AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Stimulus → receptor → coordinator → effector → response.
Full specification wording
Structure and function: Stimulus → receptor → coordinator → effector → response.
This arrow sequence summarises the pathway of a control system.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 6 of 13
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
This arrow sequence summarises the pathway of a control system. A stimulus is a change in the environment, such as a rise in blood glucose or a drop in skin temperature. A receptor detects the stimulus and generates electrical impulses. The coordinator, such as the brain, spinal cord or pancreas, receives and processes the information. The effector, a muscle or gland, then brings about a response. For example, touching something hot: temperature receptors in the skin detect the stimulus; the spinal cord coordinates a rapid reflex; the arm muscle contracts as the effector; the hand pulls away as the response. In blood glucose control, pancreatic receptors detect the change, the pancreas coordinates, and liver cells respond by storing or releasing glucose. The response restores optimum levels, usually by negative feedback.
What earns the marks
- A stimulus is a change in the environment detected by a receptor.
- The receptor detects the stimulus and sends information to the coordinator.
- The coordinator, such as the brain, spinal cord or pancreas, receives and processes the information.
- The effector, a muscle or gland, brings about the response.
- The response restores optimum levels, often by negative feedback, and the sequence can be applied to a named example.
Common mistakes and how to put them right
Reversing receptor and coordinator in the sequence.
Put it right by placing the receptor immediately after the stimulus, since detection precedes processing.
Omitting the coordinator and jumping from receptor to effector.
Put it right by naming the brain, spinal cord or pancreas as the processing stage.
Treating the response as the end of the process without linking it to restoring optimum levels.
Put it right by stating that the response reverses the change by negative feedback.
Exam tips
- Write the sequence in order and annotate each arrow with what happens at that stage.
- Apply the sequence to a named example, such as a reflex arc or blood glucose control, to show understanding.
- Use precise terms: stimulus, receptor, coordinator, effector, response, rather than vague words like 'signal' or 'message'.
Try the lesson
The start of the Structure and function: Stimulus → receptor → coordinator → effector → response. lesson, made from checked teaching notes for this specification point.
Have a go first
In the human nervous system, which part of the control sequence comes immediately after the receptor?
Listen
This arrow sequence summarises the pathway of a control system. A stimulus is a change in the environment, such as a rise in blood glucose or a drop in skin temperature. A receptor detects the stimulus and generates electrical impulses. The coordinator, such as the brain, spinal cord or pancreas, receives and processes the information. The effector, a muscle or gland, then brings about a response. For example, touching something hot: temperature receptors in the skin detect the stimulus; the spinal cord coordinates a rapid reflex; the arm muscle contracts as the effector; the hand pulls away as the response. In blood glucose control, pancreatic receptors detect the change, the pancreas coordinates, and liver cells respond by storing or releasing glucose. The response restores optimum levels, usually by negative feedback. A strong answer earns marks for these points. A stimulus is a change in the environment detected by a receptor. The receptor detects the stimulus and sends information to the coordinator. The coordinator, such as the brain, spinal cord or pancreas, receives and processes the information. The effector, a muscle or gland, brings about the response. A common slip: Reversing receptor and coordinator in the sequence. Instead, placing the receptor immediately after the stimulus, since detection precedes processing. Exam tip: Write the sequence in order and annotate each arrow with what happens at that stage.
Key words
Say what each word means before you turn the card.
Stimulus
Try answering aloud or in your head before turning the card.
Receptor
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Coordinator
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Effector
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See every definition
- Stimulus
- A change in the environment, such as a rise in blood glucose or a drop in skin temperature.
- Receptor
- Detects the stimulus and generates electrical impulses, sending information to the coordinator.
- Coordinator
- Such as the brain, spinal cord or pancreas, receives and processes the information.
- Effector
- A muscle or gland that brings about a response.
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