IB Biology: The Brain & Nervous System — FAQs

Read the command term first, then answer in three moves: name the structure, state its function, link it explicitly to the pathway or stimulus in the question. Examiners award marks for precise terms — 'saltatory conduction', 'medulla oblongata' — tied directly to function, not a general description of how nerves work.

HL students need the cerebrum, cerebellum, medulla oblongata, hypothalamus and pituitary gland, each linked to a specific function rather than described in isolation. The most commonly tested link is hypothalamus-to-pituitary control of hormone release, since it bridges the nervous and endocrine content in the same theme.

A reflex arc is fast, involuntary and processed at the spinal cord — the brain isn't involved in the decision. A voluntary response involves the cerebrum consciously interpreting sensory input before a motor neuron fires. Exam questions often ask you to explain why reflexes are faster: fewer synapses, shorter neural pathway.

A neuron at rest sits around -70mV. A stimulus opens voltage-gated sodium channels, Na⁺ floods in and depolarises the membrane past threshold (roughly -55mV), triggering an all-or-nothing action potential. Potassium channels then open, K⁺ leaves, and the membrane repolarises before a brief refractory period resets it.

A synapse is the junction between two neurons, or a neuron and an effector, where the signal changes from electrical to chemical and back. The action potential triggers calcium influx, vesicles release neurotransmitter (commonly acetylcholine) into the cleft, it diffuses across and binds receptors on the postsynaptic membrane, triggering a new impulse.

The detailed nervous system content — neurons, action potentials, synapses, reflex arcs and brain structure — is HL-only material. SL students cover a simpler comparison of nervous versus hormonal control (speed, duration, mechanism) but aren't examined on action potential graphs or brain anatomy in the same depth.

Expect 'describe' (state characteristics without reasons), 'explain' (give reasons or a mechanism), 'label' and 'annotate' on brain or neuron diagrams, and 'outline' for a brief summary of a pathway. HL Paper 2 essay-style questions may use 'discuss' or 'compare and contrast' between nervous and hormonal control.

Short-answer questions in Paper 2 Section A typically run 3-6 marks per sub-part on this content, while a full essay-style question in Section B touching nervous and hormonal integration can be worth 8-9 marks. HL Paper 1 may also include one or two multiple-choice items on synapses or reflex arcs.

Work through past paper questions on the reflex arc and action potential graph first — they repeat almost every session with minor variations. Then drill diagram labelling until you can draw a neuron and annotate an action potential from memory, under time pressure, without notes.

The biggest one I see every year: swapping sodium and potassium in the depolarisation/repolarisation explanation. Close behind — describing a brain part's function vaguely ('controls the body') instead of naming the specific process, and forgetting that reflex arcs bypass the cerebrum, which is usually the whole point of the question.

Active recall beats re-reading every time — cover the diagram, redraw it, then check. Pair each structure with one function and one exam-style verb ('the cerebellum coordinates movement'), because that's the sentence shape examiners are marking for. Flashcards work well here since the content is genuinely fact-dense rather than conceptual.

Nervous and hormonal control are taught together deliberately, because IB Biology loves a compare-and-contrast question. Nerves are fast, short-lived and localised via electrical impulses; hormones are slower, longer-lasting and travel in the blood to widespread targets. The hypothalamus-pituitary link is the exam-favourite bridge between the two systems.

Broadly yes — the core biology (action potentials, synapses, reflex arcs) overlaps closely with A-Level content, so a student moving between systems isn't starting from zero. The difference is emphasis: IB Biology weaves this into data-based questions and cross-topic essays rather than testing it as an isolated chapter, so exam technique matters more than raw recall.

Look for resources that pair labelled diagrams with exam-style practice, not just textbook prose — this topic is marked on precise terminology and sequence, so passive reading rarely converts into exam marks. On RevisionPrep, the Biology Revision Notes cover the neuron and brain structures with annotated diagrams, and the Topical Worksheets isolate this content for focused practice before it appears mixed into a full Mock Paper.