Skeletal Muscle: Contraction, Tension, And Fibre Types - Lecture 9

Question 1

What are thick filaments

Answer 1

Myosin - acts as a motor molecule , attaching to actin and generating force to pull

Question 2

What are thin filaments called

Answer 2

Actin - a structural scaffold that runs along the myofilaments

Question 3

What happens when actin and myosin are together

Answer 3

Actin and mysion bind together when calcium is present, forming cross bridges and allowing contraction to occur

Question 4

What are contracted SARCOMERES

Answer 4

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

Question 5

What is cross bridge cycling

Answer 5

This is the process of how to get relaxed and how contraction occurs

Question 6

What is stage one of cross bridge cycling

Answer 6

The myofilament has just finished a power stroke ( pulling on actin ). The actin/myosin cross bridges are still present

Question 7

Stage 2 of cross bridge cycling

Answer 7

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 !!

Question 8

Step 3 of cross bridge cycling

Answer 8

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

Question 9

Step 4 of cross bridge cycling

Answer 9

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!

Question 10

Step 5 of cross bridge cycling

Answer 10

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 !!!

Question 11

What are the 2 things that muscle tension ( or force ) depends on

Answer 11

1- the number of muscle fibres recruited
2- the rate at which the muscle is stimulated

Question 12

What is recruitment

Answer 12

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

Question 13

Muscle tension: simulation, what happens at the single action potential

Answer 13

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

Question 14

What happens when there js many action potentials

Answer 14

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

Question 15

What happens at the maximum stage of simulation

Answer 15

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.

Question 16

What is optimal length

Answer 16

Where is is the strongest, and if it’s longer or shorter than that of length, then it will be weak

Question 17

What happens if optimal length is not met

Answer 17

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.

Question 18

How does cross bridging first start

Answer 18

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

Question 19

Fast fibres

Answer 19

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

Question 20

Slow fibres

Answer 20

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

Question 21

What factor determines the maximum force a muscle can generate

Answer 21

Cross- sectional areas of the muscle

Question 22

What happens to the muscle force generation when more motor units are recruited

Answer 22

Force increase

Question 23

What accurately describes the length-tension relationship of muscles

Answer 23

Muscle force increases as the length of the muscle decreases

Question 24

What determines the fatigue resistance of muscle fibres

Answer 24

Number of mitochondria in the fibre

Question 25

What factor contributes to the fatigue resistance of slow twitch muscle fibres

Answer 25

High myoglobin content

Question 26

What initiates the realise of calcium ions from the SR during muscle contraction

Answer 26

Depolarisation of the T tubules

Question 27

What is Not of skeletal muscle force generation

Answer 27

Frequency of muscle stimulation

Question 28

What determines the strength of muscle contraction

Answer 28

Frequency of muscle stimulation

Question 29

What neurotransmitter is realised at the neuromuscular junction to stimulate muscle contraction

Answer 29

Acetylcholine

Question 30

What factor determines the strength of a muscle contraction by controlling the number of active muscle fibre

Answer 30

Frequency of motor neuron stimulation