# Explain how the nervous system and the digestive system are integrated during the ingestion and early digestion of a meal.

> IB DP Biology Standard Level (2023 syllabus) — C3.1 Integration of body systems · Explain · 4 marks

## Mark scheme (4 marks)

1. Sensory receptors (e.g. in the mouth/nose) detect food stimuli such as taste, smell or texture and generate nerve impulses
2. Nerve impulses are transmitted to the brain (medulla oblongata / brainstem) where they are processed and efferent signals are sent via the vagus nerve / parasympathetic nervous system to the digestive organs
3. Efferent nerve signals stimulate the salivary glands to secrete saliva (containing amylase and mucus), initiating chemical and mechanical digestion in the mouth
4. Nerve signals also stimulate gastric glands in the stomach wall to secrete gastric juice (hydrochloric acid and pepsinogen), preparing the stomach for protein digestion before food arrives — this nervous phase precedes (and complements) the later hormonal/gastric phase

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