Reflex Lab Procedures for Reflex Lab In this lab we will test muscle stretch reflexes and cutaneous reflexes. A partner is needed to be the subject for this lab. Purpose: To test and observe normal muscle stretch and cutaneous reflexes. Equipment: Reflex hammer, Background: In the most narrow sense, a reflex is an involuntary, unpremeditated response by the body to an external stimulus. Reflexes allow reaction to a stimulus more quickly than would be possible if conscious thought were involved. A reflex can be described as a stimulus-response cycle. Most reflexes involve the brainstem or the spinal cord and do not require interaction from higher brain centers. The muscle stretch reflexes are the simplest reflexes. They involve the sensory neuron synapsing directly upon the motor neuron. They are sometimes called monosynaptic reflexes. They are also called spinal reflexes because the reflexive action does not require input from the brain. The other reflexes we will be testing in this lab are the cutaneous reflexes. They are also called superficial reflexes because the receptors are in the superficial areas of the body. They are more complex and require the message to go up the spinal cord to the brain and then back down to elicit the response. These can be used to test for CNS injury. There are five components to a reflex; these components together are called the reflex arc. The components are as follows: sensory receptor – receives the stimulus and generates an impulse (is usually a nerve ending) afferent pathway – a neuron that carries the impulse from the receptor to a central integrating center integrating center –this is where the afferent component connects to the efferent component- this is in the CNS. One or more synapses must occur here. Interneurons are not involved in stretch reflexes but are always found in all other types of reflexes. efferent pathway - a neuron that carries the impulse from the integrating center to an effector. effector -receives the impulse and responds. The effector may by skeletal muscle, smooth muscle, or glands.
Part I. Stretch reflexes.
First do muscle stretch reflexes which are also called deep tendon reflexes.
It is important the subject relax the muscle being tested. Tell the subject to let the muscle go limp.
Rate each response according to the following scale:
+4 very brisk, hyperactive, large movement at joint.
+3 brisker than average, medium movement at joint
+2 average, small movement at joint
+1 somewhat diminished, very small or no movement at joint
0 no response
A. Patellar (also called the knee jerk reflex) – activation of femoral nerve. The receptor is located in the quadriceps muscle, the effector is the quadriceps muscle. The nerve ending is responding to the stretch of the muscle caused by striking the tendon.
1. A subject is allowed to sit comfortably on a table with knees dangling over the edge.
2. Using a reflex hammer (or substitute as described above) strike the patellar tendon just below the kneecap.
3. Observe the action caused by the reflex.
4. Record your results using the graded scale above.
B. Biceps Reflex – activation of the musculocutaneous nerve
1. Rest subject’s left forearm along your left forearm.
2. Subject’s hand should rest in or near the bend of your elbow.
3. Press your left thumb on the subject’s biceps tendon, apply a little pressure.
4. Strike your thumb with the reflex hammer, this will transfer the pressure to the biceps tendon.
5. Watch carefully for twitching of the biceps muscle. Usually, the forearm will not move.
6. Record your results using the graded scale above.
C. Triceps reflex – activation of the radial nerve.
This is a difficult reflex to observe, but give it a try.
1. The subject should have the arm relaxed and elbow bent.
2. Support the entire weight of the arm with your left hand.
3. Strike the triceps tendons, just above the elbow.
4. Watch carefully for twitching of the biceps muscle.
5. Record your results using the graded scale above.
Both B and C show up best on someone who doesn’t have a lot of subcutaneous fat and who has good muscle definition.
D. Achilles reflex (also called ankle-jerk reflex) – activation of the poplitealnerve. The principle is similar to the knee-jerk reflex. Here the stretch receptors are located in the gastrocnemius muscle.
1. Have the subject take her/his shoes and socks off, exposing the Achilles tendon on the back of the ankle.
2. Strike the Achilles with the reflex hammer (or substitute) and observe the extension of the foot downward.
3. Record the results using the graded scale above.
Part II. Cutaneous reflexes
A. Plantar reflex
This reflex differs from the four muscle stretch reflexes. In this reflex, receptors are stimulated in the sole of the foot (cutaneous receptors). The reflex pathway travels up the leg to the integrating center. While in the integrating center, the reflex travels up the spinal cord through the pyramidal tracts, which are nerve pathways between the spinal cord and brain.
1. The subject needs to lie on his or her back, with shoes and socks off.
2. Using the end of the handle of the reflex hammer, trace a path along the lateral side from heel to the little toe to the big toe.
3. Observe for the flexion (toe curling) which is recorded as a normal plantar reflex.
4. If the toes curl, this is called a Negative Babinski response and is normal. If the toes flare, then an abnormal response is recorded and is called a Positive Babinski response and indicates CNS damage.
5. Record the results.
B. Ciliospinal reflex – This reflexive pathway is from the skin to the thoracic spinal cord, through the sympathetic trunk, then to the dilator pupillae muscle of the eye. This is another test of the CNS.
1. Pinch the back of the subject’s neck,
2. Watch pupils for a response.
3. A normal response is dilation of the pupil.
4. Record your results.
