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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75.Which cusp of the maxillary molar is NOT part of the trigon (primitive cusp triangle)?

A. Mesiolingual    B. Mesiobuccal

C. Distolingual     D. Distobuccal

ANS> C. In evolution, three cusps of the maxillary molar are considered to be the 

primary cusp triangle, and the original three cusps of the evolving molar. They form the trigon, and are 

the MB, ML, and DB cusps. The fourth cusp, the DL, is the smallest, is considered to be a minor cusp, 

and is known evolutionarily as the talon, or talon cusp. This cusp is less conspicuous as you go from 

first to second to third maxillary molar. 

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