The events listed below occur during contraction of the pupil of the eye in response to increased light intensity.
(i) Impulses pass along motor neuron
(ii) Contraction of circular muscles
(iii) Stimulation of the retina
(iv) Impulses pass along sensory neuron
What is the correct order of these events?
Codes
First ⇢ Last

1 4 2 3

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2 1 3 4

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3 1 4 2

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3 4 1 2

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Solution

The correct option is D
3 4 1 2

The correct option is D.
Explanation of correct option:
When the light intensity is increased, it stimulates the retina.
Due to stimulation of the retina, the sensory organ stimulates the afferent neuron and the impulses pass along it.
The signals are then transmitted by a sensory neuron into the central nervous system.
The impulses then pass along the motor neuron to the effector.
This response will result in the contraction of circular muscles.
Final answer: The correct sequence is 3 (Stimulation of the retina) ⇢ 4 (Impulses pass along sensory neuron) ⇢ 1 (Impulses pass along motor neuron) ⇢ 2 (Contraction of circular muscles).

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