Human Anatomy & Physiology Reflex Physiology lab. Objectives: To understand what reflexes are, the processes involved, and purpose of reflexes.

Transcription

1 Human Anatomy & Physiology Reflex Physiology lab Objectives: To understand what reflexes are, the processes involved, and purpose of reflexes. Introduction: A reflex is an involuntary neural response to a specific sensory stimulus that threatens the survival or homeostatic state of an organism. Reflexes exist in the most primitive of species, usually with a protective function for animals when they encounter external and internal stimuli. In humans and other vertebrates, protective reflexes have been maintained and expanded in number. Examples are the gag reflex that occurs when objects touch the sides or the back of the throat, and the carotid sinus reflex that restores blood pressure to normal when baroreceptors detect an increase in blood pressure. A second type of reflex, the stretch reflex, has evolved to help maintain muscle tone that is important for posture and movement. Reflexes can be categorized into one of two large groups: autonomic reflexes and somatic reflexes. Autonomic (or visceral) reflexes are mediated through the autonomic nervous system, and we are not usually aware of them. These reflexes active smooth muscles, cardiac muscles, and the glands of the body and they regulate body functions such as digestion, elimination, blood pressure, salivation, and sweating. Somatic reflexes include all those reflexes that involve stimulation of the skeletal muscles by the somatic division of the nervous system. An example of such a reflex is the rapid withdrawal of a hand from a hot object. An understanding the neural circuitry underlying each type of reflex also has clinical significance. When physicians test for potential damage to various components of the nervous system, they often begin by attempting to elicit reflex responses to the appropriate stimuli. Examples of reflexes with protective and diagnostic importance are the flexor withdrawal reflex, the corneal (blink) reflex, and the accommodation reflex. The loss of the papillary light reflex in a comatose patient often indicates extreme damage deep in the brain. Loss of the knee-jerk response may indicate problems with muscle tone, chronic diabetes, or damage at the L2, L3, or L4 vertebral level. All reflex arcs have five basic components: 1) a sensory receptor, 2) a sensory (or afferent) neuron, 3) interneurons (the middle man), 4) a motor (or efferent) neuron, and 5) an effector organ (muscle fibers, or glands). General Guidelines: Use a general two-column format for this lab (similar to what many of you did in chem. Labs) You do NOT need to write all instructions for each activity, but should use the left column to briefly describe the activity, and the right column to record observations and pertinent data. Label each activity with a separate heading (e.g. Initiating the Stretch Reflex) and number each group of questions.

2 Write down all of your answers in your lab book. You should not need to re-write the questions; however, state your answer in such a way as to subtly restate the question so that your answer makes sense upon further review. Opening Questions: **Answers can be found in the introduction AND in your textbook. (pages ) Answer these questions at the beginning of the lab after you ve written the title and purpose of the lab. A. What is a reflex? What is a reflex arc? B. Explain the differences between the two basic types of reflexes. C. Why do physicians test your reflexes? D. What are the components of the Withdrawal Reflex Arc & the Knee-Jerk Reflex? Initiating the Stretch Reflex Stretch reflexes are important postural reflexes, normally acting to maintain posture, balance, and locomotion. Stretch reflexes are initiated by tapping a tendon, which stretches the muscle the tendon is attached to (the Quadriceps femoris muscle). This stimulates the muscle spindles and causes reflex contraction of the stretched muscle or muscles, which resists further stretching. Even as the primary stretch reflex is occurring, impulses are being sent to other destinations as well. For example, branches of the afferent fivers also synapse with interneurons controlling antagonist muscles. The inhibition of antagonist muscles that follows, called reciprocal inhibition, causes them to relax and prevents them from resisting (or reversing) the contraction of the stretched muscle caused by the main reflex arc. Additionally, impulses are relayed to higher brain centers to advise of muscle length, speed of shortening, and the like information needed to maintain muscle tone and posture. Stretch reflexes tend to be absent or hypoactive in cases of peripheral nerve damage or ventral horn disease, and hyperactive in corticospinal tract lesions. They are absent in deep sedation and coma. Procedures: Patellar Reflex: 1) Have your partner relax & sit on the edge of a table with his/her legs dangling loosing over the edge. 2) The experimenter should apply the stimulus by tapping, firmly, but carefully, the area just below the kneecap with the reflex hammer. (Do not hurt your partner!) 3) Test both knees and record your observations. 4) Test the effect of mental distraction on the patellar reflex by having the subject add a column of three-digit numbers or some other similar task (singing a song, reciting the alphabet backwards, etc) while you test the reflex again. Is the response greater than or less than the original response? Explain

3 5) Test the effect of muscular activity occurring simultaneously in other areas of the body. Have the subject clasp the edge of the table and vigorously attempt to pull it upward with both hands. At the same time, test the patellar reflex again. Is the response more or less vigorous than the first response? Explain 6) Fatigue also influences the reflex response. The subject should jog in position until she or he is very fatigued (no slacking!!). Test the patellar reflex again and record whether it is more or less vigorous than the first response. 7) Switch roles & repeat. Record all observations Initiating Achilles Reflex 1) With your shoe removed and your foot dorsiflexed slightly (pointed up) to increase the tension in your gastrocnemius muscle (calf muscle) have your partner sharply tap your Achilles tendon with the reflex hammer. Record your results. The experimenter should hold the subject s ankle by supporting the foot lightly in the hand & then tap the tendon just above the ankle. 2) Switch roles & repeat. Initiating the Plantar Reflex The plantar reflex, an important neurological test, is elicited by stimulating the cutaneous receptors in the sole of the foot. In adults, stimulation of these receptors causes the foot to flex and move closer together. Damage to the corticospinal tract, however, produces Babinski s sign, an abnormal response in which the toes flare and the great toe moves in an upward direction. (In newborn infants, Babinski s sign is observed due to incomplete myelination of the nervous system). 1) Have the subject remove a shoe and lie on the table with knees slightly bent and thighs rotated so that the lateral side of the foot rests on the table. Alternatively, the subject may sit up and rest the lateral surface of the foot on a chair. Draw the end of a pencil, a ruler, or your finger, firmly down the lateral side of the exposed sole from the heel to the base of the great toe. Record the response. Is this a normal plantar reflex or Babinski s sign? 2) Switch roles & repeat. Initiating the Corneal Reflex 1) Stand to one side of the subject; the subject should look away from you toward the opposite wall. Wait a few seconds and then quickly but gently, touch the subject s cornea (on the side toward you) with the tip of a Q-Tip. What reflex occurs when something touches the cornea? What is the function of this reflex? 2) Switch roles & repeat.

4 Stretch Reflex Questions: A. What are the functions of the stretch reflex? B. What is reciprocal inhibition and why does it exist? Autonomic Reflexes: The autonomic reflexes include the papillary, ciliospinal, and salivary reflex, as well as a multitude of other reflexes. Initiating the Pupillary Reflex There are several types of papillary reflexes. The papillary light reflex and the consensual reflex are two. In both of these reflexes, the retina of the eye is the receptor, the optic nerve is contains the afferent neurons, the oculomotor nerve is responsible for conducting motor impulses to the eye, and the smooth muscle of the iris is the effector. Many central nervous system centers are involved in the integration of these responses. Absence of the normal papillary reflexes is generally a late indication of severe trauma or deterioration of the vital brain stem tissue due to metabolic imbalance. 1) The lights must be dimmed in the room to conduct this portion of the lab. Before beginning, obtain a metric ruler to measure and record the size of the subject s pupil as best you can. Record the size (in mm) for both the right and left pupils. Record. 2) Stand to the left of the subject to conduct the testing. The subject should shield his or her right eye by holding a hand vertically between the eye and the right side of the nose. Shine a flashlight into the subject s left eye. Record the response and measure the size of the pupil to the best of your ability. 3) Observe the right pupil. Has the same type of change (called a consensual response) occurred in the right eye? Measure the size of the right pupil to the best of your ability. 4) Switch roles and repeat. The consensual response or any reflex observed on one side of the body when the other side has been stimulated, is called a contralateral response. The papillary light response, or any reflex occurring on the same side stimulated is referred to as an ipsilateral response. A. Was the sympathetic or the parasympathetic division of the autonomic nervous system active during the testing of these reflexes? B. What is the function of these papillary reflexes? Reaction Time of Basic and Learned or Acquired Reflexes The time required for a reaction to a stimulus depends on many factors sensitivity of the receptors, velocity of nerve conduction, the number of neurons and synapses involved, and the speed of effector activation, to name just a few. Some reflexes are basic or inborn; others are

5 learned or acquired reflexes, resulting from practice or repetition. There is no clear-cut distinction between basic and learned reflexes, as most reflex actions are subject to modification by learning or conscious effort. In general, however, if the response involves a specific reflex arc, the synapses are facilitated and the response time will be short. Learned reflexes involve a far larger number of neural pathways and many types of higher intellectual activities, including choice and decision making, which lengthens the response time. 1) Using the reflex hammer, elicit the patellar reflex in your partner. Note the relative reaction time needed for this basic reflex to occur. 2) Now test the reaction time for learned reflexes. The subject should hold a hand out, with the thumb and index finger extended. Hold a meter stick so that it s end is exactly 3 cm above the subject s outstretched hand. The meter stick should be in the vertical position with the numbers reading from the bottom up. When the meter stick is dropped, the subject should be able to grasp it between thumb and index finger as it passes, without having to change position. Have the subject catch the meter stick five times, varying the time between trials. The relative speed of reaction time can be determined by reading the number on the meter stick at the point of the subject s fingertips. **(Thus, if the number at the fingertips is 15 cm, the subject was unable to catch the meter stick until 18 cm of length had based through their fingers; 15 cm plus 3 cm. to account for the distance of the meter stick above the hand. 3) Record the number of cm that pass through the subject s fingertips for each of the five trials. 4) Perform this test again, but this time say a simple word each time you release the meter stick. Designate a specific word as a signal for the subject to catch the meter stick. (Record this word, for example your word might be "cat") On all other words, the subject is to allow the ruler to pass through their fingers. Ignore trials in which the subject erroneously catches the meter stick. Record the distance the ruler travels in five successful trials. Did the addition of a specific word to the stimulus increase or decrease the reaction time? Explain. 5) Perform the testing once again to investigate the subject s reaction time to word association. As you drop the meter stick, say a word for example hot. The subject responds with a word he or she associates with the stimulus word for example cold catching the meter stick while responding. If unable to make a word association, the subject must allow the meter stick to pass through their fingers. Record the distance the meter stick travels in five successful trials, as well as the number of times the meter stick is not caught by the subject. Do you notice a large variation in reaction times in this series of trials? Explain. A. What determines the speed of a reflex? B. What are the differences between innate and learned reflexes? C. Name at least three factors that may modify reaction time to a stimulus.

6 D. In general, how did the response time for the unlearned activity performed in the lab compare to that for the simple patellar reflex? E. Did the response time without verbal stimuli decrease with practice? Explain. F. Explain, in detail, why response time increased when the subject had to react to a word stimulus. Post Lab 1) Draw a detailed diagram of the spinal cord on a separate sheet of white paper. Label all parts. Include this diagram in your lab notebook. 2) Draw arrows to indicate the pathway of a reflex. The textbook has an example. Colored pencils may be helpful to distinguish the pathways & components of the different reflexes.