Molecule Working Together: Force and Movement Flashcards
What four factors affect the force generation in muscle contraction?
- Recruitment of motor units
- Filament overlap
- Velocity and direction of movement
- Frequency of action potentials
What is a motor unit?
One motor neuron and all the muscle fibres it innervates
What happens if all the motor units are recruited for muscle contraction?
You get maximum voluntary contraction (MVC)
Where are lower motor neurons found?
In the anterior horn of the grey matter
What is a tetanus?
Prolonger contraction of a muscle due to rapidly repeated stimuli
what happens normally, and what causes unfused tetanus?
- at low frequency of action potentials, the muscle contracts and relaxes causing individual twitches.
- usually, the force returns to 0 before the next contraction is initiated so there is no tetany.
- but if you increase the frequency of the stimuli, you can build up the force because the force of contraction doesn’t return to 0 before the next stimulus arrives. This builds up the force and is UNFUSED TETANUS.
What causes unfused tetanus?
If the frequency is not high enough for fused tetanus - there is enough time in between action potentials for the force of contraction to drop slightly before the next action potential causes the next contraction.
What causes someone to die from electrocution?
frequency is very high, which causes muscle to contract and continue to contract with no decrease in force. causing fused tetanus
What is the difference between concentric and eccentric contraction?
Eccentric (muscle lengthens) contraction generates more force
How does velocity and direction of movement affect force of contraction?
The greater the velocity the lower the force of contraction
Why is ATP needed for in muscle contraction?
ATP is needed for the detachment of myosin from actin
ATP is also needed for the reabsorption of calcium into the sarcoplasmic reticulum
What hydrolyses phosphocreatine and how much ATP does this generate?
Creatine Phosphokinase (made in the liver) 1 ATP
Why is tetanus not possible in cardiac muscle?
There is a very long absolute refractory period meaning that the once the heart muscle is available to be restimulated, it is already quite a long way through the contraction process.
Describe the excitation-contraction coupling of smooth muscle.
Depolarisation causes the opening of voltage gated calcium channels so calcium ions move into the cell. The calcium ions bind to calmodulin and form a Ca-CaM complex. The Ca-CaM complex activates myosin light chain kinase (MLCK), which then phosphorylates myosin light chains and leads to contraction.
