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principles of normal function > week 4 skeletal, smooth (and cardiac) muscle > Flashcards

week 4 skeletal, smooth (and cardiac) muscle Flashcards

1
Q

what type of muscle is striated

A
  • skeletal (voluntary muscles, diaphragm)

- cardiac

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2
Q

what type of muscle is smooth

A
  • blood vessels, airways, uterus, GI tract, bladder, etc.
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3
Q

what are the features of skeletal muscle

A
  • because skeletal muscle cells are actually fusion of multiple cells they are sometimes known as skeletal muscle fibres
  • multinucleate (because they are so packed with proteins nucleuses pushed out to the side of the cells)
  • form in utero from mononuclear myoblasts
  • myoblasts do no replace damaged cells
  • increase fibre size during growth
  • fibres are 10-100 micrometers in diameter and up to 20cm long
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4
Q

what is the structure of skeletal muscle

A
  • muscles are bundles of fibres encased in connective tissue sheaths
  • attached to bones by tendons
  • cells replaced after injury by satellite cells (limited number of satellite cells and not perfect repair)
  • satellite cells differentiate to from new muscle fibres
  • other fibres undergo hypertrophy to compensate, muscle will never completely recover
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5
Q

what is atrophy

A
  • the opposite of hypertrophy
  • you will see a reduction in protein within the cell and it will get weaker
  • if you don’t use muscle much it will become weaker and hypertrophy
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6
Q

what are myofibrils

A
  • bundles of muscle proteins
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7
Q

what are sarcomeres

A
  • the repeating units within myofibrils
  • they allow muscle to contract
  • contain actin and myosin
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8
Q

how does do sarcomeres allow muscle to contract

A
  • the way actin and myosin interact allows muscle to contract (cross bridges on myosin lock onto actin and they pull on each other
  • z lines keep the actin and myosin in a nice arrangement
  • sliding filament theory, actin and myosin slide over each other in a controlled way
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9
Q

what is the structure of actin

A
  • helical structure
  • actin proteins are polymers, basically lots of repeating units of actin molecules to form longer protein filaments to interact with myosin
  • on every actin molecule there is a binding site which lets it bind to cross bridges on myosin
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10
Q

where do you find cross bridges in skeletal muscle

A
  • myosin
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11
Q

what is the structure of myosin cross bridge

A
  • there are at least two ATP binding sites
  • there is an actin binding site (usually a few of them)
  • there are light chains which are regulatory elements
  • main body of myosin is made up of heavy chains which give it its structure and form the shape
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12
Q

what is the importance of ATP in muscle contraction

A
  • used as energy to generate muscle contraction
  • but muscle can only relax when you bind a new ATP (it is a safety mechanism to make sure you are ready for the next contraction)
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13
Q

what is the role of tropomyosin in skeletal muscle

A
  • tropomyosin partially covers the myosin binding site on the actin molecule (and so regulates when the actin and myosin interact)
  • it is held in this position by troponin (co-operative block)
  • calcium binds to troponin and troponin alters shape and pulls tropomysoin away
  • when calcium is removed the site is blocked again
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14
Q

what is the role of troponin in skeletal muscle

A
  • holds tropomyosin in position while it covers myosin binding site on actin molecule
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15
Q

what is the role of calcium in skeletal muscle

A
  • when calcium binds to troponin it removes the tropomyosin from the myosin binding site and so action and myosin can bind via cross bridges and so muscle can contract
  • when calcium is removed binding site is covered again
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16
Q

what is the job of sarcoplasmic reticulum in muscle

A
  • it is the main storage facility for calcium
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17
Q

what are transverse tubules in the skeletal muscle

A
  • do deep into muscle to conduct signals that comes from the motor neurone
  • makes sure electrical command reaches all parts of the muscle
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18
Q

what is excitation contraction coupling in skeletal muscle

A
  • the process of taking an excitatory signal which comes from a motor neurone and converting it into a mechanical force
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19
Q

what are the steps in excitation contraction coupling

A
  1. muscle action potential is propagated
  2. calcium is released from lateral sac of sarcoplasmic reticulum
  3. calcium binds to troponin and removes the blocking action of tropomyosin
  4. cross bridge moves
  5. calcium is taken back up by sarcoplasmic reticulum
  6. calcium removal from troponin restores the tropomyosin blocking action
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20
Q

what makes up a motor unit

A
  • motor neurones and motor fibres
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21
Q

what does tension mean in muscle mechanics

A
  • force exerted by the muscle
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22
Q

what does load mean in muscle mechanics

A
  • force exerted on the muscle
23
Q

what does isometric mean in muscle mechanics

A
  • contraction with constant length

- i.e. weightlifting (lifting something and holding it there - muscle length stays the same)

24
Q

what does isotonic mean in muscle mechanics

A
  • contraction with shortening length
  • (can also be called concentric)
  • e.g. running
25
Q

what is an example of lengthening contraction of muscle

A

sitting down

26
Q

what does contraction time in muscle depend on

A

calcium ion concentration

27
Q

what is the latent period in muscle contraction

A
  • the time before excitation contraction starts

- isometric has shorter latent period but longer contraction event

28
Q

what happens to muscle contraction as load increases

A
  • contraction velocity increases and distance shortened decreases
29
Q

what is contraction time

A

between the start of tension and time when we have peak tension

30
Q

what is a muscle twitch

A
  • one single action potential triggers a muscle fibre and we get a twitch
31
Q

what is tetanus

A

if we get lots of action potentials we can generate long sustained contractions until the muscle gets tired
- firing lots of action potentials in a close amount of time is called summation

32
Q

why is tetanic tension greater than twitch tension in muscle contraction

A
  • calcium concentration never gets low enough to allow troponin/tropomyosin to re-block myosin binding sites
33
Q

what is the length-tension relationship in muscle contraction

A
  • less overlap of filaments = less tension
  • too much overlap = filaments interfere with each other
  • muscle length for greatest isometric tension = optimal length
  • (if you stretch muscle it’ll contract back even harder but shouldn’t stretch it too much because actin and myosin won’t be able to bind)
34
Q

where does muscle get the energy for contraction

A

hydrolysis of ATP energises cross bridges
- ATP binds to myosin
- dissociates bridges bound to actin
- new cycle may begin
ATP also powers calcium (ATPase in sarcoplasmic reticulum)
- calcium pumped back into sarcoplasmic reticulum
- contraction ends

35
Q

what is fatigue and why does it occur

A
  • repeated muscle stimulation leads to fatigue
  • depends on the fibre type, length of contraction and fitness of individual
  • if muscle is rested can contract again
  • fatigue prevents muscles using up vast amounts of ATP which would cause rigor (because need new ATP fo activate cross bridge cycle)
36
Q

what factors cause fatigue during high intensity exercise

A
  • conduction failure due in increased concentration of potassium (leads to uncontrolled depolarisation)
  • increase in lactic acid concentration, acidifies proteins
  • increase in concentration of ADP and phosphate and this will inhibit cross bridge cycle, delays myosin detachment from actin
37
Q

what factors cause fatigue during long-term low intensity exercise

A
  • decrease in muscle glycogen
  • decrease in blood glucose (because not eating or drinking)
  • dehydration
  • central command fatigue is when you are psychologically just not able to do it (your brain is telling you no, no will to win)
38
Q

what are the three types of muscle fibres

A

slow oxidative (I) - resist fatigue

  • fast oxidative (IIa) - intermediate resistance to fatigue
  • fast glycolytic (IIb) - fatigue quickly
  • the more load the more motor units recruited
  • slow oxidative activated first, then fast oxidative, then glycotic last
39
Q

what do they mean by a fast muscle fibre

A
  • myosin has high ATPase activity
40
Q

what do they mean by a slow muscle fibre

A
  • has a low ATPase activity
41
Q

what do they mean by an oxidative type of muscle fibre

A
  • lots of mitochondria, lots of oxidative phosphorylation
  • lots of vascularisation to deliver more oxygen and nutrients
  • contain myoglobin (short term store for oxygen)
  • fibres are red and have low diameters to minimise diffusion distance from blood
42
Q

what do they mean by glycolytic type of muscle fibres

A
  • few mitochondria
  • lots of glycotic enzymes and glycogen
  • lower blood supply
  • white fibres with large diameters
43
Q

what happens to the muscle as a result of anaerobic exercise (strength)

A
  • increase in muscle diameter

- increase in glycolysis

44
Q

what happens to the muscle as a result of aerobic exercise

A
  • increase in mitochondria
  • increase in vascularisation
  • increase in fibre diameter
45
Q

what are the characteristics of smooth muscle

A
  • innervated by autonomic nervous system
  • no striations
  • exists in hollow organs (e.g. GI tract)
  • has a cross bridge cycle and uses calcium (filaments and excitation contraction coupling different)
  • spindle shaped
46
Q

what are the structural features of smooth muscle

A
  • spindle shaped
  • mononucleate
  • divide through life
  • filaments arranged diagonally across cells and are anchored to membranes and cell structures by stuff called dense bodies
  • filaments still slide together to contract cell
47
Q

what are dense bodies in smooth muscle

A
  • anchor thick and thin filaments to intracellular organelles and cellular membrane
  • give actin and myosin something to anchor onto and pull on when they contract
48
Q

what is the smooth muscle cross bridge cycle

A
  • increase in calcium concentration
  • calcium binds to calmodulin
  • calcium-calmodulin binds to myosin light chain kinase
  • kinase phosphorylates myosin cross bridges with ATP
  • phosphorylated cross bridges bind to actin filament
  • get contraction and tension
49
Q

how does smooth muscle relax

A
  • via the action of myosin light chain phosphatase

dephosphorylates cross bridges

50
Q

what happens when there is persistent stimulation and incased calcium concentration in smooth muscle

A
  • phosphorylated cross bridges may be dephosphorylated when still bound to actin
  • this decreases the rate of ATP splitting and slows the cross bridge cycle
  • means you can maintain tension for long time with low ATP consumption (useful in blood vessel walls that have to stay open for long periods of time)
51
Q

what are the sources of calcium for smooth muscle

A
  • sarcoplasmic reticulum (less SR in smooth muscle and no transverse tubules)
  • extracellular calcium (voltage gated calcium channels)
52
Q

what is tone in smooth muscle

A
  • smooth muscle has tone i.e. basal level of calcium in cells causes a constant level of tension
  • in smooth muscle we don’t see a big amplification effect as we do in skeletal muscle, in skeletal muscle 1 action potential saturates all troponin binding sites but in smooth muscle only some sites are activated, smooth muscle doesn’t have to operate as quickly as skeletal
  • the idea of tone is that smooth muscles are designed to resist fatigue
53
Q

what are factors affecting contractile activity

A

dynamic balance of the following

  • spontaneous electrical activity in muscle membranes = pacemaker activity
  • autonomic neurotransmitters from varicose veins
  • hormones
  • local factors (e.g. oxygen)
  • stretch
54
Q

what are the different types of smooth muscle

A

single or multiunit

  • single = many cells linked by gap junctions, may contain pacemaker cells. stretch evokes contraction
    (e. g. GIT, uterus, small blood vessels)
  • multiunit = few or no gap junctions, richly innervated by the ANS, don’t respond to stretch
    (e. g. airways, large arteries, hairs)
  • most smooth muscles in organs are a mix of both, means it can have different properties

principles of normal function (15 decks)

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