Skeletal Muscle: Contraction, Tension, And Fibre Types - Lecture 9 Flashcards
What are thick filaments
Myosin - acts as a motor molecule , attaching to actin and generating force to pull
What are thin filaments called
Actin - a structural scaffold that runs along the myofilaments
What happens when actin and myosin are together
Actin and mysion bind together when calcium is present, forming cross bridges and allowing contraction to occur
What are contracted SARCOMERES
this is when actin filaments pull closer to the centre of the SARCOMERES and the myosin heads touch the actin and the entire muscle contracts
What is cross bridge cycling
This is the process of how to get relaxed and how contraction occurs
What is stage one of cross bridge cycling
The myofilament has just finished a power stroke ( pulling on actin ). The actin/myosin cross bridges are still present
Stage 2 of cross bridge cycling
A molecule of ATP binds to the mysion, in preparation for releasing some energy to prime the myosin head. The binding of ATP causes the myosin head to let go of the actin and threfore result in no more cross bridge !!
Step 3 of cross bridge cycling
The mysion head burns the ATP to make energy ( and some ADP waste ). It stores the energy by changing the shape of the myosin, getting it ready to pull the actin again
Step 4 of cross bridge cycling
A cross bridge forms again and the mysion head binds to a new position on the actin, for this to happen calcium must be present, then it’s time for the next contraction!
Step 5 of cross bridge cycling
We now have a cross bridge with an energised myosin head attached to the actin. The mysion uses its stored energy to pull causing the actin filament to slide. And then the SARCOMERES shorten and contraction occurs !!!
What are the 2 things that muscle tension ( or force ) depends on
1- the number of muscle fibres recruited
2- the rate at which the muscle is stimulated
What is recruitment
It is the process of activating more fibres to make more force.
The number of fibres activated is regulated by how many neurons are active at one time, a small number of neurons means that there is low force in the muscle at that time, with the amount of force increasing as more neurons are activated
The brain can help with recruitment
Muscle tension: simulation, what happens at the single action potential
A single action potential will result in palue of calcium release into the cytoplasm and a short period of tension development, called a twitch. The muscle fibre is restimulated after it has completely relaxed, the second twitch is the same magnitude as the first twitch
What happens when there js many action potentials
Many action potential fired in rapid sequence results in sustained release of calcium from the SR, a sustained period of actin- myosin interaction and a sustained period of contraction ( summation ). The muscle fibre has restimulated before it has completely relaxed, the second twitch is added to the first twitch, resulting in a summation
What happens at the maximum stage of simulation
Eventually we reach maximal signalling and contraction capability of the muscle, at which point the force will plateau ( this is called tetanus ) ( plateau means no change/no increase in values ) This is when the muscle fibre is stimulated so rapidly that it does not have an opportunity to relax at all between stimuli, a maximal sustained contraction known as the tetanus occurs.
What is optimal length
Where is is the strongest, and if it’s longer or shorter than that of length, then it will be weak
What happens if optimal length is not met
When a muscle operates below its optimal length, its ability to generate force is diminished. This is due to the overlap between actin and myosin filaments within the muscle fibers.
At lengths shorter than optimal, there is more overlap between actin and myosin filaments, increasing the number of cross-bridges that can form and increasing the force produced during contraction. This is known as the length-tension relationship in muscles.
Conversely, at lengths longer than optimal, there is less overlap between actin and myosin filaments, which can lead to interference in the cross-bridge formation and reduced force production as well.
How does cross bridging first start
the myofilaments proteins, actin and myosin bind together when cellular calcium is high, creating cross bridges. Myosin then uses energy liberated from ATP to pull the actin filaments, causing a contraction
Fast fibres
fast fibres contract quickly, generating rapid and powerful movements, thanks to the energy, but they tire out really quickly, for example, jumping and skipping. Fast fibres are larger in diameter than slow fibres
Slow fibres
they are able to generate lots of energy even while working, so they are difficult to fatigue, for example standing there, walking. They have higher density in mitrocondra than fast fibres
What factor determines the maximum force a muscle can generate
Cross- sectional areas of the muscle
What happens to the muscle force generation when more motor units are recruited
Force increase
What accurately describes the length-tension relationship of muscles
Muscle force increases as the length of the muscle decreases
What determines the fatigue resistance of muscle fibres
Number of mitochondria in the fibre
What factor contributes to the fatigue resistance of slow twitch muscle fibres
High myoglobin content
What initiates the realise of calcium ions from the SR during muscle contraction
Depolarisation of the T tubules
What is Not of skeletal muscle force generation
Frequency of muscle stimulation
What determines the strength of muscle contraction
Frequency of muscle stimulation
What neurotransmitter is realised at the neuromuscular junction to stimulate muscle contraction
Acetylcholine
What factor determines the strength of a muscle contraction by controlling the number of active muscle fibre
Frequency of motor neuron stimulation
