Sliding Filament Model/Muscle Contraction Diagram | Quizlet

myofibril

fiber-like organelle that contracts in muscle cells

muscle fiber

long, cylindrical muscle cell containing multiple nuclei and myofibrils

sarcomere

section of a myofibril; contractile unit. Region between two z-discs

sarcolemma

plasma membrane of a muscle cell

sarcoplasmic reticulum

endoplasmic reticulum of a muscle cell; stores calcium

sarcoplasm

cytoplasm of a muscle cell; stores glycogen

TERM

actin

DEFINITION

thin filament in a sarcomere involved in muscle contraction

TERM

myosin

DEFINITION

thick filament with numerous "heads" in a sarcomere involved in muscle contraction

tropomyosin

protein that blocks the actin binding sites

Ca+

ion that binds to troponin and opens the actin binding sites

Step 1 sliding filament

Neuron releases acetylcholine (ACh), which binds to receptors on the sarcolemma

Step 2 sliding filament

Muscle fiber receives ACh signal, causes sarcoplasmic reticulum to release calcium ions

Step 3 sliding filament

Ca+ binds and shifts tropomyosin, exposing actin binding sites

Step 4 sliding filament

Myosin and actin form cross-bridges, myosin heads attach to actin. Myosin bends and pulls on actin, resulting in the 'power stroke'

Step 5 sliding filament

Once ATP is used (turns into ADP + P), myosin detaches from actin, returning to 'loaded' positoin

Step 6 sliding filament

Steps 4+5 repeat until Ca+ ions are reabsorbed and troponin/tropomyosin are repositioned on actin, blocking myosin from binding

TERM

H-zone

DEFINITION

region in the sarcomere containing only thick filaments

TERM

z-disc

DEFINITION

provides anchorage for thin filaments, separates sarcomeres

TERM

I-band

DEFINITION

region in the sarcomere containing only thin filaments

TERM

A-band

DEFINITION

dark band in the middle of the sarcomere containing both thick and thin filaments

TERM

M-line

DEFINITION

supporting proteins that hold the thick filaments together in the H zone