EXERCISE6
HUMAN REFLEX PHYSIOLOGY
INTRODUCTION
Human torso model
Neurons communicate in many ways, but much of what the body must do every day is
programmed as reflexes. Reflexes are rapid, predictable, involuntary motor responses to
stimuli and they occur over neural pathways called reflex arcs.
Reflexes can be classified as either autonomic or somatic reflexes. Autonomic (or visceral)
reflexes are not subject to conscious control. These reflexes activate smooth muscles, cardiac
muscle, and the glands of the body and they regulate body functions such as digestion and
blood pressure. Somatic reflexes include all reflexes that stimulate skeletal muscles. An
example of such a reflex is the rapid withdrawal of your foot from a piece of glass you have just
stepped on.
MATERIALS
Reflex hammer(if available), Cot (if available), Absorbent cotton (sterile).
Expected Learning Outcomes
Human torso model (dissectible)
At the end of this lab, you will be able to:
1. Define reflex and reflex arc
2. Identify and describe the function of each element of a reflex arc.
3. Describe several types of reflex activity as observed in the laboratory.
A reflex may be defined as an immediate and involuntary response to a stimulus. It is a fast
response to a change in the body's internal or external environment in an attempt to restore
homeostasis.
Evaluation of a reflex can aid a doctor in diagnosing a problem. A reflex which stops
functioning or functions abnormally may indicate that a particular central or peripheral
conduction pathway in the body has been damaged.
Parts of the Reflex Arc(Figure 6.1)
1. Receptor – detects the stimulus. a) Description: the receptor end of a particular
dendrite or a specialized receptor cell in a sensory organ. b) Function: sensitive to a
specific type of internal or external change.
2. Sensory neuron – conveys the sensory information to brain or spinal cord. a)
Description: Dendrite, cell body, and axon of a sensory neuron. b) Function: transmit
nerve impulses from the receptor into the brain or spinal cord.
3. Interneuron: relay neurons. a) Description: dendrite, cell body, and axon of a neuron
within the brain or spinal cord. b) Function: serves as processing center, conducts nerve
impulses from the sensory neuron to a motor neuron.
4. Motor neuron: conduct motor output to the periphery. a. Description: Dendrite, cell
body, and axon of a motor neuron. b. Function: transmits nerve impulse from the brain
or spinal cord out to an effector.
5. Effector: a) Description: a muscle or gland. B) Function: Response to stimulation by the
motor neuron and produces the reflex or behavioral action.
Figure 6.1 The Reflex Arc
ACTIVITY 1
Patellar or Knee-jerk Reflex
To test the patellar or knee-jerk reflex, seat a subject on the laboratory bench with legs
hanging free (or with knees crossed). Tap the patellar ligament sharply with the reflex hammer
just below the knee to elicit the response. The knee-jerk reflex assesses the L2-L4 level of the
spinal cord (Figure 6.2). Test both knees and record your observations.
______________________________________________________________________________
______________________________________________________________________________
Which muscle contracted? ________________________________________________________
Figure6.2 Testing the Patellar Reflex
ACTIVITY 2
Plantar Reflex
The plantar reflex (Figure 6.3), 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
toes to flex and move closer together. Damage to the corticospinal tract (the major voluntary
motor tract), however, produces Babinski’s sign, an abnormal response in which the toes flare
and the great toe moves upward. (in newborn infants, Babinkski’s sign is seen because the nervous
system is still incompletely myelinated).
Have the subject remove a shoe and lie on the cot or laboratory bench with knees slightly bent and
thighs rotated so that the lateral side of the foot rests on the cot. Alternatively, the subject may sit up
and rest the lateral surface of the foot on a chair. Draw the handle of the reflex hammer firmly down the
lateral side of the exposed sole from the heel to the base of the great toe.
What is the response? __________________________________________________________________
Is this a normal plantar reflex or Babinski’s sign? _____________________________________________
Figure 6.3 Testing the Plantar Reflex
ACTIVITY 3
CORNEAL REFLEX (Figure 6.4)
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 a wisp of absorbent cotton. What is the reaction?
What is the function of this reflex? _________________________________________________
Name: ______________________________
REVIEW SHEET
ID #: ________________________________
Date: _______________________________
EXERCISE 6
HUMAN REFLEX PHYSIOLOGY
1. Define reflex:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
2. Name five(5) essential components of a reflex arc:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
3. In general, what is the importance of reflex testing in a routine physical examination?
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
4. Describe briefly the function of each of the following reflexes:
A. Patellar or Knee-Jerk Reflex:
_____________________________________________________________________
_____________________________________________________________________
B. Plantar Reflex:
_____________________________________________________________________
_____________________________________________________________________
C. Corneal Reflex:
_____________________________________________________________________
_____________________________________________________________________