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The Spinal Cord · Chapter 2 of 7
Before surgery her chart filled with words she had never heard — horns, columns, the dorsalRelating to the back side of the body. root — until a surgeon sketched a cross-section on a paper towel. This chapter is that sketch: a gray butterfly of cell bodies, a white wrapper of myelinated highways, two grooves, a canal of fluid, the rule that sorts every horn, the three levels you can tell apart by shape, and the site’s Masson slide of a real cord.
The question you will answer
The cord is the brain turned inside out: gray in the middle, white around it. What lives in each horn, which column carries what, how do you know dorsal from ventralRelating to the front or belly side of the body. on an unlabeled section A cut or slice of the body or an organ for study. — and where on this poppy-seed-sized map do a numb foot, a weak foot and a burning leg each live?
Opener · The Paper Towel · about 1½ minutes
The opener is the same narrated animation you will watch in Scene 1.
Watch the opener first. It sets the question; the chapter answers it.
1
Read the chart
Patient chart · Stina
Sep 2015 · age 40 · surgical planning
Planning note
“L4/L5 left paracentral HNP with caudal migration; L5 radiculopathy; S1 root irritation; plan L4/L5 microdiscectomy.”
What she heard
Horns. Columns. Ascending tractsBundles of nerve fibers in the CNS that carry signals between brain regions.. The dorsal root. A foreign language describing her own spineProminent ridge on the posterior scapula dividing it into supraspinous and infraspinous fossae..
What she asked for
A picture. The surgeon drew a cross-section on a paper towel: a butterfly, a rim, a dot in the middle, two roots. It helped more than anything had in five years.
Both feet
Still numb in stockings, both sides — written down, blamed on the crash (the Nervous Tissue module).
Told
“We decompress the root. We never touch the cord.”
Chart clues this module: 1 · The disc that finally had a picture · 2 · this chapter
Before you go on · your prediction
A surgeon says “we will free the root and never touch the cord.” On a cross-section, where does her burning pain enter, where do the commands that should lift her foot leave, and are either of them “the cord”?
Open the one you lean toward. Nothing is recorded and nothing is revealed — you come back to it at the end.
Both enter and leave through the same place; the surgeon is splitting hairs
Ask whether sensation and motor use the same door, and what the two roots are for.
Pain enters at the back of the section, motor leaves at the front — and both run through roots before they reach gray matter
Ask what the dorsal and ventral horns hold, and why the surgeon can work on a root in the forgiving basement and leave the main floor alone.
Nothing about her leg is in the cord at all; it is all in the nerve
Ask where the first synapseThe junction between two neurons where communication occurs. of her pain happens, and whether a root is the whole story.
From Stina’s diary
2
The story
Three short movements: the case, the anatomyThe study of the structure of the human body. and physiologyThe study of how the body functions., then the tie back to Stina. Each links to the scene where you’ll see it move.
I · A candy bar turned inside out
Cut the cord across and it looks like a butterfly drawn in gray on a white field. The gray is cell bodies, dendritesBranch-like extensions from a neuron that receive signals from other neurons. and unmyelinated axons — where one neuron hands a signal to the next, slow because there is no myelin, and slow is not the point: synapsing is. The white around it is myelinated axons and almost nothing else, a bundle of telephone cable seen end-on. It is the reverse of the brain, where the gray cortex is outside — the site’s candy bar with a white shell and a dark center, and the brain the same bar turned inside out. Two grooves tell you which way is up: a deepAway from the surface of the body. valley in front, the anterior median fissureA deep groove along the front of the spinal cord that divides it into two halves., and a faint crease behind, the posterior median sulcusA shallow groove along the back of the spinal cord.. Between the wings runs the central canalA hollow canal in an osteon containing blood vessels and nerves., carrying cerebrospinal fluid(CSF) – A fluid that cushions and nourishes the brain and spinal cord., continuous with the brain’s ventricles. On a practical exam, write dorsal and ventral before anything else — because her burning pain arrives at the back of this section, and the commands that should lift her foot leave from the front.
See it move: Scene 1 · The Paper Towel · Scene 2 · The Horns, Sorted by Job
II · The butterfly is inhabited
The points of the butterfly are horns, and the horns are sorted by job. The posterior (dorsal) horn receives incoming sensation — the front door. The anteriorThe front of the body or toward the front when standing in the anatomical position. (ventral) horn houses the large motor neuronsNeurons that carry outgoing information from the CNS to effector organs. that drive skeletal muscle. A lateral hornA part of the spinal cord’s gray matter, containing autonomic motor neurons., present only from T1 to L2, holds the sympathetic visceral motor cell bodies. The gray commissureThe bridge of gray matter connecting the left and right sides of the spinal cord. joins left and right, with the central canal through it. One rule tidies the whole butterfly: somatic outside, visceral inside. Somatic and visceral sensation both arrive in the dorsal horn, somatic near the tip and visceral deeper; somatic motor cell bodies sit in the ventral horn, visceral motor in the lateralAway from the midline of the body. horn, inboard of them. And the butterfly is not the same shape twice: a ventral horn matches the muscle its segment serves — fat in the enlargements, thin in the thoracic cord — so three sections can be told apart by shape alone. Map her onto it: a quiet motor pool in the anterior hornThe front section of the spinal cord’s gray matter, housing motor neurons. at L5 gives the weak foot; a hammered posterior hornThe back section of the spinal cord’s gray matter, where sensory neurons synapse., one millimeter behind it, gives the burning.
See it move: Scene 3 · Three Levels by Shape · Scene 4 · Columns and Commissures
III · White highways, and a real cord on a slide
The white rim is divided into three columns, or funiculi — Latin for a length of rope — posterior, lateral and anterior. Within a column, a tract is a bundle of axons sharing an origin and a destination; its axons run in three directions, ascending with sensation, descending with commands, or crossing the midline through a commissure. The zoning rule is the roots’ rule: posterior sensory, anterior and lateral mostly motor. The site’s analogy is the Garden State Parkway — express and local lanes, few places to change sides. None of this is visible on a section; it is drawn until the drawing does the work the microscope cannot. What the microscope can show is on the site’s Masson slide 065-1b: a real cord in cross-section, the butterfly darker than the rim, the central canal, the deep fissureA deep groove in the brain’s surface., and beside it a dorsal root ganglionA cluster of neuron cell bodies located in the peripheral nervous system (PNS). — the bulge that marks dorsal, because there is no ventral root ganglion. Hold her chart against it: numb dorsum, weak foot, burning leg, and — later — relief, four addresses on a map a centimeter across.
See it move: Scene 5 · Under the Microscope: a Real Cord
3
Watch · explore · think · check
5 scenes. Each one has a short animation or a slide, something to explore, a true/false spot-check of your thinking, and a quick check. Every scene gives you an evidence card for your board.
How to read the scenes
- Animation (dark teal) — a short animated explainer, one idea each
- Slide (dark teal) — a still to study: a micrograph, a diagram or a map
- Explore (purple) — something to push on while you watch
- Game (purple) — a quick challenge
- Think (gold) — reason it out, then spot-check yourself with a few true/false questions; not graded
- Check (gold) — a quick H5P that scores itself
Scene 1 of 5
The Paper Towel
One cross-section that makes a surgical note readable — gray, white, two grooves, a canal.
Animation · narrated, with captions
The Paper Towel
Module 9 · 9.2 · Opener and Scene 1 · 6 scenes · 1¾ minutes · narrated. Press Play to start; the words appear in the caption box under the picture.
Scene 1
Paused
Keyboard: when the picture has focus, Space plays or pauses, the left/right arrow keys move between scenes, and M mutes or unmutes.
Text description and full narration
Six-scene animation, narrated by Amy Fenwick, with captions. Built from BioRender’s spinal cord cross-section (from the “Gray Matter Function” picture, its left half mirrored and recolored so the gray matter reads gray and the white matter white) and a brain cut across (from her asset library) recolored the same way, a surgeon icon and a neuron from her asset library, with a drawn chart card, paper towel and pen sketch, map pins, telephone cables and candy bars.
Scene 1 · Words she couldn’t place (0:00–0:22)
On screen: A white card headed “Stina’s chart · before surgery”, its lines shown as gray bars that cannot be read. As Amy names them, four of the bars turn into highlighted words: “horns”, “columns”, “ascending tracts”, “dorsal root”. Right: a surgeon icon, “to the surgeon: a precise address”, and a small red map pin appears beside each word. Then “to Stina: a foreign language, describing her own body”, and a purple question mark appears beside each word.
Narration: Before her surgery, Stina's chart filled with words that she had never really put to place. Horns, columns, ascending tracts, dorsal root. To the surgeon, they were a precise address for the problem, but to her, they were a little bit of a foreign language, describing her own body.
Scene 2 · The paper towel (0:22–0:35)
On screen: A paper towel with a quilted dot pattern. Chip: “she asked for a picture”. A blue pen line sketches an oval rim with a notch at the bottom, then a butterfly shape inside it, a line down from the top, and a dot in the middle: “the surgeon’s sketch: the cord, cut across”. The butterfly fills gray: “gray matter: the butterfly”; then “white matter: the rim”, each with a leader line.
Narration: She asked for a picture, and the surgeon drew one on a paper towel and cut the cord across, and this is what you get. He said, a butterfly of gray matter inside a rim of white.
Scene 3 · Gray: where neurons meet (0:35–0:49)
On screen: The sketch becomes BioRender’s spinal cord cross-section: a gray butterfly inside a white rim, with a gold outline around the butterfly. Chip “gray matter”, then a list: “cell bodies”, “dendrites”, “unmyelinated axons”. Two small red neurons with an arrow and a gold spark between them: “where one neuron hands a signal to the next”. Chips: “slow: no myelin” and “but the point is synapsing”.
Narration: The gray is cell bodies, dendrites, unmyelinated axons, the places where one neuron hands a signal to another one. It's slow because there's no myelin, but that's not the point. Synapsing is the point.
Scene 4 · White: the cables (0:49–0:59)
On screen: The same section with a teal outline around its rim; small round axon ends, each a dark core in a white ring, dot the white matter. Chip “white matter”, then “myelinated axons”, “almost nothing else”, and “running up and down the cord”, with an up-and-down arrow. A drawn bundle of telephone cables seen end-on, many colored wires packed inside a dark sheath: “like a bundle of telephone cables”.
Narration: The white matter is myelinated axons, almost nothing else, running up and down the cord like a bundle of telephone cables.
Scene 5 · The brain, inside out (0:59–1:14)
On screen: Chip: “the spinal cord: the brain turned inside out”. Left, the cord section, “spinal cord: white outside, gray inside”; right, a brain cut across from side to side (a coronal section) in the same gray and white, “brain: gray outside, white inside”. Below each, a drawn candy bar cut across: under the cord, a white shell around a dark center, “white chocolate shell, dark center”; under the brain, a dark shell around a white center, “dark candy shell, white center”.
Narration: The spinal cord, it's the brain turned inside out. It's the candy bar with a white chocolate shell, the spinal cord, but the brain is a dark candy shell with a white center.
Scene 6 · Two grooves and a dot (1:14–1:37)
On screen: The cord section, large, with “posterior (back)” above it and “anterior (front)” below. Chip: “two grooves tell back from front”. A red outline traces the deep notch at the bottom: “anterior median fissure: a deep valley on the front”. A short gold stroke marks the shallow groove where the thin line meets the top surface: “posterior median sulcus: a faint crease on the back”. The dot in the middle fills blue and pulses: “central canal: carries cerebrospinal fluid (CSF)”.
Narration: There are two grooves on the spinal cord that tell you which way is anterior and posterior. There's a deep valley on the front called the anterior median fissure, with a faint crease on the back called the posterior median sulcus. The dot in the middle, that's the central canal, carrying cerebrospinal fluid.
Prefer the full lecture? Intro to the Spinal Cord (original video on the site)
Explore · in production
Which way is up?
An unlabeled cross-section, rotated at random. Mark dorsal and ventral and name the clue you used — the deep fissure, the shallow sulcus, the ganglion, the horns. Flip to the brain and predict which color is outside. Then drag each phrase of the planning note — horns, columns, dorsal root, ascending tract — onto the part of the drawing it names.
Think · not graded
Gray matter is slow because it has no myelin, and that is its design, not its shortfall. What has to happen in gray matterThe inner portion of the spinal cord composed mostly of neuron cell bodies and synapses. that cannot happen through myelin — and where on her cross-section does the first such event in her pain occur?
Spot-check your thinking: true or false?
Check · Multiple Choice
Select the three features that tell you which side is front on an unlabeled cross-section.
Evidence card 1
Add it to your evidence board
The planning note was a map of a cross-section; nobody had shown her the map.
Scene 2 of 5
The Horns, Sorted by Job
Posterior in, anterior out, lateral for the organs — and one rule: somatic outside, visceral inside.
Animation · narrated, with captions
The Horns, Sorted by Job
Module 9 · 9.2 · Scene 2 · 8 scenes · 2¼ minutes · narrated. Press Play to start; the words appear in the caption box under the picture.
Scene 1
Paused
Keyboard: when the picture has focus, Space plays or pauses, the left/right arrow keys move between scenes, and M mutes or unmutes.
Text description and full narration
Eight-scene animation, narrated by Amy Fenwick, with captions. Built from BioRender’s spinal cord cross-section (from the “Gray Matter Function” picture, its left half mirrored and recolored so the gray matter reads gray and the white matter white) with BioRender’s own four colored cell-body spots from the same picture, a muscle and a neuron from her asset library, and drawn roots, horn colors, a lateral horn, a segment strip, arrows, virus particles, map pins and poppy seeds.
Scene 1 · In at the back, out at the front (0:00–0:22)
On screen: BioRender’s spinal cord cross-section (gray butterfly in a white rim, back of the cord at the top), with a drawn dorsal root, its ganglion, a ventral root and a spinal nerve on the left, running down to a skeletal muscle (from her asset library) labeled “skeletal muscle”. Chip: “the horns, sorted by job”. Gold rings mark the four points of the butterfly. The two posterior horns turn blue: “posterior (dorsal) horn: receives incoming sensation”, and a blue arrow runs in along the dorsal root into it, labeled “dorsal root”; chip “like the front door”. Then the two anterior horns turn red: “anterior (ventral) horn: big motor neurons”, and a red arrow runs out along the ventral root and spinal nerve to the muscle: “ventral root”, “→ drive skeletal muscle”.
Narration: The points of the gray matter butterfly are called horns, and the horns, you can sort them by job. The posterior horn, or dorsal horn, it receives incoming sensation. It's kind of like the front door. The anterior horn, ventral, it houses the big motor neurons that drive skeletal muscle.
Scene 2 · The lateral horn: T1–L2 (0:22–0:44)
On screen: A small third horn grows from the side of the gray on each side and turns orange: “lateral horn”, “only between T1 and L2”, “visceral motor cell bodies: sympathetic outflow”. Below, a strip of the cord’s 31 segments (C1–C8, T1–T12, L1–L5, S1–S5, Co1) with T1 to L2 shaded orange under a bracket: “T1–L2: thoracic and upper lumbar cord”.
Narration: And then there's a third horn, the lateral horn, which appears only between about T1 and L2, and it holds the visceral motor cell bodies of the sympathetic outflow. If you can see a lateral horn, you're in the thoracic cavity, or the very upper lumbar.
Scene 3 · The gray commissure (0:44–0:52)
On screen: The bar of gray across the middle turns purple: “gray commissure: joins left and right”. A dashed midline runs down through the section and a two-headed purple arrow crosses it; the dot in the commissure turns blue: “the central canal runs through it”.
Narration: The gray commissure joins the left and the right across the midline, with the central canal running through the commissure.
Scene 4 · One rule (0:52–1:08)
On screen: Chip: “one rule tidies the whole butterfly”. On the right half of the butterfly, teal tags point to the outer tips of the horns: “somatic: on the outside”; then purple tags point to the gray near the middle: “visceral: on the inside”.
Narration: One rule tidies up the entire butterfly. Somatic sensory, or even somatic motor, is on the outside of the butterfly. That's where those cell bodies are. Visceral cell bodies, they're on the inside.
Scene 5 · Sensory side, motor side (1:08–1:30)
On screen: BioRender’s four colored spots appear on the right half of the butterfly, each with a label: pink at the tip of the posterior horn, “somatic sensory: near the tip”; lavender just deeper, “visceral sensory: a little deeper”; under “sensory side” and then “motor side”: green at the outer tip of the anterior horn, “somatic motor: ventral horn, at the tip”; orange just inside it, in the lateral horn, “visceral motor: lateral horn, just inside”.
Narration: Somatic and visceral sensation both arrive in the dorsal horn, somatic near the tip, and visceral just a little bit deeper. Somatic motor cell bodies sit in the ventral horn. Visceral motor cell bodies sit just a little bit inside in the lateral horn, and the somatic ones sit on the very tip of the horn.
Scene 6 · Polio (1:30–1:48)
On screen: Chip: “the site’s mnemonic: polio”. Small red motor neurons sit in both anterior horns; purple polio virus particles arrive, “polio virus”, and the neurons fade, each marked with a red X: “destroys motor neuron cell bodies in the ventral horn”. A green check by the ventral root: “the cell bodies, not the roots”. The muscle grays out beside a flat line: “skeletal muscle goes silent”.
Narration: The site's mnemonic is polio. The virus destroys motor neuron cell bodies in the ventral horn. It destroys the cell bodies, not the roots. And this is why polio makes skeletal muscle go silent.
Scene 7 · Stina on the butterfly (1:48–2:08)
On screen: Chip: “Stina’s problem, on the butterfly · segment L5” (no lateral horn at this level). On the side with the roots, two dark wedges pinch the ventral root inside a red ring, and the motor arrow along it is faint and dashed: “anterior horn, L5: output pinched at the root”, “→ the foot lifts weakly”; the label “ventral root” moves aside. A stream of red dots runs in along the dorsal root and the posterior horn above it turns bright red: “posterior horn, a few millimeters behind: hammered → the burning”.
Narration: Now, if we put Stina's problem on the butterfly, there's a quiet motor pool in the anterior horn at L5 that gives her foot the act that it will not lift. There's a hammered posterior horn, one millimeter behind it, giving her that burning.
Scene 8 · Location is the diagnosis (2:08–2:19)
On screen: Those labels stay. Map pins drop onto the posterior horn and onto the pinch on the ventral root. Chips: “location is the diagnosis” and “real estate is everything”, and three drawn poppy seeds: “all at the scale of a poppy seed”.
Narration: So location, it's the diagnosis. Real estate is everything, even though it's all at the scale of a poppy seed.
Prefer the full lecture? Spinal Gray Matter (original video on the site)
Game · in production
Assign every finding to a horn
Her findings as cards — a weak foot, a burning leg, a numb dorsum, a bladderA muscular organ that stores urine before excretion. that stopped reporting, a sluggish ankle jerk, relief from a stimulator — and the butterfly with four drop zones. Sort each before the key and say whether it is somatic or visceral, sensory or motor. Then name three unlabeled sections from the horns alone.
Think · not graded
Somatic outside, visceral inside — in the dorsal horn and in the motor columns. Where would a signal from a full bladder arrive, where would the order to squeeze it leave, and why does that make Chapter 5’s bladder a lateral-horn-style story in the sacral cord?
Spot-check your thinking: true or false?
Check · Drag the Words
Put each tenant in its horn.
Evidence card 2
Add it to your evidence board
Her foot drop and her burning pain live a millimeter apart on one section — a motor pool in front, a sensory horn behind.
Scene 3 of 5
Three Levels by Shape
Fat ventral horns for arms and legs, thin ones for the trunk, a lateral horn only where the sympathetics live.
Slide · in production
Size Tells You the Job
If you can see a lateral horn you are in the thoracic or upper lumbar cord, full stop; no lateral horn and enormous ventral horns means cervical or lumbar, and the white matterThe outer portion of the spinal cord made of myelinated nerve fibers that transmit signals. settles which.
Prefer the full lecture? Spinal Gray Matter (original video on the site)
Explore · in production
Name the level from the shape
Three unlabeled cross-sections, shuffled. For each, commit to cervical, thoracic or lumbar before the label — and name the two clues you used (ventral horn size; lateral horn present or absent; how thick the white rim is). Then the slider: move a cut up and down the cord and watch the butterfly change shape; stop where her L5 motor pool lives and predict how fat the ventral horn is there.
Think · not graded
The lumbar enlargement is more gray matter, not more white. Why would a segment that wires a leg need more cell bodies but not more highways — and where in the cord is the white rim thickest, and why?
Spot-check your thinking: true or false?
Check · Multiple Choice
A cross-section has large ventral horns, no lateral horn, and a thick white rim. The level is…
Evidence card 3
Add it to your evidence board
Her disc sits at the busy station — the lumbar enlargement, where the leg’s motor pools are fat and crowded.
Scene 4 of 5
Columns and Commissures
Three ropes of white matter, tracts inside them, and the few places a signal can change sides.
Animation · narrated, with captions
Columns and Commissures
Module 9 · 9.2 · Scene 4 · 6 scenes · 1¾ minutes · narrated. Press Play to start; the words appear in the caption box under the picture.
Scene 1
Paused
Keyboard: when the picture has focus, Space plays or pauses, the left/right arrow keys move between scenes, and M mutes or unmutes.
Text description and full narration
Six-scene animation, narrated by Amy Fenwick, with captions. Built from BioRender’s spinal cord cross-section (from the “Gray Matter Function” picture, its left half mirrored and recolored so the gray matter reads gray and the white matter white) with BioRender’s own tract shapes from her “spinal pathways” picture laid onto it, the site’s micrograph of a real spinal cord section (slide 065-1a), and drawn column shading, a rope, a tract, a side view of the cord with arrows, and a highway with its sign, divider and cars.
Scene 1 · Three ropes (0:00–0:15)
On screen: BioRender’s spinal cord cross-section (gray butterfly in a white rim, back of the cord at the top). Chip: “the white rim: three columns”. The white matter is shaded in three parts, one after another, each with a label and leader line: purple at the back between the posterior horns, “posterior column”; teal at each side, “lateral column”; gold at the front on either side of the deep notch, “anterior column”. Below: “column = funiculus”, a drawn length of rope, and “Latin: ‘a length of rope’”.
Narration: The white rim around the spinal cord is divided into three columns, posterior, lateral, and anterior. You know, the old word for column is funiculus, which is Latin for a length of rope.
Scene 2 · Tracts: bundles (0:15–0:24)
On screen: The column shading fades; BioRender’s tract shapes appear inside the white matter in dark slate, like lanes. Label “tracts: bundles of axons”. Right, a drawn tract: a cluster of cell bodies labeled “same origin” sends six parallel axons to a target cluster labeled “same destination”.
Narration: Inside each rope runs tracts, which are bundles of axons that share a similar destination and origin.
Scene 3 · Up, down, across (0:24–0:47)
On screen: Chip: “three directions”. Right, a stretch of cord seen from the side: a white column with a gray core, “side view”, “toward the brain” at the top. A blue arrow climbs one side with dots running up it: “ascending: sensory information up into the brain”, and the BioRender tracts that ascend turn blue on the cross-section. A red arrow runs down the other side: “descending: motor commands down and out”, and the descending tracts turn red. A purple arrow crosses the middle: “transverse: across the midline through a commissure to the other half”; on the cross-section the band of white just in front of the gray, the anterior white commissure, turns purple with a two-headed arrow.
Narration: Their fibers in a tract run in three directions. You can either be ascending, carrying sensory sensation information upwards into the brain, descending, carrying motor commands down and out, or transverse, crossing the midline through a commissure to the other half of the spinal cord.
Scene 4 · The Garden State Parkway (0:47–1:08)
On screen: Chip: “an analogy from Amy’s website”. A green road sign: “Garden State Parkway”. A drawn highway seen from above: two express lanes on top, a concrete divider, two local lanes below, cars moving along (faster in the express lanes): labels “express lanes” and “local lanes”. Chip: “pick one: stuck in it for 50 miles”. Gold outlines mark the only two gaps in the divider, “only a few places to change from express to local”, and one car slips through a gap from the express lanes into the local lanes. Footnote: “lanes ≈ tracts · a few crossings ≈ commissures”.
Narration: You know, I'm sorry, I am from New Jersey. So, there is an analogy on my website about the Garden State Parkway. There is express lanes and local lanes, and once upon a time, if you chose one, you were stuck in it for 50 miles. There are only a few places where you could change from express to local.
Scene 5 · The zoning rule (1:08–1:32)
On screen: The cross-section again. Chip: “zoning rule: the same as the roots”, with “dorsal root: sensory · ventral root: motor”. The block of white at the back turns blue: “posterior: sensory”, “the dorsal columns climb at the back”. Red tracts appear at the side and front: “anterior and lateral: mostly motor”, “corticospinal fibers descend at the side and the front”; other ascending tracts show faintly in blue: “(ascending tracts share the side and front too)”. Chip: “say it three times”.
Narration: The zoning rule is the same as the roots used. As posterior is sensory, the dorsal columns climb at the back. Anterior and lateral are mostly motor, and those contain what are called corticospinal fibers, descending at the side and the front. Ugh, say it three times, don't look it up.
Scene 6 · The honest part (1:32–1:51)
On screen: Chip: “the honest part”. Left, the site’s micrograph of a real spinal cord section (site slide 065-1a): a pale pink-red section with a faint, paler butterfly and nothing else to see. Labels: “on a real section, none of this shows”, “the white matter: cold vanilla pudding”, “no fibers to see running”. The drawn section with its colored tracts slides to the right, with an arrow from the micrograph to it: “the drawing does the work the microscope cannot”.
Narration: Here's the honest part. You can't see any of this on a section. The rim just looks like cold vanilla pudding. You don't see fibers running. So, we can draw it over and over until the drawing does the work that the microscope cannot.
Prefer the full lecture? Spinal White Matter (original video on the site)
Explore · in production
Shade the columns
A blank cross-section. Shade the three columns before the overlay, then drag the four tract labels you will meet in Chapter 6 — dorsal columns, spinothalamic, spinocerebellar, corticospinal — onto the column each lives in and predict which carry sensation up and which carry commands down. Then the commissure: mark where a signal could cross and predict which of her four lanes crosses inside the cord.
Think · not graded
Funiculus means rope; tract means a bundle sharing an origin and destination. If one tract is damaged in the lateral column on the left, what does the rope analogy predict about the signals in the rest of that column — and about the right side?
Spot-check your thinking: true or false?
Check · Drag the Words
Match the direction to the lane.
Evidence card 4
Add it to your evidence board
Her numbness, her burning and her weakness each ride a different rope in this rim — and so, later, does her relief.
Scene 5 of 5
Under the Microscope: a Real Cord
Slide 065-1b at 4× and 20×: the butterfly, the canal, the deep fissure — and the ganglion that marks the back.
Slide · in production
Slide 065-1b and 065-1c, Masson
The Journey’s rule: find the ganglion and you have found dorsal. The 772 page says each spinal nerve has two ganglia — each nerve has one; the pair at a level has two.
Prefer the full lecture? Spinal Gray Matter (original video on the site) · histology page: Nervous Histology · Dorsal Root Ganglia
Explore · in production
Drive the slide
Slide 065-1b with a stage you can move. At 4×, before the overlay, outline the butterfly and mark the canal, the fissure and the sulcus; at 20×, find the ganglion and name three features that make it a ganglion and not a nerve. Then the trap: a section flipped upside down — commit to dorsal, then check for the ganglion. Last: predict what this slide would look like if it were cut through her L5 segment instead of a thoracic one.
Think · not graded
The cell bodies of her pain’s first neuron sit in a ganglion outside the cord, and a disc in the foramen can squeeze that ganglion directly. What would that predict about where a root compression hurts, and why do students lose marks by putting those cell bodies in the dorsal horn?
Spot-check your thinking: true or false?
Check · Question set
On slides 065-1a and 065-1b, find the gray matter, the anterior median fissure, the central canal and the dorsal root ganglion, and name the cellsThe basic structural and functional units of life. inside the ganglion.
Evidence card 5
Add it to your evidence board
A real cord on a slide, with a ganglion that says which way is dorsal — and the cell bodies of her pain’s first neuron sitting in it, outside the cord, where a disc can reach.
4
Your evidence board
Every scene gave you an evidence card, and the chart adds more. Sort each card into the column it supports: A map the chart was written in, which she had to ask to see, Neither on its own, or Words that meant nothing, because the surgery was elsewhere. Some cards can honestly go in more than one place — that’s allowed, and the feedback tells you which cards decide the case.
5
Your verdict
Time to decide. Look back at your bet, then build your verdict from statements that hold up — no writing needed.
Look back at your prediction
A chart that speaks in horns and columns, a patient who asked for a picture — the reading that fits best is…
Find the one you chose at the top. Does the evidence support it, refute it, or revise it?
- Both enter and leave through the same place; the surgeon is splitting hairs
- Pain enters at the back of the section, motor leaves at the front — and both run through roots before they reach gray matter
- Nothing about her leg is in the cord at all; it is all in the nerve
Build your verdict · no writing
Choose the statement that holds in each set. The ones you keep become your argument.
6
The finding
Finding · the map
The Paper Towel
September 2015: a planning note in horns, columns and a dorsal root; a sketch on a paper towel. Chart entry: the cord is a gray butterfly of cell bodies in a white rim of highways, oriented by a deep ventral fissure and a dorsal ganglion; posterior in, anterior out, lateral for the organs, somatic outside and visceral inside; her foot drop is a quiet L5 motor pool in front and her burning a hammered sensory horn behind. Held open: the surgeon can free a root; what the dorsal horn has learned is not on the operating table.
Next · Chapter 3
Three Wrappers and a Needle
Two injections went into a space outside the cord; a surgeon went through three membranes to reach the disc. Before the exam and the operation, the wrappers — and why the low back is the safe place for a needle.
Reliable information on rare diseases
NORD · NIH GARD · Orphanet · MedlinePlus Genetics: FMF · FMF & AID Global Association · Autoinflammatory Alliance · Global Genes · Amyloidosis Foundation
Stina has one rare disease. In the United States, about 1 in 10 people live with one of the more than 7,000 known rare diseases. These organizations are where patients, families and clinicians go for trustworthy information.
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All pages for Module 9 — The Spinal Cord
9.0 Module Overview
9.1 The Disc That Finally Had a Picture
9.2 Inside the Cable
9.3 Three Wrappers and a Needle
9.4 Roots to Skin
9.5 The Five-Dollar Localizer
9.6 Highways With Names
9.7 The Gate and the Generator
9.8 Conclusion and Assessment
9.9 Evidence Behind the Case
All Modules
- Anatomical Language, Membranes & Homeostasis
- Just Enough Chemistry
- The Cell & Its Transport
- Making Cells & Proteins
- The Integumentary System
- The Skeletal System
- The Muscular System
- Nervous Tissue & the Senses
- The Spinal Cord
- The Brain & the Blood–Brain Barrier
- The Autonomic Nervous System
- Special Senses (in developmentThe process of growth and differentiation.)
- The Endocrine System
- Blood
- The Heart
- Blood Vessels
- The Digestive System
- The Respiratory System
- The Urinary System
- Fluids, Electrolytes & Acid–Base Balance
- The Reproductive System
- The Immune System
List of terms
- dorsal
- ventral
- section
- tracts
- spine
- synapse
- anatomy
- physiology
- dendrites
- deep
- anterior median fissure
- posterior median sulcus
- central canal
- cerebrospinal fluid
- anterior
- motor neurons
- lateral horn
- gray commissure
- lateral
- anterior horn
- posterior horn
- fissure
- ganglion
- gray matter
- bladder
- white matter
- cells
- development