Muscle microstructure and contraction Flashcards
What muscle type do you have involuntary control over?
Smooth muscle.
What muscle type can contract autonomously?
Cardiac muscle.
What muscle type is under voluntary control from the somatic nervous system and contracts to bring about movement?
Skeletal muscle.
What are the muscle shapes?
Parallel, fusiform, triangular, unipennate, bipennate and multipennate.
What is the bundling system present in muscle?
Muscle which is made up of muscle fascicle which is made up of muscle fibres which is made up of myofibrils.
What surrounds muscle?
Epimysium.
What surrounds muscle fascicle?
Perimysium.
What surrounds muscle fibre?
Endomysium.
What is the muscle plasma membrane called?
Sarcolemma.
What does the sarcoplasm contain?
Myoglobin, mitochondria and glycogen.
What makes up a myofibril?
Repeating sarcomeres separated by z lines.
What is a sarcomere?
Basic contractile unit of a muscle fiber.
What makes up a sarcomere?
Myosin and actin.
What makes up the A band?
Myosin and actin.
What colour is the A band?
Dark.
What makes up the I band?
Only actin.
What colour is the I band?
Light.
What is the H zone?
Only myosin in the centre of the sarcomere.
What is the structure of myosin?
Two globular heads with a single tail formed by two alpha helices.
What is the structure of actin?
Filament has a helix structure. Has a myosin binding site and contains troponin and tropomyosin.
What are the sarcomere changes that occur during a muscle contraction?
I band becomes shorter, H zone becomes narrowed, A band stays the same. More myosin actin overlap occurs.
Explain the steps leading to the initial muscle contraction
Action potential occurs at the presynaptic terminal. Activation of calcium voltage gated channels causes release of calcium which causes exocytosis of vesicles contain acetylcholine. Acetylcholine diffuses across synaptic cleft and bind to acetylcholine receptors on the muscle. This results in an action potential spreading across the surface of the muscle fiber membrane. ACh is broken down by acetylcholine esterase.
Explain the steps in the initial muscle contraction after an action potential has arrived
Action potential propagates across surface of muscle membrane and T tubules. DHP receptor detects voltage and results in a change in the shape of the protein linked to the ryanodine receptor. This opens the ryanodine receptor and results in calcium leaving the sarcoplasmic reticulum and traveling deep into the muscle fiber where it binds to troponin. This causes tropomyosin to move and expose myosin binding sites. Myosin head forms a cross bridge with actin. Release of ADP and phosphate allows myosin to produce power stroke and pull actin towards centre of sarcomere. ATP binding releases myosin head from actin chain and ATP hydrolysis recharges myosin head. Calcium is actively transported back into SR while action potential continues.
What is a motor unit?
Single motor neurone and all the muscle fibers it innervates.
