Science · Body coordination

Tracing a response pathway step by step

You know the parts of the pathway but lose marks when the question asks for the order.

A response pathway is the chain of links that carries a signal from a stimulus to a response. Write the links in the right order and you collect the marks the question is asking for.

This lesson belongs to body coordination in SPM Science. For the job of each receptor and effector, see the roles of receptors and effectors.

What are the links in the chain?

There are seven items to name, from start to finish. Stimulus, receptor, sensory neurone, coordinator, motor neurone, effector, response.

Use the same template every time. It works for a touch, a sound or a bright light, because only the nouns change.

Worked example: one stimulus, two pathways

Zulaikha touches the side of a hot kettle with her fingertip. She pulls her hand away before she even feels the pain.

Stimulus: heat from the kettle.
Receptor: heat receptors in the skin of the fingertip.
Sensory neurone: carries the signal to the spinal cord.
Coordinator: the spinal cord.
Motor neurone: carries the signal to the arm.
Effector: the muscles of the arm.
Response: the hand is pulled away.

Now change the situation. Zulaikha sees a cup of coffee on a shelf and decides to pick it up.

Stimulus: light from the cup.
Receptor: the retina of the eye.
Sensory neurone: carries the signal to the brain.
Coordinator: the brain, which decides what to do.
Motor neurone: carries the signal to the arm.
Effector: the muscles of the arm.
Response: the hand reaches for the cup.

The two chains end the same way, but the coordinator differs. The reflex is fast because the signal does not wait for a decision.

The mistake that costs marks

Students write “brain” as the coordinator for every pathway. The working looks tidy, but a reflex question wants the spinal cord.

Question clue	Wrong coordinator	Right coordinator
Hand pulled away before pain is felt	Brain	Spinal cord
Decides to pick up the cup	Spinal cord	Brain

A second common slip is skipping the neurones. Writing “receptor, brain, effector” leaves out the sensory and motor links, and each of those links can carry its own mark.

Check yourself

Marcus steps on a sharp stone and lifts his foot at once. Trace the pathway in seven links and state the coordinator.

Answer

Stimulus: pressure from the sharp stone. Receptor: pressure and pain receptors in the skin of the sole. Sensory neurone: carries the signal to the spinal cord.

Coordinator: the spinal cord. Motor neurone: carries the signal to the leg muscles. Effector: the muscles of the leg. Response: the foot is lifted.

The coordinator is the spinal cord because the foot lifts before Marcus decides anything.

What to study next

Build the pathway skill into full answers with interpreting curriculum scenarios, then test yourself on the body coordination practice set. The mistake log and paper error review helps you track which link you skip.

If you want a teacher to go through your pathway answers with you, see online one-to-one Science tuition.

Tools for this page

Common questions

What is the correct order of a response pathway?

Stimulus, receptor, sensory neurone, coordinator, motor neurone, effector, response. Each link hands a signal to the next. If a question gives you only three of these, name the missing ones in order so the chain reads without gaps.

Is the brain always the coordinator?

No. In a reflex action the spinal cord can act as the coordinator, so the response happens before the brain is involved. For a voluntary action the brain coordinates. Read the situation before you write the coordinator.

Do I write the receptor as an organ or a cell?

Write what the question asks for. SPM Science usually accepts the sense organ, such as the skin or the eye, as the receptor. If the question says which part detects the stimulus, name the organ first.

What is the difference between an effector and a response?

The effector is the part that acts, usually a muscle or a gland. The response is what the effector produces, such as the arm pulling away. Give the effector as the structure and the response as the result.

Keep going

If pathway questions keep losing marks on one missing link, one-to-one Science lessons let a teacher check your chains line by line and fix the link you skip.

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Your first class is a one-hour trial, from RM50. The fee is agreed before you book.
Happy with the teacher? Continue with lessons of about 1.5 hours. If not, ask for another teacher.

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