15.7 Structure of skeletal muscle Flashcards
What are the 3 type of muscle in the body
What do they do
Cardiac muscle is found only in the heart
Smooth muscle is found in the walls of blood vessels and the gut
Skeletal muscle makes up most muscle in vertebrates, it is attached to bone and we consciously control it.
What are muscles made of
Myofibrils are tiny muscle fibres.
On their own they’re very weak and can snap however when there are loads they are very powerful, like how a rope works.
Myofibrils are arranged to line up parallel to maximise their strength, and these are grouped into muscle
Why wouldn’t muscles work if they were made up of individual cells
If they were made of individual cells joined end to end it wouldn’t be able to contract very efficiently.
Junction between adjacent cells would be a weakness point which would reduce the overall strength of the muscle.
So instead these separate cells have been fused into muscle fibres which share nuclei and cytoplasm called sarcoplasm
What is sarcoplasm
Where is it within a muscle fibre
Muscle fibres share nuclei and their cytoplasm is called sarcoplasm.
Sarcoplasm is mainly found around the circumference of the fibre.
There is a high concentration of ER and mitochondria in it
What two myofibrils is a muscle fibre made of
Two types of protein filament:
Actin and myosin
Describe structure of actin
Describe structure of myosin
Actin is thinner and consists of two strands twisted around each other
Myosin is thicker and consists of long rod shaped tails with bulbous heads that project to the side
Myofibrils appear striped due to alternating light coloured and dark coloured bands.
How
As Actin is thinner than Myosin, bands only containing actin are lighter as thin and thick filaments don’t overlap.
Dark bands are where myosin and actin overlap
What are isotropic bands (I bands)
What is in the centre of them
The light bands are called I bands, which appear lighter because thick and thin filaments don’t overlap in that region.
There is only actin present there, no myosin.
These I bands surround the A band.
In the centre of I bands, is the Z line
What does the Z line contain
It has only myosin so is a lighter colour than the A bands which contain both myosin and actin.
What are A bands (anisotropic bands)
What is found at the centre of each A band
These are the dark bands where actin and myosin filaments overlap.
The H zone is found here, where it is a light coloured region.
What are sarcomeres
What do they do
Distance between two Z lines
When muscles contract these sarcomeres shorten
What is tropomyosin
Protein found in muscle, which forms a fibrous strand around actin filament
What are slow twitch muscle fibres
- Contract more slowly than fast twitch
- Provide less powerful contractions but over a longer period
What are slow twitch muscle fibres designed for
Endurance eg running a marathon
They are common in calf muscles and back in humans which are contracting constantly to maintain body in upright condition
What respiration occurs mostly in slow twitch muscles
Aerobic so these slow twitch fibres help avoid a build up of lactic acid which would cause muscle to function less effectively and prevent long duration contraction
