Which of the following is the main excitatory neurotransmitter in the brain?

Correct Answer: D

Rationale: Glutamate . Glutamate is the primary excitatory neurotransmitter, driving most CNS synaptic activity, per neuroscience (e.g., 80% of cortical synapses). Choice A (GABA) is inhibitory, calming neurons. Choice B (dopamine) modulatreward, not broad excitation. Choice C (norepinephrine) enhancarousal, not primary excitation. (serotonin) regulatmood, not excitation. Ds truth glutamatrole in learning, memory (e.g., NMDA receptors) distinguishit from the inhibitory or modulatory (B, C, E) roles, making it the correct answer.

Correct Answer: A

Rationale: Xanthochromia refers to a yellowish discoloration of CSF due to the presence of blood breakdown products, such as bilirubin. A bloody tap occurs during the procedure when blood is introduced artifactually, resulting in red blood cells but not xanthochromia, as the blood is fresh and not yet degraded; thus, it is the exception and correct answer. Subarachnoid hemorrhage causxanthochromia due to hemolysis of RBCs over time. Carotenemia and hyperbilirubinemia can discolor CSF yellow due to elevated carotenoids or bilirubin levels, respectively. Markedly elevated CSF protein may also contribute to xanthochromia by altering CSF appearance. Since a bloody tap donot allow time for blood breakdown, it donot cause true xanthochromia, making A distinct from the others.

Correct Answer: D

Rationale: Familial autosomal recessive microcephaly, or primary microcephaly, featura small head size with a slanted forehead , prominent nose and ears due to relative facial sparing, and mild or borderline mental retardation from reduced brain volume. Surface convolutional markings may be simplified. Prominent seizur, however, are not a hallmark; seizurmay occur but are not a defining or consistent feature, unlike in secondary microcephaly (e.g., from infection). Thus, D is the exception and correct answer, as familial microcephaly primarily affects head size and cognition rather than causing significant epileptiform activity.

Correct Answer: D

Rationale: Crouzon syndrome, an autosomal dominant disorder , involvcraniosynostosis leading to brachycephaly (B, short skull), ocular proptosis from shallow orbits, and maxillary hypoplasia . Syndactyly , or fused digits, is not a feature; it is characteristic of Apert syndrome, another craniosynostosis condition. This distinction is key: Crouzon affects the skull and face without limb involvement, while Apert includsyndactyly. Thus, D is the exception and correct answer, as it donot belong to Crouzons typical presentation, rooted in its genetic and phenotypic profile.

Correct Answer: D

Rationale: Benign myoclonic epilepsies, like juvenile myoclonic epilepsy, respond best to valproate , a broad-spectrum antiepileptic that stabilizsodium channels and enhancGABA, effectively controlling myoclonic jerks. Clonazepam and other benzodiazepinare adjunctive, with sedation limiting use. Lamotrigine may worsen myoclonus in some cases, and topiramate is less preferred due to cognitive side effects. Valproatefficacy across myoclonic syndromes, supported by clinical trials, makes D the correct answer, balancing effectiveness and tolerability in this condition.