Module 4 Lecture 6 Flashcards
What is twitch summation?
Twitch summation is sending action potentials (multiple of them) before the muscle fibre has the chance to relax
Allows the muscle fibre to be repeatedly used without break
When an action potential is propagated along the muscle causing calcium to become released what is happening at the same time?
SERCA is turning on immediately after the calcium is released to take it back in, giving the muscle a slight contraction
What is one single action potential capable of doing?
It can generate enough calcium to get almost all the troponins moved (SERCA uptake) but it does not produce a max force contraction per fibre
What does the graph show in terms of action potentials propagated with respect to tetatnus?
The more action potentials that are generated without rest, the more force is produced and therefore, the likelier tetanus will be reached
What is tetanus?
If the muscle fibres are repeatedly stimulated without allowing time to relax
It is technically just the prolonged stay of calcium before it is taken up entirely
In order to get maximum tetanic what would be required?
Multiple action potentials which will allow the rate of calcium being released to be faster than the rate of calcium being taken up
How are tetanus and rigor mortis different if they keep you in a contracted state?
Tetanus unlike rigor mortis actually releases and rebinds the myosin head because after the power stroke where ADP and Pi are released the ATP releases the myosin but since calcium is available it will rebind
Myosin is constantly cycled while in rigor mortis the ATP does not release the myosin head and calcium is not available
Why is the starting length of the muscle fibre important for force production?
Depending on where the length of the fibre starts from it will generate a certain amount of force
What does the picture illustrate about optimal length of the muscle fibres?
In A, we see that the optimal length to produce the most amount of force
In the picture, what is wrong with D?
Starting off with the muscle length already being shortened, the actin overlap with one another blocking myosin from properly binding to actin.
In the picture what is wrong with C?
The length of the muscle starting at a very stretched position means that the myosin and actin are not lined up so there won’t be as much contraction occuring
Define muscle tension
It is the amount of force that a muscle exerts when contracting against a load
Define muscle load?
Force exterted on a muscle by an object
What needs to be true about tension and load for a muscle to shorten?
Tension must be greater than load
What happens when tension is equivalent to load (i.e. when you squeeze your fist and hold it)
The power stroke process of myosin and actin still occurs and the myosin will immediately go back to the flexed position because calcium is still available since “contraction” is still taking place meaning calcium is still being released and action potentials are being generated but the length of the fibre stays the same
What are the two things required for max force production?
- Frequency of stimulation
- Starting length of muscle fibre
What does Hertz mean in terms of action potential
A hert would be how many action potentials occur in one second
Isometric means?
Same length
Isotonic means?
Same tension
What is the graph explaining?
- A lighter load results in a greater velocity due to distance travelled in a shorter amount of time
- An intermediate load results in the slope decreasing meaning the velocity is slower
- A heavier load results in the slowest velocity as not much distance is travelled by the contracting fibre over time
The graph outlines with respect to one action potential
What are muscle fibre diametre and mitochondria density like for slow twitch fibres (Type 1) vs. Fast Twitch (Type 2)
Slow Twitch has more mitochondria because it is an oxidative process but it has a small muscle fibre diametre and does not produce a lot of force while the Fast Twitch produces a lot of force, bigger muscle fibre diametre and not much mitochondria
Out of the two (ST & FT) which fibre is most fatiguable and produces more force
Fast Twitch (Type IIx)
Is it possible to convert from one muscle fibre type to another?
No it is not possible to convert, rather it is possible to increase the volume
What is Myasthenia Gravis?
The immune system attacks the acetylcholine receptors which degrade
- Does not allow action potentials to go through the receptors leading into the muscle meaning muscle weakness
What is LEMS?
Body’s immune system targets the calcium voltage channels on the presynaptic axon terminal
* Less calcium = less calcium influx into terminal = less calcium activation of synaptotagmin = less vesicle fusion
* Less acetylcholine released into the neuromuscular junction/motor end plate
