Physiol 4 Skeletal muscle Flashcards
What is the term for individual muscle cells?
Fibres
What is the neuromuscular junction also known as?
Motor endplate
What triggers vesicle fusion and the release of acetylcholine (Ach) at the neuromuscular junction?
Calcium ions (Ca2+)
Fill in the blank: A single motor neuron can innervate multiple _______.
fibres
What is the effect of Myasthenia Gravis on acetylcholine receptors?
Reduces receptor number, blocks receptor, inflammatory response → damage endplate
What happens to the number of functional Ach receptors during repetitive activation in Myasthenia Gravis?
It is reduced
True or False: In Myasthenia Gravis, symptoms worsen with sustained muscle contraction.
True
What role do AchE blockers play in Myasthenia Gravis?
They keep the pool of Ach in the synaptic cleft high.
In the neuromuscular junction, what happens after Ach binds to nAchR on muscle fibre?
Na+ enters the muscle fibre
What is the first step in the sequence of events at the neuromuscular junction?
AP in axon
What anatomical structure is responsible for releasing calcium ions during excitation-contraction coupling?
Sarcoplasmic reticulum
What is the role of calcium ions in the contraction process of skeletal muscle?
Moves troponin off actin, allowing myosin heads to interact
What happens to tropomyosin when calcium levels are high?
Tropomyosin moves off binding sites
What is the cross-bridge cycle?
Interaction between myosin heads and actin during muscle contraction
What occurs if there is no ATP available for the myosin head?
The head stays attached → muscle stays stiff
What is the significance of the long duration of a muscle twitch?
More APs can arrive before the twitch finishes
How does the number of receptors occupied change with sustained contraction in a normal muscle vs. in Myasthenia Gravis?
Normal: 100% to 85%; MG: 60 to 51
What is the physiological effect of an autoimmune attack on neuromuscular Ach receptors?
Causes muscle weakness and rapid fatigue
What is the role of the T-tubule in muscle contraction?
Transmits action potentials into the muscle fibre
Fill in the blank: The _______ is the site where motor neurons communicate with muscle fibers.
neuromuscular junction
What happens during the cross-bridge cycle when calcium ions bind to troponin?
Tropomyosin moves off binding sites, allowing myosin to bind to actin
What is the final step in the excitation-contraction coupling process?
Tropomyosin moves back onto binding sites, relaxation
