Nervous control — Cambridge IGCSE Biology
The central and peripheral nervous systems, types of neurone, reflex arcs and how synapses pass impulses between neurones.
Revision notes
3 short notes, in the order of the specification. Each one in short:
The nervous system coordinates and regulates body functions using electrical impulses that travel along neurones. The central nervous system is the brain and spinal cord, and the peripheral nervous system is the nerves outside them. Sensory neurones carry impulses from receptors to the CNS, relay neurones work within the CNS, and motor neurones carry impulses to effectors.
A reflex action is a means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors, which are muscles and glands. A simple reflex arc has five parts in order: receptor, sensory neurone, relay neurone, motor neurone and effector. Reflexes are useful because they are rapid and automatic, so they protect the body from harm.
A synapse is a junction between two neurones. The electrical impulse cannot cross the synaptic gap, so an impulse arriving at the first neurone releases neurotransmitter molecules from vesicles. These diffuse across the gap and bind with receptor proteins on the next neurone, stimulating a new impulse. Synapses ensure that impulses travel in one direction only.
Exam questions
6 exam-style questions (17 marks), each with its mark scheme.
Answer the questionsFlashcards
11 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of coordination and response on one page, so you can see where this subtopic fits.
Open the mind mapPrint it
Free PDFs to print or save.
Quick check questions
What does the central nervous system consist of?
Show answer
The brain and the spinal cord.
Which neurone is found entirely within the CNS?
Show answer
The relay neurone.
Name the five parts of a simple reflex arc in order.
Show answer
Receptor, sensory neurone, relay neurone, motor neurone, effector.
What is a synapse?
Show answer
A junction between two neurones.
Supplement What diffuses across the synaptic gap?
Show answer
Neurotransmitter molecules.
Frequently asked questions
What is a reflex arc?
A reflex arc is the pathway that impulses follow in a reflex action. It has five parts in order: a receptor detects the stimulus, a sensory neurone carries impulses to the CNS, a relay neurone passes them on within the CNS, and a motor neurone carries them to an effector, a muscle or gland, which responds.
Why are reflexes faster than normal responses?
Reflexes are fast because they are automatic, so you do not have to think about the response first. Impulses pass straight from the receptor through the sensory, relay and motor neurones to the effector. This rapid, automatic response protects the body from harm, such as pulling your hand away from something hot.
How does a nerve impulse cross the synapse?
Supplement A nerve impulse crosses a synapse by chemical means, because the electrical impulse cannot cross the gap. The impulse makes vesicles release neurotransmitter molecules into the synaptic gap. These diffuse across the gap and bind with receptor proteins on the next neurone, which stimulates a new impulse in that neurone.
What are the three types of neurone?
The three types of neurone are sensory, relay and motor neurones. Sensory neurones carry impulses from a receptor to the CNS. Relay neurones are short and found entirely inside the CNS, passing impulses from the sensory neurone to the motor neurone. Motor neurones carry impulses from the CNS to an effector, a muscle or a gland.
Why do impulses only travel in one direction at a synapse?
Supplement Impulses travel in one direction only because neurotransmitter is released from only one side of the synaptic gap. The vesicles containing neurotransmitter are in the first neurone, and the receptor proteins are only on the membrane of the next neurone. So the chemical signal can only pass from the first neurone to the next.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026