Download Name__________________________________ The Spinal Cord

Name__________________________________
The Spinal Cord and Reflexes Lab
A reflex arc represents the simplest type of nerve pathway found in the brain. It may consist of only
2 or 3 neurons. The pathway is an automatic, unconscious response to a change in the external
environment and does not involve the brain. The main steps of a reflex are receptor, sensory neuron,
spinal cord, motor neuron, effector and sometimes an association neuron is involved. The purpose
of this activity is to review the characteristics of reflex arcs and to demonstrate some of the reflexes
that occur in the human body.
Part One: Label the following parts of a basic reflex arc. #5 is a collection of axons and #6 is a
collection of cell bodies.
5.
1.
6.
2.
4.
3.
1. What is the stimulus? _________________________________________
2. What type of tissue is the effector? _______________________________
3. How many synapses occur in this reflex arc? _______________________
4. Which neuron is efferent? ___________________________
5. Which neuron is afferent? __________________________
6. The sensory receptors of this reflex are located in the________________
7. Sensory neurons carry impulses ___________________the brain.
Part Two: Work with your lab partner to demonstrate each of the reflexes listed below. After
each demonstration, record your observations in the following chart.
1. Patellar Reflex- Use the point of the reflex hammer to firmly tap the knee right underneath the
patella. Observe the reaction.
2. Plantar Reflex- Rub the handle of a reflex hammer along the medial sole of the foot starting with
the heel and ending with the big toe. Time the reaction and observe what happens.
3. Pupilllary Reflex- Using a ruler measure the size of the pupil in mm. Face a light source with
closed eyes for 2 minutes. Open your eyes and have your lab partner note what happens to the size
of the pupil.
4. Accomodation Reflex- Note the size of the pupil while the subject is looking at an object across
the room. Now have the subject look at an object that is close by. What happens to the size of the
pupil.
5. Balancing Reflex- Have the subject stand on one foot while looking at the ceiling, eyes open.
Notice the attempts to maintain balance. Then have the subject repeat, but with their eyes closed.
Note the difference.
Reflex Tested
Response Observed
Effector Involved
1. Patellar Reflex
2. Plantar Reflex “Babinski”
3. Pupillary Reflex
4. Accommodation Reflex
5. Balancing Reflex
Post Lab Questions:
1. Define the terms reflex and reflex arc.
2. Explain the function of each element of a reflex arc. In order, what are the five steps of a reflex
arc?
3. Explain the importance of reflex testing in a physical examination.
4. What is a monosynaptic reflex?
5. What type of neurons conduct nerve impulses along an efferent pathway?
6. What type of reflexes are not subject to conscious control?
7. What is the effector in the pupillary reflex arc?
8. Where along a reflex arc would you find interneurons (or association neurons)?
9. What functions as the afferent pathway for the pupillary reflex arc?
10. Describe a normal plantar reflex.
11. Describe Babinski’s sign.
12. How important are the eyes in balance?
13. Why does the pupil size chance during accommodation?
14. What is the difference between innate and acquired reflexes?
15. What type of reflex is the patellar reflex?