📖 Notes
LESSON 09 OF 16
Nervous System — Neurons & Action Potential
How a Signal Actually Travels
From resting potential to depolarisation to the synapse, the action potential is one continuous electrochemical event — not a list of terms to memorise separately.
Neuron Anatomy
Structure Follows Signal Flow
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Dendrites
Receive incoming signals from other neurons.
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Axon
Transmits the signal away from the cell body.
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Myelin Sheath
Speeds transmission via saltatory conduction between Nodes of Ranvier.
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Synaptic Knob
Releases neurotransmitter into the synaptic cleft.
The Action Potential, Step by Step
1
Resting: -70mV
K+ is concentrated inside the neuron, Na+ outside.
2
Depolarisation
Na+ rushes in through voltage-gated channels, driving the potential to about +40mV.
3
Repolarisation
K+ rushes out, returning the membrane potential toward -70mV.
4
Refractory Period
The neuron cannot fire again immediately, ensuring signals travel in one direction.
Synapse & Nervous System Divisions
- Key neurotransmitters: acetylcholine, dopamine, serotonin
- CNS = brain + spinal cord
- PNS = somatic (voluntary) + autonomic (involuntary)
- Autonomic: sympathetic (fight/flight) vs parasympathetic (rest/digest)
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Exam tip
MDCAT frequently asks which ion moves during which phase — Na+ IN during depolarisation, K+ OUT during repolarisation. Reversing these is the single most common mistake.