8.2.3Unit 5: Respiration, Internal Environment, Coordination and Gene Technology
Nervous and Hormonal Coordination — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 5 parts Lesson 36 of 36 Unit quiz
Part 1 of 5Why Organisms Coordinate Responses
Organisms must respond to changes in their environment to survive.
Favourable conditions
- Responses help an organism avoid locations that are too hot or too cold.
Food
- Detecting stimuli allows an organism to locate and obtain food.
Avoiding harm
- Responses help avoid danger such as predators or a harmful rise in blood glucose.
Plants
- Plants coordinate their responses using chemical signals only.
Animals
- Animals use both nervous and hormonal control to coordinate responses.
Part 2 of 5Nervous Coordination
Information travels as electrical impulses along neurones.
1
A stimulus is detected by a receptor, for example a pain receptor in the skin of the hand touching a hot surface.
2
Impulses pass along a sensory neurone to the central nervous system.
3
The CNS coordinates the information and sends impulses along a motor neurone.
4
The effector, here an arm muscle, contracts and moves the hand away.
Part 3 of 5Hormonal Coordination
Hormones are chemical messengers made by endocrine glands and carried in the blood.
1
Endocrine glands are ductless and secrete hormones directly into the blood, after stimulation by a nerve impulse or another hormone.
2
The blood carries the hormone around the body, and it binds to specific receptors on the surface of target cells.
3
The target organ changes its activity, so the response is slower but usually longer lasting.
4
Example: high blood glucose is detected by pancreatic cells, which secrete insulin, and liver cells convert glucose to glycogen.
Part 4 of 5Comparing the Two Systems
Comparing the Two Systems
Speed
- Nervous responses are very rapid, whereas hormonal responses are slower.
Transmission
- Nerve impulses travel along neurones, while hormones are carried in the blood plasma.
Target
- Nerve impulses reach specific effectors, while hormones act on any target cells with the right receptors.
Duration
- Nervous effects are usually short-lived, and hormonal effects generally last longer.
| Feature | Nervous | Hormonal |
|---|---|---|
| Message | Electrical impulse | Chemical hormone |
| Pathway | Neurones | Blood |
| Speed of response | Fast | Slower |
| Pathway summary | Receptor, sensory neurone, CNS, motor neurone, effector | Receptor, hormone, effector |
Part 5 of 5Exam Checklist & Tips
8.2.3 – Key Points for the Exam
- Stimulus A change in the internal or external environment.
- Effector A muscle or gland that carries out a response.
- Hormone A chemical messenger secreted by an endocrine gland and carried in the blood.
- Endocrine gland A ductless gland that releases hormones directly into the blood.
- Target organ An organ whose cells have receptors for a specific hormone.
Common Mistakes
- Saying hormones travel along neurones; they are carried in the blood.
- Claiming endocrine glands release hormones through ducts; they are ductless.
- Saying plants have a nervous system; plants coordinate with chemical signals.
- Describing hormonal responses as fast; they are slower than nervous responses.
Last updated:
\n