1. General Sensory Reception

2. The Sensory System What are the senses ? How sensory systems work
Body sensors and homeostatic maintenance
Sensing the external environment
Mechanisms and pathways to perception

3. General Properties of Sensory Systems
Stimulus
Internal
External
Energy source
Receptors
Sense organs
Transducer
Afferent pathway
CNS integration

4. General Properties of Sensory Systems

5. Sensory Receptors Somatic Visceral -- Chemoreceptors (taste, smell)
-- Thermoreceptors (temperature, pain)
-- Photoreceptors (vision)
-- Proprioreceptors (muscle stretch)
--Mechanoreceptors (touch, pain, audition, balance).
Visceral
-- Chemoreceptors (chemicals in blood, osmoreceptors)
-- Baroreceptors (bp)

6. Sensory Receptor Types

7. Special Senses – External Stimuli
Vision
Hearing
Taste
Smell
Equilibrium

8. Special Senses – External Stimuli

9. Somatic Senses – Internal Stimuli
Touch
Temperature
Pain
Itch
Proprioception
Pathway

10. Somatic Pathways Receptor Sensory neurons Integration Threshold
Action potential
Sensory neurons
Primary – medulla
Secondary – thalamus
Tertiary – cortex
Integration
Receptive field
Multiple levels

11. Somatic Pathways

12. The Somatosensory System
Types of receptors
- Mechanoreceptors:
-- Proprioreceptors in tendons, ligaments
and muscles  body position
-- Touch receptors in the skin: free nerve endings, Merkel’s disks and Meissner’s corpuscles (superficial touch), hair follicles, Pacinian corpuscles and Ruffini’s ending
- Thermoreceptors: Warm receptors (30-45oC) and cold receptors (20-35oC)
- Nociceptors: respond to noxious stimuli

13. Touch (pressure)

14. Skin touch receptors

15. Sensory pathways
The sensory pathways convey the type and location of the sensory stimulus
The type: because of the type of receptor activated
The location: because the brain has a map of the location of each receptor

17. Temperature Free nerve endings Cold receptors Warm receptors
Pain receptors
Sensory coding:
Intensity
Duration

18. Pain perception
Fast pain: sharp and well localized, transmitted by myelinated axons
Slow pain: dull aching sensation, not well localized, transmitted by unmyelinated axons
Visceral pain: not as well localized as pain originating from the skin  pain impulses travel on secondary axons dedicated to the somatic afferents  referred pain

19. All the Preceding Modalities Culminate in the Propagation of Action Potentials

20. Sensory transduction
Receptors transform an external signal into a membrane potential
Two types of receptor cells:
- a nerve cell
- a specialized epithelial cell

21. Two types of sensory receptors

22. Receptor adaptation Tonic receptors Phasic receptors
-- slow acting, -- no adaptation: continue to for impulses as long as the stimulus is there
(e.g., proprioreceptors)
Phasic receptors
-- quick acting, adapt: stop firing when stimuli are constant (e.g., smell)

23. Sensory coding
A receptor must convey the type of information it is sending  the kind of receptor activated determined the signal recognition by the brain
It must convey the intensity of the stimulus  the stronger the signals, the more frequent will be the APs
It must send information about the location and receptive field, characteristic of the receptor