Reflex Activities
PART I. Reflexes and Reflex Arcs (Exercise 17, p. 309)
Nerve impulses follow routes through the nervous system called nerve pathways. Some of the simplest nerve pathways consist of little more than two neurons that communicate across a single synapse. Reflexes are rapid, involuntary responses to stimuli, which are mediated over simple nerve pathways called reflex arcs. Involuntary reflexes are very fast, traveling in milliseconds. The fastest impulses can reach 320 miles per hour. Reflex arcs have five essential components:
1. The receptor at the end of a sensory neuron reacts to a stimulus. For example, some receptors in the skin are sensitive to heat, others to pressure.
2. The sensory neuron conducts nerve impulses along an afferent pathway towards the CNS.
3. The integration center consists of one or more synapses in the CNS.
4. A motor neuron conducts a nerve impulse along an efferent pathway from the integration center to an effector.
5. An effector responds to the efferent impulses by contracting (if the effector is a muscle fiber) or secreting a product (if the effector is a gland).
Reflexes can be categorized as either autonomic or somatic. Autonomic reflexes are not subject to conscious control, are mediated by the autonomic division of the nervous system, and usually involve the activation of smooth muscle, cardiac muscle, and glands. Somatic reflexes involve stimulation of skeletal muscles by the somatic division of the nervous system. Most reflexes are polysynaptic (involving more than two neurons) and involve the activity of interneurons in the integration center. Some reflexes; however, are monosynaptic ("one synapse") and only involve two neurons, one sensory and one motor. Since there is some delay in neural transmission at the synapses, the more synapses that are encountered in a reflex pathway, the more time that is required to effect the reflex.
Reflex testing is an important diagnostic tool for assessing the condition of the nervous system. Distorted, exaggerated, or absent reflex responses may indicate degeneration or pathology of portions of the nervous system, often before other signs are apparent. If the spinal cord is damaged, then reflex tests can help determine the area of injury. For example, motor nerves above an injured area may be unaffected, whereas motor nerves at or below the damaged area may be unable to perform the usual reflex activities. Closed head injuries, such as bleeding in or around the brain, may be diagnosed by reflex testing. For example, remember that the oculomotor nerve stimulates the muscles in and around the eyes. If pressure increases in the cranium (such as from an increase in blood volume due to brain bleeding), then the pressure exerted on CN III may cause variations in the eye reflex responses.
Fig. 1. Knee Jerk Reflex Demonstrating a Reflex Arc
Testing Stretch Reflexes
The primary tool that we will be using to test reflex activity is the Reflex Hammer (Fig.2). Care must be taken to use the proper hammer technique during our lab activities. Improper techniques will not elicit the desired reflexes. The tap stretches a muscle, which stimulates stretch receptors located in the muscle. In response to the increased stretch, which normally would only occur when the muscle load has suddenly increased, the muscle contracts. In this demonstration, such a reaction seems strange, but in normal circumstances the stretch reflex allows muscles to reflexively increase the strength of contraction in response to increased load.
Fig. 2. Reflex Hammer
Activity 1: Patellar knee-jerk reflex
The patellar reflex, or knee-jerk reflex, is centered in the spinal cord and is used to assess the nervous tissue between (and including) the L2 and L4 segments.
1) Test the knee-jerk reflex for each member of the class using a reflex-hammer. Have the subject sit on the lab bench with the lower leg unsupported to create a stretch in the quadriceps muscle (see figure 22.4, p 343).
2) Record positive (+) and negative (-) responses on the attached data sheet. If the patellar reflex is abnormal (ABN), record this on the data sheet as well.
3) Diagram the patellar reflex in your lab notebook, indicating sensory neurons, interneurons, and motor neurons.
4) Answer the following questions in your lab notebook:
a. What muscle(s) contract during a normal patellar reflex? Which are relaxed?
b. What nerve is carrying afferent and efferent nerve impulses?
c. Is the reflex ipsilateral or contralateral? Monosynaptic or polysynaptic?
d. What would an abnormal patellar reflex look like? (You may need to do an internet search to answer this question).
e. What type(s) of conditions may be indicated for an abnormal patellar reflex?
Activity 3: Plantar Reflex
The plantar reflex is a superficial spinal reflex that depends both on functional upper-level motor pathways and on the cord-level reflex arc. In adults, stimulation of cutaneous receptors in the sole of the foot (as when testing the plantar reflex) usually causes the toes to flex and move together. Damage to the corticospinal tract (or incomplete myelination of the nervous system, as is the case with infants) produces Babinski's sign, an abnormal response in which the toes flare and the great toe moves in an upward direction (Fig. 3).
Fig. 3. Normal Plantar Reflex and Babinski Reflex
1) Test the plantar reflex for each member of the class using the handle of the reflex hammer. Record positive (+) and negative (-) results in the attached data table.
2) Answer the following questions in your lab notebook:
a. What muscle(s) contract during a normal plantar reflex? Which are relaxed?
(note, we have not previously discussed some of these muscles in lab)
b. What nerve is carrying afferent and efferent nerve impulses?
c. Is the reflex ipsilateral or contralateral?
d. What would an abnormal plantar reflex look like? (You may need to do an internet search to answer this question)
e. What type(s) of conditions may be indicated for an abnormal plantar reflex?
Activity 6: Pupillary Reflex
The pupillary light reflex (PLR) is the constriction of the pupil that is elicited by an increase in illumination of the retina. This is a parasympathetic response; whereas, a decrease in illumination results in the pupil dilating, a sympathetic response.
Fig. 4. Pupillary Light Reflex
1) Follow the directions outlined in activity 6 of your lab manual (p 346). Record the “normal” diameter of the pupil by holding a ruler close to the eye. (Do this for both R and L pupils.) Record these baseline measurements in the attached data table.
2) Have the subject shield the right eye with his or her hand. Then shine a flashlight into the left eye for five seconds. Measure the pupil diameter in both eyes immediately and record in the data table.
Table 1. Pupillary Reflex
Right pupil / Left PupilPupil Diameter
3) Answer the following questions:
a. What is the function of the pupillary reflex (why is it “beneficial” for the pupils to change diameter when exposed to a bright light?)
b. Which pupil showed the greatest change in diameter?
c. Did the right pupil (not exposed to light) change size after the experiment? If so, explain why.
d. What part of the brain is responsible for initiating the pupillary reflex?
e. What could an abnormal pupillary reflex indicate?
Activity 7: Ciliospinal reflex
The ciliospinal reflex consists of dilation of the ipsilateral pupil in response to pain applied to the neck, face, and upper trunk. If the right side of the neck is subjected to a painful stimulus, the right pupil dilates (increases in size 1-2mm from baseline).
1) Test the ciliospinal reflex for each member of the class. Follow the directions on p. 315 of your lab manual.
2) Use the pointed end of the reflex hammer to quickly stroke the skin on one side of the back of the neck.
3) Observe any changes of the pupil diameter on the ipsilateral side.
4) Record pupillary dilation (+) or constriction (-) in the data table below. If the subject shows no visible change in pupil diameter, record “no response” (NR) in the data table.
Table 2. Pupil Dilation Occurrence with Ciliospinal Reflex
Right pupil / Left PupilPART II. General Sensation (Exercise #18, p.323)
The following experiments test mechanoreceptors and thermoreceptors in the skin.
Activity 2: Determining two point discrimination
Two-point touch discrimination is the minimum distance at which 2 points of touch can be perceived as separate (Fig. 11).
Fig. 5. Calipers for 2-point touch discrimination
Fig. 6. Two-Point Touch discrimination.
In this exercise you will test different body areas (fingertips, ventral forearm, and back of neck) for 2-point discrimination threshold.
1) Which body area do you think will have the finest 2-point discrimination threshold? (Record your hypothesis)
2) Measure the two-point threshold for each body area using the plastic calipers supplied in lab. Repeat three times for each area.
3) Record the average two point threshold for each body area.
Table 3. Two-Point Touch discrimination (mm).
Trial / fingertip / forearm / Back of neck1
2
3
Ave
4) Was your hypothesis supported or refuted by the data? Include a brief conclusion statement in your lab notebook.
Activity #3 Testing tactile localization
As demonstrated in the last activity, different areas of the body contain different numbers of touch receptors. In this activity, you will test the ability of the body to localize (determine exact placement) of touch stimuli.
Instructions
1) Which area of the body will have the best degree of tactile localization? (Record your hypothesis).
2) Have the subject sitting down, eyes closed, with his or her palm outstretched.
3) Touch the subject’s hand with a felt-tip marker.
4) With their eyes still closed, have the subject try to hit the same spot with their own marker (must be of a different color).
5) Use calipers to measure the distance between the two dots for each body area. Record this in the data table.
6) Graph the average error of localization for each area of the body.
7) Did the results support your hypothesis? Write a brief conclusion statement.
Table 4. Tactile Localization on Palm (mm).
Trial 1 / Trial 2 / Trial 3 / Trial 4 / Trail 5Activity # 7 Demonstrating referred pain
Referred pain is the phenomenon of perceiving pain in one area of the body when another area is actually receiving the painful stimulus. This occurs because somatic and visceral pain fibers often travel through the same nerve pathways in the spinal cord and brain. For example, pain from a heart attack may be felt in the neck, jaws, arms, or abdomen.
Determine referred pain in an experiment using ice.
Instructions
1) Immerse the subjects elbow in a cooler of ice water
2) Record the quality (severity) and locality of pain at 1 minute intervals for 3 minutes (see table on p. 328 of your lab manual)
3) Remove the elbow and at the end of 1 minute continue to assess any changes in location and quality of pain.
3) Question: how did the progression and quality of pain change during the experiment?
NOTE: The ulnar nerve, which controls the ring finger, little finger, and inner side of the hand, passes over the elbow joint.
Fig. 7. Referred Pain
Fig. 8. Pain Assessment Scale Fig. 9 Elbow in ice
Table 5. Assessing Referred Pain; Elbow in Ice
TimeMinutes / Pain Scale
0-10 / Location and Quality of Pain
1
2
3
Remove elbow from ice at end of 3 minutes
4