Module 4 Lecture 5 Flashcards
What is this graph showing?
How many myosin heads cause contraction and relaxation in a myofibre
Taking the example of the single myosin head attaching to actin in a myofibril and now multiplying it by an exponential amount
In that latent period, we have an action potential which takes 1-2msec, but we see that there is not force produced. What are the reasons for that?
- It takes time for the action potential to let calcium release
- Takes time for the calcium to diffuse from T-tubules to sarcomeres
- Binding of myosin to actin takes time
In the force production graph why do we not see an immediate vertical drop in the relaxation time?
This is due to SERCA which needs to be powered on and that takes time so this allows the contraction time to reach its peak before SERCA uptakes the calcium
A single action potential making a single muscle fibre contract is called?
Muscle twitch
Single action potential creates a small and weak contraction (twitch)
What are the two things required to produce enough force to do movement?
- Changing the # of fibres recruited within the muscle
- Affecting tension developed by each contracting muscle fibre
How would you change the number of fibres recruited?
Motor recruitment
What is motor recruitment? What is a motor unit?
- Motor unit recruitment is additional motor units being recruited to produce more contraction force
- Motor unit is one neuron & all the muscle fibres it innervates
What is meant by “the type of muscle fibre within a motor unit can be different?”
Motor neurons can innervate specifically type 1 for example which are slow and produce a lot of power
Type 1 and Type 2 are depending on isoforms of myosin (different amino acids which conform their sensitivity to actin)
When you recruit a motor unit you have two themes, which are…?
- Some motor units innervate a few fibres while others innervate a lot
- Some motor units only innervate type 1 and others would innervate type 2
Big motor unit and small motor unit refers to the amount of fibres to which the motor neuron is innervating
The greater the number of fibres recruited to contract…?
The greater the total muscle tension
What is the problem of having only motor neuron innervating an entire fibre?
Way too much force produced rather than having a couple of fibres innervated by a motor neuron which allows for less force to do simple things like drink water
I.e. one motor neuron controlling entire bicep when drinking water will make you hit yourself in the face with water and the cup you’re drinking from
How can you get a difference in fine control vs bulk power?
Depending on how many motor neurons are connected to the fibres
Calf muscles have a million fibres but maybe only a couple of motor neurons are innervating it hence why it can be so powerful
What’s different about the top left picture with one motor neuron and the bottom left picture with two motor neurons?
It shows that the bottom one is more spaced out and the advantage is that if we use the motor neurons that innervate the pink fibres for example and they get exhausted it switches over to the other motor neuron and recruits the orange one
What is asynchronus recruitment of motor neurons
Motor units recruiting a bunch of motor neurons and the muscle fibres they innervate and then switching to another set of motor neurons recruiting the same muscle fibres
Benefit is preventing fatigue but also even balancing the force produced
In order to produce more force what can you do?
Innervating more fibres via recruiting more motor units or recruiting motor units with lots of fibres
Lots of power would be recruting motor units with lots of fibres or more motor units
