This is a quiz on muscle structure and pathologies. Enjoy!
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Muscle Structure and Pathologies
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What is a motor unit?
The motor neurone and the muscle fibres it innervates
A collection of motor neurones and muscle fibres
A collection of muscle fibres
A singular muscle fibre and its motor neurone
A whole muscle
Which receptors are affected in myasthenia gravis and where are they located?
Voltage-gated calcium channels. On the post synaptic membrane
Voltage-gated calcium channels. On the pre synaptic membrane
Muscarinic receptors. On the post synaptic membrane
Nicotinic acetylcholine receptors. On the pre synaptic membrane
Nicotinic acetylcholine receptors. On the post synaptic membrane
How does botulinum toxin result in paralysis?
Degrades the SNARE protein complex. Blocks calcium release from pre-synaptic terminals -> total blockade at the NMJ
Degrades the acetylcholine. Blocks calcium release from pre-synaptic terminals -> total blockade at the NMJ
Degrades the acetylcholine esterase. Blocks calcium release from pre-synaptic terminals -> total blockade at the NMJ
Degrades the SNARE protein complex. Blocks acetylcholine release from pre-synaptic terminals -> total blockade at the NMJ
Degrades the SNARE protein complex. Blocks acetylcholine release from post-synaptic terminals -> total blockade at the NMJ
Which of the following describes the M line of the sarcomere?
The darkly staining lines which run down the middle of each I band. Indicate the point where thin actin fibres from adjacent sarcomeres join.
The point at which the thick filaments meet and connect with the cell membrane
There are 2, located either side of the A band . Contain thin filaments only (not overlapping) and appear light under a light microscope
Located in the centre of the sarcomere. Mainly thick filament, but some overlapping thin filaments. Appears dark under a light microscope
The area in the centre of the A band where there only thick filaments (no overlapping filaments)
What at rest covers the myosin binding sites on the actin filaments?
What is the next stage in the excitation-contraction coupling process following, depolarisation of muscle fibre membrane leading to an action potential being propagated down T tubules?
Ca2+ released from sarcoplasmic reticulum → ↑ intracellular Ca2+ concentration
Ca2+ binds to troponin C → binding sites exposed → cross-bridge cycling → contraction!
Conformational change in dihydropyridine receptors (on T tubules) → conformational change in ryanodine receptors (on sarcoplasmic reticulum)
Conformational change in ryanodine receptors (on T tubules) → conformational change in dihydropyridine receptors (on sarcoplasmic reticulum)
Ca2+ released from endoplasmic reticulum → ↑ intracellular Ca2+ concentration
What is the first step of the cross-bridge cycle?
ATP is hydrolysed to ADP and inorganic Phosphate (Pi) by ATPase which initially both remain bound to the myosin head. The release of energy from the hydrolysis of ATP changes the conformational state of the myosin head further. The myosin head is cocked/bent into a high energy position. It is like a spring which has been loaded. The myosin head binds to actin at a point further along from its original binding site.
ADP is released and the myosin head binds tightly to the actin again (rigor position). As long as ATP is available and calcium remains bound to troponin C, the cross-bridge cycling will continue and the myosin will walk along the actin filament. Remember that there are multiple myosin heads bound to an actin filament during this cycle.
ATP binds to the myosin head and induces a conformational change, reducing the affinity of the myosin head for actin. The myosin head releases actin.
Binding of calcium to troponin C displaces tropomyosin and allows myosin heads to bind to actin forming cross-bridges. Initially the myosin head is bound tightly to actin in the rigor position. ATP is required to reduce the affinity of myosin for actin and allow to move, and if ATP is absent then this binding is permanent resulting in rigor mortis.
Phosphate is released from the myosin head and the myosin head springs back into it’s original position and pushes the actin molecule towards the M-line. The thick and thin filaments slide over each other, shortening the sarcomere. This is called the power stroke.
How is calcium taken up into the sarcoplasmic reticulum?
By sarcoplasmic reticulum calcium ATPase
By sarcoendoplasmic reticulum calcium ATPase
By Troponin C
By Troponin I
A patient presents with Gowers Sign. Which protein are they most likely to have a defect in?
A patient has been diagnosed with an autoimmune disorder, Polymyositis. How does this condition cause muscle weakness?
Causes reduced levels of dystrophin
Prevention of regeneration of muscle cells
Inflammatory cell infiltration and muscle fibre necrosis.
Increases the rate of muscle cell apoptosis
Muscle fibre degeneration
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