Synaptic Transmission

Which ion is responsible for the depolarization phase of the postsynaptic potential at an excitatory synapse?

A 32-year-old woman presents with progressive muscle weakness, ptosis, and diplopia that worsens towards evening. Antibody testing is ordered. Which investigation is most specific for confirming the diagnosis of myasthenia gravis?

A 28-year-old male presents with acute-onset muscle paralysis, autonomic instability, and respiratory compromise following a Campylobacter jejuni gastroenteritis 2 weeks prior. Lumbar puncture shows elevated protein with normal cell count. Which investigation is most appropriate to confirm the diagnosis of Guillain–Barré syndrome?

Which is the most common site of synaptic transmission failure in myasthenia gravis?

A 42-year-old Indian woman with known myasthenia gravis presents to the emergency department with acute respiratory distress and inability to swallow. She has not taken her medications for 3 days. Arterial blood gas shows pH 7.28, PaCO₂ 65 mmHg, HCO₃⁻ 28 mEq/L. Bedside spirometry reveals forced vital capacity (FVC) of 800 mL (baseline 2.5 L). She is immediately intubated and started on mechanical ventilation. Which mechanism best explains why anticholinesterase inhibitors (pyridostigmine) are effective in reversing her neuromuscular weakness?