QUESTION: 45

A premature female infant is born about 24 weeks after fertilization and develops rapid, labored breathing shortly after birth. She is immediately transferred to intensive care where she is diagnosed with hyaline membrane disease (HMD). Which of the following is most likely deficient in the infant?

alveolar ducts
lung surfactant
terminal saccules
type I alveolar cells
type II alveolar cells

Answer(s): D

Explanation:

HMD is also known as respiratory distress syndrome, which is most often caused by the lack of lung surfactant, due to a premature birth. Lung surfactant production begins around 20 weeks after fertilization.
But it is present only in small amounts until the last 2 weeks before birth when its amount increases significantly. Alveolar ducts (choice A) branch from the respiratory bronchioles during development. Type I alveolar cells (choice D) or pneumocytes are squamous epithelial cells, which participate in gas exchange.
These epithelial cells line the terminal saccules (choice C). Type II alveolar cells (choice E) synthesize surfactant.

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QUESTION: 46

Which label in following figure indicates the typical plane of separation at which retinal detachment occurs?

Answer(s): D

Explanation:

Retinal separation typically occurs at the interface between the retinal pigment epithelium and the outer limit of the sensory (neural) retina. The weakness of this plane is attributed to the manner in which the retina develops, a process that involves obliteration of the space between two of the layers of the optic cup--an inner layer from which the sensory retina arises and an outer layer from which the retinal pigment epithelium arises. Other retinal layers are bridged by neuronal processes, and Müller cells (the retina's glial cells) span the entire thickness of the neural retina. Plane A(choice A) marks the boundary between the nerve fiber layer above and the ganglion cell layer below. The nerve fiber layer is composed of axons of the retinal ganglion cells. Plane B (choice B) is within the inner plexiform layer, the site of synaptic contacts between bipolar neurons, retinal ganglion cells, and amacrine cells. Plane C (choice C) is within the outer plexiform layer, the site of synapses among bipolar cells, rods and cones, and horizontal cells. The boundary between the choroid (of the middle vascular tunic or uvea) and the sclera (of the external, fibrous tunic) is marked by plane E (choice E).

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QUESTION: 47

A 28-year-old male patient suffering from head trauma resulting from a car accident is brought unconscious to the emergency room. In performing the pupillary light reflex, you notice that even though the left pupil constricts when you shine a light directly into the left eye, it does not do so when you shine a light into the right eye. This is best explained by a disconnection between which of the following bilateral structures?

Edinger-Westphal nucleus
habenula
inferior colliculus
lateral geniculate nucleus
medial geniculate nucleus

Answer(s): A

Explanation:

The central visual pathway for the papillary light reflex is organized as follows: fibers from the ganglionic layer of the retina project posteriorly to the pretectum, which in turn innervates the Edinger- Westphal nucleus. Preganglionic parasympathetic neurons in the Edinger- Westphal nucleus project to the ciliary ganglion, which sends postganglionic parasympathetic innervation back to the constrictor pupillae of the eye. The Edinger-Westphal nuclei from each side of the midbrain are also connected to each other by projections running through the posterior commissure. Disconnection of these fibers will result in loss of the consensual papillary light reflex on the contralateral side, as happens in this case. The habenula (choice B) is a nucleus of the thalamus, which does not participate in the central visual pathways. The lateral geniculate nucleus (choice D) receives fibers from the ganglionic layer of the retina. However, fibers participating in the papillary light reflex run through this structure without synapsing and terminate in the pretectum. Thus, the lateral geniculate nucleus does not participate in the pupillary light reflex. The inferior colliculus (choice C) and the medial geniculate nucleus (choice E) are components of the auditory system.

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QUESTION: 48

A 45-year-old female patient presents to the emergency room with a headache and complains of abnormal sensations on the left side of her body. She claims that the sensory changes came on rapidly in the last few hours. Her laboratory reports come back normal, a spinal tap reveals normal cerebrospinal fluid (CSF), and her mental ability seems good. You perform a neurological examination and find she has greatly reduced sensation on the entire left side of her body, including her face. The sensory loss includes all modalities. The motor examination is normal, as is her visual examination and hearing examination. Based on the neurological findings, which of the following thalamic nuclei would be involved?

lateral and medial geniculate nuclei
lateral dorsal and lateral posterior nuclei
pulvinar
ventral anterior and ventral lateral nuclei
ventral posterior lateral and ventral posterior medial nuclei

Answer(s): E

Explanation:

The ventral posterior lateral (VPL) and ventral posterior medial (VPM) nuclei are sensory relay thalamic nuclei. The lateral and medial geniculate nuclei (choice A) are respectively concerned with visual and auditory sensory information. The lateral dorsal (LD) and lateral posterior (LP) nuclei (choice B), and the pulvinar (choice C) are association or multimodal relay nuclei. The ventral anterior (VA) and ventral lateral (VL) are motor relay nuclei.

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