# Neuroscience / 86 billion cells, talking

Canonical URL: https://shipslides.com/d/catalog-science-neuroscience
Raw viewer URL: https://content.shipslides.com/d/catalog-science-neuroscience/raw
Category: Science
Slides: 13
Updated: 2026-05-17T20:55:48.202Z
Tags: catalog, science, neuroscience

## Summary

Brain, mind, cognition — a clinical tour of the most complex object known to science. Key sections include: NEUROSCIENCE 86 billion cells, talking.; The neuron — an electrical wire that thinks.; The action potential — a 1 ms electrical spike.; Synapses — chemical conversation, ~100 trillion of them.; Anatomy — one brain, many regions, two halves.; Sensory & motor — the brain’s I/O bus.; Memory — how the brain holds onto time.; Broca, Wernicke, and what aphasia teaches us.; Cajal vs. Golgi — the 1906 Nobel.; The modern toolkit..

## Slide Outline

1. NEUROSCIENCE 86 billion cells, talking.
2. The neuron — an electrical wire that thinks.
3. The action potential — a 1 ms electrical spike.
4. Synapses — chemical conversation, ~100 trillion of them.
5. Anatomy — one brain, many regions, two halves.
6. Sensory & motor — the brain’s I/O bus.
7. Memory — how the brain holds onto time.
8. Broca, Wernicke, and what aphasia teaches us.
9. Cajal vs. Golgi — the 1906 Nobel.
10. The modern toolkit.
11. What we still don’t know.
12. Brain disorders — where the work matters.
13. Where to go next.

## Slide Transcript

### Slide 1: NEUROSCIENCE
86 billion cells,
talking.

- Neuroscience · Lecture series
- Brain, mind, cognition — a clinical tour of the most complex object known to science.
- 13 slides
- Topic The brain, the cell, the network
- Reading time ~12 min

### Slide 2: The neuron — an electrical wire that thinks.

- 02 · The cell
- ~86 billion neurons in the human brain[1], each with thousands of inputs. Specialized for one job: receive a signal, decide, transmit.
- Fig 2.1 · A typical neuron, schematic
- Dendrites — branched receivers, sum thousands of inputs.
- Soma — cell body; if input crosses threshold, fires.
- Axon — wire-like output, can stretch over a meter.
- Synapse — the gap where one neuron talks to the next.
- Glia — support cells; roughly 1:1 with neurons[2].
- [1] Azevedo et al., J Comp Neurol (2009) — isotropic fractionator count.
- [2] von Bartheld et al. (2016) revised the old "10:1 glia" myth.

### Slide 3: The action potential — a 1 ms electrical spike.

- 03 · The signal
- When inputs push the membrane past about −55 mV, voltage-gated Na⁺ channels snap open. The cell depolarizes, then K⁺ channels reset it. Repeat down the axon at up to ~100 m/s in myelinated fibres[1].
- Fig 3.1 · Membrane voltage during a single spike (~1 ms)
- Resting potential ~−70 mV, maintained by Na⁺/K⁺ pump.
- Threshold ~−55 mV — an all-or-nothing decision.
- Peak ~+40 mV — Na⁺ rushes in.
- Refractory period — can’t fire again immediately.
- Saltatory conduction — signal jumps between Nodes of Ranvier in myelinated axons[2].
- [1] Hodgkin & Huxley, J Physiol (1952) — squid giant axon model. 1963 Nobel.
- [2] Conduction velocity scales with axon diameter and myelination.

### Slide 4: Synapses — chemical conversation, ~100 trillion of them.

- 04 · The handshake
- An action potential reaches the terminal, calcium floods in, vesicles dump neurotransmitter into a 20 nm gap. The next cell’s receptors decide what to do. The whole thing takes about half a millisecond.[1]
- ~1014
- Synapses
- Roughly 100 trillion connections in an adult brain — an order of magnitude more than there are stars in our galaxy.
- ~50
- Neurotransmitters
- Glutamate (excite), GABA (inhibit), dopamine, serotonin, acetylcholine, norepinephrine, and many peptides.
- LTP
- The cellular basis of learning
- Long-term potentiation: repeatedly co-active synapses get stronger[2]. Hebb’s rule — "neurons that fire together, wire together."
- 0.5 ms
- Synaptic delay
- Time from arriving spike to postsynaptic response — the rate-limiting step in neural circuits.
- [1] Sakmann & Neher, patch-clamp methods — 1991 Nobel.
- [2] Bliss & Lømo (1973), hippocampal LTP, Journal of Physiology.

### Slide 5: Anatomy — one brain, many regions, two halves.

- 05 · The map
- Fig 5.1 · Lateral view, left hemisphere
- Cerebrum — the wrinkled outer layer; thinking, perception, voluntary action.
- Cerebellum — "little brain"; balance, motor timing, fine coordination.
- Brainstem — breathing, heart rate, the things you can’t turn off.
- Four lobes — frontal (planning), parietal (touch/space), temporal (hearing/memory), occipital (vision).
- Two hemispheres linked by the corpus callosum; each receives the opposite side of the body.

### Slide 6: Sensory & motor — the brain’s I/O bus.

- 06 · In and out
- Cortex is organized as topographic maps: neighbouring neurons code for neighbouring features. Discovered by carefully poking the cortex with electrodes — literally.
- Primary visual cortex (V1)
- Hubel & Wiesel (1959) found neurons that fire only for edges at a specific orientation[1]. The retinal image is mapped point-for-point onto V1 in the occipital lobe.
- Primary motor cortex (M1)
- A strip of cortex along the central sulcus where each patch controls a specific muscle group. Stimulate it, the body twitches.
- Somatotopy · the homunculus
- Penfield’s wartime maps showed lips, hands, and tongue claim disproportionate cortical real estate — sensitivity, not size, sets the scale[2].
- Cross-modal plasticity
- In congenitally blind people, "visual" cortex is recruited for Braille reading. Maps re-write themselves when the input changes.
- [1] Hubel & Wiesel, J Physiol (1959); 1981 Nobel.
- [2] Penfield & Boldrey, Brain (1937).

### Slide 7: Memory — how the brain holds onto time.

- 07 · The hippocampus
- In 1953, surgeons removed both hippocampi from a young man named Henry Molaison — "Patient H.M." — to stop his seizures. They worked. But H.M. could no longer form new long-term memories.[1]
- "Every day is alone in itself. Whatever enjoyment I’ve had, and whatever sorrow I’ve had."
- — Henry Molaison, c. 1980
- H.M. founded modern memory research. We learned that declarative memory (facts, events) needs the hippocampus, but procedural memory (skills) does not — he could still learn new motor tasks without remembering having practiced them.
- Encoding — hippocampus binds together cortical activity into an episode.
- Consolidation — over hours to years, memories migrate to neocortex[2].
- Sleep replays the day's hippocampal activity at high speed (sharp-wave ripples).
- Place cells — O’Keefe (1971); a hippocampal map of where you are. 2014 Nobel.
- Forgetting — not a bug; selective decay keeps memory useful.
- [1] Scoville & Milner, J Neurol Neurosurg Psychiatry (1957).
- [2] Standard model: McClelland, McNaughton & O’Reilly (1995).

### Slide 8: Broca, Wernicke, and what aphasia teaches us.

- 08 · Language
- Two 19th-century clinicians, two patients, two distinct deficits — and the first localized account of any cognitive function in the brain.
- Broca's area · left frontal
- Damage here produces Broca’s aphasia: speech is halting, ungrammatical, effortful — but comprehension is largely intact. The patient knows what they want to say.
- "Walk dog. Yes... outside. Hard."
- — A typical Broca’s aphasia utterance
- Wernicke's area · left temporal
- Damage here produces Wernicke’s aphasia: fluent, grammatical, melodic speech — but comprehension is impaired and the words come out as nonsense. Patients are often unaware.
- "I called my mother on the television and did not understand the door."
- — A typical Wernicke’s aphasia utterance
- Modern fMRI shows language is more distributed than the classical model suggested[1] — but Broca’s and Wernicke’s patients are still where every neurology resident starts.
- [1] Hagoort, Trends Cogn Sci (2014); Fedorenko et al. on the language network.

### Slide 9: Cajal vs. Golgi — the 1906 Nobel.

- 09 · History
- Camillo Golgi invented the silver-nitrate stain that, mysteriously, blackens only a few neurons at random — rendering each one in exquisite detail.[1]
- Santiago Ramón y Cajal, a Spanish histologist, used Golgi’s stain to draw thousands of neurons by hand. He concluded that the brain is made of discrete cells, not a continuous web — the neuron doctrine.
- They shared the 1906 Nobel Prize. They disagreed bitterly in their acceptance speeches. Cajal turned out to be right.[2]
- Pyramidal neuron, after Cajal (1899)
- [1] Golgi (1873), la reazione nera.
- [2] The reticular vs. neuronal theory debate — resolved by electron microscopy in the 1950s.

### Slide 10: The modern toolkit.

- 10 · Tools
- Twenty years ago neuroscience meant electrodes and post-mortem slices. Today we can image, manipulate, and reconstruct circuits at multiple scales simultaneously.
- fMRI
- Functional MRI tracks blood-oxygen changes (BOLD signal) at ~1 mm resolution — the workhorse of cognitive neuroscience since the 1990s.[1]
- Optogenetics
- Channelrhodopsins from algae let researchers switch specific neurons on or off with millisecond pulses of blue light.[2] Causation, not just correlation.
- Calcium imaging
- GCaMP fluoresces when calcium rises during a spike. Two-photon microscopy can record thousands of neurons simultaneously in a behaving mouse.
- Connectomics
- Serial electron microscopy + deep learning reconstructs every synapse in a tissue volume. Full Drosophila brain mapped in 2024[3]; mouse cortex underway.
- [1] Ogawa et al. (1990) discovered BOLD contrast.
- [2] Boyden, Deisseroth et al., Nat Neurosci (2005).
- [3] FlyWire consortium, Nature (Oct 2024) — ~140k neurons, ~50M synapses.

### Slide 11: What we still don’t know.

- 11 · Frontier
- Despite a century of progress, the deepest questions remain genuinely open. These are the problems a young researcher could bet a career on.
- Consciousness
- Why does any physical process feel like something? The "hard problem"[1]. Leading frameworks: Global Workspace Theory, Integrated Information Theory — neither yet decisive.
- YouTube · Consciousness & neuroscience →
- The binding problem
- Color, shape, motion, and location are processed in separate cortical regions. How are they fused into a single, unified percept of "red car moving left"?
- What is a dream?
- REM sleep is universal among mammals and birds. Dreams may be memory replay, threat rehearsal, noise — or essential to learning. We still don’t know.
- The engram
- If memory is stored physically in the brain, where? Recent work (Tonegawa lab) tags and reactivates specific memory traces in mice[2] — but the full code is still cryptic.
- [1] Chalmers, J Conscious Stud (1995).
- [2] Liu, Ramirez et al., Nature (2012); engram cell tagging in hippocampus.

### Slide 12: Brain disorders — where the work matters.

- 12 · Clinical
- Roughly one in three people will be affected by a neurological or psychiatric disorder in their lifetime[1]. The clinic is where neuroscience meets the world.
- Aβ
- Alzheimer’s disease
- Amyloid-β plaques and tau tangles; first hippocampal, then cortical neurodegeneration. Lecanemab (2023) is the first disease-modifying therapy — modest but real.[2]
- Parkinson’s disease
- Loss of dopamine neurons in the substantia nigra. L-DOPA (1968) was a miracle drug; deep-brain stimulation now helps refractory patients.
- 5-HT
- Depression
- SSRIs treat symptoms imperfectly. Ketamine and psilocybin show rapid antidepressant effects via NMDA / 5-HT2A receptors — reshaping the field.[3]
- ~1%
- Schizophrenia
- Lifetime prevalence around 1% globally. Heritable, dopaminergic and glutamatergic dysregulation, but cause and definitive biomarker still elusive.
- [1] WHO, Global Burden of Disease.
- [2] van Dyck et al., NEJM (2023) — CLARITY-AD trial.
- [3] Krystal et al., Cell (2019); Carhart-Harris et al., NEJM (2021).

### Slide 13: Where to go next.

- 13 · Further reading
- Books
- Principles of Neural Science — Kandel, Schwartz et al. The standard reference.
- The Idea of the Brain — Matthew Cobb. History of how we got here.
- Behave — Robert Sapolsky. Neuroscience meets behavior, written for humans.
- The Man Who Mistook His Wife for a Hat — Oliver Sacks. The case-study tradition.
- Consciousness and the Brain — Stanislas Dehaene. The science of awareness.
- Video
- Neuron & action potential — YouTube search →
- Consciousness & neuroscience — YouTube search →
- Online
- NIH BRAIN Initiative — current US funding map and data releases.
- Allen Brain Atlas — high-resolution gene expression and connectivity data.
- FlyWire.ai — the connectome of the fruit fly, free to explore.


## Related Decks

- [Neuroscience](https://shipslides.com/d/science-neuroscience)
- [CLIMATE / Earth's thermostat in motion](https://shipslides.com/d/catalog-science-climate)
- [Cosmology / 13.8 billion years, briefly](https://shipslides.com/d/catalog-science-cosmology)
- [Ecology / Webs of Dependence](https://shipslides.com/d/catalog-science-ecology)