This guide covers IGCSE Biology topic 14 (part 1): coordination and response – nervous system. You will revise the reflex arc (receptor → sensory neurone → relay neurone → motor neurone → effector), sense organs (eye, skin), and synapses (chemical transmission between neurones).

Key concepts to revise

• Stimulus → receptor → coordinator → effector → response – Know the order and one example (e.g. touch hot object → withdraw hand).
• Reflex arc – Sensory neurone → relay neurone (in spinal cord) → motor neurone → effector (muscle or gland). No conscious thought; fast.
• Neurones – Sensory (receptor to CNS); relay (CNS); motor (CNS to effector). Synapse: gap between neurones; chemical transmission.
• Eye – Cornea, lens, iris, retina, optic nerve. Accommodation (focusing): lens shape changes.

Exam tips and command words

• Describe the reflex arc – Stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response.
• State the function – Of each type of neurone; of synapse (transmit impulse from one neurone to another).
• Explain – Why reflexes are fast (few synapses; no conscious processing); why reflex is involuntary.
• Label the eye – Cornea, lens, iris, retina, optic nerve; state function of lens (focus light on retina).

Common mistakes

• Saying the reflex arc goes to the “brain” (spinal reflex goes to spinal cord; brain not involved for simple reflex).
• Confusing sensory and motor neurones (sensory: towards CNS; motor: away from CNS to effector).
• Not stating that the synapse uses chemicals (neurotransmitters) to pass the impulse.

Revision checklist

• Describe the path of a reflex arc with the correct order of neurones.
• State the function of sensory, relay and motor neurones and of the synapse.
• Label the eye and describe accommodation (near and distant objects).
• Explain why reflexes are important for survival (fast, protective).

Next steps

Book a free trial with an IGCSE Biology tutor to practise reflex arc and nervous system questions, or explore Tutopiya’s learning portal for more revision resources.