A 3-year-old boy is rushed to the emergency department after he is found underwater in the bathtub. His parents say the patient was left alone for 5 minutes. On physical examination, he does not respond to painful stimuli and is pulseless and not breathing. Cardiac rhythm is asystole and spontaneously returns after several minutes of resuscitation. While performing endotracheal intubation, stimulation of the posterior pharyngeal wall with laryngoscope elicits no soft palate movements or gagging. This patient's findings during intubation most likely indicate dysfunction of which of the following neural structures?

Question

A 3-year-old boy is rushed to the emergency department after he is found underwater in the bathtub.  His parents say the patient was left alone for 5 minutes.  On physical examination, he does not respond to painful stimuli and is pulseless and not breathing.  Cardiac rhythm is asystole and spontaneously returns after several minutes of resuscitation.  While performing endotracheal intubation, stimulation of the posterior pharyngeal wall with laryngoscope elicits no soft palate movements or gagging.  This patient's findings during intubation most likely indicate dysfunction of which of the following neural structures?

Quizplus · Accepted Answer

11ec160b_359a_c71d_9249_a1331b88e89c_MD0001_00 This patient with prolonged oxygen deprivation has an absent gag reflex. The gag reflex is an airway protective mechanism that acts to expel foreign or toxic material from the aerodigestive tract. It is mediated by the following: Sensory (afferent) signals from the back of the tongue or posterior pharyngeal wall are sent via the glossopharyngeal nerve (CN IX). Somatic sensory fibers of CN IX enter the brainstem at the medulla, descend along the spinal trigeminal tract, and synapse in the caudal spinal nucleus. Information is then sent to the bilateral nuclei ambiguus, which are also located in the medulla. Bilateral motor (efferent) signals are sent via the vagus nerves (CN X), causing elevation of the soft palate and contraction of the pharynx. Therefore, an absent gag reflex is suspicious for dysfunction of the medulla oblongata. In combination with a prolonged anoxic period, this is concerning for brain death, which is the irreversible absence of cerebral and brainstem reflexes. (Choice A) Damage to the prefrontal cortex can cause inappropriate behavior, impaired judgment, and poor problem-solving skills (ie, executive dysfunction). It cannot be evaluated in an unconscious patient. (Choice B) The motor cortex is responsible for generating voluntary motor movement and cannot be tested in an unconscious patient. The gag reflex is involuntary and mediated by cranial nerves in the medulla. (Choice C) The pupillary reflex is also assessed in patients with suspected brain death and indicates dysfunction of the midbrain. It is mediated by afferents from the optic nerve (CN II) and efferents from the oculomotor nerve (CN III) to mediate constriction of the pupils in response to light. (Choice E) The cervical spinal cord can mediate several reflexes including neck flexion, adduction of the shoulders, elbow flexion, and flexion of the trunk. These may even be present in patients with brain death. However, the gag reflex is mediated by cranial (rather than spinal) nerves. Educational objective: The gag reflex is mediated by afferents predominantly from the glossopharyngeal nerve (CN IX) and efferents from the vagus nerve (CN X). An absent gag reflex may indicate dysfunction of the medulla oblongata, where the involved cranial nerve nuclei reside.

A 3-Year-Old Boy Is Rushed to the Emergency Department After