Psychophysical laws Legge di Weber: ΔS=K*S Legge di Fechner: I=K*log(S/S 0 )
Sensory receptors Vision Smell Taste Touch Thermal senses Pain Hearing Balance Proprioception
Sensory receptors Table 21-1 Classification of Sensory Receptors Sensory system Modality Stimulus Receptor class Receptor cells Visual Vision Light (photons) Photoreceptor Rods and cones Auditory Hearing Sound (pressure waves) Vestibular Head motion Gravity, acceleration, and head motion Somatosensory Touch Proprioception Pain Skin deformation and motion Muscle length, muscle force, and joint angle Noxious stimuli (thermal, mechanical, and chemical stimuli) Mechanoreceptor Mechanoreceptor Mechanoreceptor Mechanoreceptor Thermoreceptor, mechanoreceptor, and chemoreceptor Hair cells in cochlea Hair cells in vestibular labyrinths Cranial and dorsal root ganglion cells with receptors in: Skin Itch Histamine Chemoreceptor Skin Visceral (not painful) Wide range (thermal, mechanical, and chemical stimuli) Thermoreceptor, mechanoreceptor, and chemoreceptor Gustatory Taste Chemicals Chemoreceptor Taste buds Muscle spindles and joint capsules All tissues except central nervous system Gastrointestinal tract, urinary bladder, and lungs Olfactory Smell Odorants Chemoreceptor Olfactory sensory neurons
Spatial resolution
Somatosensory afferents convey information from the skin surface to central circuits
The skin harbors a variety of morphologically distinct mechanoreceptors
Transduction in a mechanosensory afferent (a Pacinian corpuscle)
Receptive fields and two-point discrimination threshold (Part 1)
Receptive fields and two-point discrimination threshold
Slowly and rapidly adapting mechanoreceptors respond differently to a stimulus
Proprioceptors provide information about the position of body parts
Schematic representation of the main mechanosensory pathways
Schematic representation of the main mechanosensory pathways
Lateral inhibition A Neural circuits for sensory processing C Types of inhibition in relay nuclei Stimulus Skin Somatosensory cortex Receptors Output to thalamus Neurons in relay nucleus Feedback Feed-forward Descending B Spatial distribution of excitation and inhibition Stimulus To spinal cord Receptors Frequency Relay neurons
Somatic sensory portions of the thalamus and their cortical targets in postcentral gyrus
Somatotopic order in the human primary somatic sensory cortex
Connections within the somatosensory cortex establish functional hierarchies
Neurons in the primary somatosensory cortex form functionally distinct columns
Functional expansion of a cortical representation by a repetitive behavioral task
Properties of SII neurons
Thermoception
Experimental demonstration that nociception involves specialized neurons
Pain can be separated into first (sharp) and second (duller, burning) pain
The anterolateral system
The anterolateral system sends information to different parts of the brainstem/forebrain
Inflammatory response to tissue damage
Enhanced excitability of dorsal horn neurons A Repetitive stimulation of C and A fibers 80 Aδ fiber C fiber B Number of spikes 60 40 20 Response to C fiber Response to Aδ fiber 0 0 3 6 9 12 15 Stimulus number B Enhancement of excitability Aδ fiber stimulation C fiber stimulation Glutamate Substance P AMPA AMPA NMDA AMPA NMDA NMDA NK1 Ion channels Ca 2+ Ca 2+ Fast membrane depolarization (transient) Long-lasting depolarization (cumulative)
Descending systems that modulate the transmission of ascending pain signals
Descending systems that modulate the transmission of ascending pain signals
Descending systems that modulate the transmission of ascending pain signals
Referred Pain