Sensory Physiology. Concepts To Understand Receptor Potential Amplitude Coding Frequency Coding...
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Transcript of Sensory Physiology. Concepts To Understand Receptor Potential Amplitude Coding Frequency Coding...
Sensory Physiology
Concepts To Understand
Receptor PotentialAmplitude CodingFrequency Coding
Activation/InactivationNeural Adaptation
Synaptic DepressionSynaptic Depression
Receptive Field Primary: Always OnSecondary:Center:On/Surround:OffLateral Inhibition
2-point DiscriminationSharpening Receptive Field
Classification of Sensory Receptors
• Nomenclature based on sensory stimulus source
• Exteroreceptor
• Interoreceptor
• Propioceptive receptor
• Nomenclature based on type of sensory stimulus
• 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 responseto the Sensory stimulus
Leads to an action potentialin 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 PotentialAmplitude CodingFrequency Coding
Activation/InactivationNeural Adaptation
Synaptic DepressionSynaptic Depression
Receptive Field Primary: Always OnSecondary:Center:On/Surround:OffLateral Inhibition
2-point DiscriminationSharpening Receptive Field
Receptive Field:Portion of skin that can elicita response in a single neuron with sensitivity tothat particular sensory modality
Two Point Discrimination
Lateral Inhibition
Interneurons inhibit adjacent 2nd neurons
Refine receptive fieldsOf 2nd neurons by Decreasing receptiveField of 2nd neuron
Lead to increaseddiscrimination of sensory stimulus at next level
Occurs at each Ascending level of thepathway
Increased Information Input
2nd Sensory NeuronsCan be influenced byInput outside the receptiveField for their primaryReceptor neurons by synapticConnection from interneuronsActivated by adjacent primaryReceptor neurons.
2nd sensory neurons haveSmaller more refinedReceptive fields than thePrimary sensory receptorneuron
Somatosensory neuron in somatosensory cortex hasa more refined receptive field area than the primary sensory receptor neuron in the peripherythat responds to the stimuls.
Cortical somatosensory neuronsalso have more complex and selective stimulus requirements for responses, such as a specific of movement
Direction SensitiveCoritical Neurons in S1 somatosensorycortex
Inhibitory InterneuronHas only 1 synapseOn adjacent neuron