MCAT Social and Behavioral Sciences : Physiology of the Eye
Study concepts, example questions & explanations for MCAT Social and Behavioral Sciences
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Example Questions
Example Question #11 : Environment And Sensation
In order to successfully accommodate for changes in depth of field, lens of the eye must perform which of the following functions when re-focusing on a closer object?
Thicken
Rotate
Tilt
Flatten
Thicken
When looking at objects that are close, the lens of the eye must “thicken” to accommodate changes in depth of field. This is accomplished by contraction of the ciliary muscle, which allows the suspensory ligament to stretch. The lack of tension then allows the lens to draw up into its thicker resting state. If the vision is shifted to a far object, then ciliary muscles will relax, which increases tension on the lens via the suspensory ligament and causes it to "flatten." The lens does not “tilt” or “rotate.”
Example Question #11 : Vision
Ciliary and pupillary muscles are innervated by which cranial nerve?
The ocular nerve (CN II)
The trigeminal nerve (CN V)
The abducens nerve (CN IV)
The oculomotor nerve (CN III)
The oculomotor nerve (CN III)
Ciliary and pupillary muscles are innervated by CN III, the oculomotor nerve. This nerve is also responsible for elevation of the upper eyelid, and innervation of the superior rectus, medial rectus, inferior rectus, and inferior oblique muscles of the eye. The abducens nerve (CN VI) innervates a single extraocular muscle: the lateral rectus. The optic nerve is primarily involved in transmission of visual signals from the retina to the brain, and the trigeminal nerve is not directly involved in ocular movement or function.
Example Question #12 : Vision
In which of the following parts of the retina is visual acuity the highest?
Optic disc
Cornea
Fovea
Lens
Fovea
The fovea centralis is a zone of densely packed cone cells in the center of the macula lutea of the retina. Because of this it is the region capable of the highest degree of visual acuity. The optic disc is the point of exit for ganglion cell axons of the optic nerve. This is an area absent of rods or cones, and so is considered a "blind spot" of the eye. Last, the cornea and lens are not part of the retina.
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