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Flashcards in Muscle Function Deck (22):

What are the steps in the ATP hydrolysis/contraction?

1. ATP binds to myosin head - low energy state - not connected to actin

2. ATP hydrolyzes to ADP and P. Myosin head cocks to 90 degrees and binds acting

3. P (and ADP) is released and the power stroke occurs - myosin head pulls the actin towards the middle by going to 45 degrees

4. ATP binds and myosin releases the actin


What is the maximum shortening of muscles? If all the crossbridges in the muscle cycling simulataneously can shorten a muscle 1%, how can the muscle reach this?


reach by having many cycles


What will happen if ATP isn't available anymore?

the actin and myosin will have to remain attached - this is rigor mortis


Besides presence of ATP, what else is necesarily for muscle relaxation?

sequestration of calcium back into the sarcoplasmic reticulum through the Ca+ ATPase


What are three clinical presentations that affect the motor neurons, causing muscle weakiness?

1. amyotropic lateral sclerosis (Lou Gehrig's)

2. Lambert-Eaton

3. Botulism


WHat happens in Lou Gehrig's disease?

It's degeneration of motor neurons - an issue with superoxide dismutase so that free radicals break down muscle

no treatment.

average treatment is about 2 years

track the stage by their muscle function


What happens in lambert-Eaton syndrome?

autoantibodies against calcilum channels in motor neurons resulting in an inabilitu to release acetylcholine


How does Botulism prevent acetylcholine release?

It cleaves synaptic associated proteins so the vesicles can fuse with the membrane


What syndrome has autoantibodies against nicotinic receptors in skeletal muscle?


WHat happens when ryanodine receptors release too much Calcium in response to anesthetics?

malignant hyperthermia

can be life threatening


The amount of force generated by a muscle is directly proportional to what?

the number of actin-myosin cross bridges in a given cross-sectional area


At what sarcomere length do you get maximal overlap of actin and myosin heads?

What happens with the force ifyou go below this or higher than this?

2-2.2 microns
- it's where the strength will be strongest

As you go below 2.0, force will decrease because the actinf ilaments bump into each other and compress.

As you stretch beyond 2.2, force will decrease because the number of cross bridges decreases


At what sarcomere lenght will the sarcomere resist any further shortening?

1.7 microns - the point were the myosin actually contacts the Z line


If the load on the muscle is constant, what is the contraction called?

If the load on the muscle is too great to be moved, what is the contraction called?

constant = isotonic

too much = isometrid


Describe type 1 muscle fibers.

slow twitch

red fibers (more myoglobin)

slower ATPase enzyme

high proportion in long distance runners and positional muscles


Describe type 2 muscle fibers?

fast twitch

have fast ATPase activity on myoglobin

white - less myoglobin

adapted for anaerobic metabolism - lots of glycogen


What is the difference between concentric and eccentric contraction?

contraction - muscle shortens = norma

eccentric - muscle lengthens when attempting to shorten = more damaging


What does it mean to say cardiac muscle is autorhymic? Is it innervated?

It doesn't require innervation to contract, but it is innervated by sympathetic and parasympathetic fibers - would actually beat 100 bpm if it weren't innervated


Is cardiac or skeletal muscle more dependant on extracellular calcium?

cardiac muscle - the ryanodine aren't physically linked to the L channels in cardiac muscles, so you need more extracellular calcium in order for them to open.


How is contraction controlled in smooth muscle?

calcium binds to calcium-dependent myosin light chain kinase to initate contraction


Smooth muscle often has autorhythmicity controlled by...

nerves or hormones