The drug-action atlas

Enter through a molecule, a synapse, or a brain circuit. Change the conditions and trace what happens next.

All learning models

Explore the system

What can cross a membrane?

Compare an ordinary capillary with the blood-brain barrier. Change molecular properties and predict the route.

What can cross a membrane?

Diagram zoom

Passive diffusion is favored

Transporter specificity and efflux can further limit entry. These toggles illustrate relationships rather than a binary clinical prediction.

Placental barrier

The placenta is selective, not an absolute shield. Many lipid-soluble drugs can cross; transfer also depends on binding and other properties.

Diagram zoom

Animate the diagram

On a small screen, pan the diagram or increase zoom. Named controls provide the same exploration by keyboard.

Sources and model limits

Original schematic. Positions show relationships; structures and concentrations are not to scale.

Julien's Primer of Drug Action · 15 · 1 · What can cross a membrane? · PDF 13, 14 · 1.5, 1.6, 1.7

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The drug-action atlas

Enter through a molecule, a synapse, or a brain circuit. Change the conditions and trace what happens next.

All learning models

Explore the system

Compare an ordinary capillary with the blood-brain barrier. Change molecular properties and predict the route.

What can cross a membrane?

Diagram zoom

Passive diffusion is favored

Transporter specificity and efflux can further limit entry. These toggles illustrate relationships rather than a binary clinical prediction.

Placental barrier

The placenta is selective, not an absolute shield. Many lipid-soluble drugs can cross; transfer also depends on binding and other properties.

Diagram zoom

Animate the diagram

On a small screen, pan the diagram or increase zoom. Named controls provide the same exploration by keyboard.

Sources and model limits

Original schematic. Positions show relationships; structures and concentrations are not to scale.

Julien's Primer of Drug Action · 15 · 1 · What can cross a membrane? · PDF 13, 14 · 1.5, 1.6, 1.7