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

Home , Pacinian corpuscle, Receptor potential

Introduction to Sensory Systems

Sue Keirstead, Ph.D. Assistant Professor Dept. of Integrative Biology and Physiology Stem Cell Institute

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

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

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

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

[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)

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

Receptive field of a somatic sensory neuron

Skin

Somatic sensory neuron (aka primary sensory neuron)

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

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