Somatosensory System Pain Systems Systems Neuroscience 2019 Daniel J Felleman Figure 9.1 Somatosensory afferents convey information from the skin surface to central circuits Figure 9.2 Transduction in a mechanosensory afferent (a Pacinian corpuscle)
Non-encapsulated; with and without accessory structures: Free nerve ending for pain, touch and temperature; accessory- Associated for ending at hair roots and Merkel endings (slowly adapting?). Encapsulated: Pacinian; vibration (very RA), Meissner-fine touch (RA), Ruffini for pressure (SA)
Figure 9.3 Receptive fields and two-point discrimination threshold Figure 9.8 Schematic representation of the main mechanosensory pathways Figure 9.9 Proprioceptive pathways for the upper and lower body Figure 9.10 Somatic sensory portions of the thalamus and their cortical targets in postcentral gyrus Figure 9.13 Neurons in the primary somatosensory cortex form functionally distinct columns Figure 9.12 Connections within the somatosensory cortex establish functional hierarchies Figure 10.1 Experimental demonstration that nociception involves specialized neurons (Part 2)
Figure 10.2 Pain can be separated into first (sharp) and second (duller, burning) pain Box 10A Capsaicin Figure 10.3 The anterolateral system Figure 10.4 The anterolateral and dorsal column-medial leminiscal systems cross the midline at different sites Figure 10.5 The anterolateral system sends information to different parts of the brainstem/forebrain
Affective-motivational aspects of pain depend on projections to RF, SC, central gray, hypothalamus, amygdala, and midline thalamic n. Figure 10.6 Pathways mediating discriminative aspects of pain & temperature for the body & face Box 10C A Dorsal Column Pathway for Visceral Pain
Sensory discriminative aspects of pain (location, intensity and quality) depend on information relayed to cortex via VPL/VPM Figure 10.7 Inflammatory response to tissue damage Figure 10.8 Descending systems that modulate the transmission of ascending pain signals
Pain modulation: Electrical stimulation of multiple brainstem sites can lead to analgesia. Gate control theory-via parallel mechano-receptor inputs (Melzak and Wall) Endogenous opiods; enkephalins, endorphins, and dysnorphins—in the peri-aquiducatal gray and enkephalins and dysnorphins in ventral medulla and spinal cord