Muscle Function

Question 1

What are the steps in the ATP hydrolysis/contraction?

Answer 1

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

Question 2

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?

Answer 2

60%

reach by having many cycles

Question 3

What will happen if ATP isn’t available anymore?

Answer 3

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

Question 4

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

Answer 4

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

Question 5

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

Answer 5

1. amyotropic lateral sclerosis (Lou Gehrig’s)
2. Lambert-Eaton
3. Botulism

Question 6

WHat happens in Lou Gehrig’s disease?

Answer 6

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

Question 7

What happens in lambert-Eaton syndrome?

Answer 7

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

Question 8

How does Botulism prevent acetylcholine release?

Answer 8

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

Question 9

What syndrome has autoantibodies against nicotinic receptors in skeletal muscle?

Question 10

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

Answer 10

malignant hyperthermia

can be life threatening

Question 11

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

Answer 11

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

Question 12

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?

Answer 12

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

Question 13

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

Answer 13

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

Question 14

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?

Answer 14

constant = isotonic

too much = isometrid

Question 15

Describe type 1 muscle fibers.

Answer 15

slow twitch

red fibers (more myoglobin)

slower ATPase enzyme

high proportion in long distance runners and positional muscles

Question 16

Describe type 2 muscle fibers?

Answer 16

fast twitch

have fast ATPase activity on myoglobin

white - less myoglobin

adapted for anaerobic metabolism - lots of glycogen

Question 17

What is the difference between concentric and eccentric contraction?

Answer 17

contraction - muscle shortens = norma

eccentric - muscle lengthens when attempting to shorten = more damaging

Question 18

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

Answer 18

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

Question 19

Is cardiac or skeletal muscle more dependant on extracellular calcium?

Answer 19

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.

Question 20

How is contraction controlled in smooth muscle?

Answer 20

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

Question 21

Smooth muscle often has autorhythmicity controlled by…

Answer 21

nerves or hormones