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sensory information to be ignored.
(a) Generator potentials are localized depolarizations
and are graded (of different sub-threshold
magnitude). Unlike action potentials they are not
(b) It is important that a receptor does not respond
to stimuli at sub-threshold intensities as this
could mean the receptor would be responding
inappropriately and too often. Note: The threshold
level is a stimulus intensity that is established
through natural selection as appropriate in the
prevailing environment and (like other biological
responses) is subject to change over time. The Structure of the Eye (page 85) The Physiology of Vision (page 87) 1. Feature
Visual pigment(s): Rhodopsin
(no color vision) (three types)
Visual acuity: Low High Overall function: Vision in dim
sensitivity Color vision,
vision in bright
light 2. (a)-(c) in any order
(a) Photoreceptor cells (rods and cones) respond
to light by producing generator potentials.
(b) Bipolar neurons form synapses with the rods and
cones and transmit the changes in membrane
potential to the ganglion cells. Each cone
synapses with one bipolar (=high acuity) whereas
each rod synapses with many bipolar cells (=high
(c) Ganglion cells synapse with the bipolar cells
and respond with depolarization and generation
of action potentials. Their axons form the optic
nerve. 1. (a) Cornea: Responsible for most of the refraction
(bending) of the incoming light.
(b) Ciliary body: Secretes the aqueous humour
which helps to maintain the shape of the eye and
assists in refraction.
(c) Iris: Regulates the amount of light entering the eye
for vision in bright and dim light. 3. (a) Horizontal cells are interconnecting neurons
that help to integrate and regulate the input
from multiple photoreceptor cells. They enhance
information about contrast.
(b) Amacrine cells form synapses with bipolar cells
and work laterally to affect output from the bipolar
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This document was uploaded on 01/28/2014.
- Winter '13