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Third Year > MEC322: Muscle system > Flashcards

MEC322: Muscle system Flashcards

1
Q

Name the three muscle types

A

cardiac, smooth and skeletal

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2
Q

Which is the most abundant muscle type?

A

skeletal
40-45% of total weight
more than 430 pairs of skeletal muscle

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3
Q

Where will you find skeletal muscles?

A

attached to bones or for some facial muscles to skin

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4
Q

Where will you find cardiac muscles?

A

walls of the heart

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5
Q

Where will you find smooth muscles?

A

mostly in walls of hollow visceral organs (other than heart)

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6
Q

Describe the shape of skeletal muscle

A

single, very long, cylindrical, multinucleate cells with very obvious striations

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7
Q

Describe the shape of cardiac muscle

A

branching chains of cells, uninucleate, striations, intercalated discs

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8
Q

Describe the shape of visceral muscle

A

single, fusiform, uninucleate, no striations

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9
Q

What are the five key functions of muscles?

A 
producing body movements
stabilizing body positions
regulating organ volume
moving substances within the body
producing heat
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10
Q

What is a tendon?

A

extensions of connective tissue beyond muscle fibers that attach muscle to bone

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11
Q

What are skeletal muscles well supplied with?

A

nerves and blood vessels, which provide nutrients and oxygen for contraction

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12
Q

Skeletal muscles are separate organs made up of….

A

muscles fiber (cell)

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13
Q

What does each muscle fiber contain?

A

myofibrils that contain thin filament and thick filament

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14
Q

What are the filaments in the myofibrils arranged in?

A

sarcomeres

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15
Q

What do thick filaments in myofibril composed of?

A

mysoin

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16
Q

What do thin filaments in myofibril composed of?

A

actin, tropomyosin and troponin

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17
Q

How are sarcomeres separated from each other?

A

zig-zagging zones of dense protein material called z discs

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18
Q

What is an A band?

A

within each sarcomere a darker area called an a band extends the entire length of the thick filament

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19
Q

What is at the centre of each a band?

A

h zone, which contains only the thick filaments

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20
Q

Describe the i band

A

lighter coloured area either side of the a band contains the rest of the thin filament

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21
Q

what is the contraction cycle?

A

Repeating sequence that causes sliding of filaments

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22
Q

Describe the contraction cycle

A

Splitting ATP – myosin ATPase splits ATP and becomes energized
Forming cross-bridges – the myosin head attaches to actin, forming a cross-bridge
Power stroke – the cross-bridge generates force as it swivels or rotates toward the center of the sarcomere
Binding ATP & detaching – myosin detaches from actin. The myosin head again splits ATP, returns to its original position, and binds to a new site on actin as the cycle continues

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23
Q

What is the sliding filament mechanism of muscle contraction?

A

the sliding of filaments and shortening of sarcomeres that cause the shortening of muscle fibers.

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24
Q

What is ATP?

A

ATP (adenosine triphosphate) is the energy-carrying molecule used in cells because it can release energy very quickly.

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25
Q

What is needed for muscle contraction?

A

Ca2+ and energy in the form of ATP

26
Q

What must happen before a skeletal muscle fibre can contract?

A

It must be stimulated by an electrical signal called a muscle action potential delivered by its neuron called a motor neuron.

27
Q

What is a motor unit?

A

A single motor neuron along with all the muscle fibres it stimulates

28
Q

What is the neuromuscular junction (NMJ)?

A

the synapse between a motor neuron and a skeletal muscle fiber.

29
Q

What does the neuromuscular junction (NMJ) include?

A

the axon terminals, synaptic end bulbs of a motor neuron and the adjacent motor end plate of the muscle fiber sarcolemma.

30
Q

How does a motor neuron excite a skeletal muscle fiber at the NMJ?

A
  • acetylcholine (ACh) release from synaptic vesicles
  • ACh diffuses across synaptic cleft
  • binds to ACh receptors
  • muscle action potential initiated
  • the flow of Na+ generates .a muscle action potential
  • breakdown of ACh by enzyme called acetylcholinesterase
31
Q

What is a record of a contraction called?

A

myogram

consists of latent period, contraction period and relaxation period

32
Q

What is wave summation?

A

the increased strength of a contraction that occurs when a second stimulus arrives before the muscle has completely relaxed

33
Q

What can repeated stimuli produce?

A

unfused (incomplete) tetanus

34
Q

What can rapid repeated stimuli produce?

A

fused (complete) tetanus

35
Q

What is motor unit recruitment?

A

the process of increasing the number of active motor units

36
Q

What increases force potential?

A

synchronisation
large number of fibres in motor units
type IIA and IIB

37
Q

Which type of motor unit decrease force potential?

A

Type I

38
Q

What are the three types of skeletal muscle fibres?

A 
slow oxidative (SO) fibers, 
fast oxidative-glycolytic (FOG) fibers,
fast glycolytic (FG) fibers
39
Q

Which fibre do most skeletal muscle contain?

A

most contain a mixture of all three fibres in varying proportions
fibre type distribution is genetically determined

40
Q

what is the order the motor units of a muscle are recruited?

A

first SO fibers,
then FOG fibers,
and finally FG fibers.

41
Q

What is type I muscles fibre?

A

slow oxidative (SO) fibers

42
Q

What is type IIA muscles fibre?

A

fast oxidative-glycolytic (FOG) fibers

43
Q

What is type IIB muscles fibre?

A

fast glycolytic (FG) fibers

44
Q

When do sarcomeres produce maximal tension?

A

when thick and thin filaments overlap 100-120%

45
Q

What are muscles designed to do?

A

Optimise the force produced during contraction through sarcomere contraction

46
Q

What happens when a sarcomere is stretched too far?

A

Force reduced due to insufficient overlap of myofibrils

47
Q

What happens when the muscle is over contracted?

A

force reduce as potential for further contraction reduced

48
Q

What must the force of contraction for the whole muscle account for?

A

active (contractile) and passive (series and parallel elastic elements) components

49
Q

What is isometric contraction?

A

muscle contracts but does not shorten (held at position)

often used for measurements as safer to conduct

50
Q

What is concentric contraction?

A

shortening

51
Q

What is eccentric contraction?

A

lengthening

52
Q

Is the force greater during eccentric or concentric contraction?

A

eccentric

53
Q

Greater concentric velocity…..

A

smaller the force

54
Q

When can the largest force be applied?

A

fastest eccentric motion

55
Q

Why are fibres in fusiform muscle parallel to the long axis of the muscle?

A

advantage for length of contraction

56
Q

What does fusiform mean?

A

Fusiform means having a spindle-like shape that is wide in the middle and tapers at both ends (think long lemon)

57
Q

How are fibres arranged in pennate muscle?

A

Fibers arranged obliquely to long axis of muscle

uni-, bi-, and multi-

58
Q

How is the arrangement of pennate fibres advantageous?

A

advantage for force of contraction

59
Q

Which fibre arrangement tends to have a larger physiological cross-sectional area?

A

pennate

60
Q

What is the force of muscle contraction proportional to?

A

physiological cross-sectional area

61
Q

What is the velocity and excursion of muscle proportional to?

A

length of myofibril

Third Year (12 decks)

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