Midterm 1 Flashcards
Skeletal muscle makes up __-__% of BW in males. Females?
40-45%, 23-25%
Bundles of muscle fibres are called what? What CT covers them?
fasciculi - perimysium
There are _______s of fibres per muscle. 100? 1000? 10000?
1000
fibres vary from 10-___ um thick.
100
length varies from a few mm to…
several cm long
Why do the fasciculi have a polygonal shape?
allows for greater packing vs. cylindrical
Muscle fibres are made up of what? There are a few hundred to several ? _______ per fibre
myofibrils - thousand myofibrils
T or F: myofibrils only run in the middle of the muscle fibre
F - full length
Myofibrils are made up of what 2 myofilaments?
thick - myosin, thin - actin
Dimension of actin? myosin?
actin - L=1 um, T=6nm
myosin - L=1.5 um, T=16nm
T or F: dimensions of actin and myosin are proportional to the muscle and body size of the organism
F - consistent
What CT hold all the fasciculi together?
epimysium
Where is the endomysium?
around each muscle fibre
why are muscle cells multi-nucleated?
fusion of myoblast
What is the sarcolemma?
cell membrane around each fasciculi
There is a troponin every __ actins - evenly spaced
7
What is the I band (2)? A band? (2)? H zone (2)?
I band - actin only (between myosin of two adjacent sarcomeres - LIGHT BAND
A band - actin + myosin (covers myosin) - DARK BAND
H zone - bare zone - no myosin CBs
Is is said that 80-85% of the contents in the fibre is myofibrils? What about the other 15-20%?
mitochondria, glycogen, SR, Aux PROs
What holds the sarcomeres in place?
cytoskeleton made from the auxillary PROs
Organization of the _ actin to 1 myosin allow for what?
6 - fine movement
if you were to get a x-section at the M line, what would you see?
myosin with aux PROs
Average length of a sarcomere (Z-Z)
2 um
if the length of a myofibril is 30 um, how many sarcomeres would there be?
30um/2um = 15 sarcomeres
sarcomeres can vary in length depending on…
degree of filament overlap
sarcomeres can vary in number depending on…
length of muscle
What is the longest, shortest and optimal length of a sarcomere? What is the working range?
3.5, 2. 1.5 um
2 um (3.5-1.5 um)
In a 1 cm or 10 mm long muscle fibre…
how many sarcomeres are there? what’s the shortest, longest, optimal length?
10 mm/2 um (10^-3) = 5000
1.5 x 5000
2 x 5000
3.5 x 5000
T or F: The myosin molecule only includes the head…
F - and the tail
T or F: the power stroke begins once myosin (CB) lets go of actin
F - when CB attach to actin
Whether of not the sarcomere shortens is dependent on….
external force
T or F: CB cycle happens asynchronously
T
What enzyme catabolizes ATP? What are the products?
Myosin ATPase; adp, p, E
What are the two roles of ATP in the CB cycle?
de-attachment of myosin from actin + power stroke
What are the 4 steps in the CB cycle (starting at the end of the power stroke)
1) dettachment - ATP binds to myosin head
2) CB springs up right - ATP spilts
3) CB binds to actin - P released
4) powerstroke - energy and ADP released
repeat
Around ___% of the CBs are attached at one time
50
What are the two regulatory proteins?
troponin, tropomyosin
What are the 3 parts of troponin
1) troponin Calcium
2) troponin Tropomyosin
3) troponin Inhibition (prevents actin and myosin from binding at rest
Each tropomyosin covers __ actin globules
7
What is the role of Calcium in CB cycling (3 steps)?
1) released Ca binds to troponin
2) troponin pulls tropomyosin off the binding sites on actin
3) myosin head binds to actin – CB cycle begins
What happens when Ca is removed (2)
1) tropomyosin slides back over actin binding sites
2) CBs canot bind to actin sites - CB cycle stops
What is unique about the sarcolemma, up close?
it’s folded - more area to fit more ion channels for AP
What is the NT of muscles?
ACh
How does nerve AP propagate (4)?
1) travels down the motor neuron fibre, branches to reach the motor end plate (sole foot/terminal)
2) Ca enters the sole foot, causing the release of ACh into the synaptic cleft
3) ACh binds to receptor sites on the muscle cell; its membrane becomes permeable to Na (in) and K (out)
4) MAP is propagated
The NMJ consists of what two structures?
terminal + end plate
Describe the 5 sections of the membrane potential graph. When does MAP occur?
1) membrane becomes more positive (Na going in) until it reaches the threshold
2) Na influx
3) Inside of the membrane is positive
4) Na channels close (just after the peak)
5) K outflux
MAP - just after the peak, before the membrane becomes negative again (passes 0 mV)
A response to an AP is called….
twitch
What structure allows the AP to propagate centrally along the myofibril?
Transverse tubules
What is the Triad?
a junction - 2 SR and 1 T-tubule; 2 triads per sarcomere (at each end)
What are the 3 functions of the SR
1) store Ca (at rest)
2) release Ca (response to MAP)
3) Ca reuptake (after MAP)
T or F: at rest - the SR has a high permeability to Ca, keeping it in
F - low permeability
What is the anatomical basis for rigamortis?
no ATP is produced when we are dead, the Ca pumps that usually would keep Ca in the SR fail; Ca outflux = constant contraction of sarcomeres
What is the Ca pump called? What type of channel is it?
Ca ATPase - energy gated
In response to the MAP, what type of channels release the Ca?
voltage gated
What is the relationship between frequency, muscle force, and summation
all increase/decrease with each other
Define tetanus and the two types.
tentanus - contractile response to a train of MAPs causing summation; (unfused - quasi-relaxation; fused - rising phase builds on eachother)
What is the twitch and tetanus ratio?
twitch force/tetanus force
OR
tetanus force/twitch force
ratio can vary but 10 or 0.1 (10%) is common
Differentiate a twitch and tetanus.
twitch - 1 NAP = 1 MAP
tetanus - multiple NAP = multiple MAP
2 mechanisms that explain why tetanus is stronger than twitch.
1) series-elastic component (SEC)
2) greater Ca release from SR
What are the effects of the SEC on the force produced by the muscle? How does twitch/tetanus differ in force generation?
tissues like tendon, CT, cytoskeleton and CBs are elastic - they take up potential energy (assumes no elasticity); slack has to be overcome before direct force is applied to the bone
tetanus - eventually potential force = external/measured force; never happens for a twitch
What’s the time factor in terms of the SEC?
twitch - insufficient time to take up SEC: sufficient with tetanus
How does a greater release of Ca from the SR affect the force generated?
the more MAP, the greater the release of Ca, the greater the # of active CB, greater the force of contraction (PROPORTIONAL - even the graph)
Therefore the force generated is proportional to the…
amount of Ca released
The difference between the potential and external force is due to…
the time factor (taking up the SEC) - twitch < tetanus
Contraction type vs. Actions? Describe muscle load
CON
ISO
ECC
shortening (MF>load), fixed length, lengthening (MF<load)
Controlled lowering of a weight…
brain recruits fewer motor units
Isotonic? Isovelocity? plyometric?
constant force during action
constant velocity…
ECC
Talk about CON and ECC during an elbow extension. How is it both?
CON - of the triceps
ECC - of the biceps - opposes triceps and elbow extension
Which contraction types is strongest-weakest?
ECC, ISO, CON
Why is ECC the strongest? (3)
1) braking action of stretched CBs
2) passive tension of stretched cytoskeleton PROs
3) increased # of attached CBs
Explain 1.
as the actin is pulled, the CBs bound to it stretches - the recoil force is exerted into the direction of the contraction (bending of myosin head)
Explain 2.
similar to 1
Explain 3. Why are more CBs attached? (2)
1) increased probability of BOTH heads of myosin attaching (more exposed actin binding sites) - note: not 100%
2) Non-energy dependent CB detachment (removed by pulling force) - remaining in stage 3 of the CB cycle rather than starting in stage 1 - also therefore increases rate of pulling
T or F: cost of ECC is 0
F - not all CBs are suspended in stage 3
T or F - some CBs must be able to complete full CB cycles despite forced lengthening of muscle
T - why? no idea
Why are CON contractions the weakest?
1) negative braking force
2) sliding filament effect
3) slacker SEC
Why are ISO contractions in between?
no sliding of filaments…
1) no pros/cons of ECC/CON
2) CBs may repeatedly attach and detach from the SAME actin binding site
2 reasons why walking up the stairs feels harder than walking down?
ECC = fewer CBs required
fewer recruitment of motor neurons - less voluntary effort
less ATP used - lower energy cost
Would the % of CONmax be higher or lower than % of ECCmax?
lower
How can we measure ECCmax? (2)
use heaviest weight that can be slowly lowered with control
dynamometers
In the CN tower experiment?
Who will be in more pain the next day - those who go or down the stairs?
CON - soreness due to CV
ECC - crippling pain - red urine (myoglobinuria), possible kidney damage (rhabdomolysis) - DUE TO CONSTANT LENGTHENING
What does the F-V relation graph look like?
insert photo
At what point…
1) Vmax
2) isometric
3) ECC or CON
4) maximum unresisted shortening velocity
end of graph
middle where v=0
ECC - concave down; CON - concave up
at Vmax
Why does the CON F decrease as V increases? (3) When is it amplified?
1) slacker SEC
2) sliding filament effect
3) - BF
as V increases?
Why does the ECC F increase as V increases? (3)
1) + BF
2) increased # of CBs attached - very unclear
F-V relationship, if you set one and measure the other - what is the graph shape? which is less easy to do than the other?
setting the load
usually limited to CON
controlling V during ROM
safety concerns
Application of F-V relationship to shot put + Newton’s 2nd law
generate as much force as possible in a short time span to maximize acceleration and therefore distance
Difference between an olympic lift and a 1 RM
1 RM during practice would be found lower” on the Load - Velocity graph (slower velocity, larger load) because lifter feels more secure with a spotter
What does the D-V graph for a sprinter look like?
quick acceleration phase, hold phase and decrease due to fatigue
What is a possible biological reason for the difference F-V graphs for people?
types of muscle fibers
What type of strength (high or low V) do gymnasts need?
high V strength
What is the equation for Work and Power? Angular? State Units
W = Fd (J or Nm) Power = Fv or W/t (J/s or W or Nm/s)
Power = T x angular v (Nmrad/s or J/s or W)
What does the power-velocity graph look like? When is Powermax, iSOmax, and Vmax?
hill
Power - around 30-50% vmax
Force - V = 0
Velocity - F = 0 or P = 0
+ or - W and P?
CON
ECC
+
-
T or F: trained cyclers have lower power at higher speeds than untrained cyclers
F - higher
What is the SSC?
stretch-shortening cycle (SSC)
T or F - the SSC uses the same muscles in CON, ECC and ISO during the full ROM
T
What is the basis the SSC?
it is easier to bring the weight down (ECC) then lift it up (CON)…because. then starting from the bottom (relaxed) and up (CON)
stretch of SEC and CBs during ECC
forced lengthening of a relaxed muscle - stretch of SEC but NOT CBs
T or F: SSC Potentiation
isolated CON —> CON produces a greater force than ECC –> ISO –> CON
F
SSC potentiation produces a greater….
CON force
Name some examples of applications of SSC potentiation
walking, running
cutting (football -changing directions), jumping, throwing, kicking, weight training
What are the 4 mechanisms of the SSC potentiation?
1) high initial force level
2) taking up the SEC (right after ECC)
3) storage of elastic energy
4) reflex potentiation
