Skeletal Muscle Contraction

myofiber

muscle cells

myofibers have many

nuclei

myofibers are made up of

myofibril

actin

thin filament

myosin

thick filament

Z line

anchors actin and titin

titin

in between myosin

H band

myosin only

A band

myosin and action/myosin overlap

I band

actin only

myofilament types

actin, tropomyosin, troponin C

actin is made up of

a chain of G actin subunits, each with a myosin binding site

tropomyosin

lies along actin and covers myosin binding sites

troponin C

attached to tropomyosin, has Ca binding site

what happens when Ca binds to troponin C

tropomyosin is pulled off to reveal myosin binding site on actin

at rest

ATP binds to myosin head, then cleaved by myosin ATPase, creating myosin ADP complex

contraction begins

troponin C binds to Ca, allowing tropomyosin to move and uncover myosin binding sites on actin, myosin binds to actin

crossbridge

when myosin initially binds to actin

power stroke

when myosin heads, bound to actin, bend and ADP is released

rigor complex

myosin actin tightly bound, with myosin head bent

how is myosin released from actin

a new ATP binds to myosin, which releases actin and forms another ADP myosin complex

Ca is stored in

sarcoplasmic reticulum

sarcolemma

myofiber membrane with Na and K channels that carries MAP to ends of myofiber

MAP

muscle action potential

transverse tubules (T tubules)

extension of sarcolemma, carries MAP to sarcoplasmic reticulum of each sarcomere

RyR1

ryanodine receptor, lets Ca out of sarcoplasmic reticulum

DHPR

dihydropyridine receptor, L type Ca channel, pulls on RyR1 to let Ca out

SERCA1

smooth endoplasmic reticulum pump, pumps Ca back into sarcoplasmic reticulum

a motor unit includes

Aa motorneuron and muscle fibers it controls

small muscles with fine control and low power have

few motor units

large muscles with poor control and high power have

many motor units