General Sensation

Classification of Sensory System by structural Complexity General (= Somatic) senses Touch Pessure Temperature (heat and cold) Stretch Vibration Proprioception Nociception Special senses

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: _________ Graded potentials Stimuli: Chemo, Thermo, mechano, photo 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 Somato-sensory cortex Sensory Info Pathways and CNS Integration

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 Somatosensory cortex

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 Cold receptors lower than body temp. Warm receptors (37 - 45oC) > 45oC ?

Nociceptors 3 categories: 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 Bradykinin is activated by enzymes released into ECF from damaged tissue Signals from mechanical and thermal nociceptors are transmitted via A-delta-fibers. Impulses from polymodal nociceptors are carried by C fibers.

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