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