Nervous vs Hormonal

Explained

Two ways of sending a message

The body coordinates itself with two systems that solve the same problem in completely different ways. The nervous system sends electrical impulses along nerves; the hormonal system sends chemicals in the blood.

Neither is better. They suit different jobs, and every difference between them follows from the route the message takes.

The nervous system

The message is an electrical impulse travelling along a neurone.

Because a neurone runs directly from one place to another, the message arrives in milliseconds and goes only where the neurone goes. That makes the response very fast and very precise, aimed at one specific muscle or gland.

It also stops as soon as the impulses stop, so the effect is short lived.

The hormonal system

The message is a hormone, a chemical released by a gland into the blood.

Because the blood goes everywhere, the hormone reaches the whole body, and only the target organs with the right receptors respond. Delivery takes seconds or minutes rather than milliseconds, because the blood has to circulate.

The hormone stays in the blood until it is broken down, so the effect continues for much longer, sometimes for years in the case of growth and development.

The comparison, point by point

• Message: electrical impulse, or chemical.
• Route: along neurones, or in the blood.
• Speed: very fast, or slower.
• Target: precise, one effector, or general, all target organs with receptors.
• Duration: short lived, or long lasting.

Set a comparison out like that, giving both systems for each point. Describing one system fully and then the other leaves the examiner to make the comparison for you, and comparison marks usually need both halves in the same sentence.

Why each suits its job

Pulling your hand from something hot needs to happen immediately and needs to move one arm, not your whole body. That is a job for nerves.

Growing up, controlling the menstrual cycle and regulating blood glucose all involve slow, sustained changes across many organs at once. Those are jobs for hormones.

Adrenaline is the interesting middle case. It is a hormone, so it travels in the blood, but its effects are needed quickly, which is why it acts on the heart, the airways and the blood vessels all at once and produces a whole body response within seconds.

Where they work together

The two systems are not separate. The brain detects a change and triggers a gland to release a hormone, which is how the pituitary controls so much of the endocrine system.

Temperature control shows both at once: receptors and the brain are nervous, while the sweating and vasodilation they trigger are effector responses, and the whole thing is negative feedback either way.