The Neuromuscular Junction and Muscle Contractions

actin

a protein that makes up most of the thin filament. binds with myosin head.

myosin binding site

location on actin molecule that binds to the myosin head during cross-bridge formation.

myosin

ATP dependent protein that binds to actin during cross-bridge formation and pulls the thin filament towards the M-line.

tropomyosin

a protein connected to troponin that prevents myosin from binding to acing when calcium is not present - covers the myosin binding site.

troponin

Calcium dependent molecule that “shifts” tropomyosin away from the myosin binding site during contraction.

a-band

spans the length of the thick filament (myosin). Does not change during contraction.

h-zone

spans thick filaments only that shrinks during contraction and lengthens during relaxation.

i-band

span that includes the thin filaments and z-lines that shortens during contraction and lengths during relaxation.

m-line

“mid-line” of the sarcomere that anchors the thick filaments. During contraction the thin filaments move towards the m-line.

z-line

the boundary of a sarcomere anchored to the thick filament by titin.

thin filament

made of actin, troponin, and tropomyosin. Is pulled by myosin towards

the m-line during contraction

thick filament

made of myosin, pulls the thin filament towards the m-line during

contraction

axon terminal bud

the end of a nerve cell.

acetycholine

a neurotransmitter that opens protein channels on the

sarcolemma.

vesicle

a sac in the axon terminal that contains Ach

sodium ion (Na+)

a sodium ion that has lost an electron to become more positive.

synaptic cleft

the space between the con terminal bud and the sarcolemma.

muscle cell (fiber)

the type of cell found in muscles

sarcolemma

the cell membrane of a muscle cell

Ach Receptor protein channel

a protein embedded in the sarcolemma that opens in response to Ach, allowing sodium ions into the muscle cell.

Transverse Tubule (T-tubule)

an infolding of the sarcolemma.

Sarcoplasmic reticulum

an organelle inside the muscle cell that holds calcium ions

Calcium ion (Ca2+)

a calcium atom that has lost two electrons becoming more positive. Binds to troponin in the sarcomere.