Nervous system ↗Gradients store potential
Selective permeability and unequal sodium, potassium, chloride, and other ion distributions make the cell interior electrically different from the exterior.
BRAIN & NERVES / 02
Voltage travels.
Synapses transform.
Ion gradients make neurons excitable. Action potentials regenerate along axons; synapses then convert arrival into chemical or electrical influence that the next cell integrates with thousands of other inputs.
Inputs change conductance
Synaptic receptors, sensory channels, and intrinsic currents produce local graded voltage changes that can sum across space and time.
Threshold recruits channels
When a trigger zone depolarizes sufficiently, voltage-gated sodium-channel activation drives a regenerative, all-or-none action potential.
Repolarization resets excitability
Sodium-channel inactivation and potassium currents return voltage toward baseline; refractory periods shape direction and maximum firing patterns.
Myelin speeds propagation
Oligodendrocyte or Schwann-cell myelin reduces current loss; voltage-gated channels concentrated near nodes regenerate the signal along long axons.
Calcium triggers release
Terminal depolarization opens voltage-gated calcium channels, promoting synaptic-vesicle fusion and neurotransmitter release.
Receptors shape meaning
Ionotropic receptors change conductance rapidly; metabotropic receptors recruit slower signaling. The same transmitter can have different effects by receptor and cell.
Networks integrate, then adapt
Excitatory, inhibitory, and modulatory inputs alter firing probability. Reuptake, metabolism, receptor traffic, and plasticity terminate and reshape signaling.