12.1 Coordination and Response
Learn how organisms detect changes in their environments and produce suitable responses through coordination by the nervous and endocrine systems.
Learning Objectives
- Define sensitivity, stimulus, receptor, integration centre, effector, response, and coordination.
- Differentiate between external stimuli and internal stimuli with textbook examples.
- Describe the components and pathways involved in detecting and responding to changes in both external and internal environments.
- Identify the main types of sensory receptors and their corresponding stimuli.
- Explain the necessity of response to external and internal stimuli for the survival of organisms.
Pathway Flowchart: From Stimulus to Response
The sequential pathway of nerve impulses from stimulus detection to effector action in both external and internal coordination pathways.
External Stimulus Pathway
Example: the sound of a phone ringing.
- 1 Sound of phone ringing (stimulus)
- 2 Sensory receptors in the ear detect the sound and transform it into nerve impulses
- 3 Sensory neurone sends impulses to the brain
- 4 Brain interprets impulses and triggers a response
- 5 Motor neurone carries impulses to hand muscles
- 6 Hand muscles answer the telephone (response)
Internal Stimulus Pathway
Example: blood pressure increases during running.
- 1 Blood pressure increases during running (stimulus)
- 2 Baroreceptors in the aortic arch and carotid artery detect the increase and generate nerve impulses
- 3 Sensory neurone transmits impulses to the integration centre
- 4 Cardiovascular control centre in the medulla oblongata interprets the impulses
- 5 Motor neurone sends impulses to the effectors
- 6 Cardiac muscles weaken contraction and blood vessels expand to reduce blood pressure back to normal (response)
Short Explanation
Basic Concepts of Coordination and Response
Sensitivity is the ability of organisms to detect changes in their environments and respond to these changes. A stimulus is a change that stimulates a response. Receptors are special sensory cells that detect stimuli and act as energy converters by converting one form of energy into electrical signals called nerve impulses. The integration centre translates nerve impulses and coordinates an appropriate response. An effector is the part of the body that carries out the response. A response is the way organisms react after detecting a stimulus. Coordination is the stimuli detection process by receptors that ends in appropriate responses by effectors. It ensures that the overall activities and systems of an organism function and are synchronised as a complete unit. It is carried out by two systems: the nervous system and the endocrine system.
External Stimuli
Changes originating from outside the body, including light, sound, smell, taste, surrounding temperature, pressure, and touch.
Internal Stimuli
Changes originating inside the body, including changes in blood osmotic pressure, changes in body temperature, and changes in blood sugar level.
Types of Sensory Receptors and Stimuli
| Sensory Receptor | Stimulus Detected | Location / Notes |
|---|---|---|
| Photoreceptor | Light | Found in eyes; transmits via optic nerve to the brain |
| Thermoreceptor | Change in temperature | — |
| Chemoreceptor | Chemical substances | Found in nose, tongue, and internal organs such as pancreatic cells that detect blood glucose levels |
| Baroreceptor | Change in pressure | Detects blood pressure in the aortic arch and carotid artery |
| Mechanoreceptor | Touch and pressure | Found in the skin |
| Nociceptor | Pain | — |
Necessity of External Response
Essential for organism survival. Animals migrate or seek new shelter when they detect sudden changes in climate conditions. Athletes perform fast responses, such as a goalkeeper saving a goal.
Necessity of Internal Response
Crucial to maintain a stable internal environment (homeostasis). When factors such as body temperature rise above the normal range, receptors detect this, and the integration centre coordinates effectors to lower the temperature back to normal.
Try to Answer First
Answer in your mind, then press “Check Answer”.
What is the difference between a receptor and an effector?
Which sensory receptor is responsible for detecting blood pressure changes, and where is it located?
Why is it important for an animal to respond to changes in the internal environment?
Common Mistakes
- Confusing the terms sensory neurone and motor neurone: sensory neurones carry impulses to the integration centre, while motor neurones carry impulses away from the integration centre to effectors.
- Confusing baroreceptor with mechanoreceptor: baroreceptors specifically detect changes in hydrostatic/fluid pressure (e.g., blood pressure), whereas mechanoreceptors detect physical touch and mechanical pressure on the skin.
- Mixing up stimulus and response: stating the action (e.g., hitting a mosquito) as the stimulus and the feeling (e.g., the bite) as the response, instead of identifying the mosquito bite as the stimulus and hitting it as the response.
Concept Misunderstandings
Only the nervous system is involved in coordination.
Coordination is conducted by two separate systems working together: the nervous system and the endocrine system.
Receptors directly create the physical movement or response.
Receptors only detect stimuli and convert them into nerve impulses; effectors (muscles and glands) are the structures that produce the actual physical or chemical response.
The brain is the only integration centre in the human body.
While the brain is the main integration centre, specific autonomic centres like the cardiovascular control centre in the medulla oblongata or spinal cord regions also function as integration centres.
Summary
- Coordination is the process where receptors detect stimuli, and the integration centre coordinates appropriate responses through effectors.
- Stimuli can be external (e.g., light, sound, touch) or internal (e.g., blood pressure, blood glucose, temperature).
- Specialised receptors convert these stimuli into nerve impulses, which travel along sensory neurones to the integration centre.
- Motor neurones then relay commands to effectors (muscles or glands) to produce responses that ensure organism survival and internal stability.
Short Activity
Objective: identify receptors, pathways and effectors in coordination and response.
A. Objective Quiz
Which of the following correctly pairs the sensory receptor with the stimulus it detects?
What is the correct pathway of impulses during a response to an external stimulus?
B. Fill in the Blanks
Receptors act as energy converters by converting detected stimuli into impulses.
The two main types of effectors in the human body that produce responses are muscles and .
C. Matching / Drag and Drop
Match each sensory receptor to its specific stimulus detected. Drag each receptor to its correct stimulus. On a phone, tap a choice first, then tap the matching box. Tap the Answer Choices area to return a selected item.
C. Match the Sensory Receptor to Its Stimulus
Write the correct sensory receptor next to each stimulus.
| Stimulus | Sensory Receptor |
|---|---|
| 1. Light | |
| 2. Chemical substances | |
| 3. Touch and pressure | |
| 4. Pain |
Answer choices: Photoreceptor • Chemoreceptor • Mechanoreceptor • Nociceptor
