EasyBiologyHigh School (9–10)GeneralHuman Body › Nervous System and Sense OrgansConceptualBoard Exam
Meera touches a hot iron and pulls her hand away at once…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Meera touches a hot iron and pulls her hand away at once. Describe the path of the message, from the stimulus to the response, naming each part of the reflex arc.
Need a reminder? The key ideaShow
A reflex is a quick, automatic response. Its path, the reflex arc, is receptor, sensory neuron, relay neuron in the spinal cord, motor neuron, effector. The ruler-drop test gives a reaction time: , with in metres and .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Receptor. Heat receptors in the skin of her finger pick up the stimulus.
Step 2. Sensory neuron. It carries the message to the spinal cord.
Step 3. Relay neuron. In the spinal cord, it passes the message to a motor neuron.
Step 4. Motor neuron. It carries the message to the arm muscle.
Step 5. Effector. The muscle contracts and pulls the hand away.
Answer: receptor, sensory neuron, relay neuron (spinal cord), motor neuron, effector (arm muscle).
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