The Eye II: Receptor and Neural Function of the Retina
Physiology, MBBS Second Year. This chapter is split into 10 topics and has
506 practice questions. The topics covered are listed below, followed by
10 free sample questions from the chapter.
Retinal electrophysiology & signal processing50 questions
Sample questions: The Eye II: Receptor and Neural Function of the Retina
10 sample questions with the correct answer and an explanation. Try to answer each one before reading the explanation.
Q1. Why does a detached retina resist degeneration for days?
A. It contains no receptors
B. The choroid supplies it directly
C. The neural retina has an independent blood supply through the retinal artery(correct answer)
D. The vitreous nourishes it
Answer: C.Because the neural retina has its own blood supply via the retinal artery (and partial diffusion across the detachment gap), it can survive for days and may regain function if surgically re-apposed to the pigment epithelium.
Q2. Which sequence correctly describes the light-induced transduction cascade in rods?
A. Light → breakdown of rhodopsin into melanin
B. Light → closure of K+ channels → hyperpolarization
C. Photoactivation of 11-cis retinal → metarhodopsin II → transducin activation → cGMP phosphodiesterase → cGMP to 5'-GMP → closure of Na+ channels → hyperpolarization(correct answer)
D. Light → opening of Na+ channels → depolarization
Answer: C.Light photoactivates the 11-cis retinal portion, forming metarhodopsin II (activated rhodopsin), which activates transducin; cGMP phosphodiesterase then breaks down cGMP to 5'-GMP, closing cGMP-gated Na+ channels and causing hyperpolarization.
Q3. Which statement about photoreceptor signalling is TRUE?
A. Signals are conducted only by action potentials
B. The signal is all-or-none
C. The signal is independent of light intensity
D. The signal is graded (amplitude depends on light intensity) and conducted electrotonically(correct answer)
Answer: D.Photoreceptor responses are graded (greater light → greater hyperpolarization) and spread electrotonically rather than as action potentials, since the cells are short and their cytoplasm conducts current directly.
Q4. Which sequence represents the DIRECT visual pathway from cones?
A. Photoreceptors → horizontal → ganglion cells
B. Photoreceptors → bipolar cells → ganglion cells(correct answer)
Answer: B.The direct pathway from cones runs photoreceptors → bipolar cells → ganglion cells; the rod pathway adds an amacrine cell (photoreceptors → bipolar → amacrine → ganglion) and is older, slower and uses smaller neurons.
Q5. Assertion: Glutamate released by photoreceptors can either excite or inhibit a bipolar cell. Reason: Different bipolar cell types express different glutamate receptor systems (sign-conserving versus sign-inverting).
A. Assertion is true but Reason is false
B. Both are true, but the Reason does not explain the Assertion
C. Both Assertion and Reason are true, and the Reason correctly explains the Assertion(correct answer)
D. Assertion is false but Reason is true
Answer: C.Because OFF-center bipolar cells are depolarized by glutamate (excitatory) while ON-center bipolar cells are hyperpolarized by it (inhibitory), the same transmitter produces opposite effects in the two cell types — the basis of the ON/OFF dichotomy.
Q6. A toxin selectively abolishes action potentials in the retina while sparing graded potentials. Which retinal output would be lost?
A. Ganglion cell signalling to the brain(correct answer)
B. Photoreceptor responses
C. Horizontal cell inhibition
D. Bipolar cell graded responses
Answer: A.Ganglion cells are the only retinal cells that use action potentials for transmission; abolishing them would block the retina's output to the brain while sparing the graded (electrotonic) signalling of photoreceptors and other interneurons.
Q7. Why are contrast-type ganglion cells neither stimulated nor inhibited by uniform ('flat') illumination?
A. They respond only to colour
B. Direct excitatory signals from photoreceptors are balanced by inhibitory signals from lateral pathways(correct answer)
C. They cease firing entirely
D. They are saturated
Answer: B.With even illumination over the retina, direct excitatory input is balanced by lateral inhibitory input, so contrast-type ganglion cells are neither excited nor inhibited — they respond to differences, not absolute light.
Q8. At a contrast border, ganglion cell responses are accentuated because:
A. Photoreceptors stop responding
B. All inhibition ceases
C. The bright spot excites the direct pathway while the dark area reduces lateral inhibition(correct answer)
D. Both pathways are equally balanced
Answer: C.At a border, the bright region drives the direct excitatory pathway while the dark region reduces lateral inhibition, so the direct and lateral signals accentuate each other — enhancing detection of contrast borders.
Q9. Colour opponency in ganglion cells means:
A. A cell is excited by one colour type of cone but inhibited by another, via direct excitatory and indirect inhibitory routes(correct answer)
B. A cell is excited by all colours equally
C. Only white signals are transmitted
D. Colour signals are transmitted only by rods
Answer: A.In colour opponency, one cone type excites the ganglion cell through a direct excitatory route while the opponent cone type inhibits it through an indirect inhibitory route — e.g., red excites and green inhibits, or blue excites while red+green (yellow) inhibits.
Q10. Which two factors contribute to retinal detachment after eye injury?
A. Lens opacification and pupil dilation
B. Corneal flattening and dry eye
C. Increased aqueous secretion only
D. Collection of fluid or blood between neural retina and pigment epithelium, plus vitreous fibril contraction(correct answer)
Answer: D.Injury allows fluid or blood to collect between the neural retina and the pigment epithelium, while contracture of fine collagenous fibrils in the vitreous pulls areas of retina inward — together producing detachment.