1. Introduction to Sensory Receptors
Exercise 20
BI 232

2. Introduction and Terminology
There are many types of sense receptors in the body.
They are not uniformly distributed
Punctate distribution is the pattern of uneven distribution throughout the body
There is no perception without environmental input, which are listed by type, or modality.
Examples of modalities are: light, heat, sound, pressure, and specific chemicals
Receptors are the receiving units and respond to stimuli

3. Receptor Types Photoreceptors- detect light (retina)
Thermoreceptors – detect temperature (skin)
Proprioreceptors – detect changes in tension (joints)
Pain (nociceptors) receptors (free nerve endings in skin stomach etc.)
Mechanoreceptors - perceive mechanical stimuli (touch)
Baroreceptors – change in pressure (BP)
Chemoreceptors – changes in chemical environment (taste and smell)

4. Touch receptors
Light touch receptors include Meissner’s corpuscles and Merkel discs.
Found in the upper dermis.
Deep pressure receptors are the Pacinian (lamellated) corpuscles found deep in dermis or hypodermis.
Remember from 231?
Review slides

5. Two-Point Discrimination Test
Map relative density of receptors
Partner sits with eyes closed and hand resting on counter with palm up.
Use calipers to touch your lab partner’s fingertip with both points of the instrument and see if they can determine between one and two points.
Start with calipers close to closed and repeat the process opening the calipers a little with each touch.
Stop when partner feels both points.
Measure the distance.
Do this again on the forearm, palm, and back of neck and compare the results.

6. Warm and Cool Receptors
Skin has receptors that are sensitive to cool or warm temperatures:
Take 2 probes; one from ice bath and one from warm water bath.
Lab partner closes his or her eyes
Test the ability of your lab partner to distinguish between the cool and warm probes by putting the probes on forearm
Do this 5 times with each and see which temperature was more accurate

7. Mapping Temperature Receptors
Mark off a square that is 2 cm on a side on the anterior forearm of lab partner
Use hot and cold water baths again
Use pointed end of probe and place in cold water.
Test areas in the square. When partner perceives cold mark with blue marker (not just touch.
Do the same with warm probe

8. Mapping Light-Touch Receptors
Draw 2 cm square on lab partner’s forearm.
Use Von Frey hair to map the number of areas in the square that your lab partner can perceive.
Press only until the hair bends a little to simulate the touch corpuscles.
Use black felt pen to record results
Do this again on lateral side of the arm

9. Adaptation to Touch Tonic receptors constantly perceive stimuli.
Phasic receptors adapt to a stimulus
Crumple a small piece of paper into a ball.
Place ball of paper into partner’s palm.
Are light touch receptors tonic or phasic?
Taste buds are tonic because they adapt slowly while olfactory stimuli are phasic because they adapt quickly

10. Locating Stimulus with Proprioception
Have partner close eyes.
Touch partner’s forearm with a felt marker.
Have partner try to locate the same spot with a felt marker of another color.
Test 5 locations on various parts of forearm.
Repeat each location twice
Or use parts of body: corner of eye, ear lobe and chin

11. Temperature Judgement
Place one hand in cold water and another in warm water.
After hands have equilibrated, place them both in the room temperature water.
Describe to your lab partner what you feel

12. Referred Pain
Perception of pain in one area of the body when the pain is actually somewhere else.
Place your elbow into a dish of ice water and leave it there for 2 painful minutes
Describe the sensation

13. The End of Exercise 20 Go onto Exercise 26: Eye and Vision
Make sure that you understand the tests