Coordination and Response: Nervous and Endocrine Systems
The body coordinates its response to a stimulus using two systems working together: the nervous system, which sends fast, short-lived electrical signals along neurones, and the endocrine system, which sends slower, longer-lasting chemical signals (hormones) through the blood.
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The basic stimulus–response pathway
Every response to a change begins in the same basic way: a receptor detects a stimulus, a change in the internal or external environment, and passes this information to a coordinator, which processes it and sends instructions to an effector, a muscle or gland that carries out the actual response. The nervous system and endocrine system are the two coordination systems the body uses to link receptors to effectors.
Two coordination systems: nervous and endocrine
The nervous system coordinates responses using electrical impulses that travel rapidly along neurones to a precise, localised target, such as a single muscle. This makes it suited to responses that must happen almost instantly, such as pulling a hand away from something hot.
The endocrine system coordinates responses using hormones, chemical messengers secreted directly into the blood by glands. Hormones travel more slowly than nerve impulses because they rely on the flow of blood, but they can reach many cells throughout the body and their effects usually last much longer, making the endocrine system suited to gradual processes such as growth, metabolism, or the body's overall response to prolonged stress.
Comparing the two systems
| Feature | Nervous system | Endocrine system |
|---|---|---|
| Type of signal | Electrical impulse along a neurone | Hormone carried in the blood |
| Speed of response | Very fast | Slower |
| Duration of effect | Short-lived | Long-lasting |
| Target | Precise, localised (one muscle or gland) | Widespread (any cell with a matching receptor) |
How it is examined
Questions on this standard often ask you to classify a described response as nervous, hormonal, or both, and to justify your answer using speed, duration or target. A common scenario question describes a stressful or dangerous situation and asks you to explain how the nervous system produces an immediate reaction while the endocrine system (through adrenaline) sustains the body's readiness for longer.
The reflex arc: a fast nervous pathway
The clearest example of the nervous system in action is the reflex arc, the pathway that produces a reflex action. A stimulus is detected by a receptor, which sends an impulse along a sensory neuron to the spinal cord.
There the impulse passes across a synapse to a relay neuron, and then to a motor neuron that carries the impulse to an effector, a muscle or gland, which carries out the response.
Because the impulse takes a short route through the spinal cord rather than the brain, the response is very fast and automatic. This protects the body from harm, such as a hot surface or a sharp object, before the brain is even aware of it.
Key terms
- Stimulus, a change in the internal or external environment that is detected by a receptor.
- Neuron, a nerve cell that carries information as an electrical impulse.
- Synapse, the small gap between two neurons, crossed by a chemical neurotransmitter.
- Reflex action, a fast, automatic response to a stimulus that does not require conscious thought.
- Hormone, a chemical messenger secreted by a gland into the blood to act on target cells.
Worked exam-style question
Question. A student is startled by a loud bang. She immediately turns her head towards the sound, and for a few minutes afterwards her heart beats faster and she feels alert.
(a) State the receptor and the effector involved in turning her head towards the sound. (b) Name the coordination system responsible for turning her head, and explain why this system is suited to the task.
(c) The raised heart rate that lasts a few minutes is caused by a hormone. Name the coordination system involved and explain why its effect lasts longer than the turning of the head.
Model answer. (a) The receptor is the ear (sound receptor) and the effector is a neck muscle. (b) The nervous system turns her head; it sends electrical impulses along neurons that travel very fast to a precise, localised muscle, so the response is almost instant.
(c) The endocrine system is involved; the hormone adrenaline is carried in the blood, which is slower than a nerve impulse but reaches cells throughout the body, and the hormone is broken down slowly, so its effect lasts longer.
Practice question
Classify each response as controlled mainly by the nervous system or mainly by the endocrine system, and give a reason for one of your choices. (a) Blinking when dust enters the eye.
(b) The growth of a child from birth to adulthood. (c) Pulling a hand away from a sharp pin.
Exam tip
Source:SRC-DSKP-EN
Frequently asked questions
What is the difference between how the nervous system and endocrine system send signals?
Why does the body need both the nervous and endocrine systems?
How does a hormone reach only its target cells if it travels in the blood to the whole body?
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