Lab 15: Reflex Physiology
Objectives
1. To define reflex, reflex arc, stretch reflex, and protective reflex
2. To name, identify, and to describe the function of each component of a reflex arc
3. To explain why reflex testing is important in assessing the condition of the nervous system
4. To describe the components of reflex arcs involved in patellar reflex, and pupillary light reflex), and to explain the functional importance of each.
a) Work in pairs. Have the subject close his/her eyes (why?) and sit on the edge of the examining table with his/her legs dangling free.
b) Locate the patellar ligament (Which muscle is stretched when this ligament is tapped? ___________________________), palpate the soft tissue depression on either side of the ligament.
c) Illicit the reflex by tapping the ligament with a reflex hammer at the level of the knee joint, using a short, smart wrist action, note the response.
d) Test the effect of mental distraction on the patellar reflex by having the subject add a column of three-digit numbers while you test the reflex again. Is the response greater or less than the first time?
e) Now test the effect of muscular activity occurring simultaneously in other areas of the body. Tap the patellar ligament while the subject performs the Jendrassik's maneuver (the subject clasps his/her hands in front of him/her and, with fingers locked, tries vigorously to pull his/her hands apart). Is the response greater or less than the first time?
f) Change places with your partner and repeat steps "a" through "e".
g) In the space below, draw a diagram showing the reflex arc involved in the patellar reflex and label each component with specific organ names.
h) If you observed that mental distraction or Jendrassik's maneuver influences the response of patellar reflex, explain the reason in the space below.
i) Explain the protective function of patellar reflex (be specific) in the space below.
Some optic nerve fibers synapse in the midbrain on the same side that the eye was stimulated, while others cross and synapse in the midbrain on the opposite side. Therfore, the neurons in the midbrain process the signal on both sides of the brain. As a result a direct pupillary light reflex is produced in the eye that is stimulated with light and a consensual pupillary light reflex produced in the opposite eye. One cannot consciously suppress this protective reflex. Absence of the normal pupillary light reflex is generally an indication of severe trauma or deterioration of the vital brain stem tissue.
a) Conduct the reflex test in an area where the lighting is dim. Measure the size of the subject's pupils using a metric ruler.
Rt. Pupil = _____________ mm; Lt. Pupil = _____________ mm
b) The subject should shield his/her right eye by holding a hand vertically between the right eye and the right side of the nose.
c) Stand to the left of the subject, and shine a flashlight into the subject's left eye, observe the change and measure the size of the subject's left pupils (direct pupillary light reflex).
Lt. Pupil = _____________ mm
d) Observe the change of the subject's right pupil (consensual pupillary light reflex), and measure the right pupil size.
Rt. Pupil = _____________ mm
j) In the space below, draw a diagram showing the reflex arc involved in the direct pupillary light reflex and consensual pupillary light reflex, and label each component with specific organ names.
k) Explain the protective function of pupillary light reflex (be specific) in the space below.