Muscle Structure Flashcards
What are skeletal muscles?
Smooth muscle that lines an incompressible skeletons
And pulls to create movement by acting in antagonistic pairs
Movement can either be…
Reflex
Controlled by conscious thought
Levels of structure of the skeletal muscle
Gross structure (see with eye)
Microscopic structure (cells, requires seeing through microscope)
Ultra structure (proteins that require special techniques to see)
Skeletal Muscle divides into…
Bundle of muscle fibres
A single muscle fibre is..
A muscle cell
Myofibril
Divisions of muscle fibre (muscle cell)
Sarcomere
Repeating unit of the myofibril containing proteins
Proteins in the myofibril
Actin
Myosin
How is a muscle TRIGGERED in the first place to begin contracting?
If the sarcolemma (membrane of muscle fibre) is depolarised due to neurotransmitters generating an action potential and sends impulses along muscle fibres
What happens when the sarcolemma is depolarised?
Triggers release of Ca2+ ions from sarcoplasmic reticulum ER) of muscle fibre
Which diffuse into myofibril
Released Ca2+ ions can do what?
Trigger the protein called tropomyosin to move away by changing tertiary structure so it unblocks the myosin binding sites on actin
Forming a cross bridge
Myosin heads can now bind to unblocked binding sites on actin
As bonded ATP is hydrolysed to release energy to ADP and Pi
= cross bridge with tension
Formation of a cross bridge and tension means…
Actin can slide along the myosin as the ADP and Pi that had been hydrolysed in formation of the cross bridge is released
How does myosin unbind to actin?
ATP binds to myosin which causes shape in myosin head (change in tertiary structure)
So it will detach from actin
Movement of proteins that causes contraction?
The sliding of actin over myosin together and shortening of sarcomere =contraction of muscles
Neuromuscular junction
Synapse between a presynaptic neurone and 1 muscle fibre (cell)
What is the mechanism of synaptic transmission over a neuromuscular junction?
Same as over a regular cholinergenic synapse but differences in what receives the neurotransmitter
SARCOLEMMA as the post synaptic membrane
MUSCLE FIBRE as the receiving structure
What do neurotransmitters bind to in a neuromuscular junction?
omplementary protein receptors on
SARCOLEMMA as the post synaptic membrane
What is the structure that receives neurotransmitters in a neuromuscular junction?
MUSCLE FIBRE
AKA MUSCLE CELL
Where are action potentials sent along when receiving stimulation from a presynaptic neurone in the neuromuscular junction?
The muscle fibre
Is the myofibril a muscle cell>?
NO
Normal cholinergenic synapse vs neuromuscular synapse
Normal = neurone to neurone vs neuromuscular = neurone to muscle fibre
Normal = can be excitatory OR inhibitory vs neuromuscular = always excitatory
What happens at neuromuscular junction when impulses stop?
Acetyl choline in synapse hydrolysed to acetate and choline by acetylcholinesterase
Triggers Ca 2+ actively transported from the myofibril back into the sarcoplasmic reticulum
What happens when Ca2+ leaves myofibril by active transport?
Tropomyosin goes back to its original shape and blocks the myosin binding sites on actin
Myosin heads can no longer bind to actin so no actinomyosin cross-bridges form = no sliding, muscle relaxed
What happens when a muscle in an antagonistic pair is relaxed?
Freely lengthened by the pull from contraction of the other muscle in the antagonistic pair
Since when one contracts, the other relaxes
Full name for actin myosin cross bridge
Actinomyosin cross bridge
Power stroke
Pulling of actin along by myosin heads because:
Head of myosin angle changing shape when ATP is hydrolysed to ADP and Pi which causes tension in Actinomyosin cross bridge
What is required to form actinomyosin cross bridge?
Hydrolysis of ATP to ADP and Pi
