1. Analysis of Reflex Arc

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 Introduction

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% H 2 SO 4 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 H 2 SO 4 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 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. Exp 1

2. Reflex in Spinal Animals

Introduction Exp 2 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 crossed- extensor reflex enables the contralateral leg to support the body’s weight as the injured foot is lifted by flexion.

Purpose To investigate the characteristics of the reflex Exp 2

Procedure Exp 2 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.

Procedure Exp 2 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.

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 Exp 2 4. Inhibition  Put the toad’s hind limb into 1% H 2 SO 4. 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.

Procedure 5. Scratching reflex Exp 2 Paste on the inferior part of the abdominal skin with a filter disc immersed with 1% H 2 SO 4. The animal then Scratch until the filter disc is removed.

Procedure 6. Destroy the spinal cord, then repeat the above steps Exp 2

3. The Function of Anesthetic Drug on Nerve Conduction

Procedure Exp 3 1.Inject 1% procaine ml in sciatic nerve of one hind limb. 2.Immerse the ipsilateral foot of the suspended frog in 1% H 2 SO 4 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% H 2 SO 4, 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

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 Introduction

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 Exp 4