IGCSE Biology / Coordination
Central and peripheral nervous system
Edexcel International GCSE Biology (4BI1), chapter 6: Coordination, specification point 2.80, 2.82, 2.87. Free lesson.
Read the revision notes · IGCSE Biology past papers
The nervous system is divided into the central nervous system and the peripheral nervous system. A stimulus is detected by a receptor, then a coordinator directs an effector to produce a response.
How the nervous system is divided
The central nervous system (CNS) is made up of the brain and spinal cord. Everything else, including the nerves running between the CNS and the rest of the body, is part of the peripheral nervous system. The brain coordinates responses that are not spinal reflexes. The spinal cord runs inside the backbone and coordinates spinal reflexes.
What receptors and effectors do
Receptors detect changes in the environment. They are found in places such as the skin, eyes, ears, tongue and nose. Effectors carry out the action directed by the coordinator: muscles contract and glands secrete. An effector is a muscle or a gland only. A nerve is not an effector, and neither is a body part such as a hand.
How a stimulus leads to a response
Nervous-system answers can be organised using five terms in a fixed order. The receptor detects the stimulus, then the brain or spinal cord coordinates what should happen. The effector carries out that action, producing a response. Stimulus: a detectable change in the environment, such as light, heat, sound, pressure or a chemical. Receptor: a cell that detects the stimulus, such as light receptors in the retina. Coordinator: the brain or spinal cord, which decides what to do. Effector: a muscle or gland that carries out the action. Response: what happens, such as a muscle…
Applying the sequence to smelling food
When you smell food, chemicals from it act as the stimulus. Chemical receptors in the nose detect them, and the brain coordinates a response. The salivary gland is the effector because it is a gland, and secreting saliva is the response.