1. W5D3H3: Sensory Receptors
Note W5D3H4 is also in this note set, starting on slide 30. There is a GRAT group activity in between.

2. Learning Objectives
 1. Outline properties of sensory receptors including how intensity (strength) and duration are encoded and adaptation to stimulus.  
2. Discuss the importance of the frequency of action potentials and its relationship to neurotransmitter release and stimulus coding. 
3. Give examples of how sensory receptor properties are utilized by cutaneous receptors to detect and encode input.
4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells).
Note W5D3H4 is also in this note set, starting on slide 30. There is a GRAT group activity in between.

3. Why This Topic?
Understanding how external signals are detected and encoded by the nervous system is essential to a big-picture understanding of how stimuli are detected and interpreted by the nervous system. Because defects in this process constrain the well-being and quality of life for many people and because changes in how stimuli are detected and integrated can be used to identify more serious conditions, it is essential to understand this process. This material also integrates physiology, HFF, and clinical topics by explaining how nerve damage from diabetes can alter neuronal signaling.

4. LO 1. Outline properties of sensory receptors including how intensity (strength) and duration are encoded and adaptation to stimulus
 Primary problem: How do we get information about the outside world and the inside world? Labeled lines: sensory nerve cells carry information to the spinal cord and brain about specific types of stimuli.
Photons, heat, chemicals, pressure waves- detecting this range of stimuli is the challenge our sensory receptors face!
Examples of stimuli include pressure waves (hearing), electromagnetic radiation (vision), gravity (balance), temperature (heat/cold detection), distortion (stretch) and various chemicals (pain, olfaction and gustation).

5. Abstract In the somatosensory system, various different sensory receptors capture different stimuli and convey them to the sensory cortex. Each type of receptor is specialised, that is, receives the stimulus to which it is predetermined to receive. Immediately as it is stimulated, the receptor sends a signal to the somatosensory cortex, via nerve fibres, and the area of the cortex that receives the signal determines the mode of the consequent perception. This mechanism is called principle of the "labelled" lines. The somatic receptors are the structures designated to receive stimuli, however, if their afferent fibres are stimulated at any point when approaching the cortex, the mode of perception by the cortex is the same as when the somatic receptor is stimulated directly. This occurs after the amputation of a limb, wherein the remaining fibres transmit to the cortex the mode of sensation for which they were specialised, despite the lack of somatic receptors at the beginning of the afferent pathway. However, the afferent pathway ends at the same cortex area as before the deafferentation. Since the somatic receptors and the integrity of afferent pathways are important to the regulation and modulation of the received stimuli, after the deafferentation the afferent pathway becomes anatomically and functionally abnormal. We believe these factors, involved in the pathophysiology of phantom limb (PHL), might be the explanation for this intriguing phenomenon.

6. Somatosensory Homunculus
Figure 10-9

7. LO 1. Outline properties of sensory receptors including how intensity (strength) and duration are encoded and adaptation to stimulus
Three classes of sensory receptors: (a) free nerve endings, (b) with accessory structures, and (c) specialized receptor cells.
Photons, heat, chemicals, pressure waves- detecting this range of stimuli is the challenge our sensory receptors face!

8. More transmitter release
LO 1 & LO 2. Outline properties of sensory receptors including how intensity (strength) and duration are encoded and adaptation to stimulus. Discuss the importance of the frequency of action potentials and its relationship to neurotransmitter release and stimulus coding.
Transmitter release
More transmitter release

9. LO 1 . Outline properties of sensory receptors including how intensity (strength) and duration are encoded and adaptation to stimulus. 

13. LO 3. Give examples of how sensory receptor properties are utilized by cutaneous (skin) receptors to detect and encode input. 
Area on the skin that receptor responds to
rapidly adapting
slowly adapting
rapidly adapting
slowly adapting

14. LO 3. Give examples of how sensory receptor properties are utilized by cutaneous (skin) receptors to detect and encode input. 
slowly adapting
rapidly adapting
Area on the skin that receptor responds to
Stretch
Vibration
> 50 Hz
Light pressure
Fine touch
< 50 Hz
Aalpha fibers – spindles
Abeta – Golgi tendon Organs
A delta – free nerve ending and joint capsules, cold
C fibers – free nerve endings – pain, touch, warm

15. LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells).  
Photons, heat, chemicals, pressure waves- detecting this range of stimuli is the challenge our sensory receptors face!

16. LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells).  
Photons, heat, chemicals, pressure waves- detecting this range of stimuli is the challenge our sensory receptors face!

17. LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells).  
Photons, heat, chemicals, pressure waves- detecting this range of stimuli is the challenge our sensory receptors face!

18. LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells).  
Photons, heat, chemicals, pressure waves- detecting this range of stimuli is the challenge our sensory receptors face!

19. LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells).  
Photons, heat, chemicals, pressure waves- detecting this range of stimuli is the challenge our sensory receptors face!

20. LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells).  
Photons, heat, chemicals, pressure waves- detecting this range of stimuli is the challenge our sensory receptors face!

21. LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells).  
Photons, heat, chemicals, pressure waves- detecting this range of stimuli is the challenge our sensory receptors face!

22. LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells).  
Photons, heat, chemicals, pressure waves- detecting this range of stimuli is the challenge our sensory receptors face!
depolarization

23. Presynaptic cell (III)
LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells).  
Light micrograph of a taste bud
Taste pore
Taste buds are located on the dorsal surface of the tongue.
Taste buds. Each taste bud is composed of taste cells joined near the apical surface with tight junctions.
Type I support cells may sense salt when Na enters through Na channels.
Taste ligands create Ca2 signals that release serotonin or ATP.
Sweet
Umami
Bitter
Sour
Tight junction
Salt?
Presynaptic cell (III)
ATP
Serotonin
Primary sensory neurons
Receptor cells (type II)
(Adapted from Tomchik et al., J Neurosci 27(40): 10840–10848, 2007.)
(CO2)
50 – 100 neuroepithelial cells (types I-III)
Cranial afferents

24. LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells).  
Photons, heat, chemicals, pressure waves- detecting this range of stimuli is the challenge our sensory receptors face!
Panx1

25. LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells).  
Photons, heat, chemicals, pressure waves- detecting this range of stimuli is the challenge our sensory receptors face!

26. HPHY 241
Figure 10-16c

27. LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells).  
Photons, heat, chemicals, pressure waves- detecting this range of stimuli is the challenge our sensory receptors face!

28. END 

33. Somatosensory Cortex
It is in the somatosensory cortex that the brain recognizes where the ascending sensory tracts originated
Each sensory tract has a corresponding region on the cortex
Within each region, columns of neurons are devoted to particular types of receptors
Fig. 9.10
HPHY 241

34. HPHY 241

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37. HPHY 241

38. 4. The tectoral membrane and hair cells
HPHY 241

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47. HPHY 241