Neurophysiology Cheat Sheet

The core ideas of Neurophysiology distilled into a single, scannable reference — perfect for review or quick lookup.

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Quick Reference

Action Potential

A rapid, transient, all-or-none electrical depolarization that propagates along the membrane of an excitable cell such as a neuron or muscle fiber. It is generated by the sequential opening and closing of voltage-gated sodium and potassium channels.

Resting Membrane Potential

The electrical potential difference across the cell membrane of a neuron at rest, typically around -70 mV. It is maintained primarily by the sodium-potassium ATPase pump and the selective permeability of the membrane to potassium ions through leak channels.

Synaptic Transmission

The process by which a signal is transmitted from one neuron to another across a synapse. An action potential arriving at the presynaptic terminal triggers calcium influx, which causes vesicles containing neurotransmitters to fuse with the membrane and release their contents into the synaptic cleft.

Neurotransmitters

Chemical messengers released from presynaptic terminals that bind to specific receptors on postsynaptic cells to produce excitatory or inhibitory effects. Major neurotransmitters include glutamate, GABA, dopamine, serotonin, acetylcholine, and norepinephrine.

Myelin and Saltatory Conduction

Myelin is a lipid-rich insulating sheath formed by oligodendrocytes in the CNS and Schwann cells in the PNS that wraps around axons. Saltatory conduction is the process by which action potentials jump between the gaps in the myelin (nodes of Ranvier), greatly increasing conduction speed.

Synaptic Plasticity

The ability of synapses to strengthen or weaken over time in response to changes in activity. Long-term potentiation (LTP) and long-term depression (LTD) are the best-studied forms and are considered cellular mechanisms underlying learning and memory.

Ion Channels

Transmembrane proteins that form pores allowing specific ions (Na+, K+, Ca2+, Cl-) to flow down their electrochemical gradients. They can be voltage-gated, ligand-gated, or mechanically gated, and are essential for generating and propagating electrical signals.

Sensory Transduction

The process by which sensory receptor cells convert physical or chemical stimuli (light, sound, pressure, temperature, chemicals) into electrical signals (receptor potentials) that can be processed by the nervous system.

Electroencephalography (EEG)

A non-invasive neurophysiological technique that records the collective electrical activity of large populations of cortical neurons through electrodes placed on the scalp. EEG measures oscillatory brain waves categorized into frequency bands (delta, theta, alpha, beta, gamma).

Neural Coding

The study of how sensory and other information is represented by the patterns of action potentials (spike trains) fired by neurons. Rate coding, temporal coding, and population coding are the main proposed schemes by which neural activity encodes information.

Key Terms at a Glance

Action Potential:A rapid, all-or-none reversal of membrane polarity that propagates along excitable cell membranes, generated by the sequential activation of voltage-gated sodium and potassium channels.

Afferent Neuron:A sensory neuron that carries information from peripheral receptors toward the central nervous system.

Axon Hillock:The region of the neuron cell body where the axon originates, containing the highest density of voltage-gated sodium channels and serving as the integration zone where the decision to fire an action potential is made.

Calcium Signaling:The use of calcium ions (Ca2+) as intracellular messengers to trigger processes such as neurotransmitter release, muscle contraction, gene expression, and synaptic plasticity.

Depolarization:A shift in the membrane potential toward a less negative (more positive) value, typically caused by the influx of positively charged ions such as sodium or calcium.

Efferent Neuron:A motor neuron that carries signals from the central nervous system to effector organs such as muscles and glands.

Electroencephalography (EEG):A non-invasive technique that records the electrical activity of the brain through electrodes placed on the scalp, measuring the summed postsynaptic potentials of large cortical neuron populations.

Excitatory Postsynaptic Potential (EPSP):A small depolarization of the postsynaptic membrane caused by the opening of cation channels in response to neurotransmitter binding, bringing the cell closer to the threshold for firing.

GABA:Gamma-aminobutyric acid, the principal inhibitory neurotransmitter in the adult mammalian central nervous system, acting primarily through GABA-A (ionotropic) and GABA-B (metabotropic) receptors.

Glutamate:The principal excitatory neurotransmitter in the central nervous system, acting on AMPA, NMDA, and kainate ionotropic receptors as well as metabotropic glutamate receptors.

Graded Potential:A local change in membrane potential whose amplitude is proportional to stimulus strength, decreasing with distance from the point of origin. Includes EPSPs, IPSPs, and receptor potentials.

Hodgkin-Huxley Model:A set of nonlinear differential equations developed in 1952 that quantitatively describe how ionic currents through voltage-gated sodium and potassium channels produce the action potential.

Hyperpolarization:A shift in the membrane potential toward a more negative value than the resting potential, typically caused by potassium efflux or chloride influx, making the neuron less likely to fire.

Inhibitory Postsynaptic Potential (IPSP):A hyperpolarization of the postsynaptic membrane that moves the potential further from threshold, reducing the likelihood of action potential generation.

Ion Channel:A transmembrane protein that forms a selective pore allowing specific ions to pass through the cell membrane. Can be voltage-gated, ligand-gated, or mechanically gated.

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