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Flashcards in Muscles Deck (33):

Describe the structure and ultrastructure of skeletal muscle

- skeletal muscle cells are multinucleated striated fibres which are created in utero by myoblasts
- muscles are made of bundles of these fibres wrapped in connective tissue sheaths
- the striations are caused by sarcomeres


In excitation-coupling contraction, after the action potential has been fired, what is released?

Ca2+ ions are released from the sarcoplasmic reticulum


In excitation-coupling contraction, Ca2+ ions bind to

troponin on the actin filament


In excitation-coupling contraction, what happens once Ca2+ ions bind?

Tropomyosin - the blocking protein - is removed, exposing the actin binding sites


In excitation-coupling contraction, what happens once the actin binding sites are exposed?

Myosin filaments can bind to the actin and form cross bridges


In excitation-coupling contraction, what causes the contraction of the muscles?

The binding of myosin filament to actin to form cross bridges


In excitation contraction coupling, what happens once the cross bridges have been formed?

Ca2+ ions return to the sarcoplasmic reticulum through the use of ATP


In excitation-coupling contraction, what happens once the calcium ions return to the sarcoplasmic reticulum?

Tropomyosin is free to return to its original positions so the contraction ends and cross bridges are broken


In excitation-coupling contraction, as the filaments slide over each other - more overlap means

more tension


In excitation-coupling contraction, as the filaments slide over each other - what will happen if there is too much overlap?

The filaments will interfere with each other


What is an isotonic twitch?

Contraction with shortening length


What is an isometric twitch?

Contraction with constant length


In the generation of controlled force through the recruitment of motor units, as the load increases ___

What is this process known as and what does it allow?

more motor units are required to compensate


allows more muscle fibres to be involved in a movement


What is tetanus?

A state of extended contraction via the summation of APs


Is tetanic tension greater or less than twitch tension?
Why is this?

Much greater, as there is no respite in which the calcium can return to the sarcoplasmic reticulum


What is the difference between tetanus and normal contraction?

Tropomyosin is always held in the non-blocking state and so the cross bridges cannot be broken


What is fatigue?

A state caused by repeated muscle stimulation which prevents using up vast quantities of ATP in breaking and reforming cross bridges to sustain contractions


How much stimulation is require to trigger fatigue depends entirely on

- the individuals fitness
- muscle fibre type
- length of contraction


What are the two types of skeletal muscle fibres?

- oxidative fibres
- glycolytic fibres


Describe oxidative skeletal fibres

- more mitochondria for oxidative phosphorylation
- more vascular to allow for delivery of O2 and nutrients
- contain myoglobin to help oxygen delivery
- fibres are red and tend to be of low diameter


Slow oxidative fibres

resist fatigue


Fast oxidative fibres

have an intermediate resistance to fatigue


Describe glycolytic fibres

- have very few mitochondria
- higher conc of glycolytic enzymes and glycogen
- lower blood supply
- white fibres with large diameter


Fast glycolytic fibres

fatigue quickly


Where does smooth muscle exist?

In hollow organs e.g. GI tract, bladder, airways


What is the supply of smooth muscle?

Autonomic nervous system


Describe smooth muscle cels

- mononucleated non-striated spindles
- can divide throughout life
- actin and myosin filaments arranged diagonally across cells and anchored to membranes and cell structures by dense bodies


What is the difference between contraction/relaxation in smooth muscle and cardiac muscle?

Cardiac muscle also forms cross bridges between myosin and actin filaments but the mechanism is different


As calcium is released from the ___ it binds to ___

sarcoplasmic reticulum



What happens once calcium has bound to calmodulin?

Calmodulin binds to myosin light chain kinase which phosphorylates the myosin with ATP and forms cross bridges to actin filaments


Formation of cross bridges results in

contraction and tension


Relaxation is brought about through

the action of myosin light chain phosphatase which dephosphorylates the cross bridges


Contraction can be held for longer in smooth muscle due to ___ which is useful in ___

the low rate of consumption of ATP

blood vessels, as they must stay open for long periods of time