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respond to stimuli. The cat may be running because it saw a mouse. Plants |
grow towards the sunlight. We start sweating when it is hot and humid. |
The ability to react to particular stimulus in a particular situation must |
be of great importance in ensuring the survival of the organism. |
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There is a sequence of events that brings about responses. They start |
from detecting changes in environment (both external and internal) or |
stimuli, transmission of the information, processing of the same. Finally |
the response will detect and execute the appropriate action. |
Let us do the following activity to find more about response to stimuli. |
LA |
Activity-1 |
Holding a falling stick |
Take a long scale or stick at least around ½ meter. Keep your |
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fingers in holding position as shown in fig-1 . Ask your friend to |
hold the stick / scale near the end and let the other end be |
suspended between your fingers. |
Let there be a very small gap around a centimeter between |
your thumb and stick/scale and the stick/scale and fore finger. |
Now let your friend allow it to fall. Try to hold it. |
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Could you hold it exactly at the point where it was |
suspended between your fingers? |
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fig-1: Holding stick |
Mark the point where you caught the stick. |
How far up was this point from the end suspended between your fingers? |
Why did this happen? |
How fast do you think the process was? |
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Responses are brought about by rapid changes in some muscles and |
such changes are usually related to changing stimuli. Rapidity of response |
indicates an efficient communication system linking those parts that pick |
up stimuli to those that trigger a response. |
What makes this kind of communication possible? |
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Free distribution by T.S. Government 2019-20 95 |
Integrating pathways - Nervous coordination |
The Greeks believed that all functions of the body were controlled by |
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A |
the brain since damage to that organ produced remarkable changes in |
behaviour. They had very little idea on how such control could be exercised |
Though Galen, a Greek physiologist (A.D. 129-200) made one notable |
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observation. One of his patients, having suffered a blow on the neck when |
falling from his chariot, complained loss of feeling in the arm while still |
fig-2: Galen retaining normal muscular control of its moment. Galen concluded that |
nerves were of two kinds – those of sensation and those of action. |
According to him the blow in the neck had damaged the nerves of sensation |
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but had not affected it’s action. |
Why do you think Galen draw such a conclusion? |
The functioning of nerves as integrating systems was little known till |
late 18th century. Then, physiologists began to study the mechanism of |
nerve functioning and found how signals were transmitted by making the |
LA |
connection between recent work on electricity and the propositions on |
working of the nervous system made till then. |
Now we know more about how nerves from different sections of the |
brain and spinal cord control responses of different areas of the body. We |
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also know the probable pathways that transmit information but we still |
know very little about the working mechanisms of the nerve cell. |
Structure of nerve cell |
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Activity-2 |
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