In the cephalic phase of gastric acid secretion, the neural pathway involves:

• A Sight and smell of food → olfactory bulb → limbic system → anterior hypothalamus → vagal efferents → direct ACh release onto parietal cells
• B Swallowing triggers the gastroesophageal reflex → myenteric plexus → gastrin release exclusively
• C Sight/smell/taste/thought of food → cortex → dorsal vagal complex → vagal efferents releasing ACh → direct parietal cell stimulation AND stimulation of ECL cells (histamine) AND G-cells (gastrin), all potentiating acid secretion ✓
• D Sight of food → hypothalamic NPY neurons → spinal sympathetic pathways → splanchnic nerve stimulation of parietal cells

Explanation

The cephalic phase begins before food enters the stomach, triggered by the sight, smell, taste, or even thought of food (conditioned reflex, as in Pavlov's experiments). The cortex activates the dorsal motor nucleus of the vagus (DMV) via the hypothalamus. Vagal efferent fibers release ACh, which: (1) directly stimulates parietal cells (M3 muscarinic receptors) to secrete HCl; (2) stimulates ECL (enterochromaffin-like) cells in the fundus to release histamine (H2 receptors amplify parietal response); (3) stimulates G-cells in the antrum to release gastrin (via GRP — gastrin-releasing peptide), which further stimulates parietal cells via CCK-B receptors. The cephalic phase accounts for approximately 30% of total acid output.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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