What are rods and cones?
Retinal photoreceptors containing light-sensitive optical pigments.
AQA A-Level Biology - (7402) · 3.6.1.2
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What are rods and cones?
Retinal photoreceptors containing light-sensitive optical pigments.
How do signals from retinal photoreceptors reach the optic nerve?
They pass through retinal neurones to ganglion cells, whose axons form the optic nerve.
What optical pigment do rods contain?
Rhodopsin.
How do the light intensities at which rods and cones function best differ?
Rods are sensitive to low light intensities; cones function best at higher light intensities.
How does convergence of rod signals increase sensitivity in dim light?
Signals from several rods combine on the same pathway to a ganglion cell.
Why does convergence of rod signals reduce visual acuity?
It makes it harder to distinguish precisely which rod was stimulated.
Why do rods not distinguish colours?
They have only one type of optical pigment.
How do cones enable colour vision?
The three cone types have pigments with different wavelength sensitivities; comparing their responses enables colour vision.
How do cone connections support high visual acuity in the fovea?
Cones generally show less convergence than rods. In the fovea, a cone may connect through a bipolar cell to an individual ganglion cell, allowing stimulus positions to be distinguished precisely.