BMS248 Lecture 3 - Visual System Flashcards
The right visual field activates which part of the brain?
The left half of the brain (and vice versa)
What is the function of the retina?
Image acquisition
Where does the retina project to?
What occurs there?
The Lateral Geniculate Nucleus (LGN)
Preprocessing of visual information
Where does the retina project to?
What occurs there?
The Lateral Geniculate Nucleus (LGN)
Preprocessing of visual information
Where does the LGN project to?
What occurs here?
Primary visual cortex (V1)
Main processing of visual information
What are the two main pathways in the primary visual cortex
Ventral and Dorsal streams
(Go from the V1 cortex to these areas)
What is the ventral stream involved in?
What area of the brain?
Object recognition
Inferior temporal cortex
What is the dorsal stream involved in?
What area of the brain?
Spatial location + speed
Posterior parietal cortex
What does the pupil do in regards to the retina?
Regulates the amount of light that falls on the retina
Which part of the retina does the lens focus the image onto?
Fovea
What is the fovea?
The part of the retina with the most cones + highest visual acuity
The rest of the retina has contains mostly what?
What does this mean for visual acuity?
Primarily rods
Smaller acuity - detects change in the periphery
What are Muller cells?
Where are they found?
Glial cells that light passes through and onto the photoreceptors (transparent)
Grow across entire retina
The retina consists of how many layers of:
1. Neurons
2. Synapses
- 3 layers of neurons
Photoreceptor layer, Bipolar cell layer, Ganglion cell layer - 2 layers of synapses - inner and outer plexiform layers
What are the feedforward neurons in the retina? (Excitatory - glutamate)
photoreceptors, bipolar cells > ganglion cells
What are the feedback neurons in the retina? (Inhibitory - GABA)
Horizontal cells > (back onto the photoreceptors) - also inhibitory feedforward
Amacrine cells > (back onto the bipolar cells) - also inhibitory feedforward
From the photoreceptors to the ganglion cells what is the arrangement of neurons?
- Photoreceptors (back of retina)
- Horizontal cells
OPL - Bipolar cells
IPL - Amacrine cells
- Ganglion cells (front of retina)
Phototransduction occurs where in photoreceptors?
The outer segment
Rods are active in what kind of light?
Cones are active in what kind of light?
Rods: active at dim light
Cones: active at bright light
In vertebrates, photoreceptors respond to flashes of light by what?
Hyperpolarisation - decrease in membrane potential
What does cyclic GMP do on the membrane of photoreceptors and under what conditions?
Opens non-selective cation channels to keep the membrane depolarised in darkness
What is the phototransduction cascade?
- Light changes conformation of rhodopsin receptors
- G protein cascade (Gt)
- Activation of PDE (converts cGMP to GMP)
- Decrease in cGMP
- Non-selective cation channels close
- Hyperpolarisation of photoreceptors
What do photoreceptors constantly release from their synapses in darkness?
How does this change when they are activated by light - what does this effect?
Glutamate
Less glutamate is released, leading to hyperpolarisation of the photoreceptors - this affects bipolar cells
What does an OFF and ON bipolar cell do in response to light and Dark
What receptors do they use?
In light the ON bipolar cells depolarise (Turn on) and the OFF bipolar cells hyperpolarise
In dark the OFF bipolar cells depolarise and the ON bipolar cells hyperpolarise
OFF use AMPAR
ON use mGluR
