Lecture 4: Visual System Flashcards
Retina
Sheet of cells along your eyeball, composed of the ganglion cell layer, bipolar cell layer, and photoreceptor layer
Ganglion Cell Layer
Composed of ganglion cells, send information to the brain via optic nerve (ganglion cell axons)
Photoreceptor laye
Made up of Rods and Cones
Rods
Detect brightness, concentrated in periphery
Cones
Detects color, concentrated in fovea. Not ass sensitive to light as rods
Neuron
Composed of the dendrites, soma, and axon
Dendrites
Where information comes into the neuron
Soma
Cell body, contains the innerworkings of the cell
Axon
Output process of the neuron
Action Potential
Difference in charge between the inside and outside of the cell when the neuron fires
Resting Potential
Difference in charge between the inside and outside of the axon at rest (-70mV when neuron is not firing)
Threshold
Potential needs to cross this threshold to fire an action potential
All-or-None
Action potential always has same strength, either you get all of it or none of it
Propagation
Once past threshold, active process (ion pumping) propagates action potential down axon
Refractory Period
Short period after firing before the neuron can fire again
Neurotransmitters
Neurons communicate by sending these chemicals across very small gaps, synapses, between the cells
Electrochemical Transmission
Involves an electrical action potential within cells, which releases chemical neurotransmitters into the synapse
Summation
The sum of inhibitory and excitatory neurotransmitters, whichever is greater is expressed
Excitatory
Increase the potential and make it more likely to pass the threshold
Inhibitory
Decrease the potential and make it less likely to pass the threshold
Center-Surround
Ganglion cells are either on-center off-surround, or off-center on-surround. This means that the cells are responsible for exiting action potentials when the “on” section receives light, and inhibits them when the “off” section is stimulated
M-Cells
Project to magocelluar layers of LGN
P-Cell
Projects to parvocellular layer of LGN
Thalamus
Where most sensory input goes in the brain
Lateral Geniculate Nucleus
Part of thalamus responsible for vision
Magnocellular Layers
Neurons here have a transient (short burst) response, larger receptive fields, process movement and location
Parvocellular Layers
Sustained response, small receptive field, processes patterns, colors, and form
Cerebral Cortex
Sheet of grey matter outside of the brain, divided into 4 lobes, frontal, parietal, temporal, and occipital
Simple cell
Likes a bar of light, specific orientation and retinal position
Complex Cell
Likes edges/movement
Hypercomplex Cells
Recognized very specific shapes, corners, and gaps
Positron Emission Tomography (PET scanning)
Injection of a radioactive tracer, goes into the blood supply and emits positrons in the brain, which is scanned by a PET scanner to figure out neural activity
Kohler Experiment
- Had people do a where task and a what task to see what would be activated
- Had people answer questions, either if objects are in the same spots or are the objects the same
Population coding
We use populations of neurons to represent any stimulus or idea via patterns of fired neurons
Identification
The ability to recognize what a stimulus is
Localization
The ability to determine physical position or spatial location of a stimulus
Patient A.H.
○ Modality specific impairment (visual)
○ Had trouble identifying where an object is based on vision alone, but could locate objects based on audio and/or touch
Modality Specific Impairment
Problems specific to one sense or area of the brain (ex. vision but not hearing)
