axon

Meaning: The axon is the neuron's long projection that conducts action potentials away from the cell body toward the axon terminals, where neurotransmitter is released at the synapse. The impulse is usually initiated at the axon hillock, where voltage-gated Na⁺ channels are dense. In many axons, myelin (made by Schwann cells in the PNS and oligodendrocytes in the CNS) insulates segments, and voltage-gated channels cluster at the nodes of Ranvier. The signal is regenerated at each node, called saltatory conduction, which is faster than conduction along an unmyelinated axon. A wider axon also conducts faster.

On the MCAT: Passages may describe demyelination and ask you to predict slowed or failed conduction, or ask you to compare conduction speed given myelination and diameter. Another common question is what happens at the terminal: depolarization opens voltage-gated Ca²⁺ channels, and synaptic vesicles undergo exocytosis.

Common confusion: Axons are not dendrites. Dendrites receive input and carry graded potentials toward the cell body, while the axon carries all-or-none action potentials away from it. Myelin does not make the action potential larger. The amplitude stays the same, and the speed increases.