QUESTION: 37

In the skull, a network of thick-walled vessels named dural venous sinuses drains the cerebrospinal fluid and the venous blood from the brain. These vessels are formed by reflections of the dura mater, which also form partitions between major parts of the brain. Which of the following dural venous sinuses is associated with the falx cerebri?

cavernous sinus
inferior petrosal sinus
sigmoid sinus
superior sagittal sinus
transverse sinus

Answer(s): D

Explanation:

The falx cerebri is the dural partition separating the hemispheres of the brain, above the corpus callosum. It has in its superior edge the superior sagittal sinus and in its inferior border, the inferior sagittal sinus. The cavernous sinus (choice A) is a dural pocket in the middle cranial fossa and is located on either side of the sella turcica. It is unusual because it contains the internal carotid artery and cranial nerves III, IV, V1, V2, and VI. The sigmoid sinus (choice C) is located in the posterior cranial fossa, below the level of the tentorium cerebelli, which contains in its posterior border the transverse sinus (choice E).

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QUESTION: 38

A patient was thrown from a tractor, which partially ran over him and caused injury to the base of the skull. The origin of the internal jugular vein at the jugular foramen was compromised. Which of the following cranial nerves courses through the jugular foramen?

abducens (sixth cranial) nerve
facial (seventh cranial) nerve
hypoglossal (twelfth cranial) nerve
spinal accessory nerve (eleventh cranial) nerve
vestibulocochlear (eighth cranial) nerve

Answer(s): D

Explanation:

The spinal accessory (eleventh cranial) nerve takes its origins in the neck, but then runs cranially into the skull through the foramen magnum to join with its cranial component. They exit as one through the jugular foramen, along with the glossopharyngeal (ninth cranial) and vagus (tenth cranial) nerves. The abducens (sixth cranial) nerve (choice A) runs through the superior orbital fissure to reach the orbit. The facial (seventh cranial; choice B) and vestibulocochlear (eighth cranial; choice E) nerves run together through the internal acoustic meatus into the temporal bone. The facial nerve exits the skull through the stylomastoid foramen. The hypoglossal (twelfth cranial; choice C) nerve exits the skull through the hypoglossal canal.

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QUESTION: 39

Protein zero (P0) is the predominant protein in myelin in the peripheral nervous system and its function is to stabilize adjacent plasma membranes by interaction with similar P0 molecules. Which of the following cells manufacture P0?

fibrous astrocytes
microglia
oligodendrocytes
protoplasmic astrocytes
Schwann cells

Answer(s): E

Explanation:

Schwann cells produce myelin in the peripheral nervous system whereas oligodendrocytes produce myelin in the central nervous system. Oligodendrocytes manufacture the proteolipid protein, the functional equivalent to P0 in the central nervous system. Fibrous (choice A) and protoplasmic (choice D) astrocytes are supportive cells which play a role in the regulation of brain metabolism. Microglia (choice B) are mesodermal in origin and have phagocytotic activity in the central nervous system.

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QUESTION: 40

Aperilunate fracture dislocation is a devastating closed injury of the wrist. It usually results from a fall where the weight of the body is transferred onto the wrist. The hand is caught in the hyperextended and ulnar deviated position. The fracture dislocation involves rupture of interosseous ligaments, joints, and ultimately dislocation/fracture of the lunate bone. In the anatomical position, which carpal bone lies directly distal to the lunate?

capitates
hamate
scaphoid
trapezoid
triquetrum

Answer(s): A

Explanation:

The capitate bone lies directly distal to the lunate. The mechanism of perilunate fracture dislocation involves rupture of the radioscaphocapitate and scapholunate interosseous ligaments, dislocation of the capitolunate joint, rupture of the lunotriquetral interosseous ligament, and finally dislocation/rupture of the lunate. In the anatomical position, the hamate (choice B) is the most medial carpal bone, located just distal to the triquetrum. The scaphoid (choice C) lies lateral to the lunate and proximal to the trapezium (choice D), the carpal bone articulating with the thumb. The trapezoid (choice E) is medial to the trapezoid and distal to the scaphoid. The lunate bone (choice C) lies adjacent to the scaphoid in the proximal row of carpals and with the scaphoid articulates with the radius at the radiocarpal or wrist joint. It is not related to the anatomic snuffbox. The pisiform bone (choice D) is a sesamoid bone in the tendon of the flexor carpi ulnaris on the lateral wrist. It is not related to the anatomic snuffbox.

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