Chapter 5 Notes - Part Five

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Published on 18 Dec 2010
Cells located above the photoreceptors transparent
Photoreceptors respond to light and pass the info on by means of a neurotransmitter to the
bipolar cells
Bipolar cells: neuron in retina that receives info from receptors and passes it on to the
ganglion cells, from which axons proceed through the optic nerves to the brain
Ganglion cell: neuron in the retina that receives info from bipolar cells from which axons
proceed through the optic nerves to the brain
Visual information passes through a 3 cell chain to the brain:
Photoreceptor -> Bipolar cell -> Ganglion cell -> brain
Human retina contains 2 types of photoreceptors:
1 Rods (125 million): function mainly in dim light; very sensitive to light, but are insensitive
to differences between colours (cannot detect changes in hues)
2 Cones (6 million): function when the level of illumination is bright enough to see things
clearly; responsible for colour vision
Fovea: small pit in the back of the retina that contains only cones (1 mm in diameter);
responsible for the most acute and detailed vision
A molecule derived from vitamin A is the central ingredient in the transduction of energy of
light into neural activity
In the absence of light, this molecule is attached to a protein, forming a photopigment
Photopigment: complex molecule found in photoreceptors, when struck by light, it splits and
stimulates the membrane of the photoreceptor in which it resides.
When a photon strikes a photopigment, the photopigment splits into its two constituents
molecules; starting the process of transduction
Rhodopsin: Photopigment contained by rods (pink) once the photopigments are split by the
action of the light, they lose their colour (become bleached)
Detection of light requires that photons split molecules of rhodopsin or one of the other
Dark adaptation process by which the eye becomes capable of distinguishing dimly
illuminated objects after going from a bright area to a dark one.
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