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)
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
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?
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?
- 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.
red fibers (more myoglobin)
slower ATPase enzyme
high proportion in long distance runners and positional muscles
Describe type 2 muscle fibers?
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