Mechanoreception

Sensory Receptor

An excitable cell sensitve to a form of physical energy

Glabrous Skin

Smooth skin found on the palm of the hands and soles of the feet

Sensory Coding

Representation of stimulus energy in terms of action potentials

How do local anaesthetics work

Block sodium channels in mechanoreceptors

Chalfie et al (1985)

Used a laser to destroy certain nerve cells in C.Elegans

Then tested their touch behavior- if it still had an escape response- cell wasn’t involved, if they didnt, the cell was

identified candidate mechanoreceptors

O’Hagan et al

Recorded from touch receptor neurons

Measured receptor potential following touch with stimulus probe

Response was very quick- therefore a direct action of deformation of cell membrane

Patapoutian

Discoved mechanisms of sensory transduction in mammals

Coste et al (2010)

Did whole cell electrophysiology- find cells that responded electricly to touch

Found cells that generated a mechanically activated current

Did DNA microarray to find transmembane protein genes

Used siRNA knock down to stop expression of particular proteins

Interfering with Piezo1 stopped transduction current.

Pieozol 2

Expressed in mechanoreceptors

Heterologous expression

Expressing a protein in a cell where its not normally expressed

Tests to ensure piezo2 was responsible for mechanotransudcution

Heterologous expression of piezo 2- cells began to respond to touch

Piezo2 conditional knock out mouse- Mouse would withdraw far less, suggesting dampened mechanotransduction

Lam et al (2023)

Is piezo2 needed for regular sexual function

In piezo2 knockout mice- genitals lost sensitivity

Reduced mating seen in the mouse

How doe mechanoreceptor axons of the body enter the spinal cord

Dorsal Root Ganglion

How doe mechanoreceptor axons of the face enter the spinal cord

Trigeminal region

4 types of primary afferent fibre

Myelinated- A alpha, A beta, A delta

Unmyelinated- C

Adrian (1926)

First to manage electrophysiological recording of single neuron

Low threshold mechanoreceptors

Respond to gentle touch

A alpha and A beta types

High threshold mechanoreceptors

Respond to harmful or potentially harmful stimuli

A delta or C fibres

Thermoreceptors

Respond to cooling or heating of the skin

A delta or C fibres

Four kinds of mechanoreceptor located in glabrous skin

FA I, FA II, SA I, SA II

Receptive field of a mechanosensative cells

The area of skin that when stimulated increases firing rate of the neuron

Slowly adapting cell

Respond throughout the stimulus

Rapidly adapting cells

Only respond at the beginning and end of a stimulus

Types of nerve ending close to skin

Meissner Corpuscle, Merkel Disk

Deep Nerve Endings

Pacinian Corpsule

What type of mechanoreceptor are merkel cells

SA1 type

What type of mechanoreceptor are meissner’s corpuscle

FA1 type

What type of mechanoreceptor are pacinian corpuscle

FA II type

What structure is innervated by SA II fibres

Unknown

Johnson and Phillips (1981)

Blindfolded participants given surface with either horizontal or vertical grating

As the ridges got closer to one another, it became harder to detect whether they had the vertical or horizontal

1mm- discrimination theshold- where 75% of people got it right

Phillips et al (1990)

Braille on a spinning wheel- ppts had to feel and be able to sense spacial form

Very indistinct neural images from cells with large receptive fields

FA1 neural images were a bit more distinct, SA1 were the most

Maricich et al (2009)

Made knock-out mice that lack Merkel Cells- evident by lacking keratin 8

Put mice on cage with floor that was half rough and half smooth

Female KO mice showed no preference for either (equal time on both) whereas WT prefered rough

Sine Wave

Represent vibration

Mountcastle et al 1972

Determined what vibration amplitude we could detect

Determined a detection threshold (at which people detected it 50%) of 7 microns

Neuronal detection threshold

Amplitude of a sine wave where you get an action potential for every cycle of the wave

Johnsan and Westling

Recorded different cell type activation in fine grip

FA were active when item was slipping- role in fine grip control