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2.5 BRS Musculoskeletal & Rheumatology > Muscle > Flashcards

Muscle Flashcards

1
Q

What are the 3 types of muscle?

A
  1. Smooth - involuntary (ANS)
  2. Cardiac - involuntary (ANS and circulating
    chemicals)
  3. Skeletal - voluntary (SNS)
    - attach to bones (tendons) —> movement
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2
Q

What are the 4 shapes of muscle fibres?

A
  1. Parallel —> straight
  2. Fusiform —> eye
  3. Triangular
  4. Pennate —> feather-like
    - Unipennate
    - Bipennate
    - Multipennate
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3
Q

What is the structure of skeletal muscle? (5)

A
  1. Myofilaments
  2. Myofibril = bundle of myofilaments
  3. Myofibre = bundle of myofibrils (whole length)
  4. Fascicles = bundle of myofibres
  5. Muscle = bundle of fascicles
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4
Q

What are the 3 sheaths of connective tissue in skeletal muscles?

A
  1. Epimysium —> surrounds muscle
  2. Perimysium —> surrounds muscle fascicles
  3. Endomysium —> surrounds muscle fibre
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5
Q

What is the structure of a myofibre?

A
  • bundle of myofibrils
  • network of sarcoplasmic reticulum
  • T-tubules tunnel through centre
  • sarcoplasm (cytoplasm) —> myoglobin
    —> mitochondria
  • sarcolemma (plasma membrane) —> capillaries
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6
Q

What is the structure of a myofibril?

A

Overlapping sarcomeres
- 1-2 μm diameter
- striated —> light and dark bands

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7
Q

What is the structure of a myofilament?

A

Overlapping arrangement of thick (myosin) and thin (actin) filaments
H-zone = only myosin
A-band = all myosin —> dark
M-line = myosin line
I-band = only actin —> light
Z-disc = actin line
- sarcomere = Z to Z

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8
Q

Why do muscles have a striated appearance?

A

Light —> I-band
- actin = thin filament
Dark —> A-band
- myosin = thick filament

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9
Q

What are the 2 proteins in muscle?

A
  1. Myosin - two globular heads
    - single tail of 2 α-helices
    - 1 filament = hundreds of tails
  2. Actin - molecules twisted into helix
    - surrounded by tropomyosin strands with
    troponin complexes
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10
Q

What is the structure of myosin?

A
  • 2 globular heads
  • tail of 2 α-helices
  • 1 filament = hundreds of tails
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11
Q

What is the structure of actin?

A
  • Molecules twisted into helix
  • Surrounded by tropomyosin strands with troponin
    complexes
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12
Q

What is the sliding filament theory?

A

Muscle contraction:
- I-band shortens
- A-band same
- H-zone narrows/disappears
—> muscle fibre shortens

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13
Q

What are the 3 stages of muscle contraction?

A
  1. Initiation
  2. Activation
  3. Excitation contraction coupling
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14
Q

What are the 5 steps of muscle contraction initiation?

A
  1. Pre-synaptic neurone —> action potential opens
    VGCCs
  2. Ca2+ enters pre-synaptic terminal —> exocytosis of
    NT vesicles
  3. ACh diffuses across cleft —> binds to muscle ACh
    receptors
  4. Action potential induced in muscle —> AP spreads
    along muscle fibre membrane surface
  5. AP stops when ACh broken down by ACh esterase
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15
Q

What are the 4 steps of muscle contraction activation?

A
  1. Action potential to T-tubules —> sensed by DHP
    (dihydropyridine) receptors on T-tubule membrane
  2. DHP receptor shape change —> attached ryanodine
    receptor on sarcoplasmic reticulum opens
  3. Ca2+ out sarcoplasmic reticulum via ryanodine
    receptor —> Ca2+ released into filaments
  4. Sarcoplasmic reticulum continuously supplied with
    Ca2+ via active transport (ATP-driven pump)
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16
Q

What are the steps of muscle excitation contraction coupling?

A
  1. Ca2+ binds to troponin —> moves tropomyosin —>
    myosin binding sites on actin exposed
  2. ATP in myosin head hydrolysed —> ‘charges’
  3. Myosin head binds to actin binding site
    (crossbridge) —> ADP + Pi released
  4. Myosin head pivots (power stroke) —> pulls actin
    filament to centre of sarcomere (M line)
  5. New ATP binds —> actin released —> ready to
    repeat with next actin
17
Q

What are the 2 types of motor neurones?

A
  1. Upper —> brain
  2. Lower —> brainstem
    —> spinal cord
18
Q

What are motor units?

A

Motor neurone + all muscle fibres in innervates (600)
- In humans - 420,000 motor neurones
- 250,000,000 skeletal muscle fibres

19
Q

What are the 3 types of motor unit?

A
  1. Slow (S, type I) - low force, fatigue resistance
  2. Fast, fatigue resistant (FR, type IIA) - medium force
  3. Fast, fatiguable (FF, type IIB) - high force
    - depend on nerve innovating fibre
20
Q

What are the 4 differences between the properties of slow vs fast twitch motor units?

A

Slow:
1. Cell bodies —> smaller diameter
2. Smaller dendritic trees
3. Thinner axons
4. Slower conduction velocity

21
Q

What are the characteristics of S muscle fibres? (4)

A
  1. High myoglobin
  2. Red
  3. High aerobic capacity
  4. Low anaerobic capacity
22
Q

What are the characteristics of FR muscle fibres? (4)

A
  1. High myoglobin
  2. Pink
  3. Medium aerobic capacity
  4. High anaerobic capacity
23
Q

What are the characteristics of FF muscle fibres? (4)

A
  1. Low myoglobin
  2. White
  3. Low aerobic capacity
  4. High anaerobic capacity
24
Q

What are the 2 graphs used to explain the differences between S, FR and FF muscle?

A
  1. Twitch: force (g) v time
  2. Rate of fatigue: contraction (%) v time
25
Q

What are the 2 mechanisms used by the brain to regulate muscle force?

A
  1. Recruitment = number of motor neurones —>
    number of muscle fibres contracting
    • size principle —> smaller (slow) twitch units first
    • more force needed —> more units recruited
      (allows for fine control with low force)
  2. Rate coding = frequency of contraction of each unit
    • slow units —> lower frequency
    • frequency (firing rate) inc —> force from unit inc
    • summation —> frequency so fast —> no break
      between APs —> no muscle relaxation
26
Q

What are neurotrophic factors?

A

Growth factors for motor neurones
- prevent neuronal death —> promote neurone
growth after injury

27
Q

What are the 3 types of muscle contraction?

A
  1. Isometric —> hold still
  2. Concentric —> muscle shortens
  3. Eccentric —> muscle extends
28
Q

What are the 3 examples of motor units changing type?

A
  1. Training : IIB —> IIA
  2. Severe deconditioning: I —> II
  3. Spinal cord injury: I —> II
29
Q

How does aging affect muscles?

A

Muscle loss
- lose more type II —> larger proportion of type I —>
slower contraction times

2.5 BRS Musculoskeletal & Rheumatology (7 decks)

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