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Pacinian Corpuscle: Area Deformed by a Vibration Nerve Ending Stimulus (Dendrite) Multilayered Capsule

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Introduction to Sensory Systems Sue Keirstead, Ph.D. Assistant Professor Dept. of Integrative Biology and Physiology Stem Cell Institute E-mail: [email protected] Tel: 612 626 2290 Class 8: Sensory Physiology (p. 280-292, Fig 7.1, 7.3, 7.7) 1. Describe the 4 attributes of a stimulus that the central nervous system can distinguish: 1. Modality (type of stimulus) 2. Location 3. Intensity 4. Duration 2. Describe two factors that encode stimulus intensity. 3. Explain how the gating (activation) characteristics of ion channels (e.g. mechanically gated versus chemically gated) in sensory receptors contributes to the modality of sensory receptors. 4. Explain the concept of receptive field. 5. Differentiate between sensory receptor activation and perception of a stimulus. 6. Draw a diagram illustrating lateral inhibition and explain how this process modifies sensory information. Understand how this process permits precise localization of boundaries (edges) of stimuli. 7. Differentiate between presynaptic inhibition and postsynaptic inhibition (Figure 7.14 & 7.31). Right side of brain Left side of brain Cerebral cortex Brain Thalamus Primary sensory neuron Spinal cord Sensory receptor Copyright © 2016 by John Wiley & Sons, Inc. All Cerebral cortex Interneuron Thalamus Interneuron 4 Integration of sensory Stimulus input in the CNS 1 Stimulation Sensory Axon of sensory of sensory receptor neuron receptor Graded potential Action potentials 2 Transduction 3 Generation of of the stimulus action potentials Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. Characteristics of a stimulus 1. Intensity 2. Duration 3. Modality: type of stimulus (pressure, temperature, touch, etc.) 4. Location Stimulus intensity is encoded in primary sensory neurons by AP frequency Class 7, LO7: Explain how a primary sensory neuron transmits information about the intensity of a stimulus to a secondary sensory neuron at a chemical synapse (i.e. explain temporal summation of postsynaptic potentials). Coding of stimulus intensity by the number of sensory receptors activated Sensory receptor Skin Initial Stronger stimulus stimulus Class 7, LO7: Explain how a primary sensory neuron transmits information about the intensity of a stimulus to a secondary sensory neuron at a chemical synapse (i.e. explain temporal summation of postsynaptic potentials). Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. Characteristics of a stimulus 1. Intensity 2. Duration 3. Modality: type of stimulus (pressure, temperature, touch, etc.) 4. Location Coding of stimulus duration (a) Slowly adapting receptor (b) Rapidly adapting receptor Action potentials potentials Action Action potentials potentials Action in sensory in sensory neuron in sensory in sensory neuron On response Off response Receptor potential Receptor potential Stimulus strength Stimulus Stimulus strength Stimulus On Off On Off Time Time Stimulus duration What happens when a train of multiple action potentials arrives at the axon terminal ? 1 Presynaptic axon Action potential (depolarization) 2+ 2 Ca Voltage-gated Ca2+ Ca2+ 2 channel Synaptic vesicles 8 Neurotransmitter reuptake or Synaptic cleft Ca2+ degradation Neurotransmitter 3 Na+ Neurotransmitter receptor: 4 Neurotransmitter binding site Ion channel 5 Postsynaptic 7 Local current flow Postsynaptic neuron 6 potential LO 2 Figure 7.26 Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. What happens when 2 APs arrive at a presynaptic axon terminal? [Ca2+] presyn axon term [NT] syn cleft Number receptors bound by NT + + MP in postsyn cell- 70 mV Class 7, LO7: Explain how a primary sensory neuron transmits information about the intensity of a stimulus to a secondary sensory neuron at a chemical synapse (i.e. explain temporal Time (msec) summation of postsynaptic potentials). Temporal summation of postsynaptic potentials (mV) Resting membrane potential millivolts in Membrane potential Stimulus 1 Stimulus 2 Time in milliseconds (msec) Figure 7.19 Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. Spatial Presynaptic Summation neuron 3 Presynaptic neuron 4 Presynaptic EPSP neuron 2 IPSP IPSP Inhibitory neurotransmitter Presynaptic EPSP EPSP Presynaptic neuron 1 neuron 5 Excitatory neurotransmitter Trigger zone (net summation of EPSPs and IPSPs determines whether an action potential is generated here) Figure 7.30 Copyright © 2019 by John Wiley & Sons, Inc. All rights reserved. The dendrites of neurons can be very extensive and hence a single neuron can receive many thousands of synaptic inputs. e.g. spinal motoneuron Soma Axon Characteristics of a stimulus 1. Intensity 2. Duration 3. Modality: type of stimulus (pressure, temperature, touch, etc.) 4. Location Pacinian corpuscle: Area deformed by a vibration Nerve ending stimulus (dendrite) Multilayered capsule Extracellular fluid Ca2+ Mechanically- Mechanically- Na+ Plasma gated cation gated cation membrane channel closed channel open Influx of Na+ and Ca2+ causes a depolarizing Cytosol receptor potential (a) A Pacinian corpuscle at rest (b) Transduction in a Pacinian corpuscle LO3: Define sensory transduction and explain the mechanism by which this process occurs (i.e. what type of channels mediate it, how are they activated, etc.) Copyright © 2019 by John Wiley & Sons, Inc. All rights reserved. Warm receptor Thermoreceptors have Cold receptor (free nerve endings) transduction channels that open (free nerve endings) when temperature increases or when temperature decreases. Extracellular Extracellular Ca2+ fluid + 2+ Na fluid Na+ Ca Warm Camphor Cold Menthol temperatures temperatures Plasma membrane Plasma membrane of warm receptor of cold receptor Sensory Sensory neuron neuron TRPV3 TRPM8 channel channel Influx of Na+ and Ca2+ Influx of Na+ and Ca2+ causes a depolarizing causes a depolarizing receptor potential receptor potential Cytosol Cytosol Copyright © 2019 by John Wiley & Sons, Inc. All rights reserved. Nociceptors have transduction Polymodal nociceptor channels that open when exposed to: (free nerve endings) - extreme heat - intense mechanical stimuli - chemicals released from cells that have been damaged ECF Na+ Extreme Ca2+ Capsaicin heat Plasma membrane of nociceptor Sensory TRPV1 neuron channel Influx of Na+ and Ca2+ causes a depolarizing ICF receptor potential Copyright © 2019 by John Wiley & Sons, Inc. All rights reserved. Free nerve endings Merkel disc (itch, pain, temperature, (slowly adapting, touch & pressure) tickle) Meissner corpuscle Skin: (rapidly adapting, touch & Epidermis low frequency vibration) Dermis Ruffini corpuscle (slowly adapting, stretch & pressure) Hair root plexus (rapidly adapting, touch, i.e. movement of hair) Pacinian corpuscle (rapidly adapting, high Subcutaneous layer frequency vibration) What determines the modality of a sensory receptor? 1. The type of transduction channels 2. The structure within which the channels are located (e.g. Paccinian corpuscle) 3. The location of the receptor in the tissue Characteristics of a stimulus 1. Intensity 2. Duration 3. Modality: type of stimulus (pressure, temperature, touch, etc.) 4. Location Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. Coding of stimulus location Receptive field of a somatic sensory neuron Skin Somatic sensory neuron (aka primary sensory neuron) Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. Stimulus Skin surface Receptive field Somatic sensory neuron No response Action potentials Sensory neurons with separate receptive fields Sensory neurons with overlapping receptive fields Stimulus Skin surface Receptive field Somatic sensory neuron Higher frequency of Lower frequency of action potentials action potentials The size and density of receptive fields influences spatial resolution (i.e. how readily two Caliper – stimuli can be two stimuli distinguished from one another) Receptive field Skin surface Somatic sensory neurons To higher Postsynaptic One point of touch parts of perceived neuron the brain (aka secondary sensory neuron The size and density of receptive fields influences resolution (precise localization) Caliper Receptive field Skin surface Somatic sensory neurons Two points of touch To higher parts perceived because each Postsynaptic of the brain activates a neuron (i.e. thalamus) stimulus separate sensory pathway Lateral inhibition enhances the difference between signal strength in neighboring secondary Skin sensory neurons Action potentials Enhances edges of stimulus. Sensory neurons Inhibitory (Primary interneurons sensory neurons) – – – – – Postsynaptic Presynaptic inhibition neurons (secondary sensory neurons) Cerebral cortex Third-order neuron Thalamus Second-order neuron Brain stem nuclei Brain stem First-order neuron Spinal nerve Spinal cord Sensory receptors Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. Perception involves many areas of the brain, including association cortices, limbic system, hippocampus (memory), etc. PRIMARY SOMATOSENSORY CORTEX (postcentral gyrus) SOMATOSENSORY ASSOCIATION AREA COMMON INTEGRATIVE AREA VISUAL ASSOCIATION AREA PRIMARY VISUAL CORTEX PRIMARY AUDITORY CORTEX AUDITORY ASSOCIATION AREA GUSTATORY CORTEX Insula OLFACTORY CORTEX Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. .
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