PNB 2XB3Anatomy of touch

1. Title slide

http://www.microscopyu.com/galleries/confocal/index.html

Recall,

2. Neuroscience rules (pt.2)

3. Neuroscience rules (pt.2)

4. Definition - mechanotransduction

Mechanotransduction is the process whereby mechanical energy (i.e. tissue deformation) gets converted into a voltage change in sensory afferent neurons...

Pacinian Corpuscle

Stimulus

5. Definition - receptive field

A receptive field is the region of the physical world that iscapable of driving a response in a particular neuron...

Recording Electrode

GND

Microneurography

Behaviour – “2 points vs 1 point?”

6. Definition - adaptation

Adaptation is the reduction of the neural response to a sustained stimulus...

7. Definition - adaptation

Adaptation is the reduction of the neural response to a sustained stimulus...

Benefits of Adaptation:

1) Adaptation helps us ignore constant, innocuous stimuli, reducing distraction.

2) Adaptation helps to avoid saturation of neural firing rates, allowing us to detect changes in stimulus intensity over a larger range of intensities.

Cost of adaptation: We cannot unambiguously infer absolute stimulus intensity!

8. Definition - adaptation

Adaptation is the reduction of the neural response to a sustained stimulus...

Benefits of Adaptation:

1) Adaptation helps us ignore constant, innocuous stimuli, reducing distraction.

2) Adaptation helps to avoid saturation of neural firing rates, allowing us to detect changes in stimulus intensity over a larger range of intensities.

Cost of adaptation: We cannot unambiguously infer absolute stimulus intensity!

Was it intensity B or C???

9. Definition - inference

The brain in a vat...

Source Wikipedia

10. Brief overview of the somatosensory system

Pain & Temperature (Aδ & C Fibers)

Spinothalamic Tract (STT) a.k.a. Anterolateral System

Nociceptors Thermoreceptors

FineTouch (Aβ Fibers)

Dorsal Column-Medial Lemniscus (DCML) Pathway

Cutaneous Mechanoreceptors

Proprioception (1a Fibers)

DCML Pathway

Proprioceptors

- Edges, curvature, & texture- Motion across the skin- Feeling through objects- Skin stretch

- Tissue damaging - Warm/Cold - Body position

*see motor system lectureTODAY

Parallel Pathways

11. Four different classes of cutaneous mechanoreceptors

Slowly-Adapting Type 1 (Merkel Cell)

Dorsal Column-Medial Lemniscus (DCML) Pathway

Edges, curvature, & texture Skin stretch Motion across the skin Feeling through objects & grip control

Rapidly-Adapting Type 2 (Pacinian Corpuscle)

Slowly-Adapting Type 2 (Ruffini Ending)

Rapidly-Adapting Type 1(Meissner's Corpuscles)

12. Four different classes of cutaneous mechanoreceptors

Glabrous “hair-less” skin

13. Four different classes of cutaneous mechanoreceptors

Slowly-Adapting Type 1 (Merkel Cell)

Edges, curvature, & texture

Merkel Cell - Slowly-Adapting Type 1 (SA1)

http://www.vetmed.vt.edu/education/curriculum/vm8054/labs/lab14/lab14.htm#

Keratinocytes

Merkel CellPost-synaptic

terminal

Aβ primary afferent fiber

?

14. Four different classes of cutaneous mechanoreceptors

Slowly-Adapting Type 1 (Merkel Cell)

Edges, curvature, & texture

Merkel Cell - Slowly-Adapting Type 1 (SA1)

Lumpkin & Caterina 2007

Keratinocytes

Merkel Cell

Post-synaptic terminal

Aβ primary afferent fiber

?

15. Four different classes of cutaneous mechanoreceptors

Slowly-Adapting Type 1 (Merkel Cell)

Edges, curvature, & texture

Merkel Cell - Slowly-Adapting Type 1 (SA1)

Guinard et al 1998

Red: anti-neurofilament 200 (labels the nerve terminal)Green: anti-cytokeratin 20 (labels Merkel cells)

10 μm

16. Four different classes of cutaneous mechanoreceptors

Slowly-Adapting Type 2 (Ruffini Endings)

Skin stretch

Ruffini Ending - Slowly-Adapting Type 2 (SA2)

10 μm

Source: Wikipedia (originally from Gray's Anatomy by Henry Gray, 1858)

SA1

SA2

Time

*NOT IN NON-HUMAN PRIMATES

17. Four different classes of cutaneous mechanoreceptors

Rapidly-Adapting Type 1(Meissner's Corpuscles) Motion across the skin & Grip control

Meissner's Corpuscle - Rapidly-Adapting Type 1 (RA1)

10 μm

Nolano et al 2003Red: anti-myelin basic protein (labels myelin)Green: anti-protein gene product (labels the nerve terminals)Blue: anti-ulex europaeus antibody-I (labels epidermis and vasculature)

Source: http://missinglink.ucsf.edu

18. Four different classes of cutaneous mechanoreceptors

Rapidly-Adapting Type 1(Meissner's Corpuscles) Motion across the skin & Grip control

Meissner's Corpuscle - Rapidly-Adapting Type 1 (RA1)

Macefield et al 1996

Load Force

Grip Force

RA1 Spike Train

RA1 Spike Train

Spinal reflex

SN

MN

19. Four different classes of cutaneous mechanoreceptors

Rapidly-Adapting Type 2 (Pacinian Corpuscles)

Feeling through objects

Pacinian Corpuscle - Rapidly-Adapting Type 2 (RA2)

10 μm

http://bcrc.bio.umass.edu/histology/?q=node/1165&size=_original

http://www.microscopyu.com/galleries/confocal/index.html

Mean mechanical threshold = 0.08 µm!Other afferents: SA1 = 30 µm, SA2 = 300 µm, & RA1 = 6 µm

20. Cutaneous afferent type summary

Summary

10 μm

21. Afferent fiber types

Different Conduction Velocities

10 μm

22. Dermatomes

Dermatomes Topography

23. DCML Pathway

24. DCML Pathway