A.Increased Tension on the Lens Ligaments

Visual accommodation involves:

A.increased tension on the lens ligaments.

B.a decrease in the curvatureof the lens.

C.relaxation of the sphincter muscle of the iris.

D.contraction of the ciliary muscle.*

E.increased intraocular pressure.

During the visual cycle,

@ During the visual cycle, the RPE cells manufacture and store 11-cis-retinal, which is moved to the rods where it can be formed into rhodopsin (A is correct). 11-cis-retinal is combined with an opsin to form a visual pigment (rhodopsin in the case of rods), and the pigment is split back into its component parts when light hits it (B is incorrect). It is the retinoids, not the opsins that cycle between the rods and the RPE cells (C is incorrect). As part of the transduction process, rhodopsin activates transducin (not phosphodiesterase), and this is not part of the visual cycle (D is incorrect). Vitamin A (retinol) is transformed into 11-cis-retinal in order to enter the visual cycle. When rhodopsin is bleached it is split into the opsin + 11-cis-retinal (E is incorrect).

A.11-cis-retinal is moved into the rods from the retinal pigment epithelium.*

B.11-cis-retinal is split to form an opsin plus all-trans-retinal.

C.opsins are moved between the rods and the retinal pigment epithelium cells.

D.rhodopsin activates phosphodiesterase.

E.vitamin A is “bleached” to form rhodopsin.

Activation of β₂ receptors causes:

@ β₂ receptors are involved in sympathetic regulation of aqueous humour production (B is the correct answer). Activation of the parasympathetic system causes constriction of the pupils (A is incorrect) and of the pupillary muscle (see A, but C is also incorrect). Sympathetic stimulation constricts the ciliary muscle, flattening the lens (D is incorrect). Orbicularis oculi is a striated muscle (nicotinic receptors).

A.pupillary constriction.

B.increased aqueous humour production.*

C.contraction of the pupillary muscle.

D.rounding of the lens.

E.activation of the orbicularis oculi muscle.

X-chromosome-linked incomplete achromatopsia is a rare ocular disorder which is due to deletions or point mutations that decrease production of both the red and green pigments. Patients with this disorder would be expected to have:

A.decreased spatial acuity in the periphery of the retina.

B.decreased night vision.

C.decreased scotopic vision.

D.decreased temporal acuity.*

E.decreased accommodation.

Injection of <b>COLD</b> water into the <b>LEFT</b> ear of a person with normal inner ear function would result in:

@ This question tests objective #11: describe the differences in caloric nystagmus. Injection of warm water causes nystagmus to the injection (same) side. In a normal person, cold water in the left ear causes a rightward nystagmus (slow left, fast right). In a brain dead patient, neither the pursuit or the saccade would be present, therefore there would be no eye movement (G is the correct answer).

A.Leftward nystagmus: pursuit to the left, followed by a right saccade

B.Leftward nystagmus: pursuit to the right, followed by a left saccade

C.Rightward nystagmus: pursuit to the left, followed by a right saccade*

D.Rightward nystagmus: pursuit to the right, followed by a left saccade

E.Leftward pursuit only

F.Rightward pursuit only

G.No eye movement

A patient with suspected benign paroxysmal positional vertigo is being tested with the Dix-Hallpike procedure: Her head is turned 45^o to the left, and she is rapidly moved from a sitting to a supine position. What is the expected response?

@ The orientation of the stereocilia in the utricle and saccule is such that any head movement will depolarize some cells and hyperpolarize others (A is incorrect). Turning the head 45^o to the left ensures that only the right anterior and left posterior canals can be stimulated by the change in head position (B, C and D are incorrect).

A.depolarization in all cells of the utricle.

B.depolarization of both posterior semicircular canals.

C.depolarization in the left horizontal semicircular canal.

D.hyperpolarization of the left anterior semicircular canal; depolarization of the right posterior semicircular canal.

E.hyperpolarization of the right anterior semicircular canal; depolarization of the left posterior semicircular canal.*

Severe otitis media results in:

@ Otitis media results in a conductive hearing loss, initially at low frequencies due a decrease in the middle ear air space, but progressing to high frequencies if the mass of the ossicles is affected., which would reduce basilar membrane vibrations in the base of the cochlea (C is the correct answer). It is a conductive loss at many frequencies, not a high-frequency sensorineural loss that results from exposure to loud sounds (A is incorrect). Uncorrected hearing loss due to otitis media can significantly delay language development because the child cannot hear consonants (which are high frequency sounds). A middle ear defect would not affect stria vascularis function (D is incorrect). A conductive hearing loss would result in abnormal Rinne and Weber tests.

A.a hearing loss similar to the effect of exposure to gunfire.

B.earlier speech and language development, due to more clear articulation of consonants.

C.reduced basilar membrane vibration in both the base and apex of the cochlea.*

D.decreased K⁺ secretion from the stria vascularis.

E.an abnormal Rinne and normal Weber tests.