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Name: __________________________ Period: _____ Laboratory Exercise and Activity: Senses

Sensory receptors provide information about the environment outside and within our body.

General sensory information is either from somatic sensory receptors (skin and skeletal muscle) or

visceral sensory receptors (visceral organs). Special sensory information is from special sense organs

(eye, inner ear, nasal mucosae, or taste buds).

A. Sensory Receptors

Structural classes of general sensory receptors include: free nerve endings, or specialized

receptor cells. Free nerve endings are dendrites of sensory nerves that convey to the brain the

general sensations of pain, temperature, tickle, itch, and some touch sensations. Encapsulated

nerve endings are dendrites of sensory neurons enclosed by a connective tissue capsule that

convey general sensations of touch and pressure to the brain. Sensory receptors of special sense

organs are receptor cells that form synapses with sensory neurons.

ACTIVITY 1~ GENERAL SENSORY RECEPTORS

1. Identify the somatic sensory receptors in Figure 19A.1a and Figure 19A.1b. Refer to Table

19A.1 (page 2) that identifies location, structure (free or encapsulated nerve ending), and

stimuli of somatic sensory receptors.

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B. Tactile Sensitivity of Different Body Areas

Some areas of the skin have greater tactile sensitivity than others. The greater the number of

cutaneous receptors in an area (receptor density), the greater the tactile sensitivity is in that area.

The two-point discrimination test is an indirect measure of cutaneous receptor density. A

subject is touched by two closely spaced points and asked if she/he can feel both points. The objects

are moved farther apart until two points can be felt. An area of skin with a greater density of touch

receptors is more sensitive to touch and can discriminate between two points closer together than

an area with a lower density of touch receptors.

ACTIVITY 2~ TACTILE SENSITIVITY

1. Obtain the following: calipers, millimeter ruler, sandpaper, velvet or synthetic fur, and a smooth

surface such as glass.

2. Perform the two-point discrimination test on the cheek, fingertip of the index finger, palm,

posterior surface of forearm, and back of leg.

Choose a subject for the experiment, a data collector, and a data recorder.

Have the subject close her/his eyes during the experiment.

Put the two caliper points together.

Place caliper points on skin area to be tested. Touch both caliper points to the skin at

the same time.

Ask the subject if she/he can feel two points or one point.

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Increase the distance between caliper points. For the fingertip and palm, increase the

distance by 1 mm. for the cheek, forearm, and back of leg, increase the distance by

2mm.

Continue to increase the distance between the caliper points until the subject can feel

two points. This distance is the two-point discrimination distance and is to be measured

with a millimeter ruler. Record this value in Table 19A.2 below.

Calculate the reciprocal (1/ two-point distance) of the two-point discrimination distance

for each area and record the value in Table 19A.2 below, the reciprocal represents the

portion of the somatosensory receptors for a given body area. Areas with high sensory

receptor density are represented by a corresponding greater area of cerebral cortex.

Create a bar graph (graph grid provided in this lab, page 4) with the body area on the X

axis and the class averages on the reciprocals on the Y axis.

3. With eyes closed, feel objects of different textures (sandpaper, velvet, or synthetic fur, smooth

surface such as glass) with fingertips, posterior surface of forearm, and side of leg.

4. With your laboratory group, answer the discussion questions on tactile sensitivity.

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Tactile Sensitivity Graph

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Discussion Questions: Tactile Sensitivity

1. Which body area tested had the greatest density of tactile receptors?

2. Which body area tested had the lowest density of tactile receptors?

3. Which body area tested had the greatest sensitivity to different textures?

4. Which body area tested had the least sensitivity to different textures?

5. Which body area tested was represented by the largest area of cerebral cortex?

6. Which body area tested was represented by the smallest area of cerebral cortex?

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C. Visual Tests

Visual acuity tests measure the ability of the lens to focus light reflected from an object on the

central of the retina. The lens can accommodate or change shape to bend light rays to focus them

on the central fovea. At 20 feet, light rays from an object are nearly parallel and do not have to bend

as much to focus on the central fovea. At this distance, the lens is flattened and the refractive power

(ability to bend light rays) of the lens is lowest. To observe objects closer than 20 feet, the lens must

change shape or accommodate to focus light rays on the central fovea. The lens bulges to increase

the refractive power. Individuals that have normal distance vision and near vision are emmetropic,

individuals that have normal distance vision but blurry near vision are hyperopic (farsighted), and

individuals who have blurry distance vision but normal near vision are myopic (nearsighted).

As we age, the ability of the lens to accommodate diminishes and the ability to focus on very

close objects decreases, a condition called presbyopia. The near point of vision is the closest

distance that a person can focus on an object. The average near point of vision is 10 cm for a young

adult, 20 cm for an adult in their 40’s and 80 cm for someone in their 60’s.

ACTIVITY 3~ VISUAL TESTS

1. Distance visual acuity is measured using a Snellen eye chart (provided by your instructor). If you

wear eye glasses or contacts, remove them to determine visual acuity without correction or

wear them to determine visual acuity with correction.

Have subject stand 20 feet from the Snellen eye chart that is placed in a well-lighted

area, and cover their left eye with the paper card provided by your instructor.

Have subject read the smallest line of letters she/he can without squinting. If the subject

can correctly read half or more of the letters, then ask the subject to read the letters on

the next smaller line.

Record the number of the line with the smallest-sized letters read with half or greater

accuracy in Table 19B.2 on the next page.

Cover the right eye with the paper card provided and repeat the procedure.

A value of 20/20 indicates that the subject has normal vision. A value of 20/40 indicates

that the subject sees at 20 feet what a person who has normal vision sees at 40 feet. A

value of 20/15 indicates that the subject sees at 20 feet what a person with normal

vision sees at 15 feet.

B.

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2. Answer the discussion question with your lab group.

Discussion Question: Visual Test

1. Why must the subject stand 20 feet from the Snellen eye chart to test distance vision?

D. Auditory and Equilibrium Tests

Hearing loss can be either conduction deafness or sensorineural deafness. Conduction deafness

can be caused by decreased ability to conduct energy of sound waves through the external and

middle ear to hearing receptors in the inner ear. Ear wax buildup, damage to tympanic membrane,

or fusion of auditory ossicles may cause conduction deafness. Sensorineural deafness can be caused

by damage to hair cells in the spiral organ, damage to the cochlear branch of the vestibulocohlear

nerve, or damage of the neural pathways to the auditory cortex.

Inflammation of or injury to equilibrium receptors can result in an inability to maintain body

position, vertigo, and/or dizziness. Vertigo is the sensation of circular motion either of oneself or

external objects, while dizziness is often used to describe faintness, unsteadiness, or

lightheadedness. Severe vertigo may be accompanied by nystagmus rapid, involuntary movement

of eyeballs.

ACTIVITY 4~ AUDITORY AND EQUILIBRIUM TESTS

Unilateral conduction deafness can be mimicked by placing a cotton ball in one external auditory

canal.

1. Test for unilateral (one-side only) deafness using the Weber test.

Have the subject sit with head erect and facing forward.

Strike a tuning fork (middle C preferable) and place it medially on the subject’s forehead

(bone conduction).

Ask the subject if the sound is equally loud in both ears or louder in one ear. Circle the

result in Table 19B.3 on page 9.

If the sound is equally loud in both ears, the subject either has normal hearing or equal

hearing loss in both ears. If the subject hears the sound louder in one ear, then the

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subject may have either conduction deafness in that ear or sensorineural deafness in

the opposite ear.

To determine if the subject has conduction deafness or sensorineural deafness, conduct

the Rinne test.

2. Test for conduction or sensorineural deafness using the Rinne test.

Have the subject sit with head erect and facing forward.

Strike a tuning fork and place it on the subject’s right mastoid process to test hearing by

bone conduction.

Ask the subject to tell you when she/he can no longer hear the sound, then place the

still-vibrating tuning fork to her/his right ear to test hearing by air conduction. If the

subject can hear the tuning fork again when it is placed next to her/his ear, the subject

does not have conduction deafness in that ear. If the subject cannot hear the tuning fork

again, then the subject may have conduction deafness in that ear.

Circle the results in Table 19B.3 if normal.

To verify conduction deafness, test the same ear again. This time you are testing hearing

by air conduction first.

Strike the tuning fork again and place the tuning fork close to the subject’s ear.

Ask the subject to tell you when she/he can no longer hear the sound, and then place

the tuning fork on the subject’s mastoid process (bone conduction). If the subject hears

the sound again, she/he has conduction deafness in that ear. Record whether the

subject has normal hearing in that ear or conduction hearing loss by circling the results

in Table 19B.3.

Repeat this procedure to the left ear.

3. Conduct balance test to evaluate static equilibrium receptors.

Have the subject stand in front of a wall or blackboard with their arms as her/his sides.

The subject cannot lean against the wall or support herself/himself in any manner.

Tell the subject to stand perfectly still. If the subject is in front of a blackboard or

whiteboard, mark the outline of her/his shoulders to determine when she/he sways.

Tell the subject to close her/his eyes and observe movement in the shoulders. Notice

that, although the subject may sway slightly, posture is always corrected. Signals from

the maculae are helping the subject to maintain posture. If the maculae are not

functioning, the subject will to be able to maintain posture and will exhibit large swaying

movements or will fall.

4. Conduct Barany’s test to evaluate function of semicircular canals and dynamic equilibrium

receptors. We will do this together as a whole class, not separately in our lab groups.

Choose a subject for this demonstration who does not really experience dizziness or

become nauseated when rotated. If the subject experiences nausea during the

demonstration immediately stop rotation.

Choose two people who are prepared to support the subject after inducing vertigo and

dizziness.

Provide the subject with a chair or stool that can be rotated. Have the subject sit on the

chair and hold onto the arms or seat for safety. Decide how the subject will position

her/his legs during rotation to ensure safety and prevent interference. Position 3-4

students around the chair to prevent the subject from falling off the chair.

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Tell the subject to slightly tilt her/hos head forward, focus on a distant object, and keep

both eyes open during the rotation.

Carefully turn the chair or stool clockwise, one turn per 2 seconds and stop suddenly. Be

prepared to support the subject until vertigo and/or dizziness has passed. The subject

will still experience rotation, indicating that the semicircular canals are functioning.

Endolymph continues to move within the membranous semicircular ducts for a short

time after rotation has stopped.

Observe which way the subject’s eyeballs are moving immediately after stopping

rotation. Record direction in Table 19B.3.

Lateral movement of the eyes indicates stimulation of the crista ampullaris in

the lateral semicircular canals.

Vertical movement of the eyes indicates stimulation of the crista ampullaris in

the anterior semicircular canals.

Rotational movement of the eyes indicates stimulation of the crista ampullaris

in the posterior semicircular canals.

Repeat the demonstration with the subject’s head tilted toward one shoulder, and then

again with the subject’s chin resting on her/his chest.

E. The Nose and Olfaction

The nose contains the receptors for the sense of smell or olfaction. Olfactory receptors are found

within the olfactory epithelium, a specialized area of the epithelium lining of the nasal cavity. The

olfactory epithelium covers the inferior surface of the cribform plate, the superior nasal concha, and

the upper part of the middle nasal concha.

The olfactory epithelium contains olfactory receptor cells, basal stem cells, and ducts of

olfactory glands. The olfactory receptor cells are bipolar neurons whose dendritic end is imbedded

in the mucus layer covering the surface of the olfactory epithelium and whose axons form the

olfactory nerves. The olfactory receptors are located on olfactory hairs that project from the

dendrites of the olfactory receptor cells.

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Olfactory nerves pass through the cribform plate and synapse on neurons in the olfactory bulb.

Nerve impulses then travel along the olfactory tract to the lateral olfactory area of the cerebral

cortex.

Olfactory receptors adapt to odors very quickly. This explains why when we are trying to

determine the source of an odor; we often lose the smell before we find it. If we leave the area and

return, we can smell the odor again.

ACTIVITY 5~ STRUCTURE OF THE OLFACTORY EPITHELIUM AND OLFACTORY ADAPTATION

1. Label the structures of the olfactory epithelium in Figure 19B.15.

2. Observe olfactory adaptation. Instructions start below Figure 19B.15.

3. Answer discussion questions about olfactory adaptation with your lab partners.

OLFACTORY ADAPTATION

1. Choose a subject, a timer, an experimenter (holds vial under subject’s nose), and a recorder.

2. Have the subject plug one nostril with cotton and close both eyes.

3. Hold a container of cloves just under the open nostril (time 0; keep the vial below the subject’s

nostril) and ask the subject to inhale through the open nostril and exhale through the mouth.

4. Ask the subject to tell you when the odor has disappeared, note the time, and record it in Table

19B.4 on the next page. Instruct the subject to immediately pull out the cotton in the other

nostril and inhale (vial still under nose).

5. Ask the subject if she/he can smell cloves. Record the results in Table 19B.4.

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6. Repeat the experiment with another distinct smell, such as peppermint or cinnamon. Avoid

irritating odors.

Discussion Questions: Olfactory Adaptation

1. Is the time of adaptation the same for all odors?

2. After the nostril was unplugged, explain why the subject was able to smell the odor again.

F. The Taste Buds and Gustation

Taste buds, which are found on the tongue, soft palate, pharynx (throat), and larynx, are

microscopic, onion-shaped structures that contain gustatory cells, gustatory hairs, and

supporting cells. Each gustatory cell has one gustatory hair that projects through an opening,

the taste pore, on the apical end of the taste bud. Gustatory receptors are located on the

gustatory hairs. The basal ends of the gustatory cells synapse onto the dendritic end of the

sensory neurons. Axons from the sensory neurons contribute fibers to the facial (cranial nerve

VII), glossopharyngeal nerve (IX), or vagus nerve (X), depending on the location of the taste bud.

Taste buds on the tongue are located in papillae, elevated structures that give the

tongue its rough appearance. There are three types of papillae: vallate (circumvallate),

fungiform, and filiform. Vallate (circumvallate) papillae are the largest papillae and form an

inverted V at the posterior of the tongue. Fungiform papillae are mushroom-shaped and are

scattered over the surface of the tongue. Filiform papillae are slender pointed projections that

cover the surface of the tongue and give the tongue a rough texture. Taste buds are found in all

vallate papillae, but rarely in filiform papillae.

There are four primary taste sensations: sweet, bitter, salty, and sour, and a possible

fifth, MSG (monosodium glutamate). Gustatory receptors most sensitive to sweet and salty

sensations are found on the tip of the tongue, while bitter sensations are in the back and sour

sensations on the sides of the tongue. Other taste sensations are a mixture of these four. Smell,

temperature, and texture (tactile sensation) contribute to our sense of taste. A person with a

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cold often has a loss of taste due to a loss of smell. Cold French fries are not as tasty as hot ones,

and mushy apples are not as good as crisp ones.

ACTIVITY 6~ GUSTATORY STRUCTURES AND SENSATIONS

1. Label the gustatory structures in Figure 19B.16a, Figure 19B.16b, and Figure 19B. 16c.

2. Examine the contribution of texture and smell to the sense of taste.

Choose a subject, an experimenter (who will give the food cubes to the subject), and a

recorder. The subject will first try to identify food by texture only (rolling food on

surface of tongue), then by taste (chewing food increases the amount of chemicals

dissolved in saliva and capable of interacting with taste receptors), finally with the

addition of smell.

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Place ½-inch cubes of carrot, banana, apple, raw potato, and cheese on a plate.

Have the subject pinch both nostrils, close both eyes, and open her/his mouth.

Randomly choose one of the cubes and place it in the subject’s mouth.

Instruct the subject to roll the food around the surface of the tongue and attempt to

identify the food. If identification is correct, check the texture only column in Table

19B.5 below.

Instruct the subject to chew the food and attempt to identify the food. If identification is

correct, check the texture and taste column in Table 19B.5.

Instruct the subject to open both nostrils and attempt to identify the food. If

identification is correct, check the texture, taste, and smell column in Table 19B.5.

Repeat procedure with other food cubes.

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4. Inability to maintain posture while standing would indicate a problem with which equilibrium receptor?

A.

B.

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C.

D.