Muscle Flashcards
T tubules
Continuous w sarcolemma and circle each sarcomete at end of junction of A and I bands.
Allows action potentials to be carried deep within muscle cell
Sarcoplasmic reticlum
Calcium storage site
Terminal cisternae of SR lies close to T tubules
Thick filament myosin
Each myosin has 2 subunits each with globular head and tail (2 tails intertwine into helix) head is binding site for actin
Myosin heads are what
Enzymes that hydrolyse ATP. Arranged where myosin heads face away from M line
Titian anchors thick filaments to Z line
Thin filament
Made of globular actin proteins
Filament composed of double stranded helical actin chain
Has troponin and tropomyosin
Four major steps in the cross bridge cycle
Crossbridge formation
Power stroke
Detachment
Energisation of myosin head
Crossbridge formation
Myosin binds to the actin binding site to form across bridge
The power stroke
ADP released and myosin head rotates to low energy state pulling thin filament with it, and the result is shortening of the sarcomere.
detachment
new atp binds to myosin which detaches the myosin due to weakening of bond
energization
myosin head hydrolyses atp to adp + pi which moves myosin head back to high energy state
how does calcium move into cytosol
In skeletal muscle opening of calcium channels in the SR allows the movement of calcium ions into the cytosol.
why is Ca2+ important
provides ‘on switch’ for cross bridge cycle to begin
When the calcium binds with troponin the tropomyosin moves to expose the myosin binding
sites on actin
The cross-bridge cycle will continue as long as calcium levels remain above the critical threshold
active transport of calcium
Active transport pumps (Ca 2+ ATPase) are constantlymoving Ca 2+ from the
cytoplasm back into the sarcoplasma reticulum
isometric and isotonic
Isotonic
Shortening
Tension constant
Velocity variable
Isometric
No shortening
Length constant
Tension variable
