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Difference Between Axon and Dendrites

Axon-vs-Dendrites

Every human being is blessed with a complex nervous system comprising the brain, sensory organs, spinal cords, and neurons. These function to connect different nervous systems, including the central and the peripheral nervous system, with other parts of the body, and also transmit signals. The neurons particularly have:

Dendron (dendrites)

Axon

Cell body

Dendrons and axons are involved in the conduction of nerve impulses through the nerve cell. Moreover, both are unique cytoplasmic projections of neurons. If a dendrite brings information to the cell body from the other neurons, the other (axon) takes information from the body. There are a lot more differences that we will look into in this article. First, check out the comparison table listed below!

Comparison Table

Basis of
Comparison
AxonDendrites
Type of
Signal
Signal TransmitterSignal Receptor
LengthLongerComparatively Shorter
OriginFrom an
Axon Hillock
Directly from
Nerve Cells
Number
of Cells
A single axon
in a neuron
Multiple dendrites
in a neuron
Surface NatureSmoothRough (Dendritic Spines)
Myelin PresencePresentAbsent
Branched AtDistal EndEverywhere
Neurotransmitter
Containing Vesicles
PresentAbsent

Explain Axon

An individual, most extended nerve cell projection is called an axon. It mainly functions to carry impulses away from the cell. Axons are originated from specialized regions further called axonal hillocks. In addition, they may sometimes arise from the dendrites. The axon’s proximal part adjacent to the axon hillock is the initial segment that starts right after the axon hillock.

Axon

These cell types are further branched at the distal end, which is usually swollen. There are abundant proteins present in axons, primarily containing the microtubules and microfilaments. As a result, the special axonal microtubules are aligned with the long axis of the axon. They have a uniform polarity that is distal to the soma. Microtubules also play a critical role in the transport of metabolites and organelles in the axon. Besides, they have a highly phosphorylated cytoskeleton.

Axons send their signals through a unique axonal transport procedure, working certainly for the growth and survival of a living body. It is the active process by which proteins and other substances get synthesized in the neurosome and are also transported further. Axonal transport is of the following types:

  • Fast Axonal Transport (up to 400 mm/day): It is employed during development to grow axons and dendrite. It is elongated by adding new material to its tips.
  • Slow Axonal Transport (5 mm/day): It is also known as axoplasmic flow.

Explain Dendrites

On the other hand, dendrites are short extensions that carry nerve impulses towards a cell body from the synapsis. A single cell body gives rise to numerous dendrites. Hence these are highly branched structures. A cluster of dendron occupies a large surface area, around 300,000 μm3 of the neuron (motor neuron), and provide 370,000μm3 for synaptic input. Like an axon, dendrites also have several organelles, such as microtubules, microfilaments, ribosomes, etc. These enable them to alter protein density in response to changes in the frequency of neuronal inputs and help in the regular activity of neurons. Furthermore, dendrites help to prevent neurological disorders such as epilepsy.

Dendrite

If we consider the different organelles of a dendritic cell, its free ribosomes are present throughout the cytoplasm. Moreover, the smooth endoplasmic reticulum situated helps in the regulation of cytoplasmic calcium. Besides, it has a cytoskeleton that is poorly phosphorylated, unlike an axon. Some other unique dendritic organelles are dendritic spines and dendritic swellings.

Differences between Axons & Dendrites

We will further continue with the apparent differences between the two terms.

Definition

Axon

Axons are derived from the Greek language, also called nerve fibers, as they appear elongated and slender with uniform thickness and smooth surface throughout the length.

Dendrites

The dendritic name comes from the Greek word “Dendron,” meaning “tree.” These are the receptive surface of the neuron and are also termed as the output devices. In the mature nervous system, the dendritic branching of a neuron is changeable, either growing or retracting.

The Direction of Electrochemical Impulses

Axon

They are protoplasmic projections of nerve cells arising from the discharge end of the nerve. Secondly, axons carry electrochemical impulses away from the cell body of neurons.

Dendrites

These are also membranous tree-like protoplasmic projections arising from the body of a neuron that operates through signaling from other neurons (electrochemical impulses).

Presynaptic/Postsynaptic Terminals

Axon

These neuron types are presynaptic in the branched function at the distal end, often producing hundreds or thousands of Presynaptic terminals.

Dendrites

The impulses they receive transports them inwards and towards the soma or cell body. They are shorter and postsynaptic as compared to axons.

Length

Axon

A neuron typically contains a single axon that varies in length depending on its type. As compared to the dendrites, these may be several meters long, above 50mm. Axons are long to carry information throughout the body. The axon of the sciatic nerve is the most extended in the human body, which runs from the spinal cord and reaches the big toe of each foot.

Dendrites

The size and complexity of dendritic arbors increase during development, which is almost 5-7 per neuron. Furthermore, the length of a dendrite goes to 2μm, most of the time.

The Shape of the Neurons

Axon

The axonal shape doesn’t change, where its radius remains constant.

Dendrites

In contrast, such nerve cells usually have tube-like bodies that are typically tapered.

Nature of Biosynthesis

Axon

Axons do not have ribosomes or Golgi elements. These structures are mainly rich in smooth ER, however, rough ER is also present in low quantities. Thus metabolic activity (biosynthesis) in axons is limited. Moreover, they are enriched with low molecule weight microtubules associated proteins.

Dendrites

Also called cell bodies, dendrites have high molecular weight microtubule-associated proteins designated MAP2. Dendrites also possess organelles such as neurofilaments, microtubules, endoplasmic reticulum, mitochondria, and ribosomes. These organelles are the sites of protein synthesis that help in memory formation.

Abundant Proteins

Axon

The most abundant proteins in the axon are the proteins forming microtubules, neurofilaments, and actin filaments (microfilaments). Microtubules are a dominant feature of all axons.

Dendrites

On the contrary, there are many dendrites per neuron and arise from the receiving end of the neuron. They receive the impulses via synapses and contain specialized proteins that accept processes and additionally transfer these to the cell body.

Myelinated/Non-Myelinated

Axon

Some axons have an insulating layer called myelin sheath made of protein and fatty substances in the vertebrates. It protects the axons from electrical impulses. In addition, the myelin sheath speeds up the nerve transmission. In large axons, transmit impulses transmit at speeds up to 90 meters (300 feet) per second.

Dendrites

Unlike axons, these neurons do not contain any myelinated sheath for insulation.

Synaptic Knob

Axon

The terminal branch of the axon forms an enlarged synaptic knob that links one neuron part (usually its axon) and the dendrites, cell body, or axon of a second neuron. A neurotransmitter is present in the synaptic knob, such as acetylcholine, norepinephrine, and dopamine.

Dendrites

On the contrary, there are no synaptic knots on the tip of dendrites.

Neurofibrils & Nissl’s Granules

Axon

Axons contain neurofibrils all over, but they lack Nissl’s granules.

Dendrites

They contain both neurofibrils and Nissl’s granules. The complexity of the dendrites reflects the number of connections that a neuron receives.

Conclusion

Axon and dendrites are like any other essential part of a human body that have similarities and differences too. Above all, both are the nerve cell’s projections whose primary function is to transmit nerve impulses. These branched structures are also common in consisting of several neurofibrils. Despite everything, the primary difference between an axon and a dendrite will still remain in its direction of transmitting an impulse.

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