General Sensation Classification of Sensory System by structural

General Sensation

Classification of Sensory System by structural Complexity General (= Somatic) senses • Touch • Pessure • Temperature (heat and cold) • Stretch • Vibration • Proprioception • Nociception Special senses 1. 2. 3. 4. 5.

Sensory Pathway Stimulus Sensory receptor (= transducer) ____________ CNS Integration, perception

Sensory Receptors - Overview • are transducers → convert stimuli into _____ potential (receptor potential) • are of various complexity • Can be classified by stimulus type they detect. For skin: – _________ Simple Complex neural receptor Special senses receptor

Touch Receptors Free or encapsulated dendritic endings in skin and deep organs. e. g. : Pacinian corpuscles concentric layers of c. t. large receptive field. Detect vibration by opening _______ gated ion channels.

Somatic Senses • Primary sensory neurons from receptor to spinal cord or medulla • Secondary sensory neurons always cross over (in spinal cord or medulla) thalamus • Tertiary sensory neurons somatosensory cortex (post central gyrus)

Sensory Info Pathways and CNS Integration Somatosensory cortex

Two Point Discrimination Test looks at Receptive Fields Each 1° sensory neuron picks up info from a receptive field Often convergence onto 2° sensory neuron summation of multiple stimuli Size of receptive field determines sensitivity to stimulus Two point discrimination test

Testing Tactile Localization Integration in ______cortex Sensory Homunculus

Adaptation of Sensory Receptors Sustained stimulation leads to adaptation – Tonic receptors do NOT adapt or adapt slowly. E. g. : – Phasic receptors adapt rapidly. E. g. :

Temperature Receptors • Free dendritic endings in hypodermis • Function in thermoregulation • Cold receptors (< _____) • Warm receptors (>_____) • Test if more cold or warm receptors • Nociceptors • Adaptation only between 20 and 40 C

Nociceptors • Free dendritic endings • Activation by strong, noxious stimuli leading to tissue damage - Function? • 3 categories: – Mechanical – Thermal (menthol and cold / capsaicin and hot) – Chemical (includes chemicals from injured tissues) • May activate 2 different pathways: – Reflexive protective – integrated in spinal cord – Ascending to cortex (pain or pruritus) • Perception of pain is modulated by psychology

Referred Pain in organs is poorly localized May be displaced if Multiple 1° sensory neurons converge on single ascending neuron