Laboratory Worksheet Exercise: Sensory Receptors Sense Organs - Sensory Receptors A sensory receptor is a specialized ending of a sensory neuron that detects a specific stimulus. Receptors can range from simple nerve endings of a sensory neuron (e.g., pain, touch), to a complex combination of nervous, epithelial, connective and muscular tissue (e.g., the eyes).

Figure 1. Diagram of a sensory neuron with sensory information being detected by sensory receptors located at the incoming end of the neuron. This information travels along the axon and delivers its signal to the central nervous system (CNS) via the synaptic end bulbs with the release of neurotransmitters.

The function of a sensory receptor is to act as a transducer. Transducers convert one form of energy into another. In the human body, sensory receptors convert stimulus energy into electrical impulses called action potentials. The frequency and duration of action potential firing gives meaning to the information coming in from a specific receptor.

The nervous system helps to maintain homeostasis in the body by monitoring the internal and external environments of the body using receptors to achieve this.

Sensations are things in our environment that we detect with our 5 senses. The 5 basic senses are:

Sight Hearing Touch Taste Smell An adequate stimulus is a particular form of energy to which a receptor is most responsive. For example, thermoreceptors are more sensitive to temperature than to pressure. The threshold of a receptor is the minimum stimulus required to activate that receptor. Information about Receptor Transmission Sensory receptors transmit four kinds of information - modality, location, intensity and duration. 1. Modality - describes the type of stimulus (or the sensation) it produces. A stimulated receptor typically elicits the same perception in the brain. 2. Location - the ability of the brain to identify the site of the stimulation. The precision with which the location of a stimulus is perceived is called acuity. 3. Intensity - refers to the strength of the signal that is detected by the receptors. If a stimulus intensity increases, it can be encoded three ways: 1) increasing action potential rate; 2) recruitment of more nerve fibers; 3) activating nerve fibers with higher thresholds (less sensitive fibers). 4. Duration – is the way a nerve fiber changes its rate of firing over time. Some receptors fire briefly when a stimulus begins, then become 'silent' and fire again briefly when the stimulus ends (e.g., corpuscles of touch). Other receptors fire continually, but all receptors exhibit some adaptation.

Sensory Receptors

Axon Synaptic end bulbs

info.

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Adaptation occurs after a long period of stimulation. The receptors responds by decreasing action potential firing. The way you adapt to the hot water of a shower is an example of sensory receptor adaptation. In terms of adaptation, there are phasic receptors and tonic receptors.

Phasic receptors generate a burst of action potentials when first stimulated; then they quickly adapt and stop transmitting impulses even if the stimulus continues. In other words, they are fast to adapt to the stimulus. Examples of phasic receptors are touch and smell receptors.

Tonic receptors are slow to adapt and generate nerve impulses continually. Examples of tonic receptors are proprioceptors (for balance) and baroreceptors (for blood pressure).

Sensory Receptors Classification

Table 1. Shows a summary of sensory receptor classifications and naming, using modalities for the general receptors they stimulate and their specific names.

Classification

Sensory Modality General Type of Receptor

Specific Name of Receptor

Cutaneous

Senses

Heat

Cold

Touch (vibration)

Pressure

Pain

Tickle and Itch

Thermoreceptor

Thermoreceptor

Mechanoreceptor

Mechanoreceptor

Nociceptor

(Chemoreceptor)

Mechanoreceptor

Ruffini's End Organ

Krause's End Bulbs

Meissner's Corpuscles

Pacinian Corpuscles

Free Nerve Endings

Free Nerve Endings

Proprioceptors

Muscle stretch

Muscle contraction

Limb position

Mechanoreceptor

Mechanoreceptor

Proprioceptor

Muscle Spindles

Tendon Organs

Joint Receptors

Special Senses

Low intensity of Light

High intensity of Light

Sound

Equilibrium

Smell (olfaction)

Taste (gustation)

Photoreceptor

Photoreceptor

Mechanoreceptor

Chemoreceptor

Chemoreceptor

Chemoreceptor

Rods (Black and White)

Cones (Color)

Inner Ear (Hair Cells)

Inner Ear (Vestibular)

Nasal Mucosa

(Vomeronasal Organ)

Taste Buds

(Papillae of Tongue)

Classification Sensory Modality General Receptor Specific Receptor Region

Visceral Senses

Blood Pressure

Blood Chemistry

Plasma Oncotic Pressure

Plasma Temperature

Pain

Mechanoreceptor

Chemoreceptor

Chemoreceptor

Thermoreceptor

Nociceptor

(Chemoreceptor)

Aortic Arch, Carotid Sinus

Aortic and Carotid Bodies

Osmoreceptors

Hypothalamus

Free Nerve Endings

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Other ways to Classify Sensory Receptors

A) By Modality (type of stimulus to which each is most sensitive):

Thermoreceptors - stimulated by changes in temperature (heat and cold).

Mechanoreceptors - stimulated by the physical deformation of the plasma membrane caused by touch, pressure, stretch, tension or vibration. Can also be called stretch receptors.

Nociceptors - pain receptors, stimulated by physical or chemical damage to tissue. Damage can result from trauma, ischemia (reduced blood flow) or excessive heat and chemicals.

Photoreceptors - stimulated by light or changes in light intensity (in retina of the eyes).

Chemoreceptors - stimulated by chemicals, including food, odors, & molecules in body fluids.

B) By Origin of their stimuli:

Exteroceptors - detect changes external to the body, including surface receptors (e.g., for touch, temperature and cutaneous pain). They also include receptors for vision, hearing, taste and smell.

Interoceptors or Visceroceptors - these detect stimuli that originate in the internal organs (viscera); they are responsible for feeling visceral pain, nausea, stretch and pressure.

Proprioceptors - detect changes in the position of the body and movement of the body or its parts. They are located in muscles, tendons, joint capsules and the inner ear.

Surface pain can be accurately located whereas Visceral pain is referred pain and typically poorly localized; e.g., heart pain felt in the shoulder and arm, kidney pain can be felt in the lower back. C) By General or Special categories:

General Senses are somatic or somatosensory senses and have receptors that are widely distributed in the body rather than limited to specific locations. These receptors occur in the skin, muscles, tendons, joint capsules and viscera (internal organs). They detect touch, pressure, stretch, heat, cold and pain, as well as other stimuli that we are not consciously aware of, such as blood pressure and chemistry of body fluids.

Special Senses have receptors which are very complex and are limited to the head and innervated by cranial nerves. There are 5 special senses:

1. Vision 2. Hearing 3. Equilibrium (Balance) 4. Gustation (Taste) 5. Olfaction (Smell)

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Table 2. From the information provided throughout this worksheet about receptors, take a look at the types of “stimulus” below that we are going to study and fill in the table for the modality, general type of receptor, and the specific name (if applicable) for each stimulus.

Stimulus

Modality (Sensation Produced)

General Receptor Activated

Specific Receptor (Name)

1) (stepping on a tack)

2)

(flame)

3) (an ice cube)

4)

(coins on an arm)

5) (a molecule to taste)

6)

(Light)

7) (measuring sensitivity)

High

intensity

Low

intensity

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Sensory Lab – Data and Q’s from Activities Part 1: In the Lab We examined how sensitive the skin on different areas of the body is to touch using calipers (see drawing to the right) to assess ‘Two-Point Sensitivity’ on the palm, the fingertip, the back of the neck, and the inside of the forearm.

Data was collected in pervious physiology labs and the averages are shown in Table 3. In the diagram to the right, we see that some areas of the body have different receptive fields than others. By measuring the distance that 2 points can be perceived as separate (and not one point) we can determine the variations in sensitivity in different regions of the body.

Q1. In the diagram of receptive fields above, which area is more sensitive, the one with the larger receptive field, or the one with the smaller receptive fields? ________________________________. Q2. Why? Table 3. Here are the results each area of the body, showing the average smallest distance (mm) at which two points can be identified as separate.

Palm Fingertip Back of Neck Inside Forearm

Class Average: 9.1 2.3 18.5 21.2

Q3. From the class average data in Table 3: a) Which of these areas is the least sensitive? b) Which of these areas is the most sensitive? c) For the most sensitive area, why do you suppose it was so much more sensitive than the others? Part 2: Sensory Modality Read the “Sense Organs” section above (p.1-2) and define the terms and answer the question using these concepts to explain your perceptions.

Q4. The function of a sensory receptor is to act as a ______________________; it converts one form

of ________________ into another. Q5. Define adequate stimulus of a receptor: Q6. Define the threshold of a receptor:

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Q7. Consult Table 1 (p 2) in the lab manual for information about these receptors. a) Nociceptors detect ____________, their receptors are ____________ _____________ endings. b) The general type of receptors the detect heat and cold in the skin are? ______________________. c) The specific type of cutaneous receptors for heat is _______________________________. d) The specific type of cutaneous receptors for cold is _______________________________. e) From p 3, what are proprioceptors used for? Part 3: Cutaneous Receptors There are several different types of receptors in the skin. Specialized sensory organs and free nerve endings in the skin can be categorized into four independent modalities of cutaneous sensation - Heat, Cold, Touch and Pain. The acuteness of sensation depends on the density of the cutaneous receptors. Thus, the more receptors, the greater the acuity (or sensitivity) of the sensation. Adaptation of Receptors Many of our sensory receptors respond strongly to acute changes in our environment and then they cease responding when these stimuli become constant - this phenomenon is known as sensory adaptation. For example, our sense of smell typically adapts quickly to the odors in a room and our touch receptors soon cease to inform us of our clothing etc., until these stimuli change in intensity. Find the info in this document on rapidly adapting (phasic) and slowly adapting receptors (tonic). Q8. Define phasic receptors and give an example. Q9. Define tonic receptors and give an example. Procedure In this test, we examined the concept of adaptation (the ability of the body to "ignore" certain types of stimuli after a period of time). This time it was for "touch" receptors of the surface of the skin. Subjects sat quietly with eyes closed and a forearm extended. They then had and either a single coin or four of the same coins placed on the forearm arm and the stop watch started timing (in seconds) until the subject indicated they could not feel the coin any longer. Table 4. Results for the adaptation of touch receptors using coins on forearm.

Trial (time in sec) One Coin Four Coins

Class Average: 19.6 36.8

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Q10. With the data from the experiment with the coins: a) The general receptors that detect touch in the skin are: __________________________________. b) Which stimulus took longer to ignore: One coin or four coins? _____________________________. c) What kind of receptors are these in terms of adaptation? ________________________________. d) The specific type of receptors cutaneous light touch (vibration) ____________________________. e) The specific type of receptors cutaneous touch (pressure) ________________________________. Q11. In the body, blood pressure is detected by baroreceptors. Look up how baroreceptors work. Briefly describe them. Hypothesize if they phasic or tonic in terms of adaptation, and why? Part 4: Olfactory Sensation, Vital Signs and Taste Discrimination In this section, we examine the sense of smell (olfaction).Do you think fragrances can affect a person’s mood? Why or why not? The sensations of taste (gustation) and smell (olfaction) are detected by chemoreceptors. The epithelial surface of the tongue contains taste receptors which are specialized cells grouped into barrel-shaped structures called taste buds. The receptors for the sense of smell are located in the olfactory cells in the mucous membrane lining of the upper portion of the nasal cavity. Only volatile substances (gaseous molecules) in solution can stimulate these receptors.

The gaseous particles enter the nasal cavity by diffusion from the circulating air in the external environment (see figure at left). Glands that surround olfactory cells secrete fluid in which the particles dissolve and this solution acts as a chemical stimulus to a nerve impulse. Does taste sensation depends on the ability to smell? If a person bites a lemon, the solution in the mouth stimulates chemoreceptors on the tongue. The chemicals act as the stimuli to activate chemoreceptors. Once activated, they send signals to specific regions of the brain that recognize and interpret the stimulus. Although there are only five basic modalities for taste (sour, sweet, salt, bitter and umami), the combination of these, together

with the sense of olfaction, provides a wide variety of different sensory experiences regarding gustation or taste.

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You can do a Taste Test at home: A good test material are fruits or fruity flavored foods. See the jelly beans to the left? What flavor are

they? They could be orange, mango, tangerine, cantaloupe… but you can’t be sure from just the color. If you had some you could plug your nose, put one in your mouth and chew chew chew. You’d be likely to tell that it is sweet, but unlikely to be able to differentiate between those flavors listed - until you unplugged your nose! Then your ability to identifying the variations in sweet tastes are able to blossom, like a flower in the daylight.

Q12. Olfactory receptors are classified as _____________________ (in terms of modality) and __________________ (in terms of origin) (p. 3). Q13. Explain why there is any difference in taste discrimination with or without olfaction. Q 14. What other factor might contribute to taste discrimination? Can your ‘tastes’ change? Part 5: Light and the Eye The drawing below show the basic anatomy of an eye. Fill in the names of the structures indicated.

1) Identify only the structures (a to f below) for the light fixing apparatus of the eye.

a _________________________; b _________________________; c _________________________;

d _________________________; e _________________________; f _________________________;

Q15. The retina of the eye contain the ____________________ that detect light intensity. The retina converts light energy into _______________ ________________.

a

b

c

d

e

f

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Q16. The ________ are photoreceptors for black & white vision, the _________ are for color vision.

Q17. Look up the “electromagnetic spectrum”. This spectrum ranges from long waves of ______ m to

short waves that are ______ nm. List the wavelength range of visible light _____________________. Part 6: Pupillary Reflexes Adaptation to changes in light intensity. The pupil is the hole in the iris (the colored portion of the eye) and it controls the amount of light that can enter the eye (shown to the right). The iris is complex and is composed of two different arrangements of contractile tissue in order to change the diameter of the pupil. The pupillary light reflex regulates the intensity of light entering the eye and we will be testing it. In Lab: If light is shined into your eyes at a close distance, the pupils will constrict. Also, if light is shined into only one eye (and the other eye is not exposed to the light), both pupils will constrict! Q18. Which cranial nerve is responsible for this response? Q19. What is the stimulus for the dilation or contraction of the iris muscles? Q20. What are the specific receptors for that stimulus? Q21. Look up the pupillary light reflex and find out what structures control the size of the pupil, as shown in drawing above, and give the names for structures a) and b) in the drawing.

a) b) In terms of medical terminology with reference to the pupil of the eye:

Miosis (myosis) means ____________________ of the pupil.

Mydriasis means ____________________ of the pupil.

Other Pupillary Reflexes: The size of the pupil also changes when the eye are engaged in wither distant or near focus. The same structures are involved and we want to determine how this is controlled and why. While focusing on an object across the room, pupils get bigger. Shifting to focus on a book of fine print, up close and persona, the pupils get smaller!

Q22. What is the sympathetic control of the iris? What's the purpose of this? Q23. What is the parasympathetic control of the iris? What's the purpose of this? Q24. There are other eye reflexes that are protective in nature. For instance the “corneal reflex” is also known as the __________________________. It is triggered by stimulation of the __________ and can also be stimulated by loud sounds!

a)

Pupil

b)

a)

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Part 7: Sound and Your Ears Sound has qualities of pitch (wave length) and loudness (amplitude).

Pitch describes how high or low a tone is and depends on the frequency of vibration. Higher frequencies gives higher tones and lower frequencies give lower tones, measured in length.

Loudness of a sound depends upon the amplitude (size) of vibration. The greater the amplitude of the sound wave, the louder the sound. It is measured in decibels.

Vibrations create sound waves which move through mediums such as air and water before reaching our ears. Since the ability to conduct sound depends on the density of the medium, solids are better conductors than liquids and liquids are better conductors than gases. The speed of sound in air is around 767 miles per hour or 1,230 kilometers per hour. When traveling through water, sound moves about four times faster than through air. The hearing apparatus of our ears vibrate in a similar way to the original source of the vibration, allowing us to hear many different sounds. Dogs can hear higher frequencies than humans, thus they hear noises we cannot. It is believed the loudest sounds made by any animal are by the blue whale, measured at up to 188 decibels – since the decibel scale is exponential, that’s a million times more intense than a jet engine, which is only about 120-140 decibels! Some Interesting Questions about Sound: a) Which of the 5 wave forms in the Figure above would have the highest tone? _____. Which would have the lowest? ____. b) The speed of Sound through air = _____________ per hr; through water = ______________ per hr. c) Why does sound travel (faster/slower) through water than air? f) Dogs can hear _________ frequencies than us and blue whale make sounds as loud as _______ dB. Sound Perception and Hearing Hearing is the ability to perceive sound by detecting vibrations – which are changes in the pressure of the surrounding medium through time. The ear is our organ of sound. Sounds waves hit the ear drum (tympanic membrane) and cause it to vibrate at a certain rate in accordance with the frequency (pitch) and amplitude (loudness) of the sound. The inability to hear is called deafness; it can be mild or profound, temporary or permanent. Normal hearing ranges from 0 to 20 dB in all frequencies. At what decibel threshold does damage to your ears and your hearing typically occur? ________.

1

2

3

4

5

Sound Waves

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Search for information to match environmental noises with their typical decibel levels (loudness). Environmental Noise

a) Telephone dial tone b) Subway train c) Jet engine

d) Softest sounds heard e) Normal conversation f) City traffic (inside car)

g) Loud rock concert

h) Whisper quiet library

Decibel Level (dB) (place the letter for each estimation of sound level) 0-20 dB = ____; 30 dB = ____; 60 dB = ____; 80 dB = ____; 85 dB = ____; 95 dB = ____; 115 dB= ____; 140 dB= ____ Part 8: Reflex & Voluntary Reactions A. Reflexes are rapid, automated, stereotyped responses to sensory stimuli that are usually protective. Reflexes do not require higher brain activity, that is, they can be considered a "subconscious" or “involuntary” action. Voluntary response follow the same basic neural pathway but with varying integrations centers that enable conscious control.

A Feedback Loop is seen in both reflex and voluntary actions. Review the parts of the ‘reflex arc’

(which is just an automated feedback loop) from your class notes and any physiology textbook and label the critical components of the polysynaptic spinal reflex shown below.

1

c)

6 5

4 3 2

a)

b)

Figure 1. The Feedback Loop above shows the basic components of a stimulus being processed for a response at the end of the loop. Use this drawing as an opportunity to identify all of the steps in a typical negative feedback loop by providing names for the numbers (below) and letters shown in the diagram.

1. __________________________ 2. __________________________ 3. __________________________ 4. __________________________ 5. __________________________ 6. __________________________

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B. Measuring Voluntary Reaction Times with an Electronic Reaction Timer. We used an electronic reaction timer (Hubbard Scientific, 6027) to measure reaction times to two different cues; visual (red light) and auditory (buzzer sound). 1) Visual Cue: Subjects sat comfortably and placed a foot over the top of the foot pad on the floor. Randomly, the light displays was activated and the subject stepped on the foot pad as soon as they saw the red light. Reaction time was recorded in miliseconds (msec). 2) Auditory Cue: Subjects sat comfortably and placed a foot over the top of the foot pad on the floor. Randomly, the buzzer sound was activated and the subject steppedon the foot pad as soon as they heard the sound. Reaction time was recorded in miliseconds (msec). Below in Table 5 are the reaction times data results collected form students in the lab for the two types of cues for reaction time, the visual and auditory stimuli. Table 5. Results for the reaction time responses to visual and auditory stimuli.

Reaction Time (msec)

Light Stimulus

Sound Stimulus

Class Average:

262.7

249.3

The data from the table has been made into a graph below.

240

245

250

255

260

265

Light Sound

Rea

ctio

n T

ime

(mse

c)

Stimulus

The Reaction Time Responses to Visual and Auditory Stimuli

We will look at how to make figure legends for graphs that we make from the lab data gathered. Q25. What does the graph above tell you about reaction time?