All parts of the brain › Pathways

Pathways of the brain, lit step by step

A tract is a bundle of nerve fibres (axons) connecting parts of the central nervous system. The corticospinal tract carries commands for voluntary movement down to the spinal cord; the spinothalamic tract and the dorsal column–medial lemniscus pathway carry touch, temperature and pain up to the cortex; the visual pathway runs from the eye to the occipital lobe. A circuit is a chain of such links that returns to where it began: the Papez circuit starts and ends in the hippocampus, and the basal ganglia loops run from the cortex back to the cortex. [1][2][3][4][5][6] A tract has no shape of its own in this atlas; lit: the parts it runs through, in order. Each page below lights them on a 3D brain you can turn and slice, one step at a time or the whole route at once, with every step cited.

The 6 pathways

• Where does the corticospinal tract run? 6 steps, lit in order: Precentral gyrus → Internal capsule → Cerebral peduncles → Pons → Medulla oblongata → Spinal cord
• Where does the spinothalamic tract run? 6 steps, lit in order: Spinal cord → Medulla oblongata → Pons → Midbrain → Thalamus → Postcentral gyrus
• Where does the dorsal column–medial lemniscus pathway run? 6 steps, lit in order: Spinal cord → Medulla oblongata → Pons → Midbrain → Thalamus → Postcentral gyrus
• Where does the visual pathway run? 6 steps, lit in order: Optic nerve → Optic chiasm → Optic tract → Lateral geniculate body → (optic radiation: nothing new lit) → Occipital lobe
• Where does the Papez circuit run? 8 steps, a loop, lit in order: Hippocampus → Fornix → Mammillary bodies → (mammillothalamic tract: nothing new lit) → Thalamus → Cingulate gyrus → Parahippocampal gyrus → (entorhinal cortex: nothing new lit) → back to step 1
• How do the basal ganglia loops run? The direct and indirect pathways Direct pathway, 4 steps: Frontal lobe → Caudate nucleus + Putamen → Globus pallidus → Thalamus → back to step 1. Indirect pathway, 6 steps: Frontal lobe → Caudate nucleus + Putamen → Globus pallidus → (subthalamic nucleus: Thalamus + Midbrain lit) → (globus pallidus, internal segment (GPi): nothing new lit) → Thalamus → back to step 1.