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MODULE 8:
NERVOUS TISSUE
PART 3 OF 7
Nerve conduction study: signals present but slowed, especially in the legs. Read as “mild, nonspecific.” A slow signal is exactly what damaged insulation produces.
Slide 1 Transcript
PATIENT CHART
STINA
THIS PART
Age 35
PRESENTING WITH
Numbness, tingling, and a hot stripe of pain down her left leg, slowly creeping, symmetric foot numbness
DIAGNOSIS
Anti-MAG peripheral neuropathy
DRUGS ORDERED
Rituximab
CHART CLUES
COLLECTED AS YOU GO
Radiating Leg Pain & Numbness After a ‘Clear’ Crash
Symmetric Loss of Light-Touch & Vibration
Slowed Nerve Conduction
Synapse Intact — the Fault Is Upstream
Anti-MAG Antibodies
A Map Pointing at Two Nerve Roots
Anti-MAG, Sensory-Predominant Peripheral Neuropathy
Put your money down: ‘Slowed but present’ — nothing, or a clue?
Her nerves signalled, only slowly. Is a slowed signal trivial noise, or the fingerprint of failing insulation?
Pick the answer you believe now. We’ll come back to it later!
Signals That Arrived Late
The conductionThe transmission of nerve impulses along neurons. study clipped electrodes to Stina’s legs and timed how fast her nerves answered. The signals were there — but late, dragging behind where they should have been, worst in the longest nerves running to her feet. “Mild, nonspecific slowing,” the report concluded, and it was filed. To Stina it confirmed only that the numbness was real and measurable. What no one said out loud was that slowed conduction is not random noise; it is the specific signature of insulation that has come loose.
Voltage & the Resting Potential
A neuron at rest is not idle — it’s a charged spring, held at a cost.
Slide 2 Transcript
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Fill in the Blanks: Fill in the numbers and pumps behind the resting voltage.
Three Kinds of Channel
Three ways a membrane gate can open — and the one that fires the spark.
Slide 3 Transcript
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Drag the Words: Drag each channel type to how it opens.
How a Nerve Fires — and Leaps
A neuron at rest holds a voltage across its membrane — the resting membrane potential, about −70 millivolts inside relative to outside, maintained by ion pumps and channelsProtein passages in the cell membrane that allow specific molecules to pass through. that sort sodium(Na⁺): Major ECF cation; important for fluid balance, nerve function. (Na⁺), potassium(K⁺): Major ICF cation; essential for muscle and nerve function. (K⁺), and other ionsCharged atoms or molecules.. When a stimulus pushes the membrane past a thresholdThe minimum voltage needed to trigger an action potential., voltage-gated Na⁺ channels snap open, Na⁺ floods in, and the voltage spikes — an action potentialA rapid, temporary electrical charge that travels along neurons, allowing signal transmission., the all-or-nothing electrical signal. It then races down the axon. On a myelinated axon it doesn’t crawl; it leaps from one bare gap to the next — the nodes of Ranvier — in saltatory conductionThe rapid transmission of impulses in myelinated axons by jumping between nodes of Ranvier., which is what makes signaling fast. Strip or loosen the myelin and the leap fails: the signal must crawl, and conduction slows — exactly Stina’s result.
Local (Graded) Potentials
Small ‘maybe’ signals that fade as they travel — unless they add up.
Slide 4 Transcript
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Multiple Choice: What happens to a graded potential as it spreads?
Excitatory & Inhibitory
Every input either nudges the neuron toward firing or pulls it away.
Slide 5 Transcript
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Mark the Words: Mark only the events that push the neuron TOWARD firing.
The Calcium Thread Reaches the Nerve
Notice the ions. Na⁺ and K⁺ run the action potential, and Ca²⁺ — the calcium that built her bone and contracted her muscle earlier in the course — is about to take the lead role at the synapseThe junction between two neurons where communication occurs.. The same calcium thread now wires the nervous systemThe organ system that controls body functions using electrical and chemical signals..
Threshold & All-or-Nothing
Reach the trigger point and there is no halfway — the axon fires fully or not at all.
Slide 6 Transcript
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Multiple Choice: The membrane reaches threshold at the axon hillockCone-shaped region of the neuron where the axon originates and where action potentials begin.. What happens?
Refractory Periods
A built-in one-way valve that keeps the signal moving forward.
Slide 7 Transcript
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Flip Cards: Flip each refractory period to reveal its rule.
Saltatory Propagation
On a myelinated axon the signal doesn’t crawl — it leaps.
Slide 8 Transcript
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Fill in the Blanks: Fill in why a myelinated signal is so fast.
Speed & Its Limits
What sets conduction speed — and what breaks it in Stina’s legs.
Slide 7 Transcript
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Summary: Pick the true statement about conduction speed in each set.
FINDING!
Slowed Nerve Conduction — the Signature of Failing Myelin
Nerve signals present but slowed, worst in the legs, filed as ‘mild, nonspecific.’ New evidence: myelin exists to make conduction leap node-to-node and fast. Strip the wrap and the signal doesn’t vanish — it slows. Her ‘nonspecific’ result is exactly the fingerprint of a demyelinating process.
Confirm or refute your bet:
Her nerves signalled, only slowly. Is a slowed signal trivial noise, or the fingerprint of failing insulation?
Now that you’ve read the story, confirm or overturn it — step by step, with the evidence in hand.
Slide 8 Transcript
NEXT PART
The spark reaches the end of the axon and stops at a gap it cannot cross by electricity alone. Next: how the signal jumps the synapse — and why calcium is the key.
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QUICK QUESTIONS
QUICK QUESTIONS
List of terms
- conduction
- channels
- sodium
- potassium
- ions
- threshold
- action potential
- saltatory conduction
- synapse
- nervous system
- axon hillock