1 Classes of Receptors Classes of Receptors Skin Mechanoreceptors - - PDF document

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Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Sensing

Tactile Kinesthetic

(position / force) B R A I L L E

Manipulation HAPTICS

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Haptic Perception & Human Response to Vibrations Haptic Perception & Human Response to Vibrations

Outline:

• 1. Neural Coding of Touch Primitives
• 2. Functions of Peripheral Receptors

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

• 1. Neural Coding of Touch Primitives
• 1. Neural Coding of Touch Primitives
• Touch Receptors

– Mechanoreceptors and their Function – Other skin receptors: thermal, pain – Kinesthetic receptors

• Pathways from receptors to brain

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Touch Receptors Touch Receptors

• Touch sensations are mediated by receptors

that respond to pressure, vibration, and heat flow.

• The receptors are found in two regions:
• Within skin: cutaneous sensing

pressure, temperature, pain

• Beneath skin in muscles, tendons, joints:

kinesthetic sensing

limb position and movement

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Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Classes of Receptors Classes of Receptors

• Receptors that respond to pressure and vibration are called

mechanoreceptors

• Mechanoreceptors are found in skin (cutaneous) and muscles,

tendons, and joints (kinesthesis)

• The skin also includes other receptors

– that signal skin warming and cooling (thermo-receptors) – that signal pain (nociceptors)

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Skin Mechanoreceptors have specialized endings Skin Mechanoreceptors have specialized endings

Johannson & Valbo, 1983

Meissner Merkel Ruffini Pacinian Epidermis Dermis Subcutis

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Functional characteristics of Skin Mechanoreceptors: Receptive field size (I = small, II = large) and adaptation rate (FA = fast adapting, SA = slow adapting) Functional characteristics of Skin Mechanoreceptors: Receptive field size (I = small, II = large) and adaptation rate (FA = fast adapting, SA = slow adapting)

Kandel et. al., 2000

Meissner’s Merkel Pacinian Ruffini Corpuscle Cell Complex Corpuscle Ending Receptors Receptive Field Intensity and Time Course of Neural Signal (adaptation)

Neural Spike train Stimulus

FA I SA I FA II SA II

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Distribution of Mechanoreceptors on the Palm: Receptors with small receptive fields are densely packed on fingertips. Distribution of Mechanoreceptors on the Palm: Receptors with small receptive fields are densely packed on fingertips.

Result: ~.5 mm 2-point discrimination

• n fingertip

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Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Frequency Sensitivity: One-channel- per-mechanoreceptor model Frequency Sensitivity: One-channel- per-mechanoreceptor model

Amplitude required for threshold response at given frequency (dB relative to 1 m)

Bolanowski et al., 1988

SA I SA II FA I FA II (PC)

Average data Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Thermo-Receptors Thermo-Receptors

Thermo-receptors lack specialized endings; respond to temperature change. Two populations of nerve fibers: warm and cold

Kenshalo, 1976

Normal Body temp

Cold fibers Warm fibers

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

The brain: Primary and Secondary Somatosensory Cortex The brain: Primary and Secondary Somatosensory Cortex

SI includes Brodmann areas: 3a: Muscle 3b: Skin (SA and FA) 1: Skin (FA) 2: Pressure, joints SI projects to SII, 5, 7

SI SII

Central Sulcus SI Areas 5 & 7

SII

Lateral Sulcus Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Somatosensory “Homunculus” in SI results from somatotopic mapping* Somatosensory “Homunculus” in SI results from somatotopic mapping*

*Adjacent on skin Adjacent in SI There are several such maps in SI and SII.

Penfield & Rasmussan, 1950

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Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Somatosensory areas in brain are plastic:

Re-assignment of receptive fields after amputation of a digit

Somatosensory areas in brain are plastic:

Re-assignment of receptive fields after amputation of a digit

Areas in SI that

• nce responded

to 3rd fingertip are now activated by finger 2 and 4, plus base of 3

Merzenich et al., 1984

Amputation point

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Cortical plasticity causes phantom limb pain Cortical plasticity causes phantom limb pain

Thumb Index finger 5th digit Stimulating face and arm activates cortical areas previously responsive to fingers, now taken over by face and arm.

face arm

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

• 2. Functions of peripheral receptors
• 2. Functions of peripheral receptors
• Slowly adapting cutaneous mechanoreceptors

provide array (tactile) sensing.

• Fast adapting cutaneous receptors signal

pressure changes on the skin.

• Kinesthetic mechanoreceptors provide a sense
• f limb position.
• Therefore, the mechanoreceptor populations

support different human abilities.

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Grasping is supported by FAI mechanoreceptors that detect incipient slip Grasping is supported by FAI mechanoreceptors that detect incipient slip

FAIs fire under near-slip Grasp, lift… Return

Load Force N Grip Force N Position mm Grip: Load ratio

Time

Load Force N Grip Force N Position mm Force Ratio FA I SA I FA II SA II Slip threshold Johansson & Westling, 1984; Westling, 1986

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Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Tactile Pattern Perception is based on SAI mechanoreceptors Tactile Pattern Perception is based on SAI mechanoreceptors

Input pattern R e s p

• n

s e

Phillips, Johansson & Johnson, 1990

Spatial plot of the response of a skin mechanoreceptor to a Braille pattern swept through its receptive field: Each tick mark is a neural impulse given contact from that stimulus location.

Pattern preservation SA I FA I SA II FA II

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Curvature perception also reflects SA I responses Curvature perception also reflects SA I responses

• 4 -2 0 2 4

Distance of receptive field from center of indentation (mm) Mean SA I Response Data are shown for 7 curves, ranging from radius zero to radius 1.44 mm

Goodwin et al., 1995 Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

PC receptors (FA II) signal causes of deep vibrations PC receptors (FA II) signal causes of deep vibrations

 Transient vibrations from contact  Micron-element textural variations, as in this stimulus

Only Pacinian Corpuscles respond continuously to the textured portion of a half-textured plate with ht. 1 m

Srinivasan, Whitehouse, & LaMotte, 1990

Stimulus plate

Receptor Responses Therefore, PCs underlie roughness percept at micro-scale.

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Impact on functions of cutaneous receptors when skin is covered with a rigid sheath Impact on functions of cutaneous receptors when skin is covered with a rigid sheath

Decrements in spatial resolution, differential force sensing, pattern perception -- but vibration (sensed by deeper PCs) remains essentially intact

Lederman & Klatzky, 1999

This simulates some force-feedback environments.