PHYS20008 Lecture Notes - Lecture 8: Olfactory Bulb, Receptive Field, Sensory Neuron
21 Jun 2018
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Lecture 8: Vision
Sensory coding
Sensory coding is a type of information processing that occurs in nervous systems and can
be thought of as four separate yet related phenomena.
1) Reception, whereby specialised sensory receptors absorb physical energy from
sensory stimuli
2) Transduction, which involves the conversion of this physical energy into electrical
energy in the form of neuronal firing
3) Coding, which is the correspondence between specific parameters of the stimulus
and specific parameters of the neuronal firing that represents it
4) Awareness, the possible conscious perception of encoded sensory stimuli
*Proprioception is the understanding where we are in space
Reception:
There are 3 main types of receptors:
1) Simple receptors: Neurons with free nerve endings and unmyelinated axons (E.g.
mechanoreceptors)
2) Complex neural receptors: Have nerve endings enclosed in connective tissue
capsules and have unmyelinated axons (e.g. Chemoreceptors)
3) Most special sense receptors: Cells that release neurotransmitters onto sensory
neurons, initiating an action potential. These also have unmyelinated axons (e.g.
Photoreceptors)
There are 4 classes of receptors:
1) Chemoreceptors: Chemical changes
2) Mechanoreceptors: Mechanial changes
3) Photoreceptors: Specialised cells
4) Thermoreceptors: Temperature changes
Receptive fields of sensory neurons:
For a given sensory receptor cell or neuron, the receptive field is that region of sensory
space within which adequate stimulus will evoke a change in the cell’s activity. Additionally,
the more receptors per receptive field, the better the acuity.
If 3 primary sensory neurons converge on one secondary sensory neuron, the
receptive fields of the neurons will have overlapped and the secondary sensory
neuron will have a large receptive field.
Convergence creates receptive fields that lower resolution
Some systems don’t need as high of a resolution because it is a waste of ATP and neural
activity (e.g. locating an itch on your back vs. locating pain on your body)
Sensory pathways in the brain:
1) Olfactory pathways: From the nose through the olfactory bulb to the olfactory
cortex
2) Thalamus: The ‘sensory relay system’ modifying and relaying information to cortical
centres (All sense except for sight (cell receptors) are processed here and then sent
to the cortex).
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
*proprioception is the understanding where we are in space. There are 4 classes of receptors: chemoreceptors: chemical changes, mechanoreceptors: mechanial changes, photoreceptors: specialised cells, thermoreceptors: temperature changes. For a given sensory receptor cell or neuron, the receptive field is that region of sensory space within which adequate stimulus will evoke a change in the cell"s activity. Additionally, the more receptors per receptive field, the better the acuity. If 3 primary sensory neurons converge on one secondary sensory neuron, the receptive fields of the neurons will have overlapped and the secondary sensory neuron will have a large receptive field. Some systems don"t need as high of a resolution because it is a waste of atp and neural activity (e. g. locating an itch on your back vs. locating pain on your body) *the minimum stimulus required to activate a sensory receptor is its threshold.
