Final answer:
Not all neurons contain a myelin sheath; while the dendrite, nucleus, and axon are essential components of every neuron, myelin is not present on every neuron.
Step-by-step explanation:
The components of a neuron include the dendrite, which branches off the cell body to receive signals; the nucleus, which is contained within the cell body or soma and houses the neuron's genetic material; and the axon, a long 'tail' that transmits electrical signals to target cells and can be wrapped in a myelin sheath for insulation and faster transmission. The only option listed that is not a component of every neuron is the myelin. Although many neurons are myelinated, not all have this insulating layer, as it is formed by accessory cells and some neurons in the body are unmyelinated.