Transcript Muscular System Part 2 Microscopic Contraction

Microscopic Structure of Skeletal Muscle
Muscle Tissue: made of special contractile cells muscle fibers
Each fiber filled with: Thick Myofilaments protein Myosin
Thin Myofilaments  protein Actin
Sarcomere: basic structure & functional contractile unit of
skeletal muscle (runs Z line to Z line)
Thin Actin & Thick Myosin filaments overlap each
other  Dark A band
Light area between Z line & A band is I band
Each I band is made of (thin) Actin filaments
Each M band (line) is made of (thick) Myosin filaments
H zone is (thick)
myosin
During Contraction:
Energy from ATP enables (thin) Actin and
(thick) Myosin myofilaments to slide toward
each other and shorten sarcomere, eventually,
entire muscle
 Sliding Filament Theory
So, you ask, how does it happen?????
When actin & myosin filaments come near each
other, knowblike projcetions on (thick) myosin form
“cross-bridges” with (thin) actin filament
When muscle stimulated to contract, “cross-bridges”
move, pulling 2 filaments past each other
Thousands of actin & myosin filaments interacting
 entire muscle shortens
 Sliding Filament Theory
ATP provides energy to make/break connections
between actin & myosin filaments
So…muscle cells have lots of… mitochondria!!!
ATP powers movement of cross bridges by
attaching itself to each myosin knob/head
(to make cross bridge)
Then it breaks ↓ into ADP + P
Large amounts of ATP from Carbs (& other organic
compounds) produced through CR (w/ O2)
otherwise fermentation  builds up lactic acid
sore, burning muscles, fatigue & cramps
Lactic acid  blood stream  liver  glycogen
(stored carbs, for later)
Now, down to the nitty gritty!
Thin Actin filaments: 2 strands of protein actin
(2x helix protein)
w/ binding sites for
Troponin and Tropomyosin
Thick Myosin filaments: groups of protein myosin
w/ knobs/heads in opposite
direction
In mitochondria,
cells convert food energy  ATP to run chemical
rxs and muscle contraction
Steps of skeletal muscle contraction
Sliding Filament Theory
ATP binds to (thick) myosin knob  ADP + P
(attached to knob)
Ca++ binds to Troponin on (thin) actin  causing
tropomyosin to move & expose binding sites (for
myosin knobs to attach to) on actin
Myosin gives up ADP + P to bind to actin & forms
“cross-bridges”
ATP hooks to mysoin knob to dissolve cross-bridge &
release contraction.
Hmmm… what does this make you think of?
The Last Contraction  Rigor Mortis
(cold & stiff or rigidity of death)
After death, cells don’t make ATP (no CR going on)
No breathing, No O2, heart stops pumping, NS
stops, metabolic rxs stop
No ATP flooding myofibrils SO..
No new contractions
and
“last” contraction not released b/c no ATP to dissolve
cross-bridges
No heat produced from muscles & no blood flow
 corpse “cold & stiff” (about 36 hours)