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Bsc Physiology (Year 1) > Skeletal Muscles (Part 1) > Flashcards

Skeletal Muscles (Part 1) Flashcards

1
Q

what proportion of human body weight is made up by muscle

A

40%

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2
Q

state what it is meant by the key term - excitability

A

the ability of muscle tissue to be electrically stimulated

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3
Q

state what it is meant by the key term - extensibility

A

the ability of muscle to be stretched it’s resting length (passive)

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4
Q

state what it is meant by the key term - elasticity

A

the ability of a muscle to return to it’s resting length (passive)

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5
Q

state what it is meant by the key term - contractility

A

the ability of a muscle to actively generate tension

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6
Q

state 3 facts about cardiac muscle

A
  1. actin and myosin form cross bridges - sliding filament mechanism
  2. node cells (pacemaker cells) produce spontaneous AP’s - autorhythmicity
  3. electrical coupling between cells
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7
Q

what is the refractory period time in cardiac cells? and what is the reason for this?

A

refractory period of 250 ms to prevent tetanic contractions

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8
Q

state 4 facts about smooth muscle

A
  1. actin and myosin form cross bridges - sliding filament mechanism
  2. surrounds cell structures
  3. changes in lengths changes the shape of cells
  4. controlled by the amount of Ca2+ in the cells
  5. Ca2+ release controlled by the autonomic NS
  6. spontaneous AP’s or drifting of polarity in some smooth muscle cells
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9
Q

state 3 facts about skeletal muscle

A
  1. changes in skeletal muscle moves skeleton
  2. actin and myosin form cross bridges - sliding filament theory
  3. controlled by motor neurones (voluntary and reflex)
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10
Q

how does skeletal muscle create and control movement? (2 things)

A
  1. skeletal muscle generates force to act on the skeleton

2. skeletal muscle changes length whilst generating force to move and control the skeleton

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11
Q

state 3 characteristics of skeletal muscle fibres

A
  1. multinucleate
  2. contains many mitochondria
  3. has transverse tubules (t tubules)
  4. myofibrils and sarcomeres
  5. sarcolemma, sarcoplasm, sarcoplasmic reticulum (SR)
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12
Q

state what it is meant by the key term - myofibrils

A

myofibrils are the structures that give skeletal and cardiac muscle their characterised striated appearance

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13
Q

state the two types of myofibrils

A
  1. actin (thin filament)

2. myosin (thick filament)

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14
Q

state what it is meant by the key term - sliding filament theory

A

muscle force and length change is generated buy the overlapping and interaction of actin and myosin filaments

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15
Q

which two people came up with the sliding filament theory?

A
  1. Andrew Huxley

2. Hugh Huxley

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16
Q

state 3 facts about actin

A
  1. contractile protein
  2. structure is like a string of pearls on a string and then the strand of pearls are twisted together
  3. each actin has a binding site for myosin
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17
Q

state 2 facts about tropomyosin

A
  1. regulatory protein

2. overlaps binding sites for myosin and inhibits interaction when the muscle is in it’s relaxed sate

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18
Q

state 3 facts about troponin

A
  1. regulatory protein
  2. troponin binds to Ca2+ reversibly and once bound change the conformation to pull tropomyosin away from the myosin binding site
  3. Ca2+ binding to troponin regulates skeletal muscle contraction because it moves the tropomyosin away and allow myosin to interact with the actin
19
Q

state 2 facts about the sarcoplasmic reticulum (SR)

A
  1. homologous to ER
  2. stores and releases Ca2+
  3. T tubules connected to SR via junctions
  4. T tubule protein is a modified voltage gated Ca2+ channel known as dihydropyridine
20
Q

explain the 6 steps of the excitation-contraction coupling reaction

A
  1. muscle AP propagated into T tubules
  2. Ca2+ released from lateral sac of SR
  3. Ca2+ binding to troponin removes blocking action of tropomyosin
  4. actin-myosin cross bridges form
  5. AP ends, Ca2+ re-uptake by SR
  6. Ca2+ removal from troponin restores tropomyosin binding action
21
Q

state 3 things that occur when actin-myosin cross bridges form (expanding upon step 4 in the excitation-contraction coupling reaction)

A
  1. cross bridges move through power stroke sliding actin past myosin
  2. ATP cause release of myosin head and return to original state
  3. if Ca2+ still present, myosin head will attach again to new binding site
22
Q

state what it is meant by the key term - motor unit

A

a motor unit is a motor neurone plus all the muscle fibres it innervates

23
Q

state 2 additional facts about motor units

A
  1. one motor unit can innervate many muscle fibres, but one muscle fibre can only be innervated by one motor unit
  2. within a whole muscle there are many motor units
24
Q

state what it is meant by the key term - neuromuscular junction

A

the neuromuscular junction is where the axon terminals establish synaptic contact with the motor end plate

25
Q

state what it is meant by the key term - motor end plate

A

the region of the muscle fibre plasma membrane that lies directly under the terminal portion of the axon is known as the motor end plate

26
Q

state the 8 steps of a neuromuscular junction

A
  1. AP propagates down motor neurone to axon terminals
  2. causes voltage-gated Ca2+ ion channels to open
  3. inc^ fluidity of ACh containing vesicles + causes them to fuse with membrane + release ACh into synapse
  4. ACh diffuses across synapse + binds to muscarinic receptors receptors which open Na+ channels
  5. Na+ entry cross motor end plate - depolarisation
  6. current spreads down sarcolemma
  7. muscle fibre AP propagated
  8. AP propagates along sarcolemma
27
Q

state 3 facts about neuromuscular junctions

A
  1. are all excitatory
  2. ‘all or nothing’ principle
  3. contain acetylcholinesterase
28
Q

state what it is meant by the key term - twitch contraction

A

the mechanical response to a single action potential

29
Q

state the 3 phases of a twitch contraction (in order)

A
  1. latent period
  2. contraction time
  3. relaxation phase
30
Q

state what it is meant by the key term - latent period (of a twitch contraction)

A

the period of time from the action potential to the onset of contraction. the time delay is due to the excitation-contraction coupling reaction

31
Q

state what it is meant by the key term - contraction phase (of a twitch contraction)

A

this is the time when tension is developing due to cross-bridge cycling

32
Q

state what it is meant by the key term - relaxation phase (of a twitch contraction)

A

this is the time where tension is decreasing (i.e., relaxing) and is longer than the contraction phase. this is due to the time it takes to get all the Ca2+ sequestered

33
Q

state 3 facts about tetanic contractions

A
  1. multiple AP’s result in summation of tension/force
  2. if frequency is high, tetanic contraction occur when force remains constant(ish) for the period of activation
  3. typically a muscle force in functional activities
34
Q

state what it is meant by the key term - tetanic contraction

A

is a sustained muscle contraction evoked when the motor nerve that innervates a skeletal muscle emits action potentials at a very high rate

35
Q

skeletal muscle fibres do not have the same mechanical and metabolic characteristics. state the two characteristics muscle fibres are determined by

A
  1. the maximum shortening velocities (fast or slow)

2. the major pathway they use to re-synthesise ATP

36
Q

state what it is meant by the key term - slow oxidative (SO) fibres

A

SO fibres combine low myosin ATPase activity with high oxidative activity

37
Q

state what it is meant by the key term - fast oxidative glycolytic (FOG) fibres

A

FOG fibres combine high myosin ATPase activity with high oxidative capacity and intermediate glycolytic capacity

38
Q

state what it is meant by the key term - fast glycolytic (FG) fibres

A

FG fibres combine high myosin ATPase activity with a high glycolytic capacity

39
Q

state what it is meant by the key term - myosin isoforms

A

Some isoforms have specialised functions in certain cell types (such as muscle), while other isoforms are ubiquitous

40
Q

state the 3 types of myosin isoforms

A
  1. myosin heavy chain 1
  2. myosin heavy chain 2a
  3. myosin heavy chain 2x
41
Q

what is the function of the myosin isoforms ?

A

the type of myosin isoform determines the maximal rate of cross-bridge cycling, and thus, the maximal shortening velocities

42
Q

state what it is meant by the key term - electromyography

A

the recording of the electrical activity of muscle tissue, or its representation as a visual display or audible signal, using electrodes attached to the skin or inserted into the muscle

43
Q

what do oxidative fibres depend on ?

A

blood flow - the delivery of oxygen and nutrients

Bsc Physiology (Year 1) (34 decks)

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