ gradient
Power stroke
Cross bridge dissociation

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8
Q

State the role of ATP in Membrane potential

A

Sodium/Potassium ATPase in sacrolemma maintains Na+ and K+ gradients, allowing production and propagation of action potentials.

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9
Q

State the role of ATP in Ca2+ gradient

A

Active transport of calcium ions into the sarcoplasmic reticulum - lowering [Ca2+]i

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10
Q

State the role of ATP in Power Stroke

A

Hydrolysis of ATP by myosin - ATPase energises the cross-bridge formation, enabling sarcomere shortening and contraction.

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11
Q

State the role of ATP in Cross bridge dissociation

A

Binding of ATP to myosin dissociates cross-bridges bound to actin.

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12
Q

How much ATP do muscles contain ?

A

4mM of ATP
which is enough for 2 seconds of contraction

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13
Q

State an energy source available for contraction

A

Stores of Creatine Phosphate in muscle provide enough energy for around 8 seconds of contraction.

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14
Q

Myosin + ATPase

A

Contraction

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15
Q

Ca2+ ATPase

A

Relaxation

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16
Q

Describe events during cross-bridge formation to generate sarcomere shortening

A

6 STEPS

  1. ATP binding
  2. ATP hydrolysis
  3. Cross-bridge formation
  4. Release of Pi from myosin
  5. Power stroke
  6. ADP release
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17
Q

How is cross bridge formation regulated ?

A

Regulation of cross-bridge formation is due to availability of myosin binding sites on actin, via [Ca2+]i and tropomyosin.

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18
Q

What is rigor mortis ?

A

Muscular stiffness that occurs after death - post mortem rigidity.

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19
Q

When does rigor mortis occur ?

A

Can begin around 4 hours after death, peaks at about 13 hours and lasts around 50 hours.

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20
Q

Describe how rigor mortis happens

A

Death

Loss of muscle cell integrity

Ca2+ leaks into the cytosol from the SR

Ca2+ binds to tropomyosin

Myosin binds to actin

Metabolism and ATP production ceases

No ATP present to break cross-bridge

Muscles become stiff

Proteolytic enzymes work within a few days

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21
Q

State the main different types of skeletal muscle fibre

A

Type IIB/IIX - Fast

Type IIA - Intermediate

Type I - Slow

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22
Q

State some properties of Type IIB/IIX skeletal muscle fibre

A

Fast
Glycolytic Anaerobic

Low in myoglobin oxygen

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23
Q

State some properties of Type IIA skeletal muscle fibre

A

Intermediate
Mixture of fast oxidative and glycolytic

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24
Q

State some properties of Type I skeletal muscle fibre

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A

Slow
Oxidative Aerobic

High in Myoglobin oxygen

25
How can skeletal muscle fibres be classified ?
Based on mechanical and metabolic characteristics : - Maximal velocities of contraction (fast/slow) - Major pathway for generation of ATP (oxidative or glycolytic)
26
State the different physiological properties of skeletal muscle fibre types
Number of mitochondria Amount of myoglobin Blood vessels/capillaries Stores of glycogen / glycolytic enzymes/ creatine phosphate Size
27
Which physiological properties are greater in slow oxidative fibres ?
Number of mitochondria Amount of myoglobin Blood vessels/capillaries
28
Which physiological properties are greater in fast glycolytic fibres ?
Stores of glycogen / glycolytic enzymes/ creatine phosphate Size
29
Describe Slow oxidative fibres (Type I)
Combine slow myosin-ATPase activity with high oxidative capacity
30
Describe Fast oxidative-glycolytic fibres (Type IIa)
Combine fast myosin-ATPase activity with high oxidative capacity and intermediate glycolytic capacity.
31
Describe Fast glycolytic fibres (Type IIb or Iix in human)
Combines fast myosin-ATPase activity with high glycolytic capacity
32
Where do skeletal muscles receive stimuli from ?
From a motor neurone Each myofibre/muscle cell has its own neuromuscular junction
33
What does duration of contraction depend on ?
Fibre type composition of individual muscles
34
Ocular muscle
Extremely rapid contraction velocity
35
Gastrocnemius muscle
Moderately rapid contraction velocity
36
Soleus muscle
Relatively slow contraction velocity
37
How does force change ?
Force changes depending on recruitment of muscle fibres.
38
What is a motor unit ?
All fibres innervated by a single neurone are called a motor unit. A single motor neurone innervates multiple muscle fibres.
39
Describe the muscle fibres of small muscles
Small muscles with fine control have fewer muscle fibres per neurone. e.g. laryngeal muscles
40
Describe the muscle fibres of large muscles
Large muscles may have hundreds of fibres in a motor unit. e.g. soleus
41
What does the force of contraction depend on ?
Number of motor neurons recruited Frequency of action potentials
42
How are motor units recruited ?
In a progressive way from smallest (weakest) to large (strongest)
43
Describe small motor units
More excitable Conduct action potentials more slowly Typically Type I (slow) fibres
44
Describe large motor units
Less excitable Conduct action potentials more rapidly Typically Type II (fast) fibres
45
What is muscle tension ?
The force exerted by a contracting muscle
46
What is load ?
The force exerted by an object to be moved
47
What must muscle do in order to shorten ?
Overcome the force exerted by an object to be moved (the load). Greater force required --> More motor units recruited
48
What is summation ?
As muscle twitch far exceeds duration of AP, it is possible to initiate a second AP before 1st contraction has subsided. The 2nd twitch is stronger than the 1st due to higher [Ca2+]i
49
What is frequency summation ?
Multiple action potentials occurring close together
50
What is tetanus ?
Stimulation frequency is so high that individual contractions fuse.
51
What is isotonic contraction ?
Muscle shortening will occur of peak tension is greater than the load force.
52
What is isometric contraction ?
Muscle stimulation will increase tension, but no shortening will occur if load force is greater than muscle peak force.
53
Define the length tension relationship
Length tension is directly related to the overlap between actin and myosin within the sarcomere.
54
When is tension high ?
When actin and myosin overlap within the sarcomere
55
Zero tension
No actin/myosin overlap
56
Describe the load-velocity relationship
When loads are applied, contraction velocity decreases with increasing load.
57
Describe the load-velocity relationship of muscle contraction
When the load equals the maximum force or tension that a muscle can exert, velocity of contraction is zero (isometric contraction)
58
Describe full muscle contraction with no load
Rapid around 100ms

Medicine Year 1 - Semester 2 - Part 1 (51 decks)

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