Midterm Flashcards

Question

What is a power stroke?

Answer 1

Sarcomere shortening occurs via power strokes

Answer 2

CB formed by myosin head Cross bridge is connection b/w myosin head and actin filament Once this attaches to actin the head ends up pulling actin towards it Sarcomeres can only shorten by pulling towards each other (NOT LENGHTENED) Only one of heads is involved in power stoke (one of the 2 myosin heads)

Answer 3

Cross bridge is detached – myosin head not attached to actin Cross bridge attaches to actin; power stroke begins – myosin head attaches to point on actin filament and begins to do that power stoke Z line starts to move towards myosin Power stroke proceed; pulling actin and z-disk; goes to how far it can, pulling acti and z disk inwards – shortening the sarcomere (only 10% of the total time) CB detaches and “springs” back; Once power stroke is completed – myosin head detaches and springs back into ready position Myosin head attaches pulls and springs back

Answer 4

There's a section in middle called bare zone Segemtn of myosin filament with no corss bridges (corresponds to H zone) As sarcomere shortens bare zone becomes overlapped with actin filament

Answer 5

``` When muscle contracts the Z line moves toward each other when muscle contracts Some of the bands narrow and some don’t A band (actin and myosin) – doesn’t actually get shorter b/c myosin filaments make up inside of a band and they don’t get shorter – A band stays constant I band gets shorter – area where there is no overlap of actin and myosin gets smaller Muscle contracts when there's more overlapping myosin and actin (muscle contracting = muscle shortening ```

Answer 6

Muscles always become shorter – When muscle is contracting and this happens Concentric = muscle shortening (muscle contracts and it gets shorter) Eccentric = muscle lengthening (muscle is contracting and it’s lengthening – losing the battle, it’s trying to get shorter, but it’s getting longer Static contraction = no change (same amount of contraction force upwards as downwards) – no change in muscle length while the muscle is contracting

Answer 7

If you had a concentric contraction – the sarcomere gets shorter (pull together Eccentric – the sarcomere is getting longer (even though its trying to get shorter) – actin and z line move apart Static – equal shortening as lengthening

Answer 8

Power strokes always want to cause sarcomere shortening Always pulling in shortening direction even if they don’t succed Whethere they succeed depends on the external laod imposed on the muscle and if cross-bridges are cycling (not enough force to shorten and external load is higher = eccentric Tug of war – myosin pulls one way – muscle pulls another way – whatever one wins is the direction muscle

Answer 9

Muscles getting you up = Muscles letting you down Same muscles for up, down and static Pulling up – you are shortening elbow flexors and lats – concentric (sarcomeres overcoming force of gravity) Down – lengthening contractions in elbow flexors and lats – force of contracting less – gravity overtakes If you completely let go you just fall so you apply a little bit of force to slowly move down Static – just hold steady/ stop half way – isometric – same amount of force to elbow flexors as gravity – neither lengthening or shortening – you aren’t using dif muscles on way up or down

Answer 10

Cross bridges look like people are rowing – in rowing people are synchronized and each time balde is in the water it's all at same time then they all let go and stoke again Muscle cross bridges are Asynchronous – at any given time some cross bridges are attach and other arne’t – doing power stokes at different rate s Muscle wouldn’t work well other wise

Answer 11

You’re climbing a rope – alternating with hands and feet – one hand holding on while other moved – if you tried to use both hands to grab up higher – you’d fall as you let go Same idea with actin – if cross bridges were synched everytime a cross bridge let go all would let go and we have opposing forces that corss bridge would not be contracting and allowing actin to slip away – so during non-attached phases actin would slide away and amount of time cross bridge is attached is less than the time it is unattached – inefficient movement – asynchronously – at any given time always cross bridges attached so there's no slipping of the muscle and allows for effective shortening

Answer 12

We get energy from the breakdown from ATP to ADP and Pi and How most energy is provided ATP attaches to myosin head in the muscle

Answer 13

Cross bridge has contracted sarcomere moves closer to itself and now it needs to detach ATP binds to myosin head and causes detachment from actin The ATP in the second step splits in half and released energy and causes myosin head to spring upright (adds energy to system -pull back arrow In archery – costs energy) Inorganic phosphate is released and myosin can bind to actin Once ADP is released (like letting go of bow) – causes energy to be released and causes cross bridge to go 2 ROLES of ATP 1. Provide energy to power stroke (– splitting of ATP) -PULLING BACK 2. Detachment of myosin from actin – attaches to myosin Green circles are ATP – everytime atp attaches it allows myosin to detach and when atp splits it causes it to cock back and be ready to cause muscle contraction

Answer 14

Troponin Circular protein Made up of 3 complexes (3 parts) Role: allows ca to bind to it, binds to tropomyosin, helps to inhibit binding b/w acting and myosin – inbits myosin head cross-bridge formation Tropomyosin Physically blocks binding site where myosin ahs to attach Myosin head has to bind to a binding site which is hidden underneath tropomyosin, no corss bridge occurs when tropomyosin is covering the site What happen is when ca is present then ca binds to troponin binding site – whne ca is bound to troponin it pulls aside the tropomyosin and expposes actin binding sites for myosin Once they are exposed as long as theres eough atp ther we have myosin heads binds – ATP isn’t require for binding it’s requored for cross bridge cycle to occur Need atp and Calcium for muscel contracting

Answer 15

WE Need calcium and if it's not there we don’t get state 3 of myosin binding to actin w/o Ca (you can have all ATP you want, still need Ca Yellow balls are Calcium once they attach to troponin it moves the tropomyosin and exposes myosin-binding site s IF NO CA is there? Then tropomyosin slides back over actin-binding sites and myosin can’t bind and cross-bridge cycling stops and the muscle relaxes

Answer 16

``` sarcoplasmic reticulum (wrap around myofibrils ) controls amount of Ca available to myofribrils Sarcoplasmic reticulum holds a lot of calclium the concetnraiton of Ca inside is very high ```

Answer 17

3 main functions: Store Ca at trest Releases ca Uptake when it wants to cause muscle concentration to occur (Ca leaves SR – binds to troponin moving tropomyosin and exposing binding sites) Ca reuptake (removing ca from cytosol – remove availability to CB so no more cycling (requires ATP to pump it out of the cytosol

Answer 18

How neuo system tells muscle to release or uptake that Calcium

Answer 19

Neurons communicate via changes in the charges across membrane CNS communicate with muscles via motor neurons A resting membrane neuron: more negatively charged inside membrane than outside When we have depolarization charge of neuron changes in on area and change spreads and moves down the axon and down the cell to communicate with other parts of body (to communicate with muscle fibers) Looking at one small area of neuron – we’d see a change in charge that looks like graph (depolarization) Action potential moves down the neuron (areas beside it and so on till it makes it to end and acts on axon terminal Change in charge that moves down nerves and is used to communicate with CNS and rest of boy

Answer 20

Depolarization (becoming more positive) Occurs when cell depolarized to threshold (-55 mV) Once at threshold it triggers depolarization and it happens automatically (once at -55) - Voltage gated Na+ channels open (charge becomes more positive) – sodium rushes in (positive charge moving inside = depolarization

Answer 21

Repolarization (return to negative charge) Voltage gated K+ channels open (charge becomes more negative again) K+ allows K+ to rush out of cell (positive rushing out and it brings it back down to negative

Answer 22

Hyperpolarization: Overshoot, voltage gated K+ channels close Sodium potassium pump return k+ AND Na+ to OG positions

Answer 23

Once we make it to the end of that motor neuron we have a neuromuscular junction Where neuron contacts muscle fibre and communicates AP from CNS to fibre to tell it to contract A single motor neuron talks to multiple muscle fibres

Answer 24

Motor neuron to postsynaptic cell (muscle fiber) Action potential depolarizing axon terminal At axon terminal it activates voltage gated Ca channels – it opens Ca channel and calcium floods into the motor neuron and it acts on the vesicale (bubbles of neurotransmitter floating around axon terminal) – it causes them to move towards the edge of axon terminal and spew contents into neuromuscular junction – in this cause acetylcholine Neurotransmitters move across junction and attach to receptor on muscle fiber – receptors are voltage gated Na channels (this causes Na into the cell =depolarization) – depolarization occurs in one area of cell and spreads across cell membrane

Answer 25

Neuromuscular junction and AP makes it ot cell membrane and spreads across outer membrane of muscle fiber As Ap makes it way to muscle fiber to finds its way to these divots or holes which go into the muscle fiber/myofibrils – hole called transverse tubules – action potential moves across sarcolemma of muscle fiber then down transverse tubules towards interior change in charge is infiltrating inside of muscle fiber allowing AP to reach each f the myofibrils and inside the muscle fibre – w/o transverse tubules we’d only have myofibrils working right close to the edge and we’d never get AP in the middle sarcolemma needs to extend into the centre of the muscle fiber

Answer 26

the myofibrils make up 85% of muscle fiber contents rest is sarcoplasmic reticulum and mitochondria t tubules dive into muscle cell and reach/contact all myofibrils – make their way to myofibrils on either side are large parts of sarcoplasmic reticulum called terminal cisternae of SR junction b/w sarcoplasmic reticulum, the terminal cisternae and t-tubules is called a “triad” 2 triads per sarcomere in human skeletal muscle The t -tubules which carry ap are right beside sarcoplasmic reticulum which carries the Caclicum

Answer 27

``` Stores Ca (At rest) – sarcoplasmic reticulum is not permeable to Calcium at rest, calcium pump is active any axcess Ca cto be pumped back into SR. Ca is -10,000 times greater in SR (rigor mortis – calcium leaks out of Sr and XCa pump is not active – calcium cross bridges can attach but not enough atp so it stays in contracted condition Release Ca (in response to motor action potential) – as signal makes its way down t-tubules it open calcium channels (Calcium channels open, and the ca rushes out and into the myofibril space – CA binds to troponin and causes CB cycling to be able to occur b/c myosin binding site is active Re-uptake Ca after motor action potential is no longer there No more MAP no more depolarization – Ca channels close Ca pump work to pump Ca back into SR nad once Ca returns then CB cycling stops – troponin is no longer bound to Ca and tropomyosin covers up binding site – ATP dependant process – used energy to cause muscle relaxation ```

Answer 28

Action potential causes synapse to release Ach AP in the sarcolemma/membrane of muscle fiber Ap moves down the muscle fibers and down t-tubules where it is paired with SR Once it reaches SR it releases Ca into the myofibril space – in cytosol Lots of CA IN cytosol we get Ca binding to troponin and exposes the binding site so myosin can bind Cross bridge cycling (as long as binding site is exposed – CB keep cycling over and over – as long as ATP and CA available Stop AP – Ca is removed -causes less ca to attach to troponin, Tropomyosin blocks binding sites and muscle relax

Answer 29

tick myosin on to plate Put actin filaments on top of myosin heads in a fluid As long as they get CA and ATP they keep contracting and actin moves around Actin is fluorescent and you can see actin moving record this and record velocity – faster more CB cycling is occurring Add something to slow movement – impairs muscle filament Say you added MORE Calcium and Atp = increase velocity, more Ca and ATP more binding sites available more CB cycling can occur. More ATP does the same thing = greater velocity, there is a point where all the binding sites available being used and are saturated with ATP there Is a maximum rate of contraction

Answer 30

concentric – trying to shorten and shortens Eccentric Isometric = force being applied is the same as the muscle is applying (by CB cycling – no movement Isometric contraction doesn’t necessarily mean there;s no movement Person is sitting in a chair and they are trying ot kick but they can’t move it (isometric) You’d think no movement – in reality ther’s a lot of movement! No external work you are performing a lot of internal movement – due to the elasticity of the muscle Difference b.e no movement around and joint and no movement within a muscle

Answer 31

More frequent acetylcholine release. • More firing of action potentials along sarcolemma • More frequent propagation of AP down T-tubules • More Calcium released • More open Calcium channels • More calcium in the cytosol • More calcium binding to troponin exposing more binding sites are available • More cross bridge cycling • Overall force of muscle contraction increases.

Answer 32

• Less likely to be a detachment from myosin • Calcium can enter cytosol but less ATP to pump back into SR Cross bridge cycle happens slower due to less ATP interaction • Smaller force of contraction

Answer 33

Less myosin to bind • Less binding, can cause slipping • Fewer myosin and actin interactions = less cross bridge cycling • Decrease force

Answer 34

Muscle wouldn’t be able to relax, slower calcium reuptake into SR • More calcium around in cytoplasm more exposed binding sites and this inhibits relaxation • Impairs muscle function • More contraction, probably more cross bridge cycling – force doesn’t increase, but lasts for longer cause relaxation can’t occur – more time for cross bridges to cycle

Answer 35

* No area of neuron where there can be contact between neuron and sarcolemma * No acetylcholine release * No muscle action potential (nothing passed down t-tubules) * Calcium stuck in SR - not able to expose binding sites * No contraction – muscle relaxed

Answer 36

an Alpha motor neuron (nerve from spinal cord and innervates muscle fibers) + innervated muscle fibers Each motor neuron is going to innervate a bunch of muscle fibers All the muscle fibers innervated by one neuron is called a motor unit May see motor neuron from SC and axon splits and innervates b/w 10 and 2,000 muscel fibers The eye innervates 10 msucel fibers ratio of 1 to 10 In gluteus amximus each mortor neuron innervates 2000 suchle fibers

Answer 37

number of fibers controlled by one neuron

Answer 38

all muscle fibers fire with alpha-motorneruron action potential. When an action potential goes down that motot neuron – all msucel fibers in that motor uit are going to contract – you can’t differentiate b/w differntnmuscle fibers within that mototr unit. If you’re activating that motot neuron than all the fibers are going to contrac t In msucels where fine movemetns are rewuired each motor neuron only innervtates a few muscle fibers at the same time and the eye moves a little bit – this is good for fine movemetns In the glute it doesn’t require fine movement – soyou can have a lot of movement with a little efforet form SC

Answer 39

Imagine this is one motor neuron and all muscle fibers it innervates Motor neuron sends APP down and it splits off and innervates different fibre – once AP reaches motor end plate it reaches muscle fiber and spreads out sarcolemma (AP progate/spread along the fibers) Causes muscle to contract and causes and increase in force Amount of force over time – if just one AP is fired it is gonna cause blip in force that is increased than decreases (muscle twitch) If you see it looks like two MAP being sent out (NOT TRUE) – just one MAP that spreads across muscle Stone in pond – having waves spread across pond – like if you cause ap down a motor neuron – after it reaches end pa,te and reaches sarcolemma it spreads across sarcoleme like waves acoss a ponf (one AP spread, one wave)

Answer 40

Contractile response to single nerve impulse/muscle action potential Single twitiches are rare in normal function Evoked (ST) artificially in research to study muscle function

Answer 41

2 electods and send electrical impulse into femoral nerve (below) and it evoke muscle twitch – muscle contracts and use EMG – tell us about electrical acitivt of the msucel EMG measue AP as they go across the msucel fibers Muscle twitch is a small contraction and doesn’t cause much movement Force applied by nuscle tiwthc may be 40 n.m at it’s peak and tis over short period of tiem – 220 md =0.22 Ca release/contraction par = 80ms Ca reutpaek/relacxtaion = 140ms

Answer 42

Low=full relaxation b/w twitches If you stimulate at low frequency and have full relaciton b/w twitches = twitches abck to back and they won’t affect each other Summation: High frequency of Ap, incomplete relaxation, stronger contraction 2 AP back to back – 3 back to back 6 back to back evokes each time there’s a seconds ap before other one fully relaxed it causes increase in a force and it compounds on itself

Answer 43

Twitch Summation Contractile response to a “train” of MAPs causing summation 5AP/sec (5HZ) Contraction and a bit of relaxation(not full) before next AP comes Jagged line =unfused tetanus Unfused tetanus indicates that there jagged line and we haven't fully allowed relactation before next AP Ap very frequently (50 hz/50 times per sec) – don't even time for relaxation to start! It causes smooth increase and plateau at top – no jagged force production its smooth – this is fused tetanus (bumps fused, completely fused Strongest contraction you can initiate is via fused tetanus Double frequency to 100 hz it won’t increase muscle contraction there is a plateau and that’s at fused tetanus – no relaxation in between it is at maximum contractile force Summation causes tetanus to be stronger than twitch = more summation in fused teatmnsu than unf

Answer 44

Muscle twitch evokes less force/increase in force than tetanus Each muscle ahs different in Twitch/Tetanus Ratio or Tetanus/twitch ratio This is the ratio b/w amount of force evoke by twitch and force produced by tetanus Say 5 N of force in twitch and in tetanus you produce 50 N 5/50 = 0.1 10% Or 50/5 = 10

Answer 45

Muscles exert their force on the bones they are attached to Say looking at bicep – it exerts force on bones it’s attahces to (inward force sent down msucel on tendon and orgin of muscle and insertions – forces pulled on bones its attached to Inward force on origin and insertion Muscle/tendon complex works like an elastic – when you pull on it it stretches a little bit and it tries to react by snapping abck together Tendon and muscle are a bit elastic – once you shorten it doesn’t immediately occur b/c of elasticity it’s a bit delayed Muscle itself acts like an elastic

Answer 46

Tendon b/w the bone is elastic (the major elastic compoinent of the muscle Connective tissue b/w the tendon and muscle Titin – from z line t myosin head is elastic Cross bridges themeseld All contribute to series elastic compent: they are end ot end. Act in series ontop of each other

Answer 47

Series vs parallel Contractile unit is a bit elastic and tension is elastic Surrounding contractile unit/muscle fiber is sarcolemma which is also elastic – since it surrounds it has different elastic properties – elasticity in parallel (round contractile unit) Series vs parallel – you're trying to move a rock with a few elastic bands attached end to end (attached in series). Still very difficult to apply force of you pulling onto the rock b/c they stretch adding more end to end/in series just causes it to stretch a longer distance. Say you wanted to add force in parallel – attached elastic bands side by side . Attache them in other hand and more bands side by side then the force you apply will more be applied to the rock

Answer 48

the SEC means that less force is applied to the bone initially once the SEC is taken up: CB force=force applied to bone

Answer 49

External force- rise much smaller and is a bit higher than internal force during relation – reason is b/c SEC Analogy – person holding a spring – muscle twitch s one quick step out (starting to stretch Elastic component of muscle – only going to apply a bit of force ot bone – block only feels a bit og forfc e Once you relax not more steps – elasticity has some potential force and it’s trying to pull you back towards blaokc – elasticity tries to add to the force inot more contacted position – even though CB aren’t minimally contracting Elastic component tries to apply that force You provide energy and it comes back somehow by bringing muscle to a more contracited potion

Answer 50

THE FORCE is being applied by the CB every single time there’s a cross bridge there's a max force apply internally External force takes a bit of time to reach potential amount of internal force Person holding a spring 1 AP = 1 sig step Cb keeps shorting more AP – taking up more spring – spring gets stiffer and pulls block a bit more Once you’ve been stretching/pulling for extended period it’ll be full extended – like pulling on metal wire no elasticity and put force you’re using to run/pull into the block and then At this point , The external force = to internal force no more elastic stretch occurs and all force from CB is being applied to bone Once sec of a muscle is fully stretch there's no force lost to elasticity

Answer 51

Rising phase of twitch lasts only ~50-100ms (short) not enough time for CB to shorten enough to take up SEC A tetanus can lasts seconds (logner) sufficient time to take up elastic component easily and apply CB force directly to bone

Answer 52

Force – Ca concentration Relationship if we graph Ca that’s available in the cytosol to amount of force being applied by muscle we can see that there's an increase in force applied to muscle with more ca Little Ca (like with low frequency AP) = little force applied Saturating Ca (high frequency) = large force applied Certain point we reach saturating Ca = interaction b/w ca and troponin all the troponin have ca bound to them and all sites available – adding more Ca won’t free up any more sites b/c they are all available = most amount of force possible – not more increase in force with more added ca

Answer 53

experimental setting – apply electoral impulse to femoral nerve 1 impulse = muscle twitch Apply electrical signals at low rate 10 x per sec = unfused tetanus – not as strong as fused tetanus Impulse at 50 times per sec = fused tetanus – more frequent MAP more frequent release of Ca from SR More Ap that reach SR per sec more Ca release and we will reach suturing ca rate = fused tetanus Unfused gap b/w each AP and ca taken up Fused Ca – no time for Ca to be taken up and always lots Ca available and cause max contraction Higher frequency MAP more Ca release from SR more force produced

Answer 54

More ca = more force Take forec ca relationship and overly oaver frwuency ca relations And increasing frwuency of AP (twitch = lowest AP frwuncy) Increasing frwuncy AP = more CA released = more force applied 10 hz (10AP/sec) vs 50HZ = max force Diminishing returns diff b/w 1AP/sec to 10 hz increase foec from 5 – 50% Diff b/e 10hz to 50hx increases forec gives you an increase of force from 50 – 100 % So more ap per sec the elss each ap contributes to an increase in force

Answer 55

1 AP/SEC and 50 AP/SEC In tetanus 1AP intiate little blip and this is internl force vs many AP cause large internal force (potential force) However at external force (applied to bone) – not as much applied ot bone during tiwthc and suring tetanus the extrenal force lags behind due to SEC External force vs internal during a twitch due to SEC During tetanus external force lags behind because of SEC, delay in equalizing external and internal force during tetanus is due to SEC (being taken up ) takes time for ti to be taken up and twich doesn’t case enough time for shortening Tetanus more ap and more ca relase = more mysin to actin and cause more CB cyucling and more force generated