Muscle Contractions

What are the three types of muscle

Smooth, skeletal, cardiac

What are the major features of skeletal muscle

Voluntary, striated, multinucleated 40% of body mass

What are the major features of smooth muscle

Involuntary, unstriated, uninucleated

What are muscle fibers

Muscle cells; span origin to insertion

What are myofibrils

Fine threadlike fiber packed within myocyte cytoplasm

What is the contractile until of skeletal muscle

Sarcomere

What are the major components of the sarcomere

Z disk, titan, actin, myosin

Describe structure of actin filament

Helical Strucutre consisting of 2 intertwined strands of actin polymers

What are the regulatory proteins associated with actin and how do they interact

Tropomyosin: blocks interaction of actin and myosin; Troponin: calcium regulated protein that regulates tropomyosin

Describe the Strucutre of myosin filament

Intertwined helical tails with globular heads that bind ATP and actin

What skeletal muscle is highly developed and proves storage for calcium

Sarcoplasmic reticulum

What Strucutre allows for propagation of APs to the interior of the myocytes

T tubules

Where are action potentials generated in the myocyte and where are they propagated from

The midpoint where its innervates and then spreads in both directions

What is required to initiate a muscle contraction

Increase in cytoplasmic levels of calcium

How does action potential propagation within t-tubles lead to calcium influx

Voltage gated calcium channels (DHPRs) open at TP and calcium moves down its concentration gradient.

What happens after DHPRs are activated and calcium influxes into the cytoplasm

RyRs open allows calcium from SR to enter the cytoplasm

What first initiates skeletal muscle relaxation

AP passes, and resting membrane potential returns, DHPRs and RyRs close

Once muscle relaxes what happens to intercellular calcium

SERCA pumps ca from cytoplasm into the SR for storage (always active)

What prevents actin myosin association when calcium levels are normal

Tropomyosin blocks myosin binding sites on actin

How does calcium affect troponin and thus tropomyosin

Binds and causes a conformational change causing tropomyosin to move away from the binding sites of actin

At rest what is happing in the power stroke

Myosin heads bound to ATP

What happens after partial hydrolysis of ATP to myosin why

Allows for myosin to bind actin because ATP is now ADP and Pi

What happens after complete hydrolysis of ATP on myosin heads

Flexion of myosin and actin

What must happen to stop the cross bridge of actin and myosin

ATP binds back to myosin releasing actin

What is the main cause of rigor morris

All ATP stores are depleted so myosin remains bound to actin

What are the three ways to produce ATP

Oxidative phosphorylation, glycolysis, creatine phosphate

how does creatine phosphate produce ATP

Allows for rapid donation of phosphate to ADP to make ATP; depleted rapidly

What is a single unit smooth muscle

Gap junctions allow for one cell to be innervates and propage signals to its neighbors.

What is a multi unit smooth muscle

Electrically isolated muscle cells that contract independently

How is smooth muscle regulated

Autonomic nervous system

What are the primary neurotransmitters involved in smooth muscle

Acetylcholine and norepinephrine

Where are the voltage gated calcium channels in a smooth muscle cells

Shallow depressions (caveolae)

How is smooth muscle contraction terminated

Decrease in calcium concentration in cytoplasm

In smooth muscle how is calcium removed from the cytoplasm

3Na+ Ca2+ exchanger( secondary active) and Ca2+ ATPase(primary active) pump calcium out of the cell against its gradient

What activates myosin head ATPase smooth muscle

Increased cytoplasmic calcium

What events happened when calcium activates ATPase

Calcium binds calmodulin, calcium calmodulin complex bind and activate MLCK, MLCK phosporylates and activates myosin ATPase

What molecule dephosphorylates myosin (inactivates)

Myosin light chain phosphatase (MLCP)

What happens if myosin is dephosphorylated when unattached to actin

Prevents contraction

What happens if myosin is dephosphorylated while attached to actin

Prolonged contraction