a) Define a reflex action (2mks) b) Using a diagram describe what happens in the nervous system of a person who withdraws a finger from a very hot object (18mks)

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a) Define a reflex action (2mks)
  • Is a rapid automatic response to a certain stimulus
A – sense organ (Receptor)
B – Sensory neurone
C – Relay neurone
D – Synapse
E – Motor neurone
F – Effector organ
b) Using a diagram describe what happens in the nervous system of a person who withdraws a finger from a very hot object (18mks)
Image result for REMOVING A FINGER FROM A HOT OBJECT REFLEX ARC
  • When the finger touches a very hot object; pain receptors; in the skin of the finger
  • are stimulated;
  • Nerve impulses are triggered off; and transmitted through the sensory neurone; to grey matter of the spinal cord;
  • The impulse is then transmitted to the relay neurone; through the synapse; then to the motor
  • neurone; through another synapse;
  • Through the ventral root, the impulse is transmitted to the effector organ (bicep of the arm); which contracts; and the forearm is withdrawn; and thus the finger is raised from the hot object;

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