12 Difference Between Myelinated And Unmyelinated Neurons (Nerve Fiber) With Examples

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Neurons are electrically excitable cells in the human bodies that communicate with other cells through specialized connection referred to as Synapses. Each neuron has a cell body with many minute branched short protoplasmic extensions referred to as dendrites and an elongated unbranched protoplasmic extension referred to as Axon.

What Are Myelinated Nerve Fibers?

Myelinated Nerve Fibers are nerve fibers that are insulated by a myelin sheath. The myelin sheath is a protective covering that surrounds fibres called axons, the long thin projections that extend from the main body of a nerve cell or neuron. This sheath is composed of protein and lipids (fatty substance), that insulates the nerve cell axons so as to increase the speed at which information travels from one nerve cell body to another for example from a nerve cell body to a muscle.

Majority of neurons in the central and peripheral nervous system are Myelinated. In the central nervous system, myelin is produced by oligodendroglia, whereas in the peripheral nervous system, it is produced by Schwann cells.

Majority of neurons in the central and peripheral nervous system are Myelinated. In the central nervous system, myelin is produced by oligodendroglia, whereas in the peripheral nervous system, it is produced by Schwann cells.

The main function of myelin is to protect and insulate these axons and enhance their transmission of electrical impulses. A neuron with Myelinated axons can conduct the impulse at a faster speed since myelin sheath acts as the insulator that help to propagate the electrical signal faster. If myelin is damaged, the transmission of these impulses is slowed down, which is seen in severe neurological conditions such as multiple sclerosis.

Characteristics of Myelinated Nerve Fibers

  • Structure: Myelinated nerve fibers consist of a nerve cell, or neuron, with a long, thin projection known as an axon. The axon is surrounded by a series of concentric layers of myelin sheath, created by specialized glial cells called oligodendrocytes in the CNS and Schwann cells in the PNS.
  • Conduction Speed: The myelin sheath acts as an insulator, allowing for saltatory conduction, a process where the action potential “jumps” from one node of Ranvier (small gaps in the myelin sheath) to another. This dramatically increases the speed at which nerve signals travel.
  • Diameter: Myelinated fibers are of diameters, with larger-diameter fibers generally conducting signals faster than smaller ones. This variation in size allows for the transmission of different types of sensory and motor information.

Facts About Myelinated Nerve Fibers (Neuron)

  • Myelinated Nerve Fibers are nerve fibers that are insulated by a myelin sheath.
  • The nerve fibers with long axons are myelinated.
  • The axis cylinder of the myelinated nerve fibres has two sheaths.
  • Myelinated fibres show nodes and internodes.
  • The myelinated nerve fibers appear white in color.
  • The myelinated nerve fibers have nodes of Ranvier.
  • The Schwann cells wrap tightly around the nerve axon and form the myelin sheath.
  • Due to presence of nodes of Ranvier on myelinated nerve fibers, the speed of transmission of nerve impulses is high in myelinated nerve fibers. 
  • Most neurons in the central and peripheral nervous system are myelinated because they require fast conduction speed such as neuron involved in spinal reflexes.
  • Due to presence of myelin sheath, myelinated nerves do not lose the impulse during conduction.
  • In myelinated fibers electrical impulses (action potentials) travel as continuous waves.
  • Myelinated nerve fibres may give off collateral nerve fibres.

Also Read: Difference Between Sensory And Motor Neurons

What Are Unmyelinated Nerve Fibers?

Unmyelinated nerve fibers are nerve fibers that do not have a myelin sheath. Unmyelinated nerve fibers conduct impulses at low velocities. They represent the majority of peripheral sensory and autonomic fibers. They are also found in the spinal cord and brain. In Unmyelinated fibers electrical impulses (action potentials) ”hop” or propagate by saltatory conduction and can lose the nerve impulse during conduction.

Unmyelinated nerve fibers do not have nodes of Ranvier. Nodes of Ranvier are the spaces between the myelin coatings on the neuron’s axon. The nodes of Ranvier serve to facilitate the rapid conduction of nerve impulses.

Characteristics of Unmyelinated Nerve Fibers

  • Structure: Unmyelinated nerve fibers are relatively thin compared to myelinated nerve fibers. They consist of a single axon surrounded by Schwann cells, but the axon lacks the myelin sheath that typically insulates and speeds up signal transmission in myelinated fibers.
  • Conduction Speed: Unmyelinated fibers conduct nerve impulses more slowly compared to myelinated fibers. This is because myelin acts as an insulator, allowing the nerve impulse to “jump” from one node of Ranvier to another in myelinated fibers, which significantly speeds up signal propagation.
  • Diameter: Unmyelinated fibers are generally smaller in diameter, which contributes to their slower conduction speed.
  • Function: These fibers predominantly transmit signals related to pain, temperature, and some involuntary bodily functions. They are also responsible for conveying information from autonomic reflexes, such as those regulating blood pressure, heart rate, and digestion.

Facts About Unmyelinated Nerve Fibers (Neuron)

  • Unmyelinated nerve fibers are nerve fibers that do not have a myelin sheath.
  • The short axon nerve fibers are unmyelinated.
  • The axis cylinder of unmyelinated nerve fibres has only one sheath.
  • Unmyelinated nerve fibres do not show notes and internodes.
  • The nerve fibers appear gray in color.
  • Schwann cells are not wound around the axons but simply form a groove.
  • They do not have nodes of Ranvier.
  • They do not have myelin insulations, and therefore, the speed of the transmission of the nerve impulses is low.
  • Unmyelinated neurons can be found in both the peripheral and central nervous system in the group c nerve fibers, responsible for transmission of secondary pain or itch.
  • Unmyelinated nerve fibers can lose the nerve impulse during conduction.
  • In Unmyelinated fibers electrical impulses (action potentials) ”hop” or propagate by saltatory conduction.
  • collateral fibres are not produced in Unmyelinated nerves.

Also Read: Difference Between Action Potential And Resting Potential

Myelinated And Unmyelinated Neurons (Nerve Fiber): Key Differences

CharacteristicMyelinated NeuronsUnmyelinated Neurons
Presence of Myelin SheathPresentAbsent
Axon InsulationAxon is insulated by myelin sheathAxon is not insulated
Conduction SpeedFaster transmission of impulsesSlower transmission of impulses
Energy EfficiencyMore energy-efficientLess energy-efficient
Node of RanvierPresent (gaps in myelin sheath)Absent
Saltatory ConductionOccurs (jumping between nodes)Does not occur (continuous conduction)
Axon DiameterLargerSmaller
Size of Nerve FiberThickThin
Types of NeuronsMotor and sensory neuronsAutonomic and some sensory neurons
Role in Reflex ArcsOften involvedLess commonly involved
Location in the Nervous SystemCentral and peripheral nervous systemMainly in the peripheral nervous system
Susceptibility to DiseasesLess susceptible to demyelinating diseases like multiple sclerosisMore susceptible to demyelinating diseases like Guillain-Barré syndrome

Also Read: Difference Between Axon And Dendrites