INTRODUCTION TO SENSORY RECEPTORSExercise 20BI 232

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

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)

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

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.

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

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

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

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?

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

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

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

THE END OF EXERCISE 20 Go onto Exercise 26:

Eye and Vision Make sure that you

understand the tests