1. General Sensation

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

3. Sensory Pathway Stimulus Sensory receptor (= transducer)
_______________________
CNS
Integration, perception

4. 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

6. 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.

7. 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)

8. Sensory Info Pathways and CNS Integration
Somato-sensory cortex
Sensory Info Pathways and CNS Integration

9. 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

10. Testing Tactile Localization Integration in ____________cortex
Sensory Homunculus
Somatosensory cortex

11. 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.:

12. 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 ( oC) > 45oC ?

13. 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.

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