Final Material Prep Flashcards
What is systems neuroscience?
The science of networks or circuits of neurons having specific functions
What does firing rate code for?
The firing rate codes for the strength of the sensory signal (rate code)
Synchrony code is responsible for coordinated activity
Electroencephalography (EEG) is a synchrony code **refer to lecture
What does the amplitude of depolarization code for?
The amplitude of depolarization codes for the strength of the sensory signal
- The more depolarization, the more transmitter is released
Central Pathway is responsible for:
Sensory signals transmitted from peripheral neurons to “central” neurons in the brain
Sensory Receptor Cells:
- Modality specific
- Transduce energy of different forms to electrical activity so that can be passed onto other neurons
- Even within a single sensory system, different populations of neurons are specialized to detect different features of the same input
Receptive field is….
The location in the environment (or the surface of the body) from which the appropriate stimulus will change that cell’s activity
What is shown in a topographic map?
- Neurons positioned side by side in one region project neurons so they are positioned in the next region
- Orderly representation of the sensory space in the nervous system
Why does light energy undergo phototransduction?
Light energy undergoes phototransduction to trigger neural activities
Pupil
The opening that allows light to enter the eye
- Light goes into the retina
Iris
Surrounds the pupil
- Responsible for eye color
- Contains muscles that can change the size of the pupil (controls the amount of light reaching the eye)
Cornea
Covers the pupil and iris
- Responsible for light refraction
Sclera
Continuous with the cornea
- “White of the eye”; is a tough outer wall
Extraocular muscles
Move the eye
Where does phototransduction occur?
In the retina
What are the five major cell types in the retina?
- Retinal ganglion cells
- Amacrine cells
- Bipolar cells
- Horizontal cells
- Photoreceptor cells
Retinal information processing
What is the process of retinal information processing in the linear (direct) pathway?
Photoreceptor cells -> bipolar cells -> retinal ganglion cells -> brain
Why are photoreceptor cells unique?
Photoreceptor cells are the only cell type directly affected by light
Why are retinal ganglion cells unique?
Retinal ganglion cells are the retina’s only output cell type
What is the process of retinal information processing in the lateral (indirect) pathway?
- Bipolar and photoreceptor cells target horizontal cells (and vice versa)
- Retinal ganglion cells and bipolar cells target amacrine cells (and vice versa)
What are the two types of photoreceptor cells?
- Rods: ~120 million
- high sensitivity to light
- low acuity vision
- achromatic
- rare in fovea - Cones: ~ 6 million
- high acuity vision
- low sensitivity to light
- color sensitive (red, blue, green)
- concentrated in fovea
Cones help detect light of specific wavelengths
Where is the fovea located?
The fovea is the center of the visual field
What is the process of light reaching photoreceptor cells?
Light directly reaches photoreceptor cells at the fovea
The fovea provides color & high resolution vision
Where are photoreceptor cells depolarized?
Photoreceptor cells are depolarized in the dark
What is the process of depolarizing a photoreceptor cell?
- Intracellular cyclic guanosine monophosphate (cGMP) binds to cGMP gated Na+ channel
- cGMP keeps the channel open and allows Na+ influx
- Photoreceptor cell membrane is kept depolarized (-30 mV; DARK CURRENT)
- Neuro transmitter glutamate is constantly released at the terminal
Where are photoreceptor cells hyperpolarized?
Photoreceptor cells are hyperpolarized in the light
How are photoreceptor cells hyperpolarized?
- Light stimulation reduces cGMP
- Na+ channel closes which allows membrane hyperpolarization (-65 mV)
- Glutame release stops at the terminal
What is used by light to decrease cGMP?
Light decreases cGMP through transducin (g-protein)
Light intensity gradually changes membrane potential and glutamate release **
Glutamate release increases the darker it is
How is a visual image mapped onto the retina?
Cells in different locations in the retina have receptive fields in different locations in the visual field
The photoreceptor receptive field:
1. Is circular
2. The receptive field of a given photoreceptor is determined by its location in the retina
3. Photoreceptors respond to changes of light intensity in its receptive field
What is a receptive field?
In the visual system, a neuron’s receptive field is the location in the visual field (sensory space) from which light changes the cell’s activity
- All cells in the visual system have receptive fields
What types of cells are activated by signals from photoreceptor cells?
- Retinal ganglion cells (RGCs)
- Amacrine cells
- Bipolar cells
- Horizontal cells
Receptive field size differences in distinct RGC types:
- RGCs in peripheral: convergence of synaptic input = large receptive field= M (magno) type
- RGCs in central: no or less convergence of synaptic input = small receptive field= P (parvo) type
Divergence of single photoreceptor cells onto multiple RGCs leads to…?
Overlapping receptive fields
Neighboring RG cells have overlapping receptive fields
What are the 2 different glutamate receptors in bipolar cells?
- Inhibitory
- Excitatory
What is the process of using an inhibitory glutamate receptor process?
- Glutamate release from pre-synapse in PR cell
- Received by inhibitory receptor at post-synapse in BP cell
- Decrease membrane potential in BP cell
- No neurotransmitter release
In what order do the cells show up in retinal structures?
Retinal ganglion cells, bipolar cells, photoreceptor cells
In the visual system, what is the difference between a neuron’s receptive and visual fields?
A neuron’s receptive field is the location inside of the visual field (sensory space in which light changes the cell’s activity
Light on in an ON center RG cell… Light on in an OFF center RG cell…
Increases APs; decreases APs
The receptive field is comprised of the center + surround