1. Part 2: Dr. Steve I. Perlmutter Touch Temperature & Pain Proprioception Sensorimotor Neurophysiology of Active Sensing Somatosensory System Receptor Function Spinal Cord Circuitry

2. Signaling in the Nervous System: Action Potential Generation

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

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

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

6. In primary sensory neurons, action potentials are elicited by transduction of a sensory stimulus into a receptor potential Receptor potential Spike generation Spike conduction

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

8. Touch receptors endings in the skin Hair follicle Receptor (RA, SA)

9. Merkel receptors Pacinian corpuscle Touch acuity : receptive field size of receptors Ruffini corpuscle Meissner corpuscle

10. Meissner corpuscles Merkel disk receptors Johansson & Valbo Touch acuity: receptor density

11. Touch acuity: 2-point discrimination

12. Temporal resolution of touch : slowly vs. rapidly adapting receptors

13. Meissner corpuscle Merkel disk receptor Ruffini ending Torebjork & Ochoa

14. Touch sensitivity: response to stimulus intensity

15. Activation Threshold Touch sensitivity: frequency response of receptors

16. Monkey hand Human psychophysics Touch sensitivity: receptor firing vs. perception

17. Axon branches to other CNS regions Primary sensory afferents enter the spinal cord and project to 3 main targets

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

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