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Musculoskeletal Rheumatology > Muscle Microstructure and Contraction > Flashcards

Muscle Microstructure and Contraction Flashcards

1
Q

What type of control is smooth muscle under?

A

-smooth muscle is under involuntary control from the autonomic nervous system

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2
Q

What type of control is cardiac muscle under?

A

-cardiac muscle can contract autonomously, but is under the influence of the autonomic nervous system and circulating chemicals

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3
Q

What type of control is skeletal muscle under?

A

-skeletal muscles are under voluntary control from the SOMATIC NERVOUS SYSTEM, usually attached to bones and contract to bring about movement

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4
Q

What are fascicles?

A

-bundles of muscle fibres (myofibres)

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5
Q

What is compartment syndrome?

A

-loss of blood into a compartment

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6
Q

What is the connective tissue surrounding muscles?

A

-epimysium

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7
Q

What is the connective tissue that surrounds muscle fascicles?

A

-perimysium

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8
Q

What is the connective tissue that surrounds muscle fibres?

A

-endomysium

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9
Q

What plasma membrane surrounds muscle fibres?

A

-sarcolemma

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10
Q

What is the sarcoplasmic reticulum?

A

-network of fluid-filled tubules

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11
Q

What is the sarcoplasm?

A
  • cytoplasm of myofibres

- contain myoglobin and mitochondria

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12
Q

Tell me about the structure of myofibrils.

A
  • 1-2 micrometres in diameter
  • extend along entire length of myofibres
  • actin and myosin
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13
Q

What is a sarcomere?

A

-repeating unit in myofibrils between two Z discs

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14
Q

Why do muscles have striated appearance?

A

-light and dark bands give muscles striped appearance

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15
Q

Which muscles types are called striated?

A

-cardiac and skeletal muscle

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16
Q

What is the A-band?

A

-thick myosin

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17
Q

What is the I-band?

A

-thin actin

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18
Q

What is the M-line?

A

-middle of two adjacent z-discs

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19
Q

What is the structure of actin?

A
  • actin molecules are twisted into helix
  • each molecule has a myosin binding site
  • actin filaments contain troponin and tropomyosin
20
Q

What is the structure of myosin?

A
  • two globular heads
  • single tail formed by two alpha helices
  • tails of several hundred molecules form one filament
21
Q

What is the sliding filament theory?

A
  • during contraction, I-band becomes shorter (and so sarcomere shortens)
  • A-band remains same length
  • H-zone narrowed or disappeared
22
Q

What is the H-zone?

A

-contains only thick myosin

23
Q

How is muscle contraction initiated?

A
  1. AP opens voltage gated Ca channels
  2. Ca enters pre-synaptic terminal
  3. Ca triggers exocytosis of vesicles
  4. Acetylcholine diffuses across cleft
  5. Binds to acetylcholine receptors and induces APs in muscle
  6. Local currents flow from depolarised region and adjacent region. AP spreads along surface of muscle fibre membrane.
  7. Acetylcholine broken down by acetylcholine esterase. Muscle fibre response to that molecule of acetylcholine ceases.
24
Q

What is process of muscle activation?

A
  1. AP propagates along surface membrane and into T-tubules
  2. Dihydropyridine (DHP) receptor in T-tubule membrane: senses V and changes shape of the protein linked to ryanodine receptor.
  3. Ryanodine receptor Ca channel opens in the sarcoplasmic reticulum (SR)
  4. Ca released from SR into space around the filaments
  5. Ca binds to troponin and tropomyosin moves, allowing crossbridges to attach to actin
  6. Ca is actively transported into the SR continuously which APs continue. ATP-driven pump (uptake rate < or =release rate)
25
Q

What is process of excitation contraction coupling?

A
  1. in the presence of Ca, there is movement of troponin from tropomyosin
  2. Movement exposes myosin binding site on the actin chain
  3. Charged myosin heads bind to exposed site on actin filament
  4. this binding and discharge of ADP causes myosin head to pivot- power stroke, pulling actin filament towards centre of sarcomere
  5. ATP binding releases myosin head from actin chain
  6. ATP hydrolysis provides energy to recharge the myosin head
26
Q

Which protein filament does the pulling during a muscle contraction?

A

-myosin

27
Q

What is the neural control of muscle contraction?

A
  • voluntary neural control from upper and lower motor neurons
  • upper motor neurons in brain
  • lower motor neurone in brainstem or spinal cord.
28
Q

What is a motor unit?

A
  • a single motor neuron with all the muscle fibres that it innervates
  • human have 420,000 motor neurone and 250 million skeletal muscle fibres
  • on average each neuronesupplies about 600 muscle fibres
  • stimulation of one motor unit causes contraction of all the muscle fibres in that unit
29
Q

Why is there variability in the motor unit (innervation ratio) ?

A

-large muscle (e.g quadriceps) don’t need to be dextrous so the innervation ratio is much greater

30
Q

What is the innervation ratio?

A

-how many muscle fibres are innervated by the nerve

31
Q

What are the types of motor units?

A
  • slow: S, type I)
  • fast, fatigue resistant: FR, type IIA
  • fast, fatiguable: FF, type IIB

-motor units types are classified by the amount of tension generated, speed of contraction and fatiguability of the motor unit.

32
Q

What are slow motor units?

A
  • type I
  • smallest diameter cell bodies
  • small dendritic trees
  • thinnest axons
  • slowest conduction velocity
33
Q

What are fast, fatigue resistant motor units?

A
  • type IIA
  • larger diameter cell bodies
  • larger dendritic trees
  • thicker axons
  • faster conduction velocity
34
Q

What are fast, fatiguable motor units?

A
  • type IIB
  • larger diameter cell bodies
  • larger dendritic trees
  • thicker axons
  • faster conduction velocity
35
Q

What are the following fibre characterises for slow fibres? :

  • myoglobin content
  • colour
  • aerobic capacity
  • anaerobic capacity
A
  • high
  • red
  • high
  • low
36
Q

What are the following fibre characterises for FR fibres? :

  • myoglobin content
  • colour
  • aerobic capacity
  • anaerobic capacity
A
  • high
  • pink
  • moderate
  • high
37
Q

What are the following fibre characterises for FF fibres? :

  • myoglobin content
  • colour
  • aerobic capacity
  • anaerobic capacity
A
  • low
  • white
  • low
  • high
38
Q

Which muscle has the greatest proportion of slow type muscle fibres?

A

-back muscles

posture muscles

39
Q

How is muscle force regulated?

A

-two mechanics by which the brain regulates the force that a single muscle can produce

  1. Recruitment:
    - motor units are not randomly recruited
    - recruitment governed by the “size principle”- smaller units are recruited first - the slow twitch units
    - as more force is required, more units recruited, allowing finer control under which low force levels are required
  2. Rate coding:
    - a motor unit can fire at a range of frequencies. Slow units fire at a lower frequency
    - as the firing rate increases, the force produced by the unit increases
    - summation occurs when units fire at frequency too fast to allow the muscle to relax between arriving APs.
40
Q

What are neutrophi factors?

A
  • -type of growth factors
  • prevent neuronal death
  • promote growth of neurones after injury
  • motor unit and fibre characteristics are dependent on the nerve which innervates them
  • if a fast and slow twitch muscle are cross innervated, the slow one becomes fast and vice versa
  • the motor neuron has some effect on the properties of the muscle fibres it innervates
41
Q

What are the types of muscle contraction?

A
  • concentric
  • eccentric
  • isometric (no movement)
42
Q

If someone placed a book on your outstretched hand and it was slightly too heavy for you too hold, which contraction type would you be making?

A

-eccentric

43
Q

What happens to the types of fibres present as we age and what is the evidence for this?

A

-ageing associated with loss of TI and TII fibres but also preferential loss of TII fibres. This results in a larger proportion of T1 fibres in aged muscle (evidence from slower contraction times)

44
Q

What happens to the types of fibres present as we age and what is the evidence for this?

A
  • ageing associated with loss of TI and TII fibres but also preferential loss of TII fibres. This results in a larger proportion of T1 fibres in aged muscle
  • evidence from slower contraction times
45
Q

lecture slides

A

https://d3c33hcgiwev3.cloudfront.net/1_hIL79QSeC4SC-_UBngnA_14b8eccecbfc4df0af58e1ffd33508c7_Final_MSK_LE02Muscle_microstructure_and_contraction_SV.pdf?Expires=1580774400&Signature=J9hZjza2xflC0bJfip8M2zWRSEWH5fQ6koVOECEE8CtRlJ78qzuTnqviXJGYHxO1hckm~VXkKUC~qIoHzMvctAehCApfWlsDUXXEjf7~Cd76VZ8Tvl6QdN0p6D2RLdKjdPdGnyhJHvI6ZrOcWtMtcRsEautAbuz5b1hKFOHrtec&Key-Pair-Id=APKAJLTNE6QMUY6HBC5A

Musculoskeletal Rheumatology (6 decks)

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