Ex phys 1 sliding filament theory

module 1 topic 2

sliding filament theory basics

-sarcomeres shorten with no change in length of any protein or filament

-filaments slide past one another (increase in overlap)

-muscles shorten, but proteins and filaments do not

___ filaments slide past ___ filaments

thin, thick

more overlap = (longer/shorter) sarcomeres

shorter

striation

pattern of alternating dark and light bands along the length of the muscle fiber

what are the light bands on a muscle fiber

I bands

what are the dark bands on a muscle fiber

A bands

what are the dark lines on a muscle fiber

Z lines

sarcomere

-fundamental contractile unit (smallest part of a muscle that shortens)

-consists of overlapping thick and thin filaments

Z lines (or Z discs)

boundaries of a sarcomere

connected to thin filaments

M line

middle of sarcomere

connected to thick filaments

A band

-dark band

-contains thick filament

-it is the length of the thick filament

I band

-light band

-contains no thick filament, space between thick filaments

-thin filament only, but not the length of the thin filament

H zone

-lighter band in the middle of the dark band

-thick filament only

-space between thin filaments

filament length (increases/decreases/same) during contraction

same

areas of overlap (increase/decreases/same) in length during contraction

increase

areas of no overlap (increases/decreases/same) in length during contraction

decrease

sarcomeres (lengthen/shorten/same) during contraction

shorten

Sarcomere changes: A band

-no change in length (due to being length of thick filament)

Sarcomere changes: I band

-shortens

-extends into next sarcomere

(area of no overlap: space between thick filaments)

Sarcomere changes: H zone

shortens and may disappear

(area of no overlap within A band: space between thin filaments)

Sarcomere changes: Z lines

-move closer together

(boundaries of sarcomeres)

muscle contraction summary

-A band no change

- I band shortens

- H zone shortens and may disappear

- Z lines move closer together

Actin & Myosin (lengthen/shorten/same) during muscle contraction

same

(*remember: proteins do not change length during contraction)

resting muscle

-calcium ions are bound to the SR

-tropomyosin-troponin complex blocks attachment sites for myosin

-ATP is bound to myosin heads

muscle contraction steps

-nerve impulse exceeds resting potential spreads across sarcolemma and down transverse tubules, causing release of calcium from SR

-calcium binds with troponin, which permits actin and myosin to form cross bridges

-myosin ATPase is activated, splitting ATP; this transfer of energy causes movement of the myosin cross bridges, generating tension

-crossbridges uncouple when ATP binds to the myosin bridge

relaxation

-coupling and uncoupling continue until calcium concentration becomes insufficient

-when the nerve impulse ceases, calcium is taken up the SR, actin and myosin return to a resting state