Neuron: a nerve cell, each part has one job
A neuron is a nerve cell carrying an electrical impulse. Learn each part as a name and a job, since a name alone earns nothing: dendrites receive, the cell body holds the nucleus, the axon carries the impulse away, the myelin sheath speeds it, the axon terminals meet the next neuron at a synapse. Learn the three types by direction: sensory runs from a sense organ to the CNS, relay sits inside the CNS, motor runs out to a muscle or gland.
Synapse: a sequence, electrical then chemical
A synapse is the junction between two neurons, which do not touch. A neurotransmitter is the chemical that crosses the gap. Learn the sequence, since a question can ask for two processes: the impulse reaches the terminal; vesicles release neurotransmitter into the gap; it diffuses across; it binds to receptor sites; a new impulse starts; leftover transmitter is cleared. Excitatory transmitters make the next impulse more likely, inhibitory less likely.
CNS: brain + spinal cord, its role in 3 steps
The CNS is the brain and the spinal cord — the body's control centre. Its role earns credit in three steps: it receives information via sensory neurons; it processes it and decides a response; it sends instructions out along motor neurons to muscles and glands. The CNS is only brain and spinal cord — the nerves to limbs and organs are the peripheral system. "It controls the body" is too vague; name the two structures and at least one step.
Drawn from real examiner reports.
Process question answered with structure
Asked to describe two processes in synaptic functioning, many list parts — "a terminal, a gap, the next dendrite" — a diagram in words. A process happens: release (the impulse makes vesicles release neurotransmitter into the gap) and binding (it crosses and binds to receptor sites). Either can be swapped for reuptake. One process reworded twice scores 1 of 2.
Examiners record that a question requiring two processes in synaptic functioning produced mixed responses (June 2022 Paper 1 Q16), and that labelling a diagram of the synapse was likewise answered with mixed success (June 2024 Paper 1 Q17). The separate rule that a 2-mark describe needs two unique points rather than the same point reworded is stated at June 2023 Paper 2 Q22.
Neuron, synapse, neurotransmitter muddled up
Three similar words; swap any two and a right sentence turns wrong. A neuron is a nerve cell carrying an impulse along itself; a synapse is the junction between two neurons; a neurotransmitter is a chemical crossing between them. A nerve is a bundle of fibres, not one cell. "The synapse sends the message down the axon" scores nothing — the axon does that.
Examiners record that parts of the brain and nervous system were "muddled up" in answers (June 2019 Paper 1 Q16), and that zero-scoring candidates on a structure question tended to treat a named structure as something it is not — thinking the corpus callosum was another part of the brain (Nov 2020 Paper 1 Q15b). The habit of defining a term when one feature was asked for is recorded at June 2023 Paper 1 Q6.
CNS role stated but never applied
The CNS question is often found difficult — usually a missing second half, not missing knowledge. It asks for the role and how it explains the scenario; answers give the role and stop. Keep the knowledge, then use the specific detail (the heat of the pan, the hand pulling away). Naming the person or repeating the stem is not application, so no evaluation marks follow.
Examiners report that the central nervous system question was one candidates "generally found difficult", and that the role AND its application to the scenario were both required (June 2024 Paper 1 Q20). The supporting rules are that the character's name alone is not enough (June 2022 Paper 1 Q4b), that repeating the question stem is not application (June 2024 Paper 2 Q10), and that AO3 cannot be awarded without AO2 being present (June 2023 Paper 2 Q31).
Sensory and motor neuron directions swapped
The three neuron types differ only by direction, and that is what gets reversed. A sensory neuron runs from a sense organ towards the CNS; a motor neuron runs from the CNS out to a muscle or gland; a relay neuron sits inside the CNS. "A motor neuron carries the message to the brain" describes a sensory one and scores nothing.
Examiners record that parts of the brain and nervous system were "muddled up" in answers (June 2019 P1 Q16).
Difference written as two definitions
Asked for the difference between the impulse and the neurotransmitter, most write two definitions side by side and stop. Mark schemes treat that implicit difference as one mark, keeping the second for a comparison. Use a connective — whereas — that names the axis: the impulse is electrical, along a neuron, whereas the neurotransmitter is chemical, between neurons.
Examiners record that "describe the difference" items are answered with two separate definitions, treated as an implicit difference worth one mark, while connectives such as "whereas" earn the second (June 2019 P1 Q6; June 2022 P1 Q7).
"State one feature" answered as a definition
Command words are precise. "State one feature" wants one short point, not the full definition. A candidate asked for one feature of a neurotransmitter who writes out the whole "chemical messenger that crosses the gap" has over-written and can lose the mark. State = one crisp point; describe = a developed or two unique points; explain = a point plus why.
The habit of defining a term when one feature was asked for is recorded at June 2023 P1 Q6.
The impulse does not jump the synaptic gap
Students picture the nervous system as one continuous wire. But the neurons are not joined: every junction has a gap electricity cannot cross, so the message changes form — electrical along the neuron, chemical across the synapse, electrical again in the next. That change of form is the key examinable idea, and it is why the gap is a control point, not a fault.
Learn the synapse as a labelled picture
Assessed two ways, one picture answers both. Labelling: know the axon terminal, vesicles, synaptic gap and receptor sites. Describing: the same picture read left to right is the process. For two unique points, pick two different events — release, then binding — not a rewording.
Extended item: biology, scenario, evaluation
Extended answers lose the 7-9 band for lack of AO3 and balance. Order: AO1 biology; AO2 the specific detail, not the name or stem; AO3 one for and one against, each with a so what, then a conclusion. Lenses: objectivity, validity, reductionism. Prose only.
No application, no evaluation
On explain and assess items, AO3 cannot be awarded unless AO2 is present — evaluation on a generic answer scores nothing. Apply first: take a described detail (a drug slowing a reaction) and say what it shows, not the name or stem, then evaluate and conclude.
Neuron — a nerve cell that carries information around the body as an electrical impulse.
Synapse — the junction between two neurons, made up of the axon terminal of one, a tiny gap, and the dendrite of the next. The two neurons never touch.
Neurotransmitter — a chemical messenger released at a synapse that crosses the gap and either starts or stops the impulse in the next neuron.
Central nervous system (CNS) — the brain and the spinal cord together; the body's control and processing centre.
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