lecture 30 - Skeletal muscle 1 Flashcards
which type of muscle tissue is pictured here?
skeletal
what is shown by numbers 1 - 5 and by the red arrow?
- Z disc
- H zone
- I band
- A band
- M line
arrow shows 1 sarcomere
label number 1-7
which muscle type if pictured here?
cardiac
what muscle type is this?
skeletal
what’s this mayne?
smooth muscle
is this cardiac, smooth, or skeletal muscle? why?
smooth (no strirations)
which muscle type is under voluntary control?
skeletal
which muscle types are striated?
cardiac and skeletal
in skeletal muscle the nuclei are ________ whereas in cardiac muscle there are 1-3 ______ nuclei. Smooth muscles are _____-shaped and u______d
in skeletal muscle the nuclei are _peripheral_ whereas in cardiac muscle there are 1-3 _central_ nuclei. Smooth muscles are _spindle_-shaped and uninucleated.
structure of skeletal muscle
- attach to bones via tendons
- 1 muscle fibre/cell goes from tendon to tendon (up to 35cm)
- reasonably wide at 0.1mm
- composed of myofibrils, containing filaments
protein of thick filament
myosin
protein of thin filament
globular actin
myofibrils connect at the…
Z-disc
where would you find only myosin and no actin?
H-zone
at the _-line thick filaments are held together by the protein ______.
at the _M_-line thick filaments are held together by the protein _myomesin_.
T-tubules
deep invaginations, continuous with the sarcolemma, which circle each sarcomere at the junctions of the A and I bands.
in skeletal muscle, how many tubules per sarcomere?
2
function of transverse tubules
allow action potentials to be carried deep within the muscle cell.
sarcoplasmic reticulum
calcium storage site. The terminal cisternae of the SR lie close to the T-tubules
what does this image show
contracted myofibril
order the follwing from smallest to largest
- myofibril
- muscle
- sarcomere
- myofilament
- myocyte
smallest
- myofilament
- sarcomere
- myofibril
- myocyte
- muscle
largest
How many myosin subunits?
- 2
- one globular head and one tail
- tails intertwine to form a helix
Each myosin head is an enzyme that…
hydrolyses ATP (ATPase)
where would you find the binding site to which actin attaches?
myosin head
how is actin arranged in thin filaments
double stranded helical actin chains
__________ and _________ are regulatory proteins associated with actin in skeletal/cardiac muscle
_Troponin_ and _tropomyosin_ are regulatory proteins associated with actin in skeletal/cardiac muscle
label 1,2 and 3
1 .troponin
- actin
- tropomyosin
sliding filament theory of muscle conrtaction
sarcomere shortens as thin filaments are pulled over thick filaments
outline the 4 steps of the cross-bridge cycle
- cross-bridge formation
- power stroke
- detachment
- energization of myosin head
what must be present for the cross-bridge to form? why?
Ca2+ makes the actin site available
what is the one region of the sarcomere that doesn’t change in length/size during contraction?
A bands
what is happening when the crossbridge forms?
myosin binds to the actin binding site (to form the crossbridge)
what is occuring in the power stroke
- ADP is released (energy has been used)
- the myosin head rotates to its low energy state (45o to the actin)
= sarcomere shortens
what must happen for myosin to detach from actin?
a new ATP molecule binds to the myosin. This weakens the actin-myosin binding.
energization of the myosin head
- myosin head hydrolyses the ATP to ADP + Pi
- myosin moves back to its high energy conformation (90o to the actin)
Calcium binds to the _______, inducing a conformational change which pulls _________ off the ______ binding site. Therefore these sites are now available. As long as _______ is present above its threshold of (____-____mM) the cycle will continue.
Calcium binds to the _troponin_, inducing a conformational change which pulls _tropomyosin_ off the _myosin_ binding site. Therefore these sites are now available. As long as _calcium_ is present above its threshold of (_0.001_-_0.01_mM) the cycle will continue.
how does calcium enter the cytosol of muscle fibres/cells?
calcium moves down its electrochemical gradient when the calcium channels in the sarcoplasmic reticulum open
how does Ca2+ return to the SR?
Ca2+ ATPase transport pumps are constantly working to move calcium from the cytoplasm to the SR.
what is Isotonic muscle contraction? what stays the same and what changes?
- shortening
- tension constant
- velocity variable
what is isomeric muscle contraction? what stays the same and what changes?
- no shortening
- length constant
- tension variable
where would you find Intercalated discs?
in cardiac muscle, connecting the cells together
where would you find the I-band and the A-band?
I band = 2 (notice how it has become much smaller in length during contraction)
A band = 1 (same length always)
calcium interact with troponin in ______ regulated muscle and interact with calmodulin in _______ regulated muscle.
calcium interact with troponin in _actin_ regulated muscle and interact with calmodulin in _myosin__ regulated muscle.
what is rigor mortis and what causes it?
stiff muscles caused by the absence of ATP, so the cross bridge can’t detach
when does the cross bridge cycle end?
when Ca2+ is actively transported back into the sarcoplasmic reticulum
which number shows…
(a) active tension
(b) passive tension
(c) total tension
- = total tension
- = passive tension
- = active tension
length-tension relationship
maximum force produced by the sarcomere is dependent on the degree of actin and myosin overlap
in which type of muscle contraction can the legth-tension relationship be observed?
isometric
what happens when the sarcomere is less than 2.0μm?
filaments collide and interfere with each other, reducing the force developed
what happens, in the sarcomere, at lengths greater than 2.2μm?
active forced decline because the extent of overlap between filaments reduces, reducing the number of cross-bridges that can form
at which length is the sarcomere able to produce the greatest force?
2.0μm-2.2μm
pasive force =
as muscle is streched, the connective tissue around the muscle fibres resist the stretch
active tension is dependent on?
sarcomere legnth
total tension =
passive tension + active tension
myocyte
another name for a muscle cell
