Part 2: Dr. Steve I. Perlmutter

Touch

Temperature & Pain

Proprioception

Sensorimotor Neurophysiology of Active Sensing

Somatosensory SystemSomatosensory SystemReceptor Function Spinal Cord Circuitry

Signaling in the Nervous System: Action Potential Generation

Ionic gradients generate a voltage across the membranes of neurons; membrane voltage is regulated by ionic channels and pumps

The action potential is a brief, all-or-none electrical depolarization of the neuron membrane

The rate and timing of action potentials convey information from one neuron to another.

In primary sensory neurons, action potentials are elicitedby transduction of a sensory stimulus into a receptor potential

Receptorpotential

Spikegeneration

Spikeconduction

In mechanoreceptors, mechanical energy causes ionic channels in the cell’s membrane to open, leading to a change in membrane voltage, the receptor potential

Touch receptors endings in the skin

Hair follicleReceptor(RA, SA)

Merkel receptors

Pacinian corpuscle

Touch acuity: receptive field size of receptors

Ruffini corpuscle

Meissner corpuscle

Meissner corpuscles

Merkel disk receptors

Johansson & Valbo

Touch acuity: receptor density

Touch acuity: 2-point discrimination

Temporal resolution of touch: slowly vs. rapidly adapting receptors

Meissner corpuscle

Merkel disk receptor

Ruffini ending

Torebjork & Ochoa

Touch sensitivity: response to stimulus intensity

Activ

ation

Thr

esho

ld

Touch sensitivity: frequency response of receptors

Monkey hand Human psychophysics

Touch sensitivity: receptor firing vs. perception

Axon branches toother CNS regions

Primary sensory afferents enter the spinal cord and project to 3 main targets

Information is transmitted from the primary sensory afferent to other neurons in the CNS at synapses.

First main target for somatosensory information is other neurons in the spinal cord