sensory system physiology and pain sensation

1. Sensory Physiology
Datu Agasi Bin Mohd Kamal
P92695

2. Learning Objective:
• State stimulus and its type
• Describe sensory receptor function and its
type and form
• Explain receptor potential and adaptation of
receptor
• Explain pain sensation and its pathway

3. Introduction
Question:
What is the role of the afferent division of the peripheral
nervous system?
Answer:
Send information (stimulus) about the external and the
internal environment to CNS
Note:
Sensory signals can reach conscious awareness, but others
are processed completely at the subconscious level.

4. Subconscious
Somatic
Muscle length and tension
Visceral
Blood pressure
pH/oxygen content in
blood
pH of cerebrospinal fluid
Lung inflation
Osmolarity of body fluids
Blood glucose
Conscious
Special senses
Vision
Hearing
Taste
Smell
Equilibrium
Somatic senses
Touch/pressure
Temperature
Pain
Proprioception
Sensory System

5. Stimulus
• Stimulus – change detectable by the body(receptor)
• Exist in various form : heat,light,sound,chemical
• Peripheral ending of afferent neuron
• Each type is specialized to respond to one type of
stimulus(adequate stimulus)
Sensory Receptor

6. Type of Receptor
• Photoreceptor : Visible wavelength of light.
• Mechanoreceptor : Mechanical energy –eg. skeletal
muscle receptor sensitive to stretch, receptor in ear
contain fine hair that bent by sound waves.
• Thermoreceptor : Heat and cold.
• Osmoreceptors : Change in the concentration of
solutes in ECF and resultant changes in osmotic
activity

7. Type of Receptor
• Chemoreceptor : Specific chemical- receptor
for taste and smell, detect O2 and CO2
concentration in blood
• Nociceptor(pain receptor) : Tissue damage-
eg. Cutting or burning. Intense stimulation of
any receptor perceived as painful.

8. Two Form of
Receptor
Specialized
ending of
afferent neuron
Separate
receptor cell

9. How the stimulus is send to CNS?
Stimulus
Sensory
receptor
CNS

11. Receptor potential : stimulus strength

12. Adaptation of receptor
Tonic Receptor
Do not adapt or
adapt slowly
Eg : muscle
stretch receptor
& joint
proprioceptor
Phasic receptor
Rapidly adapt
with off
response
Eg : tactile(touch
receptor) esp
Pacinian
corpuscle

13. Pain Sensation

14. Introduction
• Protective mechanism
• Nociceptor do not adapt to sustained stimulation
• Pain sensation – motivated response + emotion
• Nociceptor sensitized by prostaglandin – lower
threshold level
• Nociceptor categories:
i. Mechanical nociceptor
ii. Thermal nociceptor
iii. Polymodal nociceptor

15. Fast and Slow Pain
Fast pain Slow pain
Occur on stimulation of
mechanical and thermal
nocireceptor
Occur on stimulation of
polymodal nociceptor by
bradykinin
Carried by small , myelinated
A- delta fibers
Carried by small, unmyelinated
C fibers
Sharp , prickling sensation Dull,aching,burning sensation
Easily localized Poorly localized
Occur first Occurs second, persists for
longer time,more unpleasant

16. Pain Pathway

17. Pain neurotransmitter - Glutamate
• Excitatory neurotransmitter
• Act on receptor of dorsal horn in two ways.
1. Generation of action potential to transmit pain
messages to higher centre
2. Lead to Ca2+ entry that make dorsal horn cells
hyperexcitable
• Hyperexcitability – exaggerated sensitivity

18. Brain Built-in analgesic system
• Endogenous opiate
 Endorphin
 Enkaphalin
 Dynorphin

19. Thank You