Q2 of 102 Page 110

Categorize the following under stimulus and response.


(i) Withdrawal of hand on touching a hot plate ____________


 


(ii) Seeing a green light turning red at a road crossing before applying the brakes ____________


 


(iii) Pain in the eye if something falls into it. ____________

(i) Withdrawal of hand on touching a hot plate: Response


Explanation: When we touch a hot plate, the sensory neurons get activated. These sensory nerve cells carry information to the brain/spinal cord which activates the motor neurons. The motor neurons transmit the signal to the hand muscles to remove the hand from the hot plate. Hence the withdrawal of hand on touching a hot plate is the response.


(ii) Seeing a green light turning red at a road crossing before applying the brakes: Stimulus


Explanation: Here the emphasis is given to “seeing” the green light turning red at a road crossing. The sensory nerves sense the message of green light turning to red. These nerve cells transmit this message to the brain. The brain interprets the message (that we should apply the brake) and sends it via the motor nerves to the muscles which express the response (applying the brake).


(iii) Pain in the eye if something falls into it: Response


Explanation: The transparent cornea of the eye contains many fine nerve fibers, which react very sensitively to touch and injury. That is why it is so uncomfortable when a foreign object like a grain of sand or an insect enters the space between your eyeball and your eyelid or gets under your contact lens. Your eye starts to hurt and it waters a lot. If the cornea is scratched, it will feel as though something is stuck in your eye. And this can also cause other symptoms, like sensitivity to light and blurry vision.


More from this chapter

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1

Write one word for each of the following:


(i) The structural and functional unit of nervous system _____________


 


(ii) A wave of electrical disturbance that sweeps over the nerve cell. _____________


 


(iii) Long thread-like part of the nerve cell. _____________


 


(iv) Point of contact between two nerve cells. _____________


 


(v) A bundle of axons enclosed in a tubular sheath _____________


 


(vi) The kind of nerve carrying impulses from the brain to a gland or muscle. _____________

 1

Fill in the blanks by choosing the correct alternative given for each.


(i) Brain and spinal cord are the parts of __________ nervous system (central/peripheral/autonomous)


 


(ii) __________ is the largest part of the brain. (Cerebellum/cerebrum/medulla oblongata).


 


(iii) White matter consists mainly of __________ (axons/dendrites/cytons)


 


(iv) The part of the brain concerned with body balance is __________ (cerebrum, cerebellum, medulla oblongata).

 2

Given below are a few common reflexes in humans. Write against each the kind of reflex it is (simple or conditioned).

(i) Knee-jerk ___________


(ii) Watering of mouth on seeing a favourite dish ___________


(iii) Tying of shoelaces while talking ___________


(iv) The closing of eyelids if a strong beam of light is flashed across ___________

 3

Given alongside is a partial diagrammatic representation of a certain phenomenon pertaining to the nervous system.


(i) Name the parts numbered 1-7


(ii) What phenomenon does the diagram represent? ____________


(iii) Name the parts not shown in the diagram that should be included to complete the pathway of the phenomenon. ______________