Muscles Flashcards
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
recruitment
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
calmodulin
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
