1. Analysis of Reflex Arc
Exp 1
Introduction

The neural pathway involved in accomplishing reflex
activity is known as a reflex arc, which typically
includes the five following basic components:
1. Receptor
2. Afferent pathway
3. intergrating center
4. Efferent pathway
5. effector
Exp 1
Purpose

To investigate the relationship between
reflex and the integrity of reflex arc.
Exp 1
Procedure


Spinal frog
Cut off the head in front of a line passing behind the
tympanic membrane. This leaves the animal with only
the spinal cord portion of the CNS intact, called spinal
preparation.
Suspend the frog on a stand by its lower jaw. Study
the different properties of withdrawal reflex by
applying nocuous stimulus.
Exp 1
Procedure
1. Immerse the left foot of the suspended frog in 1%
H2SO4 and observe the withdrawal of the limb. Then
wash off the acid with water.
2. Remove the skin of toad’s foot, repeat step 1. and
observe the withdrawal reflex.
3. Immerse the right foot in H2SO4 solution, then
observe the reflex. Wash off the acid with water.
4. Cut off right sciatic nerve, repeat step 3. , then
observe the withdrawal reflex.
Exp 1
5. Stimulate the central end of the sciatic nerve,
then observe the response of left limb.
6. Destroy the spinal cord by pushing the pithing
needle down the vertebral column. Repeat step 5.
7. Stimulate the peripheral end of the sciatic nerve,
then observe the left limb.
8. Stimulate right gastrocnemius muscle, then
observe the response of the muscle.
2. Reflex in Spinal Animals
Exp 2
Introduction


Painful stimulation of the skin, as occurs from stepping on a
tack, activates the flexor muscles and inhibits the extensor
muscles of the ipsilateral (on the same side of the body) leg.
The resulting action moves the affected limb away from the
harmful stimulus, and is thus known as a withdrawal reflex.
The same stimulus causes just the opposite response in the
contralateral leg (on the opposite side of the body from the
stimulus). Motor neurons to the extensors are activated while
the flexor muscle motor neurons are inhibited. This crossedextensor reflex enables the contralateral leg to support the
body’s weight as the injured foot is lifted by flexion.
Exp 2
Purpose

To investigate the characteristics of the
reflex
Exp 2
Procedure
1. Summation
 Stimulate a toe with single electrical stimulus, find the
subthreshold intensity. One single subthreshold stimulus does
not produce a response; but stimulate the consecutive skin
with two electrical stimuli at the subthreshold intensity, cause
reflex.
 Stimulate a toe with single electrical stimulus, find the
subthreshold stimulus. One single subthreshold stimulus does
not produce a response; but the repeated stimuli, although
weak, cause summation of stimuli and produce reflex
movements.
Exp 2
Procedure
2. After discharge
Stimulate a toe with repeated electrical stimulus, then
 Observe if the reflex movement stop immediately
after the stimulation?
 Record the duration between the terminal time of
stimulation and the terminal time of reflex.
 Observe the duration between strong and weak stimulation.
Exp 2
Procedure
3. Irradiation


Stimulate the forelimb with weak repeated electrical
stimulus. The same limb is gradually withdrawn with only
a slight reflex movement of the corresponding limb.
Increase the stimulus more and more; the movement
increases also. At first the same limb responds; with
stronger movements, opposite limb begins to take part in
the reflex, and finally, the hind limb (hole toad).
Exp 2
Procedure
4. Inhibition
 Put the toad’s hind limb into 1% H2SO4. Determine the
reflex time of the preparation which is from the
stimulation to withdrawal of the limb. Wash off the acid
with water.
 Place a forceps on the forelimb of the frog; wait until
the frog stops moving and then determine the reflex time
again. It will now be much longer on account of the
inhibitory action of the second stimulus.
Exp 2
Procedure
5. Scratching reflex
Paste on the inferior part of the abdominal skin with a
filter disc immersed with 1% H2SO4. The animal then
Scratch until the filter disc is removed.
Exp 2
Procedure
6. Destroy the spinal cord, then repeat
the above steps
3. The Function of Anesthetic
Drug on Nerve Conduction
Exp 3
Procedure
1. Inject 1% procaine 0.3-0.5ml in sciatic nerve of one hind
limb.
2. Immerse the ipsilateral foot of the suspended frog in 1%
H2SO4 and observe the withdrawal of the limb. Record the
reflex time every 5 min until the withdrawal of the lime
disappear. (afferent nerve fiber is anesthetized first)
3. Paste on the abdominal skin of ipsilateral side with a filter
disc immersed with 1% H2SO4, Scratching reflex of the hind
limb of ipsilateral side will occur. Repeat it every 1 min until
the response of the hind limb of ipsilateral side disappear.
(efferent nerve fiber is anesthetized)
Decerebrate Rigidity
Exp 4
Introduction
 Transection between superior and inferior colliculus,
marked spasticity.
 Brain areas facilitate stretch reflex: reticular facilitatory
area, vestibular nuclei and bilateralisin anterior lobe of
cerebellum.
 Brain areas inhibit stretch reflex: reticular inhibitory
area, motor cortex, basal ganglia, vermis
cerebellum
Exp 4
Procedure


Inject 2% procaine between the two ears of
the rabbit. Cut off the skin in the midline of
the head. Expose the skull. Find the
posterior fontanelle. Put the metal probe into
the bone at the site 0.2 cm away from
posterior fontanelle. Then Transect the brain
between superior and inferior colliculus with
metal probe.
Opisthotonus