2.1 Electrical Signals of Neurons

A complete set of vocabulary flashcards derived from the lecture notes on neuronal electrical signals, resting potential, action potential mechanism/propagation, and synaptic transmission.

Ions

Electrically charged molecules in the neuron

Anions

Negatively charged ions (majority inside the cell, including large proteins that can't leave)

Cations

Positively charged ions

Intracellular/extracellular fluid

Fluid inside/outside the cell membrane where ions are dissolved

Polarized

Having a charge difference between inside and outside the cell

Resting potential

The steady voltage difference across the membrane at rest ($\sim -50\,\text{mV}$ to $-80\,\text{mV}$, typically $-65\,\text{mV}$)

Millivolts (mV)

Unit used to measure this tiny voltage

Ion channel

A membrane protein that lets specific ions cross

Selective permeability

The membrane's property of letting some ions ($\text{K}^+$) through easily but not others ($\text{Na}^+$)

Sodium-potassium pump

Protein that pumps $3\,\text{Na}^+$ out for every $2\,\text{K}^+$ in, maintaining the ion gradients

Diffusion

Movement of particles from high to low concentration

Electrostatic pressure

Force where like charges repel and opposite charges attract

Equilibrium potential

The voltage at which the concentration gradient and electrostatic pull on an ion exactly balance (this sets the resting potential)

Depolarization

Membrane potential moves toward zero (less negative)

Hyperpolarization

Membrane potential becomes more negative

Threshold

The depolarization level ($\sim -40\,\text{mV}$) that triggers an action potential

Local/graded potentials

Small, variable responses that shrink as they spread — not yet an action potential

Action potential (spike)

The brief, large, all-or-none voltage reversal ($\sim +40\,\text{mV}$) that travels down the axon

All-or-none property

Action potentials fire at full size or not at all, regardless of stimulus strength

Afterpotential

Small voltage changes right after the spike, as ion channels reset

Voltage-gated Na⁺ channel

Opens at threshold to let $\text{Na}^+$ rush in, causing the action potential's rising phase

Voltage-gated K⁺ channel

Opens after $\text{Na}^+$ channels close, letting $\text{K}^+$ rush out to repolarize the cell

Refractory period

Time after firing when the neuron can't (absolute) or is less likely (relative) to fire again; sets the max firing rate

Absolute refractory phase

No stimulus can trigger another action potential

Relative refractory phase

Only a stronger-than-usual stimulus can trigger one

Conduction velocity

Speed of action potential travel; increases with axon diameter

Myelin

Fatty insulating sheath (from glial cells) around the axon that speeds conduction

Nodes of Ranvier

Gaps in the myelin where the membrane is exposed

Saltatory conduction

The action potential "jumping" node to node in myelinated axons, making it faster

Multiple sclerosis (MS)

Disease where the immune system damages myelin, disrupting saltatory conduction

Neurotransmitter

Chemical released by the axon terminal into the synapse

Presynaptic/postsynaptic cell

The sending/receiving neuron at a synapse

Postsynaptic potential

Brief voltage change in the receiving cell caused by neurotransmitter

EPSP (excitatory postsynaptic potential)

Depolarizing, pushes cell toward threshold

IPSP (inhibitory postsynaptic potential)

Hyperpolarizing, pushes cell away from threshold (often via $\text{Cl}^-$ influx)

Spatial summation

Adding up potentials arriving at different locations on the neuron at the same time

Temporal summation

Adding up potentials arriving at (nearly) the same location in quick succession