1.2.1-1.2.2 Causes of Contraction & Makeup of a Muscle

striated muscle

muscle that has a striped appearance

skeletal muscle

striated muscle that is throughout the body and attached to bones via tendons which aids in movement, posture, and heat protection

smooth muscle

muscle in the walls of several organs that helps organ function and maintaining homeostasis

cardiac muscle

striated muscle in the heart used to pump blood

phosphate groups

group where the energy of ATP is located

ADP

low energy molecule because it doesn't have a 3rd phosphate group

sarcomere

fundamental unit of a muscle fiber

actin

thin/light filaments of globular proteins

myosin

thick/dark fibrous protein filaments, "motor proteins"

M-line

the middle of the sarcomere

A-band

contains entire length of the myosin filaments

H-zone

region where myosin is located without actin overlapping

Z-line

anchors the actin at the ends of the sarcomere

tropomyosin/troponin

filament that wraps around actin

I-band

extends from the Z-line to the edge of the A-band, where actin and myosin filaments overlap

sliding filament theory

explains muscle contraction, where muscle cells shorten as thin actin filaments slide past thick myosin filaments within the sarcomere, the muscle's basic unit

muscle contraction (1)

as a nerve impulse reaches the ends of the axon terminal, ACh is released from synaptic vesicles & attaches to receptors

action potential (2)

muscle fibers become more positively charged which generates this to happen along the sarcolemma to the T-tubules

calcium (3)

ion released from the SR (sarcoplasmic reticulum)

troponin binding (4)

calcium binds to this on the actin filaments of muscle fibers to signal tropomyosin to leave myosin

powerstroke (5)

energized myosin heads, ADP+Pi, bind to the open myosin binding site, forming the actin-myosin cross bridge and the myosin heads rotate and release ADP+Pi, thin actin slides past thick filament

actin-myosin detachment (6)

cross-bridge stays intact until ATP binds to myosin head and myosin detaches from actin

fasicle

bundles of myocytes (muscle cells)

perimysium

sheath that surrounds each fasicle

endomysium

sheath that surrounds each myocyte

tendon

connects muscle to bone

epimysium

ensheathes entire muscle and protects against friction

t-tubules

extensions of sarcolemma that penetrate into myocyte and bring the SR closer to calcium

sarcolemma

under endomysium, semi-permeable membrane

sarcoplasmic reticulum

stores, releases, and reabsorbs Ca+2

myofibril

"rod-like" organelles made of sarcomeres end-to-end