Sensation—Neurology 2
Background Information:
Nervous sensory receptors provide information from the external environment.
Information perceived by receptors is relayed via afferent pathways to the central nervous
system where the information is integrated and a response may be initiated. The time it
takes for signals to travel from a sensory receptor to the central nervous system and out to
an effector to elicit a response is often very rapid and can sometimes be measured as
reaction time. If a stimulus may indicate potential damage to an individual, the response
is a very rapid one known as a reflex arc. A simple reflex arc involves only two neurons,
one sensory neuron and one motor. Other types of reflexes have additional neurons
inserted in the pathway.
In order for sensations to be perceived and for an initial nerve impulse to be fired,
thresholds of stimulation must be reached. If a nervous impulse is fired repeatedly,
adaptation can occur. Adaptation occurs when the continued stimulus of sensor y
receptors results in a decrease in nerve impulse generation. Receptors may adapt rapidly
or slowly to continued stimulation dependent upon the stimulus.
Some areas of the skin have greater tactile sensitivity than others. The greater
number of cutaneous receptors in an area (receptor density), the greater the tactile
sensitivity of that area. The size of an area receiving sensory information from a specific
body area is directly proportional to the cutaneous receptor density. 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 he/she 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.
In certain cases, pain is perceived as arising in one area when in fact another is
receiving the stimulus. The pain is then said to be “referred” to a different area. Many
of us have experienced referred pain when we’ve experience the phenomenon known as
“brain freeze”. Referred pain is also often important in many types of clinical diagnoses
because damage to many visceral organs results in the phenomenon. For example,
inadequate oxygenation of the heart muscle often results in pain being referred to the left
shoulder and the reflux of gastric juice into the esophagus causes a sensation of intense
discomfort in the thorax referred to as ‘heartburn’.
The purpose of these laboratory exercises is to familiarize you with some central
concepts of nervous system function, particularly with respect to reflexes and the
sensation.
Experimental Protocol:
Activity A
1.) The density of touch receptors in the skin of various body parts varies
significantly. Areas that have a higher density of touch receptors have a greater
ability to distinguish between, or resolve, two close but disparate stimuli. Using
calipers and a metric ruler, you will be determining the ‘two-point threshold’ of
different body areas.
2.) Using the calipers provided, touch the various areas of your lab partner’s body
listed in the table below to determine the distance betwee n the points that must be
used in order for the subject to sense that it is indeed two separate points. His or
her eyes should be closed when touched. Begin with the two points together;
touch your partner in one of the places specified and ask if he/she can feel two
points or one. Increase the distance between the points by 1mm and touch again.
Continue to increase the distance in 1 mm increments until your partner can feel
two points. Record and be able to explain your observations. Have your partne r
repeat this protocol using you as the subject.
Area of Body
Distance recognizable as
two points (mm)
Back of hand
Palm of hand
Arm
Neck
Back
Cheek
Lips
Leg
Activity B
1.) Everyone has different likes and dislikes when it comes to food. Some people
have strong aversions to specific foods either due to a previous experience or
because something about the food—the taste or texture—does not appeal to them.
Some individuals seem to experience a greater intensity of taste and are deemed
supertasters. It is thought that the biological basis of ‘supertasting’ is the presence
of bitter taste receptors as well as an increased density of fungiform papillae and
therefore an increased number of taste buds. ‘Supertasters’ tend to have aversions
to alcoholic beverages, vegetables in the Brassica family, coffee, grapefruit juice,
green tea, spinach and soy products. Many ‘supertasters’ may be considered
‘picky eaters’.
‘Non-tasters’, on the other hand, are people who seem to have a lower intens ity of
taste and prefer foods with intense flavors, such as spicy and very sweet foods.
The biological basis of ‘non-tasting’ is thought to be a lower density of fungiform
papillae on the tongue.
In this activity, we will be testing the hypothesis that ‘supertasters’ have more
fungiform papillae than normal tasters or ‘non-tasters’.
2.) Obtain a small amount of the saccharine solution, a hole punch reinforcer blue
food coloring, a flashlight and a magnifying glass.
3.) Take a sip of the saccharine solution. Note whether its taste is: a.) sweet, b.) sweet
and bitter, or c.) bitter. If you select ‘sweet’, you are considered a ‘non-taster’; if
you select ‘sweet and bitter’, you are considered a normal taster, and if you select
‘bitter’, you are considered a ‘supertaster’.
4.) Place a drop of blue food coloring on the tip of your tongue. Swallow a few times
to evenly distribute the dye and remove any excess.
5.) Making your tongue as dry as possible, stick out your tongue and place a paper
hole reinforcer on the tip of your tongue in the area shown in the picture below.
The blue dye will stain the epithelium everywhere except on the fungiform
papillae.
6.) Using a flashlight and a magnifying glass, count the number of fungiform papillae
inside the hole.
7.) Compare your results with those of your classmates to determine the average
number of fungiform papillae for each group of ‘supertasters’, normal tasters, and
‘non-tasters’.
Activity C
1.) Stretch reflexes play an important role in maintaining posture. When a muscle is
stretched, a stretch reflex causes involuntary contraction of the muscle to prevent
further stretching plus the same reflex arc sends a signal to the antagonistic
muscle to cause it to relax to prevent further stretching of the muscle. An easily
examined example of a stretch reflex is the patellar, or knee-jerk, reflex.
2.) Obtain a reflex hammer.
3.) Have your lab partner sit on the laboratory bench with his/her legs hanging freely.
Lightly tap the patellar ligament (just below the knee) with the reflex hammer.
Note the reaction time.
4.) Next, have your lab partner do a ‘wall sit’ (back against the wall with legs bent to
a 90o angle at the knee) until he/she can no longer hold himself up (i.e., becomes
fatigued).
5.) Immediately re-test the patellar reflex by repeating step 3. Note the reaction time
relative to that which occurred in step 3.
Activity D
1.) The amount of time it takes to respond to a stimulus depends on a number of
factors such as sensitivity, the speed of neuronal conduction, the number of
neurons involved, etc. Some reflexes are basic or innate while others are learned
or acquired. The knee-jerk reflex is an example of a basic reflex, while a tennis
serve is a learned reflex. Learned reflexes tend to be more complicated, including
larger numbers of neuronal pathways and higher areas of the brain. Therefore,
they may be slower, having longer reaction times. In this activity, you will be
testing the reaction time for an acquired reflex. This can be compared to the
reaction time you noted in Activity C, above.
2.) Obtain a metric ruler.
3.) Have your lab partner hold out his/her hand with the index finger and thumb
extended. Hold the ruler approximately 3cm above your partner’s outstretched
hand. The ruler should be vertical with the numbers reading from bottom to top.
4.) Drop the ruler, having your lab partner attempting to catch the ruler between
his/her thumb and index finger. Record the distance that the ruler traveled before
it was caught by noting the location of his/her finger/thumb on the ruler.
5.) Repeat the activity 4 times, so that you obtain 5 total trials. Note whether there
was a change in reaction time from trial #1 to trial #5.
6.) Repeat steps 3-5, but this time, say a word when you drop the ruler. Have your
partner only catch the ruler if you say the specific signal word (e.g., dog, cat). On
all other ‘non-specified’ words, your partner should be instructed to let the ruler
fall through his/her hand. Record the distance that the ruler travels in each of the 5
trials.
7.) Compare your results from steps 3-5 versus step 6. Note whether the inclusion of
a ‘signal word’ increased or decreased reaction time.
Activity E
1.) In this activity, you will record four different segments of data using the BioPac
machine. In the first two segments, you will respond to random ‘click’ stimuli. In
the second two segments, you will respond to ‘click’ stimuli at fixed intervals (~4
seconds apart). Your lab partner will push ‘Record’ to initiate the first segment;
your lab partner will push ‘Resume’ to initiate segments 2-4.
2.) Lesson L11 (React 1) should be selected and running on the BioPac. If the
program is not running, consult your laboratory instructor.
3.) Put on the headphones and grab the hand-held device.
4.) When you are ready, have your lab
partner select the “Record” icon.
Each time a sound is heard, press the
button on the hand switch (this is a
‘click’) as quickly as possible. The
recording will stop automatically
after 10 clicks. The screen should
look similar to the one in the picture
to the left. If it does not, have your
lab partner select the “Redo” icon
and repeat the trial.
5.) When you are ready, have your lab partner select the “Resume ” icon. Each time a
sound is heard, press the button on the hand switch.
6.) When you are ready, have your lab partner select the “Resume ” icon for the 3rd
segment—the first of the ‘random interval’ trials.
7.) When you are ready, have your lab partner select the “Resume ” icon for the 4th
segment—the first of the ‘random interval’ trials.
8.) Have your lab partner select the “Done ” icon after all 4 trials have been
completed. A ‘pop up box’ will appear, providing you with some options.
9.) Select the “Analyze current data file” on the ‘pop up box’.
10.) All 10 reaction times are automatically calculated for each segment of the
experiment and have been documented in the ‘journal’ at the bottom of the
computer screen.
11.) Copy the reaction times for each segment into the chart below.
12.) When finished, exit the program by going to the File menu at the top of the page
and selecting “Quit”. An option will appear to “Record from another Subject”.
Select that option.
13.) Operate the program by selecting “Record” and “Resume” when appropriate so
that your lab partner can perform the four segments described in steps 3-12.
14.) On the data table below, delete the highest and lowest values for each segment,
and calculate and record the average value for the remaining 8 data points.
15.) Compare your data for each segment with the values obtained by others in your
class.
Activity F
1.) Obtain a bucket of ice water.
2.) Immerse your elbow in the bucket of ice water, and have your lab partner record
the location and quality of sensation (i.e., pain, tingling, discomfort) for 2
minutes.
3.) Record the same parameters as your lab partner immerses his/her elbow in the ice
water.