• 20 parts
  • Checked October 2026

Ascending and Descending Pathways Diagram

Follow one signal up from the skin to the cortex, then one command down to a muscle.

Ascending and Descending Pathways Diagram

Name Date

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
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Write the name of each numbered part.Answer key

  1. Receptor
  2. First-order neuron
  3. Dorsal root ganglion
  4. Fasciculus gracilis (dorsal column)
  5. Second-order neuron
  6. Decussation (crossing in the medulla)
  7. Medial lemniscus
  8. Thalamus
  9. Third-order neuron
  10. Primary somatosensory cortex
  11. Spinothalamic tract
  12. Primary motor cortex
  13. Upper motor neuron
  14. Internal capsule
  15. Cerebral peduncle (crus cerebri)
  16. Pyramid
  17. Decussation of the pyramids
  18. Lateral corticospinal tract
  19. Anterior corticospinal tract
  20. Lower motor neuron

Drawn for this site on 2026-10-03 from plain geometry. Licence: own work.

Each numbered ring is a button. Use the arrow keys to move between them and Enter to choose. Names are read out in Study, and once a part is answered.

Next step Next: every tract of the cord in one slice

All 20 parts on the diagram

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Ascending (sensory) 11

  1. Receptor Where the pathway begins: a touch receptor in the skin. The first neuron's fiber ends in it.
  2. First-order neuron Runs from the receptor into the cord and up to the medulla. Its cell body sits in the dorsal root ganglion.
  3. Dorsal root ganglion Holds the cell bodies of the first-order neurons. It lies on the dorsal root, outside the cord.
  4. Fasciculus gracilis (dorsal column) The inner strip of the dorsal column. First-order fibers from the lower body climb in it without crossing.
  5. Second-order neuron Starts in the medulla, crosses the midline and climbs to the thalamus.
  6. Decussation (crossing in the medulla) Where the second-order fibers cross the midline. Above it, each side of the body is carried on the opposite side.
  7. Medial lemniscus The band of crossed second-order fibers. It climbs through the brainstem to the thalamus.
  8. Thalamus The relay where the second-order neuron ends and the third begins.
  9. Third-order neuron Runs from the thalamus up to the cortex. It is the last neuron of the chain.
  10. Primary somatosensory cortex Where the pathway ends: the parietal lobe's postcentral gyrus.
  11. Spinothalamic tract A second route, for pain and temperature. Its second neuron crosses in the cord and climbs to the thalamus.

Descending (motor) 9

  1. Primary motor cortex Where the pathway starts, in front of the central sulcus. The upper motor neuron's cell body lies here.
  2. Upper motor neuron Runs from the motor cortex down to the cord. It ends on a lower motor neuron.
  3. Internal capsule A white-matter band that lies between thalamus and basal ganglia. The fibers gather in it.
  4. Cerebral peduncle (crus cerebri) The stalk at the front of the midbrain. The fibers run down through it.
  5. Pyramid A bump on the front of the medulla, made by the fibers. It gives the pyramidal tract its name.
  6. Decussation of the pyramids Where most of the fibers cross to the other side. It lies at the lower end of the medulla.
  7. Lateral corticospinal tract The crossed fibers. They run down the side of the cord.
  8. Anterior corticospinal tract The fibers that stay uncrossed at the medulla. They run down the front of the cord.
  9. Lower motor neuron Its cell body is in the front horn of the cord. Its axon leaves the cord and reaches a skeletal muscle.

How this list was compiled: Every name and step checked on 2026-10-03 in at least two of these. (1) Wikipedia, English edition: Dorsal column-medial lemniscus pathway, Spinothalamic tract, Pyramidal tracts, Upper motor neuron and Lower motor neuron, text only. (2) Neuroscience Online, McGovern Medical School at UTHealth Houston: Section 2, Chapter 4, Somatosensory Pathways; Section 3, Chapter 1, Motor Units and Muscle Receptors; Section 3, Chapter 2, Spinal Reflexes and Descending Motor Pathways; Section 3, Chapter 3, Motor Cortex. (3) TeachMeAnatomy: The Ascending Tracts and The Descending Tracts. Hints and detail lines are in our own words. Licence: own work

The drawing: Drawn for this site on 2026-10-03 from plain geometry; nothing traced. A plan, not to scale. Licence: own work

How it works

An ascending pathway carries a sensation up to the brain in a chain of three neurons. A descending pathway carries a command down in two. Each drawing stacks slices of the cord, the brainstem and the cerebrum.

Read the full guide

Up: three neurons

From the receptor (1), the first-order neuron (2) passes the dorsal root ganglion (3) and climbs the fasciculus gracilis (4). The second-order neuron (5) crosses (6) and climbs in the medial lemniscus (7) to the thalamus (8). The third-order neuron (9) ends in the primary somatosensory cortex (10). The dashed route is the spinothalamic tract (11).

Down: two neurons

The upper motor neuron (13) leaves the primary motor cortex (12), passes the internal capsule (14), the cerebral peduncle (15) and the pyramid (16), and crosses (17) into the lateral corticospinal tract (18). Uncrossed fibers form the anterior tract (19). The lower motor neuron (20) reaches the muscle.

  • Ascending means up to the brain and sensory; descending means down from it and motor.
  • Both main routes cross in the medulla, so each half of the brain serves the opposite side of the body.

Questions and answers

What are the ascending and descending pathways of the CNS?

Ascending pathways carry sensory signals up the spinal cord to the brain; descending pathways carry motor commands down from the brain. This page draws one of each: the dorsal column-medial lemniscus pathway and the corticospinal tract.

What are first-, second- and third-order neurons?

The three neurons of a sensory chain. The first-order neuron runs from the receptor into the cord, the second-order neuron crosses and climbs to the thalamus, and the third-order neuron runs from the thalamus to the cortex.

Where do the pathways cross to the other side?

The touch pathway crosses in the medulla, where the second-order neuron starts. The spinothalamic tract crosses in the spinal cord. Most corticospinal fibers cross at the decussation of the pyramids, at the lower end of the medulla.

What is the difference between an upper and a lower motor neuron?

An upper motor neuron has its cell body in the brain, and its axon stays inside the central nervous system. A lower motor neuron's axon leaves the cord and reaches a skeletal muscle.

Can I practice here for “correctly identify and label the structures associated with some ascending pathways of the CNS.”?

Yes, and for “correctly identify and label the structures associated with two descending pathways of the CNS.” Both are instructions of labeling exercises. The drawing here is our own and not a copy of any course figure, so yours may ask for other names.

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