Class Notes (839,469)
Canada (511,354)
Neuroscience (303)
NROC34H3 (27)

NROC34 - Lec 8 - Olfaction in Locusts.doc

8 Pages

Course Code
Andrew Mason

This preview shows pages 1,2 and half of page 3. Sign up to view the full 8 pages of the document.
Lec 8: Olfaction in Locusts Sensory Systems: o Stimulus characteristics Predictability (how does this allow certain sensory coding strategies to identify the info) Dimensionality (how many variables are needed to define a stimulus) o Sensory sys Topographical org Response properties of neurons o Neural coding o Olfaction Hearing and Sound o Sound = temporal pattern of medium mvt = propagating waves of pressure in medium o Defined as: 1) amplitude vs. time 2) freq of fluctuations vs. relative power o Predictable propagations o Sound = sinusoid plots of propagation thru time o Another predictable property of sound = as sound waves propagate thru space, theres predictable drop-off in amplitude of wave o Therefore, sound is defineable w/ few variables = freq, phase, amplitude o Low dimensionality o Stimulus dimensions reflected in structure of auditory sys: Tonotopic array of receptors (freq) Sensory map Anatomical location related to freq sensitivity = orderly map of sound freq in peripheral aud sys Stimulus amplitude encoded by response amplitude Sensory code = rate code = rate of AP generation is proportional to intensity/loudness of sound Stimulus amp changes and therefore neuronal response amplitude also changes = more/less spikes or earlier/later spikes Vision and Light o Has few more variables than sound Luminance Color Spatial arrangement (=pattern) Temporal pattern (=motion or temporal changes in color/luminance that arent due to motion) Predictable propagation o Sensory mapes: Retinotopy = physical neuron arrangement that is related to spatial/fxnl arrangement of enviro Visual info preserved thru several layers of visual sys in flys = retina lamina medulla Neural Coding: o Rate coding: Stimulus intensity is represented in spike rate = requires that spike rate b measured over some time interval = look at some window of time and count how many spikes in that window For neurons, if the stimulus intensity is below threshold = nothing happens If above threshold = get graded response with increasing spike rate Above some level, neurons arent capable of generating APs any more quickly b/c of refractory o Temporal coding Alternative to rate coding Timing of individual spikes may signify stimulus info Rather than counting throughout some interval to obtain a rate, occurrences of spikes are meaningful in real time Every AP says something about the stimulus and its when those Aps occur individually that is meaningful The 2 neural coding ways, rate code and temporal code, is really a question of time-scales Difference btn temporal and rate coding is how big the time interval is NS needs to avg activity over longer/shorter periods of time to generate meaningful responses Dimensionality: o Set of all possible aud or visual stimuli is huge But only few parameters are needed to define an aud or visual stimulus because not all stimuli are meaningful (discriminable) o Structured stimuli o Random stimuli A lot of variable stimuli that isnt informative and not encoded in a sense o Dimensionality: Spatial location = 3 dimensions An n*n pixel visual array has n squared dimensions (intensity of each pixel) Visual sys reduces this complexity by processing higher- order features; they dont encode visual stimuli as a literal map of the activity of each receptor in retina Look at things like spatial/temporal freq, contrast, luminance (edges, motion patterns, etc;) OLFACTION: Intensities in odor are possible BUT o Diff odor substances = not clear how to define variation in odor identityo Hard to define simple set of parameters that describes the range of variation in chemical structure or molecular shape Olfaction: o High dimensionality o No clear parameters to describe btn diff odors o But olf sys highly structures and seems to be related to odor stimuli o This commonality in olf sys seems to be convergent rather than due to a common ancestor Similarities in the transduction mechanism and in early stages of processing in neural pathway Molluscs, crustaceans, insects, fish, amphibians, mammals Invert and vert = similar Propagation and Spatial patterns o Turbulent flow If chem in air and there is turbulent flow = complex spatial patterns of the distribution of the stimuli Hard to follow altho there are some animals that navigate by following odors o Undisturbed diffusion May have orderly gradient of intensity Olfactory sys in arthropods: o Chemosensory regions of antenna olf sensilla multiple ORCs w/ diff odorant specificities ORC dendrite stuck in medium in which odorant mocs dissolve and then bind to membrane surface to initiate a re
More Less
Unlock Document

Only pages 1,2 and half of page 3 are available for preview. Some parts have been intentionally blurred.

Unlock Document
You're Reading a Preview

Unlock to view full version

Unlock Document

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.