Nervous System is basically composed of the neurons.Neurons act as basic functional and structural unit of the nervous system. In the vertebrates,there are three types of neurons; sensory neurons (or afferent neurons); which carry nerve impulses from sensory receptors to the central nervous system (CNS), (2) motor neurons (or efferent neurons ); which carry impulses from the CNS to effectors located in muscles and glands, and (3) interneurons (or association neurons); which help to provide more complex reflexes and associate functions such as learning and memory. These three types of neurons have different appearances, but with the same architecture.

Generally, neuron has a cell body and cytoplasmic extension arising from the cell body. The two types of cytoplasmic extensions are axons and dendrites. The physiology of axons and dendrites differ from each other, both structurally and functionally. However, both structures arise from the cell body of the neuron.

Dendrites

Dendrites are the short cytoplasmic extension arising from the cell body and enable neurons to receive nerve impulses simultaneously from different receptors located all over the body. Motor neurons and interneurons usually possess highly branched dendrites. Certain neurons have numerous extensions arising from their dendrites called dendritic spines and that increase the surface area available to receive nerve impulses.

Axons

Axon is a long cytoplasmic extension arising from the cell body of the neuron and passes nerve impulses away from the cell body to effectors located in muscles and glands. Each neuron has a single axon, although an axon may also branch to stimulate a number of cells. There are axons which have diameter more than a meter such as the axons extend from the skull to pelvis, which are about 3 m long.  Many axons in the body are encased by a myelin sheath, with multiple membrane layers. Schwann cells form the myelin sheaths located in peripheral nervous system (PNS) while extensions of oligodendrocytes form the myelin sheaths in the CNS. During the development of axons, these cells wrap several times around axons to form the myelin sheaths. Small gaps called nodes of Ranvier interrupt the myelin sheaths at regular intervals.  The axons with myelin sheaths are called myelinated, and those that don’t are called unmyelinated. In CNS, the myelinated axons form the white matter while the unmyelinated dendrites and cell bodies form the gray matter. In the PNS, few myelinated axons are bundled together to form nerve fibers.

What is the difference between Dendrites and Axons?

• A neuron has only one axon and few dendrites.

• Axon is a long cellular process with uniform thickness and smooth surface, whereas dendrite is short cellular process, which does not have uniform thickness and smooth surface due to the tiny projection called dendritic spines.

• Axons usually carry information away from the cell body, while dendrites bring information to the cell body.

• Axons have myelin sheaths and nodes of Ranvier, whereas dendrites don’t.

• Myelinated axons conduct impulses faster than dendrites.

• Dendrites have ribosomes and axons don’t.

• Axons are branched far from the cell body, whereas dendrites are branched near the cell body