Central Nervous System Physiology

 

 

An experiment using a live frog to study the EFFECTS OF DIFFERENT STRENGTHS OF STIMULUS ON THE TIME OF REFLEX.

 

Part 1 - Introduction

In this video, our Physiology teacher,Dr Dmitriy generally explains to us how the experiment should be carried out. Here, a few physiological terms such as 'time of reflex',EPSP etc are noteworthy.

After explaining briefly, cutting the frog's forebrain and hanging it to give an 'oh-pity-that-hanging-frog' impression, Dr Dima made a mistake in diluting the acid,so I skipped the mistaken part,and without wasting my precious uploading time,I declare the main part of this experiment, Part 2 as the continuation of this part : ).Enjoy watching and LEARNING!!

 

Part 2 - Temporal summation

Definition: Temporal or sequential summation is an effect generated by a single neuron as way of achieving action potential.

In this part, Dr Dima applied two types of stimulus: strong (around 0.1 M) and weak (around 0.02 M) acids. Then,we can compare the time taken for the frog to react on each of the stimuli.

Note that in this part,the area of stimulation should be considered as the constant variable, whereas the strength of acid is the main manipulated variable.

Part 3 - Spatial summation

Firstly, we ought to know what does 'spatial summation' mean, which is actually a way of achieving action potential in a neuron which involves input from multiple cells ( compare to its counterpart,'temporal summation',as described in the previous part,Part 2).

In this part we consider the area which is exposed to the stimuli as the manipulated variable. For this reason:
1. We dip only the fingers of the frog's leg into the acidic solution.
2. We dip a whole extremity into the solution.

Finally we should observe that the time of reflex for the 2nd case is much shorter (2 seconds),compared to the 1st one (18 seconds).

 

Part 4 - Removal of the receptors and its effects on the reflex arc

If we remove or destroy any critical parts of the reflex arc, the reflex will never occur. In this video, it is proven that when we peel off the frog's skin (where the receptors,which is a critical component of the reflex arc, are situated), no reaction can be detected.

Spinal cord, being the central portion of the reflex arc, when removed will also give the same result ( please proceed to the next part, Part 5 ).

 

Part 5 - Removal of the spinal cord and its effects on the reflex arc

If we remove or destroy any critical parts of the reflex arc, the reflex will never occur. In this video, it is proven that when we remove the frog's spinal cord (the central portion of the reflex arc), no reaction can be detected.