Sensory Physiology
Concepts To Understand
Receptor Potential
Amplitude Coding
Frequency Coding
Activation/Inactivation
Neural Adaptation
Synaptic Depression
Synaptic Depression
Receptive Field
Primary: Always On
Secondary:Center:On/Surround:Off
Lateral Inhibition
2-point Discrimination
Sharpening Receptive Field
Classification of Sensory Receptors
• Nomenclature based on • Nomenclature based on
sensory stimulus source
type of sensory stimulus
• Exteroreceptor
• Interoreceptor
• Propioceptive receptor
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•
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Mechanoreceptor
Chemoreceptor
Thermoreceptor
Nocireceptor
Photoreceptor
Electroreceptor
How to Code the Stimulus
Strength
• Amplitude Coding
• Frequency Coding
• Population Coding
– How many neurons responded to stimulus?
• Sensitivity of Neurons
– Did you activate neurons with low as well as
high threshold for activation?
Receptor Potential:
the neuron’s electrical response
to the Sensory stimulus
Leads to an action potential
in the primary or 2nd
sensory neuron
Amplitude Coding
• The amplitude of the receptor potential
increases as the sensory input increases
• It modifies the firing rate of action potential
• The size of the receptor potential gives
information about the strength of the
sensory stimulus.
Action Potential Firing Rate
• The steady state rate of action potential
firing can increase or decrease in frequency
known as “On” pathway and
“Off” pathway.
• Secondary neurons can receive inputs from
both “on” and “off” neurons and that leads
to more sensitivity.
Frequency Coding
• Firing rate of
action potential
encodes the
strength of the
stimulus.
Concepts To Understand
Receptor Potential
Amplitude Coding
Frequency Coding
Activation/Inactivation
Neural Adaptation
Synaptic Depression
Synaptic Depression
Receptive Field
Primary: Always On
Secondary:Center:On/Surround:Off
Lateral Inhibition
2-point Discrimination
Sharpening Receptive Field
Two Point Discrimination
Receptive Field:
Portion of skin
that can elicit
a response in a
single neuron
with sensitivity to
that particular
sensory modality
Lateral Inhibition
Interneurons
inhibit adjacent 2nd neurons
Refine receptive fields
Of 2nd neurons by
Decreasing receptive
Field of 2nd neuron
Lead to increased
discrimination of sensory
stimulus at next level
Occurs at each
Ascending level of the
pathway
Increased Information Input
2nd Sensory Neurons
Can be influenced by
Input outside the receptive
Field for their primary
Receptor neurons by synaptic
Connection from interneurons
Activated by adjacent primary
Receptor neurons.
2nd sensory neurons have
Smaller more refined
Receptive fields than the
Primary sensory receptor
neuron
Somatosensory neuron in
somatosensory cortex has
a more refined receptive field
area than the primary sensory
receptor neuron in the periphery
that responds to the stimuls.
Cortical somatosensory neurons
also have more complex and
selective stimulus requirements for
responses, such as a specific of
movement
Direction Sensitive
Coritical Neurons in
S1 somatosensory
cortex
Inhibitory Interneuron
Has only 1 synapse
On adjacent neuron