Chapter 2 · 18 min

How a Nerve Cell Sends a Signal

Chapter 2 of How the Brain Works: How a Nerve Cell Sends a Signal.

How the Brain Works | Ch 2 Part 1/2: How a Nerve Cell Sends a Signal ↗How the Brain Works | Ch 2 Part 2/2: How a Nerve Cell Sends a Signal ↗

Visual credits

5 sources

Sources and credits for imagery used in this film, including material incorporated into explanatory animations.

The knee jerk
William Richard Gowers; Wellcome Library, London / Wellcome Images
View original source ↗Source licence: CC BY 4.0
Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
The knee jerk — William Richard Gowers; Wellcome Library, London / Wellcome Images. CC BY 4.0.
Doctor Checking Knee Reflexes of a Patient
gpointstudio
View original source ↗Source licence: Envato Elements project licence
Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Giant Axon of Squid (14356033761)
NIH History Office from Bethesda
View original source ↗Source licence: Public domain
Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Giant Axon of Squid — NIH History Office, public domain, via Wikimedia Commons.
Kroll et al. 2025 Figure 3b — seven observed tomogram slices
Jana Kroll and coauthors
View original source ↗Source licence: CC BY 4.0
Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Patch rig
Peter Duncan
View original source ↗Source licence: CC BY-SA 4.0
Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Patch rig — Peter Duncan, CC BY-SA 4.0, via Wikimedia Commons.

Animation design references 4 sources

These works informed the design of explanatory animations. A reference listed here is not necessarily reproduced on screen.

Мышечное веретено
Вера Вирясова
View original source ↗Source licence: Public domain
Muscle spindle diagram — Vera Viryasova, public domain, via Wikimedia Commons.
Patellar tendon reflex arc
Amiya Sarkar
View original source ↗Source licence: CC BY-SA 4.0
Patellar tendon reflex arc — Amiya Sarkar, CC BY-SA 4.0, via Wikimedia Commons.
Voltage clamp setup
smonsays
View original source ↗Source licence: CC BY-SA 4.0
Voltage clamp setup — smonsays, CC BY-SA 4.0, via Wikimedia Commons.
Action potential propagation in unmyelinated axon
Germis
View original source ↗Source licence: CC BY-SA 3.0
Action potential propagation in unmyelinated axon — Germis, CC BY-SA 3.0, via Wikimedia Commons; converted from GIF to MP4.

Research references

Selected sources from the episode’s research and scientific figures.

How this film was made

Created and editorially directed by Anders Lunde using a custom production system developed over six months. AI assists research, drafting, programming, and visual production; I review and edit the material and make the final editorial decisions. Narration uses text-to-speech. Visuals combine custom-built scientific animations, AI-generated reconstructions, and credited scientific imagery.

Generated reconstructions illustrate scientific interpretations. They are distinct from photographs, specimens, and measured data.

More about the creator and production →

Visual credits

The knee jerk

Doctor Checking Knee Reflexes of a Patient

Giant Axon of Squid (14356033761)

Kroll et al. 2025 Figure 3b — seven observed tomogram slices

Patch rig

Мышечное веретено

Patellar tendon reflex arc

Voltage clamp setup

Action potential propagation in unmyelinated axon

Research references

How this film was made