A 68-year-old male is brought to the emergency department by his wife. She reports that her husband has been unable to speak or move the right side of his body. She states that his symptoms occurred suddenly, while they were discussing vacation plans. He suddenly fell to the right, was unable to speak or follow commands, or move his right arm or leg. Past medical history is significant for hypertension and atrial fibrillation. He has smoked 1 pack of cigarettes daily for the past 40 years. His temperature is 100.4 deg F (38 deg C), blood pressure 186/108 mmHg, pulse is 109/min and irregularly irregular, and respirations are 17/min. On exam, he has a left-gaze preference, with marked weakness and sensory loss of the right side. EKG reveals atrial fibrillation. D-dimer level is 320 ng/mL (normal ≤ 250 ng/mL). Head imaging shows an occlusion of the proximal left middle cerebral artery. Which of the following is most likely the cause of this patient's clinical presentation?

A 68-year-old male is brought to the emergency department by his wife. She reports that her husband has been unable to speak or move the right side of his body. She states that his symptoms occurred suddenly, while they were discussing vacation plans. He suddenly fell to the right, was unable to speak or follow commands, or move his right arm or leg. Past medical history is significant for hypertension and atrial fibrillation. He has smoked 1 pack of cigarettes daily for the past 40 years. His temperature is 100.4 deg F (38 deg C), blood pressure 186/108 mmHg, pulse is 109/min and irregularly irregular, and respirations are 17/min. On exam, he has a left-gaze preference, with marked weakness and sensory loss of the right side. EKG reveals atrial fibrillation. D-dimer level is 320 ng/mL (normal ≤ 250 ng/mL). Head imaging shows an occlusion of the proximal left middle cerebral artery. Which of the following is most likely the cause of this patient's clinical presentation?

A 34-year-old woman is brought to the emergency department by her husband due to worsening lower extremity weakness. Her symptoms began approximately one week prior to presentation, when she experienced mild weakness of the left leg, causing her to limp. The lower extremity weakness progressed to the point of not being able to get out of bed. The patient also reports a period of left arm weakness and numbness eight months ago that spontaneously resolved over the course of a few days. Approximately two weeks ago, she experienced an upper respiratory infection that has resolved. Her temperature is 98.6°F (37°C), pulse is 74/min, respiratory rate 18/min, blood pressure 129/75 mm Hg. Neurological exam is significant for 1/5 strength in both lower extremities and 3+ patellar tendon reflexes. A magnetic resonance imaging (MRI) of the brain and spine is performed. Which of the following is the best initial treatment?

The tiny space between neurons or a neuron and its target muscle is the:

The speed of impulse conduction along an axon may be increased by

One neurotransmitter associated with sleep, mood, attention, and learning is