Introduction to Sensory Receptors

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’scorpuscles 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?

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