Cambridge Notes, Past Papers, Revision Questions

Control and Coordination in Mammals – Nervous vs Endocrine Systems

Control and Coordination in Mammals

In mammals, two major signalling systems maintain internal stability and enable responses to the external environment: the nervous system and the endocrine system. Both systems transmit information, but they differ in speed, duration, mode of transport and the type of responses they generate.

1. The Nervous System

The nervous system uses electrical impulses (action potentials) and chemical neurotransmitters to convey information rapidly over long distances.

Structure: Brain, spinal cord, peripheral nerves, sensory receptors.

Signal carrier: Neurons (electrical) and neurotransmitters (chemical).

Speed of response: Milliseconds.

Duration of effect: Very short – typically seconds to minutes.

Typical actions: Muscle contraction, glandular secretion, rapid behavioural responses.

2. The Endocrine System

The endocrine system releases hormones into the bloodstream, allowing signals to reach distant target cells.

Structure: Endocrine glands (pituitary, thyroid, adrenal, pancreas, gonads, etc.).

Signal carrier: Hormones (peptides, steroids, amines).

Speed of response: Seconds to hours.

Duration of effect: Long‑lasting – from minutes to days or even weeks.

Typical actions: Metabolic regulation, growth and development, long‑term stress responses.

3. Direct Comparison

Feature	Nervous System	Endocrine System
Primary signalling molecules	Neurotransmitters (e.g., acetylcholine, dopamine)	Hormones (e.g., insulin, cortisol)
Mode of transport	Electrical impulse along neurons; synaptic cleft diffusion	Bloodstream (circulatory system)
Speed of transmission	\overline{0}.5–120 m s⁻¹ (milliseconds)	\overline{0}.01–0.1 m s⁻¹ (seconds to hours)
Duration of action	Very brief (seconds)	Prolonged (minutes to weeks)
Target specificity	Highly specific – synapse between a single neuron and a single target cell	Less specific – hormones can affect many cell types that possess the appropriate receptor
Typical effects	Rapid, precise control of muscles and glands	Regulation of metabolism, growth, development, and long‑term homeostasis
Feedback control	Negative feedback via reflex arcs; limited hormonal involvement	Extensive negative (and occasional positive) feedback loops, often involving the hypothalamus‑pituitary axis

4. Integration of the Two Systems

Although they can act independently, the nervous and endocrine systems are tightly integrated. The hypothalamus is a key neuro‑endocrine centre that receives neural inputs and releases releasing or inhibiting hormones to control the anterior pituitary. This coordination ensures that rapid neural signals can be translated into longer‑lasting hormonal responses when required.

5. Summary of Key Points

Neural signalling is fast, short‑lived, and highly targeted; endocrine signalling is slower, longer‑lasting, and can affect many cells.

Neurons use electrical impulses; endocrine glands use chemical hormones released into the blood.

Both systems employ feedback mechanisms, but endocrine feedback often involves multiple glands and hormones.

The hypothalamus bridges the two systems, allowing coordinated control of physiological processes.

Suggested diagram: Flowchart showing the interaction between the hypothalamus, pituitary gland, target endocrine glands, and the nervous system (including a reflex arc).