78.The major structural component of the sperm flagellum is the:

A. microtubule
B. microfilament
C. actin filament
D. mysosin filament
E. ciliary body

ANS A. This is a basic histological question of a type found commonly on NBDE, which asks about basic cellular organelles and structures. The sperm cell flagellum is notable for a “9+2” arrangement of fibers formed from microtubules. The 9 single fibers form a circular ring in cross section around the 2 doubled fibers in the center. One of the significant facts about the fibers is
that they are composed of microtubules, made up of tubulin. The other significant fact is that all eucaryotic flagella and cilia have this same structure (for example, cilia form the tracheal lining). Note that procaryotic (bacterial) flagellea do NOT share this structure.


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77.Which muscle is the chief mover of the mandible TOWARD the left?

A. Left medial pterygoid
B. Left lateral pterygoid
C. Right medial pterygoid
D. Right lateral pterygoid

ANS.D. There are two methods for answering this question. The formula method

states that the right lateral pterygoid moves the mandible left, whereas the left lateral pterygoid moves

the mandible right. The understanding method begins with the idea that the medial pterygoid is a

closer (elevator). The lateral pterygoid connects to the condyle and is a protruder. If the right lateral

pterygoid pulls the right condyle out while the left lateral pterygoid and condyle remain stable, the left

side will act as a stationary pivot point while the right side protrudes outward and also toward the left

(medially).

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76.Damage to which of the following structures might produce hair cell loss?

A.Basilar membrane B.Organ of Corti
C.Reissner's membraneD.Scala tympani
E.Scala vestibuli

ANS B.

Hearing is the detection of sound, which consists of pressure waves

conducted through air or water. The receptors of the cochlear duct provide us with a sense of hearing

that allows us to detect the quietest whisper and yet remain functional in a crowded, noisy

environment. The organ of Corti contains hair cells from the cochlear branch of the vestibulocochlear

nerve (CN VIII). These cells rest on the basilar membrane (choice A), which separates the scala

tympani (choice D) from the scala media. The hair cells are embedded in the tectorial membrane,

and movement of the basilar membrane below the cells causes the hairs to bend, which generates

action potentials. The tectorial membrane that lies on the hair cells does not form a boundary between

the different scala; the membrane separating the scala media from the scala vestibuli (choice E) is

Reissner's (vestibular) membrane (choice C).

1H

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