How the retina turns light into signals

Science · The Human Body · ages 19-20

Name ______________________ Date ____________

Which order describes a direct cone pathway into the optic nerve?
- Cone to bipolar cell to ganglion cell to optic nerve
- Cone to ganglion cell to bipolar cell to optic nerve
- Bipolar cell to cone to ganglion cell to optic nerve
A flash reaches a dark-adapted photoreceptor. What is its usual response?
- It depolarises and releases more glutamate
- It hyperpolarises and releases less glutamate
- It produces spikes that travel directly through the optic nerve
After dark adaptation, which photoreceptors mainly support seeing a very dim path?
- Cones
- Horizontal cells
- Rods
After adapting to darkness, you see a faint star more easily by looking slightly beside it. Why can this help?
- Its image moves outside the rod-free foveal centre
- The image reaches the optic disc, where rods detect the faintest light
- The image stays on foveal cones, which are most sensitive to dim light
For an ON-centre bipolar cell, why can centre-only light produce a larger depolarisation than light covering both centre and surround?
- Surround illumination reinforces the centre-driven response
- Surround illumination opposes the centre-driven response
- Surround illumination bypasses the centre and starts optic-nerve spikes
How do horizontal cells contribute to centre-surround organisation?
- They carry ganglion-cell spikes through their own axons to the brain
- They absorb photons and produce the retina's light-sensitive inward current
- They help form surround effects by feedback to photoreceptors
In separate trials, light increases only in an ON bipolar cell's receptive-field centre and an OFF bipolar cell's centre. Each surround stays unchanged. How do the bipolar cells respond?
- ON depolarises; OFF hyperpolarises
- Both depolarise equally because they receive less glutamate
- ON hyperpolarises; OFF depolarises
A drug blocks transducin's activation of PDE in a dark-adapted rod. The normal rhodopsin-transducin-PDE pathway can still produce its usual light-driven cGMP fall and channel closure.
Circle one: True False

Answer key

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How the retina turns light into signals W1-mt_kviN7WskmP-s1

Cone to bipolar cell to ganglion cell to optic nerve · A cone signals to a bipolar cell, which signals to a ganglion cell. The ganglion cell's axon enters the optic nerve.
It hyperpolarises and releases less glutamate · Light closes cGMP-gated channels. Inward current falls while potassium continues to leave, so the membrane becomes more negative and glutamate release decreases.
Rods · Rods are more sensitive to dim light than cones. After dark adaptation, they mainly support vision under these very dim conditions.
Its image moves outside the rod-free foveal centre · Looking aside moves the image from the rod-free foveal centre onto retina containing rods. Rods are more sensitive to dim light than cones.
Surround illumination opposes the centre-driven response · Centre and surround have opposing effects. Adding surround illumination can reduce the depolarisation produced by centre-only light.
They help form surround effects by feedback to photoreceptors · Horizontal cells collect photoreceptor signals and provide feedback to photoreceptors. This helps create opposing surround effects in many bipolar cells.
ON depolarises; OFF hyperpolarises · Centre light reduces photoreceptor glutamate release. Different glutamate receptors make this depolarise ON bipolar cells but hyperpolarise OFF bipolar cells.
False · PDE activation normally increases cGMP breakdown. Blocking that activation interrupts this pathway's usual light-driven cGMP decrease and channel closure. The statement is false.