How does the nervous system carry information, and how does a reflex protect the body?
Explain the structure and function of sensory, relay and motor neurones and synapses in the transmission of electrical impulses, and the structure and function of a reflex arc.
A focused answer to Edexcel GCSE Biology 2.13 to 2.14, covering sensory, relay and motor neurones, how synapses transmit signals, and the structure and function of a reflex arc.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
Edexcel statements 2.13 and 2.14 want you to explain the structure and function of the three types of neurone (sensory, relay and motor) and the synapse, and to describe the reflex arc. The key ideas are how an electrical impulse travels, how it crosses the gap between neurones, and why reflexes are fast and protective.
The three types of neurone
A neurone has a cell body, branched dendrites that receive signals, and a long axon that carries the impulse to the next cell.
The synapse
When an impulse reaches the synapse, the first neurone releases neurotransmitter chemicals into the gap. These diffuse across and bind to receptors on the next neurone, which starts a new electrical impulse. This chemical step explains why the signal can only travel one way across a synapse, and why some drugs and toxins (which interfere with neurotransmitters) affect the nervous system.
The reflex arc
A reflex action is a fast, automatic response that does not involve conscious thought, for example pulling your hand away from a hot object or blinking when something approaches your eye. The pathway is the reflex arc:
- A receptor detects the stimulus (heat).
- A sensory neurone carries the impulse to the spinal cord.
- A relay neurone in the spinal cord passes it on.
- A motor neurone carries the impulse to the effector.
- The effector (a muscle) contracts to move the hand away.
Because the signal goes through the spinal cord and not the conscious brain, the response is very fast, which protects the body before you even feel the pain.
Try this
Q1. State the function of a motor neurone. [1 mark]
- Cue. It carries electrical impulses from the central nervous system to an effector (a muscle or gland).
Q2. Explain why neurotransmitters mean a synapse only transmits a signal in one direction. [2 marks]
- Cue. The neurotransmitter is released by the first neurone and the receptors are only on the next neurone, so the chemical signal can only cross from the first to the second.
Exam-style practice questions
Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Edexcel 20194 marksDescribe how a nerve impulse passes from one neurone to the next across a synapse.Show worked answer →
A 4-mark describe question rewards the sequence of events at a synapse.
- The electrical impulse arrives at the end of the first neurone (at the synapse).
- This causes the neurone to release chemicals called neurotransmitters into the gap (synaptic cleft).
- The neurotransmitters diffuse across the gap.
- They bind to receptors on the next neurone, triggering a new electrical impulse in it.
Markers reward the release of neurotransmitter, diffusion across the gap and binding to receptors to start a new impulse. Saying the electrical impulse jumps the gap is wrong; the signal is chemical across the synapse.
Edexcel 20213 marksA person touches a hot object and pulls their hand away before they feel the pain. Explain why this reflex action is fast.Show worked answer →
A 3-mark explain question rewards linking the reflex arc to speed and protection.
The reflex is fast because the impulse travels along a short pathway (the reflex arc): receptor, sensory neurone, relay neurone in the spinal cord, motor neurone, effector. It does not involve the conscious brain, so no decision-making time is needed.
Being automatic and not requiring the brain means the hand is moved away quickly, protecting the body from harm. Markers reward the reflex arc route, the fact that it bypasses the conscious brain, and the protective function. Saying the brain reacts quickly contradicts the point of a reflex.
Related dot points
- Describe the structures and functions of the brain and how brain function is investigated with CT and PET scanning, the limitations of treating nervous-system damage, and the structure of the eye and its common defects and their correction.
A focused answer to Edexcel GCSE Biology 2.10B to 2.17B, covering the cerebellum, cerebral hemispheres and medulla, CT and PET scans, treatment limitations, the structure and function of the eye, and the correction of eye defects.
- Describe growth in organisms and the use of percentile charts, explain the importance of cell differentiation, describe the function of embryonic stem cells, adult stem cells and meristems, and discuss the benefits and risks of using stem cells in medicine.
A focused answer to Edexcel GCSE Biology 2.5 to 2.9, covering growth by cell division, differentiation and elongation, percentile charts, cell differentiation, embryonic and adult stem cells, meristems, and the benefits and risks of stem cells.
- Describe where hormones are produced and how they reach their target organs, explain the role of adrenalin in the fight or flight response, and how thyroxine controls metabolic rate by negative feedback.
A focused answer to Edexcel GCSE Biology 7.1 to 7.3, covering the endocrine glands and how hormones travel to target organs, the role of adrenalin in fight or flight, and the control of thyroxine by negative feedback.
- Explain the importance of homeostasis, how insulin and glucagon control blood glucose concentration, the causes and control of type 1 and type 2 diabetes, and the correlation between body mass and type 2 diabetes.
A focused answer to Edexcel GCSE Biology 7.9 and 7.13 to 7.17, covering homeostasis, the control of blood glucose by insulin and glucagon, type 1 and type 2 diabetes, and BMI and waist-to-hip calculations.
Sources & how we know this
- Pearson Edexcel GCSE (9-1) Biology (1BI0) specification — Pearson (2016)