Describe the structure of a muscle fiber ?

I can say that the muscle fiber is a few centimeters long and is multinucleated and that it contains myofibrils. In addition to that, It has a sarcoplasmic reticulum.

That’s all I got, does anybody have a better a level description?

And about slow/fast twitch muscle fibres, I know a lot of structural differences but no physiological differences I don’t think, can someone give me examples of some ?

this AQA?

edexcel maybe?

y, do u do AQA?

@Jpw1097 do you mind answering this question ?

I didn’t know how to reply to sections so I included my replies in this
Okay slow twitch muscle fibres are less powerful than fast twitch fuvres but are more resistant to fatigue and so these can be used for long periods of time (e.g. postural muscles keeping us upright). Slow twitch fibres have a large supply of triglycerides - these triglycerides are broken down into free fatty acids and then into acetyl CoA (via beta oxidation) which are then fed into the Krebs cycle. Simply, triglycerides can be used as an energy source for aerobic respiration. This is why they are resistant to fatigue.

Do you mean that they are less likely to run out of a respiratory substrate so less likely to respire anaerobically so less likely to cause the build up of acid hence resistant to fatigue ?

They also have a lot of myoglobin and mitochondria as they need a lot of oxygen since they respire aerobically - the high myoglobin quantity is why these muscle fibres are red.
Fast twitch fibres are more powerful as they are much larger. They are less resistant to fatigue and therefore are only used for short bursts - this is because they respire anaerobically, causing a build up of acid (and lactate). Fast twitch fibres rely on glycolysis - therefore they require a lot of glucose, therefore they have large amounts of glycogen and little triglycerides.

I don’t think I know the link between triglycerides and the the type of respiration . Why is it that they have little triglycerides ?

They also don't need many mitochondria or much myoglobin as they do not carry out aerobic respiration so they don't need much oxygen - the lack of myoglobin is why these fibres appear white. Also as a side note, there are two sub-types of fast twitch fibres - you have fast glycolytic fibres (which are very fast and powerful as described here) and fast oxidative glycolytic (they are somewhere in between slow and fast twitch fibres, as the name suggests, they carry out both anaerobic (glycolytic) and aerobic (oxidative) respiration).

Hope that helps.