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Musculoskeletal and Rheumatology > Muscle structure > Flashcards

Muscle structure Flashcards

1
Q

What type of nerve control is smooth muscle

A

Involuntary

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2
Q

What type of nerve control is cardiac muscle

A

Autonomous

Autonomic nervous system and circulating chemicals

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3
Q

What type of nerve control is skeletal

A

Voluntary control - soamtic nervous system

Attached to bones and contract to bring about movement

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4
Q

Arrangement of muscle fibres

A
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5
Q

Structure of skeletal muscles

A
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6
Q

Structure of skeletal muscles

A

Plasma membrane - sarcolemma

T-tubules tunnel into the centre

Sarcoplasm- cytoplasm

Network of fluid filled tubules - sarcoplasmic reticulum

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7
Q

Structure of skeletal muscles myofibrils

A

Sacomere - repeating pattern from Z to Z disc

Thin filament - actin (I band)

Thick filament - myosin (A band)

Light and dark bands give striated appearance

Cause contraction - changes in filaments overlap

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8
Q

Structure of skeletal muscles - actin and myosin

A
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9
Q

Structure of skeletal muscles - myosin

A

Two globular heads

Move using ATP

Cause sliding

Two a helices tail

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10
Q

Structure of skeletal muscles - actin

A

Actin molecule twisted into helix

Each molecule has myosin binding site

Filaments also contain troponin and tropomyosin

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11
Q

Initiation of muscle contraction

A
  1. Action potential open voltage gated Ca
  2. Ca enters pre-synaptic terminal
  3. Ca triggers exocytosis of vesicles
  4. Acetylcholine diffuses
  5. Binds to acetylcholine receptors and induces action potentials in muscle
  6. Local currents flow from depolarised region and adjacent region
  7. Acetylcholine broken down by acetylcholine esterase
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12
Q

Initation of muscle contraction - activation inside muscle

A
  1. AP propagates along surface membrane and into T-tubules
  2. Dihydropyridine receptor in T tubules sense voltage and changes shape of protein linked to ryanodine receptor which opens ryanodine receptor Ca channel in sarcoplasmic reticulum
  3. Ca released from SR into space around the filaments and binds to troponin which allows tropomyosin to move
  4. Crossbridges attach to actin
  5. Ca is actively transported continuously while action potentials continue
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13
Q

Excitation contraction coupline

A
  1. In the presence of Ca - movement of troponin from tropomyosin chain
  2. Movement exposes myosin binding site on surface of actin
  3. Myosin head binds to exposed site on actin filament
  4. Binding and discharge of ADP cause myosin head to pivot
  5. ATP binding - releases myosin head from actin chain
  6. ATP hydrolysis - recharge
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14
Q

Neural control of muscle contraction

A

Upper motor neurons in the brain

lower motor neurons in brainstem or spinal cord

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15
Q

Diagram of the motor unit

A

A single motor unit causes contraction of all the muscle fibres in that unit

No 2 motor neurons innervate the same muscle fibre

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16
Q

Slow motor units

A

Smallest diameter cell bodies

Small dendritic trees

Thinnest axons

Slowest conduction velocity

High myoglobin content

Red colour

High aerobic capcity

Low anaerobic capacity

17
Q

Fast, fastigue resistant (FR, type IIA)

Fast, fatiguable (FF, type IIB)

A

Larger diameter cell bodies

Larger dendritic trees

Thicker axons

Faster conduction velocity

18
Q

What is the difference between fast, fatigue resistant (FR, type IIA) and fast, fatiguable (FF, type IIB)

A

Myoglobin content - FR - HIGH, FF - LOW

Colour - FR - PINK, FF - WHITE

Aerobic capacity - FR - MODERATE, FF - LOW

Anaerobic capacity - FR - HIGH, FF, HIGH

19
Q

Force graph of the different types of motor units

A
20
Q

Fatigue graph of the different types of motor units

A
21
Q

Regulation of muscle force - recruitment

A

Smaller units are recruited first (slow twitch units)

As more force required, more units are recruited which allows fine control under which low force levels are required

22
Q

Regulation of muscle force - rate coding

A

Motor unit can fire a range of frequencies, slow units fire at lower frequency

Firing rate increases, force produced by the unit increases

Summation occurs when firing too fast to allow muscle to relax in between action potentials

23
Q

Effect of transferring nerves from different muscle fibres

A

Fast and slow twitch muscle are cross innervates, slow one becomes fast and vice versa

Motor neuron has some effect on the properties of the muscle fibres it innervates

24
Q

What are neurotrophic factors

A

Food

Type of growth factor

Prevent neuronal death

Promote growth of neurons after injury

25
Q

What is an isometric contraction

A

Muscle produces force but doesn’t change length

26
Q

What is a concentric muscles

A

Shorten muscles to produce movement

27
Q

Eccentric muscles

A

Muscles becomes longer

More force produced

28
Q

Plastivity of motor units

A

Type IIB to IIA - following training

Type 1 and 2 possibel in severe deconditioning or spinal cord injury

Microravity results in shift from slow to fast

Ageing associated with loss of type 1 and 2, preferentionally type 2 fibres, slower movements

Musculoskeletal and Rheumatology (3 decks)

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