1. CH 8. The somatic sensory system
Sensitize mechanical stimuli (light, vibration, pressure, tension), pain and temp
Ascending pathway (peripheral to brain)
Cutaneous and subcutenous somatic sensory receptors
Free nerve ending and specialized nerve ends
Functional classification; Mechanoreceptor/nociceptor/thermoceptor
Morphological classification; free nerve and encapsulated types
Quality of stimulus; specific receptor and location of central target
Quantity; rate of action poetntial
adapt

2. The Major Classes of Somatic Sensory Receptors
Table 8.1 .
   The Major Classes of Somatic Sensory Receptors
Receptor type
Anatomical characteristics
Associated axonsa (and diameters)
Axonal conduction velocities
Location
Function
Rate of adaptation
Threshold of activation
Free nerve endings
Minimally specialized nerve endings
C, Aδ
2–20 m/s
All skin
Pain, temperature, crude touch
Slow
High
Meissner's corpuscles
Encapsulated; between dermal papillae
Aβ 6–12 μm
Principally glabrous skin
Touch, pressure (dynamic)
Rapid
Low
Pacinian corpuscles
Encapsulated; onionlike covering
Subcutaneous tissue, interosseous membranes, viscera
Deep pressure, vibration (dynamic)
Merkel's disks
Encapsulated; associated with peptide- releasing cells Aβ
All skin, hair follicles
Touch, pressure (static)
Ruffini's corpuscles
Encapsulated; oriented along stretch lines
Stretching of skin
Muscle spindles
Highly specialized (see Figure 9.5 and Chapter 15)
Ia and II
Muscles
Muscle length
Both slow and rapid
Golgi tendon organs
Highly specialized (see Chapter 15) Ib
Tendons
Muscle tension
Joint receptors
Minimally specialized —
Joints
Joint position

3. Different adaptation by nerve fiber
Slow adapting/tonic
Rapid adapting/phasic
Adaptation
Different adaptation by nerve fiber

4. All of them-low threshold (sensitive receptor)
Meissner carpuscle; 40% of afferent fiber, glabrous skin (low frequency-vibration)
Pacinian corpuscle; fine surface texture, high-frequency vibration, rapid adapted. Located in Interosseous membrane (vibrations, transmitted to skeleton)- wings of bird, bills of goose,
merkel’s disk slow adapting, highly inervated in palm (shape, edges, rough texture) and light pressure
Ruffini’s corpuscle extension, slow adapting. Linked to special vesicle containing cells-> peptide release, interal stimuli

5. Two points discrimination
Density of receptor
Receptive field large-receptive field  low discrimination
In finger tip; receptive field 1-2mm
Palm; 5-10 mm
Practice, fatigue, stress also affect the sensitivity.
Central nerve system (phatom limb)

8. Proprioceptor ; self receptor
continuous information about position of limbs or body (visceral motor system)
Low threshold mechanoceptor, intergrated into vestibular system, bloood pressure (in heart, and major vessels)
Located in muscle spindle, golgi tendon

9. Active tactile exploration
Muscle spindles few in large skeletal muscle, whereas extraocular and intrinsic muscle of head and neck show the rich-location
For fine regulation and accurate control
Muscle spindle is absent in middle ear
Joint receptor limb position and joint movement
Golgi tendon, collagen fiber
Active tactile exploration
Haptics ; mouse

11. Dorsal column-medial lemniscus pathway; mechano/propioception
Spino-talamic (anterolateral )pathway-pain, temp
3 neuron
Ventral posterior lateral nucleus (VPL)

12. Ophthalmic, maxillary, mandibular branches
Principle nucleus mechanosensory
Spinal nucleus pain, Temp
# ventral posterior medial (VPM) nucleus

14. Somatic sensory cortex
brodmann’s area
3b and 1 cuteous stimuli
3a proprioceptor
2 area tactile and proprioceptor

15. Somatotopic maps Functional reception is different
Ex) 3b area sensing single finger, whereas multifingers stimulation are received by 1 and 2 area
Area 1 sense direct skin stimulation; area 2 required the complx stimulation (shape)

16. CH 9 pain
nociceptor ; cell body in dorsal root ganglia, afferent action potential
Free nerve ending, slow conduction, unmyelinated
Ad – 20m/s, myelinated axon; sensing mechanical and mechanothermo-stimuli
C-fiber- 2m/s, unmyelinated; mechnical, thermal, chemical (polymodal)
Ad-mechanosensitive, Ad-mechanothermal, polymodal

17. 2 kinds of pain
First pain-rapid and sharp
Second pain-long lasting

18. Transduction of nociceptive signals
Nociceptor sensing heat and capsaicin
vanilloid receptor (VR-1 or TRPV1) in A and C fiber; it can sense 45oC and capsaicin
Vanilloid like receptor (VRL-1 or TRPV2) ; 52oC but not capsaicin
Transiet receptor potential (TRP) cnannel; voltage-gated potassium or cyclinc nuleotide channel
Resting stage closed.
Endovanilloids produced in injury tissue

20. Central pain pathway
Spinal injury
Dissociated sensory loss

21. Referred pain; visceral pain  cutaneous pain
Anginal pain (heart muscleupper chest, left arm)

22. Affective-motivational pain

24. Hyperalgesia sunburn
Sensitization
Hyperalgesia sunburn
Peripheral sensitization inflammatiory soup
Product of damaged tissue  TRPV1
Prostagland GPCR cAMP; Figure 9.6
Central sensitization
Sensitized pain neuron activated by mechanoreceptor
Allodynia 무해자극통증
Windup NMDA receptor blocker
LTP-like enhancement of postsynaptic potential long lasting eg) COX-2

25. Primary afferent fibers
Substances Released Following Tissue Damage
Source: Modified from Fields, 1987.
Substance
Source
Potassium
Damaged cells
Serotonin
Platelets
Bradykinin
Plasma
Histamine
Mast cells
Prostaglandins
Leukotrienes
Substance P
Primary afferent fibers

26. Neuropathic pain
Phantom limbs and phantom pain

27. Descending control of pain perception
Interpretation of pain
World war II
Injury in battle vs injury in domestic life reward, benefit, curcumstance
Topdown influence
The placebo effect
Physiological basis of pain modulation
Midbrain pain relief produce (figure 9.7); periaqueductal gray of midebrain
Gate theory of pain pain modulation ; broken bone
Endo-opinoids