Neuron — from synaptic input to transmitter release
One signal traced end to end: summation of EPSPs at the axon hillock, the −55 mV threshold, sodium influx to +40 mV and potassium efflux back, saltatory conduction at up to 100 m s⁻¹ between nodes of Ranvier, then calcium-triggered vesicle fusion across a 20 nm cleft with a 0.5 ms synaptic delay.
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{
"nodes": [
{ "id": "dendrites", "type": "network-globe", "label": "Dendrites — thousands of synaptic inputs", "x": 40, "y": 40, "width": 150, "height": 104, "fill": "#ede9fe", "stroke": "#6d28d9", "bold": true },
{ "id": "psp", "type": "line-chart", "label": "EPSP +2 mV, IPSP −2 mV, graded", "x": 215, "y": 40, "width": 150, "height": 104, "fill": "#e0f2fe", "stroke": "#0369a1" },
{ "id": "hillock", "type": "target", "label": "Axon hillock — most Na⁺ channels per µm²", "x": 390, "y": 40, "width": 150, "height": 104, "fill": "#e0f2fe", "stroke": "#0369a1", "bold": true },
{ "id": "threshold", "type": "gate", "label": "Threshold −55 mV — all or nothing", "x": 565, "y": 40, "width": 150, "height": 104, "fill": "#e0f2fe", "stroke": "#0369a1", "bold": true },
{ "id": "depolarise", "type": "chevron", "label": "Na⁺ floods in — the spike hits +40 mV", "x": 740, "y": 40, "width": 150, "height": 104, "fill": "#fef3c7", "stroke": "#b45309", "bold": true },
{ "id": "repolarise", "type": "chevron", "label": "K⁺ leaves — repolarise, then undershoot", "x": 915, "y": 40, "width": 150, "height": 104, "fill": "#fef3c7", "stroke": "#b45309", "bold": true },
{ "id": "summation", "type": "summing-junction", "label": "Spatial and temporal summation", "x": 40, "y": 200, "width": 150, "height": 104, "fill": "#fef3c7", "stroke": "#b45309", "bold": true },
{ "id": "resting", "type": "battery", "label": "Resting −70 mV, pumped 3 Na⁺ : 2 K⁺", "x": 215, "y": 200, "width": 150, "height": 104, "fill": "#dbeafe", "stroke": "#1d4ed8", "bold": true },
{ "id": "refractory", "type": "clock", "label": "Refractory 1–2 ms — sets the direction", "x": 390, "y": 200, "width": 150, "height": 104, "fill": "#e0f2fe", "stroke": "#0369a1", "bold": true },
{ "id": "myelin", "type": "layers", "label": "Myelin sheath, nodes about 1 mm apart", "x": 565, "y": 200, "width": 150, "height": 104, "fill": "#e0f2fe", "stroke": "#0369a1", "bold": true },
{ "id": "saltatory", "type": "arrow-right", "label": "Saltatory conduction up to 100 m s⁻¹", "x": 740, "y": 200, "width": 150, "height": 104, "fill": "#fef3c7", "stroke": "#b45309", "bold": true },
{ "id": "terminal", "type": "stadium", "label": "Axon terminal — the presynaptic bouton", "x": 915, "y": 200, "width": 150, "height": 104, "fill": "#dcfce7", "stroke": "#15803d", "bold": true },
{ "id": "pump", "type": "motor", "label": "Na⁺/K⁺ ATPase restores the gradients", "x": 40, "y": 360, "width": 150, "height": 104, "fill": "#e0f2fe", "stroke": "#0369a1", "bold": true },
{ "id": "duration", "type": "gauge-chart", "label": "The whole spike lasts about 1 ms", "x": 215, "y": 360, "width": 150, "height": 104, "fill": "#ccfbf1", "stroke": "#0f766e" },
{ "id": "coding", "type": "bar-chart", "label": "Frequency codes intensity, not amplitude", "x": 390, "y": 360, "width": 150, "height": 104, "fill": "#ccfbf1", "stroke": "#0f766e", "bold": true },
{ "id": "calcium", "type": "valve", "label": "Ca²⁺ enters through voltage-gated channels", "x": 565, "y": 360, "width": 150, "height": 104, "fill": "#fef3c7", "stroke": "#b45309", "bold": true },
{ "id": "vesicles", "type": "sphere", "label": "Vesicles fuse — 5000 ACh molecules each", "x": 740, "y": 360, "width": 150, "height": 104, "fill": "#fce7f3", "stroke": "#be185d", "bold": true },
{ "id": "cleft", "type": "dimension-line", "label": "Cleft 20 nm wide — 0.5 ms of delay", "x": 915, "y": 360, "width": 150, "height": 104, "fill": "#fef3c7", "stroke": "#b45309", "bold": true },
{ "id": "demyelination", "type": "cross", "label": "Demyelination slows or blocks the spike", "x": 390, "y": 520, "width": 150, "height": 104, "fill": "#fee2e2", "stroke": "#b91c1c", "bold": true },
{ "id": "receptors", "type": "gate", "label": "Postsynaptic receptors open ion channels", "x": 740, "y": 520, "width": 150, "height": 104, "fill": "#e0f2fe", "stroke": "#0369a1", "bold": true },
{ "id": "esterase", "type": "bucket", "label": "Acetylcholinesterase clears the cleft", "x": 915, "y": 520, "width": 150, "height": 104, "fill": "#fef3c7", "stroke": "#b45309" }
],
"edges": [
{ "id": "e1", "source": "dendrites", "target": "summation", "thickness": 2.5 },
{ "id": "e2", "source": "psp", "target": "summation", "label": "excitation minus inhibition", "style": "dashed" },
{ "id": "e3", "source": "summation", "target": "hillock", "thickness": 2.5 },
{ "id": "e4", "source": "resting", "target": "hillock", "label": "the −70 mV starting point", "style": "dashed" },
{ "id": "e5", "source": "hillock", "target": "threshold", "thickness": 2.5 },
{ "id": "e6", "source": "threshold", "target": "depolarise", "label": "reached — or nothing happens", "thickness": 2.5 },
{ "id": "e7", "source": "depolarise", "target": "repolarise", "thickness": 2.5 },
{ "id": "e8", "source": "repolarise", "target": "pump" },
{ "id": "e9", "source": "pump", "target": "resting", "label": "gradients restored", "thickness": 2.5 },
{ "id": "e10", "source": "repolarise", "target": "refractory", "style": "dashed" },
{ "id": "e11", "source": "refractory", "target": "coding", "label": "caps the firing rate", "style": "dashed" },
{ "id": "e12", "source": "depolarise", "target": "saltatory", "thickness": 2.5 },
{ "id": "e13", "source": "myelin", "target": "saltatory", "label": "the spike jumps node to node", "style": "dashed" },
{ "id": "e14", "source": "saltatory", "target": "terminal", "thickness": 2.5 },
{ "id": "e15", "source": "terminal", "target": "calcium", "thickness": 2.5 },
{ "id": "e16", "source": "calcium", "target": "vesicles", "thickness": 2.5 },
{ "id": "e17", "source": "vesicles", "target": "cleft", "thickness": 2.5 },
{ "id": "e18", "source": "cleft", "target": "receptors", "thickness": 2.5 },
{ "id": "e19", "source": "receptors", "target": "dendrites", "label": "the input to the next neuron", "style": "dashed" },
{ "id": "e20", "source": "esterase", "target": "cleft", "label": "otherwise the signal never stops", "style": "dashed" },
{ "id": "e21", "source": "duration", "target": "depolarise", "style": "dashed" },
{ "id": "e22", "source": "demyelination", "target": "myelin", "style": "dashed" },
{ "id": "e23", "source": "coding", "target": "terminal", "label": "more spikes, more transmitter", "style": "dashed" }
]
}